Claude Saegerman
email: claude.saegerman@uliege.be

Julien Evrard
email: julien.evrard@arsia.be

Je-Yves Houtain
email: jeanyves.houtain@arsia.be

Jean-Pier Alzieu

Juana Bianchini
email: juana.bianchini@uliege.be

Serge Eugène Mpouam
email: sempouam@yahoo.fr

Gereon Schares
email: gereon.schares@fli.de

Emmanu Liénard
email: emmanuel.lienard@envt.fr

Philip Jacquiet
email: philippe.jacquiet@envt.fr

Luca Villa
email: luca.villa@unimi.it

Gema Álvarez-García
email: gemaga@ucm.es

Alessia Libera Gazzonis
email: alessia.gazzonis@unimi.it

Arcangelo Gentile
email: arcangelo.gentile@unibo.it

Laurent Delooz
email: laurent.delooz@arsia.be

First Expert Elicitation of Knowledge on Drivers of Emergence of Bovine Besnoitiosis in Europe

Keywords: bovine besnoitiosis, Besnoitia besnoiti, drivers, expert elicitation, cattle, multi-criteria decision analysis (MCDA), clustering analysis, sensitivity analysis

Bovine besnoitiosis (BB) is a chronic and debilitating parasitic disease in cattle caused by the protozoan parasite Besnoitia besnoiti. South European countries are affected and have reported clinical cases of BB. However, BB is considered as emerging in other countries/regions of central, eastern and northern Europe. Yet, data on drivers of emergence of BB in Europe are scarce. In this study, fifty possible drivers of emergence of BB in cattle were identified. A scoring system was developed per driver. Then, the scoring was elicited from eleven recognized European experts to: (i) allocate a score to each driver, (ii) weight the score of drivers within each domain and (iii) weight the different domains among themselves. An overall weighted score was calculated per driver, and drivers were ranked in decreasing order of importance. Regression tree analysis was used to group drivers with comparable likelihoods to play a role in the emergence of BB in cattle in Europe. Finally, robustness testing of expert elicitation was performed for the seven drivers having the highest probability to play a key role in the emergence of BB: i.e., (i) legal/illegal movements of live animals from neighbouring/European Union member states or (ii) from third countries, (iii) risk of showing no clinical sign and silent spread during infection and post infection, (iv) as a consequence, difficulty to detect the emergence, (v) existence of vectors and their potential spread, (vi) European geographical proximity of the pathogen/disease to the country, and (vii) animal density of farms. Provided the limited scientific knowledge on the topic, expert elicitation of knowledge, multi-criteria decision analysis, cluster and sensitivity analyses are very important to prioritize future studies, e.g., the need for quantitative import risk assessment and estimation of the burden of BB to evidence and influence policymaking towards changing (or not) its status as a reportable disease, with prevention and control activities targeting, firstly, the top seven drivers. The present methodology could be applied to other emerging animal diseases.

Introduction

Bovine besnoitiosis (BB) is a chronic and a debilitating parasitic disease of cattle caused by a protozoan parasite called Besnoitia besnoiti [1]. Besnoitia spp. belong to the phylum Alveolata, subphylum Apicomplexa, a diverse group of largely parasitic protozoa of considerable veterinary and medical importance. Members include the genera Plasmodium, Cryptosporidium, Eimeria, Isospora, Sarcocystis, Toxoplasma, Neospora, Theileria and Babesia [START_REF] Watt | Bovine Besnoitiosis, an Emerging Disease[END_REF]. There are several recognized species (B. besnoiti, B. caprae, B. bennetti and B. tarandi) in the genus Besnoitia [START_REF] Dubey | Redescription of Besnoitia bennetti (Protozoa: Apicomplexa) from the donkey (Equus asinus)[END_REF] infecting domestic and wild ungulates (cattle, goats, equids and cervids, respectively). This study focuses exclusively on drivers of emergence of BB due to B. besnoiti in Europe. Cattle are the predominant intermediate hosts of B. besnoiti in Europe and it is also reported to be able to infect antelopes [START_REF] Mccully | Observations on Besnoitia cysts in the cardiovascular system of some wild antelopes and domestic cattle[END_REF] and roe deer (Capreolus capreolus) [START_REF] Arnal | Systemic Besnoitiosis in a Juvenile Roe Deer (Capreolus capreolus)[END_REF]. The life cycle of the parasite species infecting ruminants is not completely known, especially with regard to the definitive host [START_REF] Cortes | Besnoitiosis in bulls in Portugal[END_REF]. In addition, a recent survey reported a B. besnoiti-like sequence (99.57% homology) from 4 out of 187 red foxes (Vulpes vulpes) feces tested in Spain, necessitating further investigation to confirm or refute the role of this species in the epidemiology of B. besnoiti in Europe [START_REF] González-Barrio | Molecular survey of Besnoitia spp. (Apicomplexa) in faeces from European wild mesocarnivores in Spain[END_REF].

There is evidence that biting insects or the re-use of a contaminated needle for group injections can mechanically transmit B. besnoiti [START_REF] Alzieu | La besnoitiose bovine: Actualités épidémiologiques et diagnostiques[END_REF][START_REF] Liénard | A longitudinal study of Besnoitia besnoiti infections and seasonal abundance of Stomoxys calcitrans in a dairy cattle farm of southwest France[END_REF][START_REF] Liénard | Development of a protocol testing the ability of Stomoxys calcitrans (Linnaeus, 1758) (Diptera: Muscidae) to transmit Besnoitia besnoiti (Henry, 1913) (Apicomplexa: Sarcocystidae)[END_REF]. In Europe, different species of bloodsucking insects, such as tabanid species and stable flies (Stomoxys calcitrans), may transmit B. besnoiti mechanically from chronically or asymptomatic infected cattle. The vector insects remain infectious for only a few hours after their blood meal on a carrier animal [START_REF] Bigalke | New concepts on the epidemiological features of bovine besnoitiosis as determined by laboratory and field investigations[END_REF][START_REF] Sharif | Assessment of persistence of Besnoitia besnoiti (Henry, 1913) bradyzoites in Stomoxys calcitrans (Diptera: Muscidae)[END_REF]. The time period during which vectors remain infectious after blood meal on an infected animal is short and varies according to species. It is 1 h in the case of S. calcitrans, 3 h for Glossina brevipalpis and 24 h for tabanids [START_REF] Bigalke | New concepts on the epidemiological features of bovine besnoitiosis as determined by laboratory and field investigations[END_REF]. Although transmission by mosquitoes (Culex simpsoni and other unidentified Culex spp.) has not been demonstrated, it has been shown that mosquitoes are able to ingest B. besnoiti from bovine skin and that the parasites remain infectious for hours (50 h). Thus, their role as vectors remains not well established yet [START_REF] Bigalke | New concepts on the epidemiological features of bovine besnoitiosis as determined by laboratory and field investigations[END_REF]. Another study showed that Stomoxys were able to transmit in vitro parasites 48 h after their last meal on infected cattle [START_REF] Sharif | Assessment of persistence of Besnoitia besnoiti (Henry, 1913) bradyzoites in Stomoxys calcitrans (Diptera: Muscidae)[END_REF].

This disease presents two distinct phases: a first acute phase followed by a chronic phase. In the acute phase, clinical signs are non-specific and do not really help in the diagnosis. Otherwise, in the chronic phase, clinical signs could be very suggestive of BB [START_REF] Alzieu | La besnoitiose bovine: Actualités physio-pathogéniques, cliniques et épidémiologiques[END_REF], but this is only true for a small proportion of animals. Indeed, a large proportion of concerned animals are sub-clinically infected without clinical signs. Those animals represent a huge risk for parasite transmission on farm [START_REF] Gutierrez-Exposito | Advances in the diagnosis of bovine besnoitiosis: Current options and applications for control[END_REF][START_REF] Álvarez-García | Dynamics of Besnoitia besnoiti infection in cattle[END_REF][START_REF] Villa | Bovine besnoitiosis in an endemically infected dairy cattle herd in Italy: Serological and clinical observations, risk factors, and effects on reproductive and productive performances[END_REF]. Relying only on clinical signs for detection can lead to misdiagnosis, as BB can be confused with other infectious diseases characterized by similar clinical signs [START_REF] Alzieu | La besnoitiose bovine: Actualités physio-pathogéniques, cliniques et épidémiologiques[END_REF]. It is therefore essential to carry out confirmatory laboratory tests.

Different laboratory diagnostic methods (histopathology, polymerase chain reaction (PCR), immunofluorescence antibody test (IFAT), Western blot (WB) and enzyme-linked immunosorbent assay (ELISA)) are available for detection of B. besnoiti infection in cattle. The use of one of these methods or their combination depends on the animal's and corresponding herd's clinical status [START_REF] Gutierrez-Exposito | Advances in the diagnosis of bovine besnoitiosis: Current options and applications for control[END_REF].

Concerning BB control, there is no effective drug or vaccine available, although in South Africa and Israel, a live-attenuated vaccine has been used [START_REF]Scientific statement on Bovine besnoitiosis[END_REF]. Detection followed by culling is also a management option. However, the lack of detection/regulation in animals' movements within a country and between countries has led to its rapid spread from Western Europe towards eastern countries and to the north [START_REF] Gutierrez-Exposito | Advances in the diagnosis of bovine besnoitiosis: Current options and applications for control[END_REF][START_REF]Scientific statement on Bovine besnoitiosis[END_REF]. There are few references available concerning control measures against insects (vectors) related specif-ically to BB. In 1968, Bigalke demonstrated the possibility of vector control [START_REF] Bigalke | New concepts on the epidemiological features of bovine besnoitiosis as determined by laboratory and field investigations[END_REF]. Some pyrethroids are active on stomoxes, but controlling the latter becomes difficult because of insecticide resistance development [START_REF] Salem | Susceptibility of two European strains of Stomoxys calcitrans (L.) to cypermethrin, deltamethrin, fenvalerate, lambda-cyhalothrin, permethrin and phoxim[END_REF][START_REF] Tainchum | Phenotypic susceptibility to pyrethroids and organophosphate of wild Stomoxys calcitrans (Diptera: Muscidae) populations in southwestern France[END_REF]. For tabanids, only a short time effect of pyrethroid insecticides has been cited [START_REF] Mullens | Chapter 16: Horse flies and deer flies (Tabanidae)[END_REF] and they are considered far less effective than similar applications targeting other vectors (e.g., mosquitoes).

Outbreaks of BB have been reported in Africa, mainly in the South [START_REF] Gutierrez-Exposito | Advances in the diagnosis of bovine besnoitiosis: Current options and applications for control[END_REF]. BB has also been reported in Israel, Kazakhstan, the People's Republic of China, India and Venezuela [START_REF] Duvallet | Other vector-borne parasitic diseases: Animal helminthiases, bovine besnoitiosis and malaria[END_REF][START_REF] Álvarez-García | A century of bovine besnoitiosis: An unknown disease re-emerging in Europe[END_REF]. In Europe, the disease is endemic (referring to a clinically expressed or non-expressed disease that occurs regularly in animals in a given area) in Spain, Portugal, Italy and France [START_REF] Duvallet | Other vector-borne parasitic diseases: Animal helminthiases, bovine besnoitiosis and malaria[END_REF][START_REF] Mutinelli | Bovine besnoitiosis in imported cattle in Italy[END_REF][START_REF] Gentile | Evidence for bovine besnoitiosis being endemic in Italy-First in vitro isolation of Besnoitia besnoiti from cattle born in Italy[END_REF]. In endemic areas, there are very few studies on the economic impact of BB. However, recently, a paper has revealed an association with a higher milk somatic cell count and BB, which can induce important economic losses [START_REF] Anastácio | Impact of Endemic Besnoitiosis on the Performance of a Dairy Cattle Herd[END_REF].

Several outbreaks have been reported in European non-endemic countries [START_REF] Álvarez-García | A century of bovine besnoitiosis: An unknown disease re-emerging in Europe[END_REF] such as Germany [START_REF] Mehlhorn | Another African disease in Central Europa: Besnoitiosis of cattle. I. Light and electron microscopical study[END_REF], Switzerland [START_REF] Lesser | First cases of besnoitiosis in cattle in Switzerland[END_REF], Croatia [START_REF] Cortes | A review on bovine besnoitiosis: A disease with economic impact in herd health management, caused by Besnoitia besnoiti (Franco and Borges)[END_REF], Hungary [START_REF] Hornok | Bovine besnoitiosis emerging in Central-Eastern Europe, Hungary[END_REF], Ireland [START_REF] Ryan | Bovine besnoitiosis (Besnoitia besnoiti) in an Irish dairy herd[END_REF] and Belgium [START_REF] Vanhoudt | First confirmed case of bovine besnoitiosis in an imported bull in Belgium. Vlaams Diergeneeskd[END_REF][START_REF] Delooz | Emergence of Besnoitia besnoiti in Belgium[END_REF]. A range of reasons could explain this new scenario, including the animal trade, management practices such as sharing pastures, and climate change by modification of the vector activity [START_REF] Bianchini | Prioritization of livestock transboundary diseases in Belgium using a multicriteria decision analysis tool based on drivers of emergence[END_REF]. Indeed, disease emergence is related to the joint presence of several factors, called "drivers". The knowledge of these drivers is crucial to properly understand hostpathogen-environment interactions [START_REF] Saegerman | First expert elicitation of knowledge on drivers of emergence of influenza D in Europe[END_REF].

The aim of this study was to investigate, for the first time, the drivers of emergence of BB in Europe using expert elicitation. Multi-criteria decision analysis (MCDA) was chosen to allow systematic integration of information from a range of sources [START_REF] Cox | Multi-Criteria Decision Analysis Tools for Prioritising Emerging or Re-Emerging Infectious Diseases Associated with Climate Change in Canada[END_REF] and improve repeatability and transparency [START_REF]Best Practices in Ranking Emerging Infectious Disease Threats. A Literature Review[END_REF].

Results

Response Rate and Field of Expertise Mobilised by the Experts

Eleven European professionals with recognized scientific knowledge and/or field knowledge or experience on BB in cattle were contacted and all agreed to participate. The fields of expertise were summarized in Appendix A Table A1.

Estimating the Overall Weighted Score and Ranking of Drivers of Bovine Besnoitiosis in Cattle

The medians of the weight between domains of drivers as well as for the different drivers were not equal according to the non-parametric Kruskal-Wallis test (Chi-squared test = 30.1 with 7 d.f. and α = 0.05, p-value = 0.0001; and Chi-squared test = 119.1 with 49 d.f. and α = 0.05, p-value = 0.0001, for the weights between domains and weights of the different drivers, respectively) (Figure 1).

The median of the weight of the domain D6 (wildlife interface) was significantly lower than the median of the other domains (bootstrapped regression; p-value < 0.001).

Ten drivers out of 50 were ranked as having the highest probability to play a key role in the emergence of BB in Europe. Indeed, the following drivers were ranked in a descending order of importance: the most likely influence of (il)legal movements of live animals (i.e., cattle) from neighboring/European Union member states (MS) (D8-4) or Third countries (a country that is not a member of the European Union as well as a country or territory whose citizens do not enjoy the European Union right to free movement) (D8-7) for the disease to (re)emerge in a given country, the risk of showing no clinical sign and silent spread during infection and post infection (D1-5) and as consequence, the difficulty of detecting the emergence (D3-7), the existence of vectors and its potential spread (D1-7), the European geographic proximity of the pathogen/disease to the country (D2-2), the animal density of farms with extensive (small holders with a few animals) versus intensive farming (D4-3), the disease's last reported case in Europe (D2-3), the mode of transmission of the pathogen (D1-8) and the problem of the ability of preventive/control measures to stop the disease from entering the country or spreading, excluding treatment, vaccination and vector(s)/reservoir(s) control (D3-1) (Figure 2).

Cluster Analysis

Two significantly different clusters were identified by regression tree analysis (Figure 3) (non-parametric Kruskal-Wallis equality-of-populations rank test; Chi-squared test = 102 with 1 d.f. and α = 0.05; p-value = 0.0001). These two clusters were classified as having "less importance" with 43 drivers and "more importance" with 7 drivers (D1_5, D1_7, D2_2, D3_7, D4_3, D8_4, D8_7), respectively.

Sensitivity Analysis of the Impact of Experts on the Final Ranking of Bovine Besnoitiosis Top Drivers of Emergence in Cattle

The result of the sensitivity analysis indicated that irrespective of the expert ignored, ignoring an expert only had no effect on the ranking of top 5 or 7 drivers (i.e., drivers included in the cluster with significantly more importance) considering a change of one or two ranks, respectively. These results were confirmed using a Kruskal-Wallis equality-of-populations rank test on experts for the top five or seven drivers identified. Indeed, results were very conclusive and respectively: chi-squared = 9.61 with 10 d.f. and probability = 0.48 (top five drivers) and chi-squared = 11.17 with 10 d.f. and probability = 0.34 (top seven drivers).

Discussion

Fifty drivers of BB in cattle were ranked and aggregated into two homogenous groups according to the present expert elicitation. Only the first ten most important ranked drivers will be further discussed with a focus on the seven categorized in the "more importance" node. In addition, for ranking of the first seven drivers, there was no expert effect when assessed by sensitivity analysis, indicating an acceptable robustness of the elicitation for the seven drivers included in the first node.

The first and second most important drivers were the influence of (il)legal movements of live animals from neighboring/European Union MS (D8-4) or from Third countries (D8-7), respectively. In European countries there are currently fewer movements of live animals originating from Third countries (note that BB was also reported in Africa and Asia) than from neighboring/European Union MS, explaining the difference in rank of these two drivers (see also international trade statistics, available at the following URL address: https://www.trademap.org/tradestat/Index.aspx; accessed on 15 December 2021). However, the animal trade from Africa to Europe may explain why the disease appeared in Europe by the end of 19th century and the beginning of 20th century in Portugal and France. In addition, there are very few studies available on the estimation of illegal movements of live animals in the scientific literature (e.g., [START_REF] Avila | Risk of Introduction of Bovine Tuberculosis (TB) Into TB-Free Herds in Southern Bahia, Brazil, Associated with Movement of Live Cattle[END_REF][START_REF] Beltran-Alcrudo | Transboundary spread of pig diseases: The role of international trade and travel[END_REF]). Nevertheless, a proper estimation of the relative importance of illegal movements of live animals and their introduction pathways is deemed essential to set up risk-based awareness, prevention and surveillance programs that correspond to reality [START_REF] Saegerman | First expert elicitation of knowledge on drivers of emergence of influenza D in Europe[END_REF]. Direct (isolation of the protozoan parasite and real-time polymerase chain reaction (rtPCR)) and indirect (IFAT, WB and ELISA) diagnostic tests have been set up for BB [START_REF] Gutierrez-Exposito | Advances in the diagnosis of bovine besnoitiosis: Current options and applications for control[END_REF]. Some commercial assays permit to implement a proper testing strategy in order to control the trade of live animals and to certify the sanitary BB status of the herd of origin. In order to identify mitigation measures, we strongly recommend developing a quantitative import risk assessment (QIRA) modelling similar to those developed for Lumpy skin disease that involved live bovines as well as S. calcitrans as a mechanic vector [START_REF] Saegerman | Risk of introduction of lumpy skin disease in France by the import of vectors in animal trucks[END_REF][START_REF] Saegerman | Risk of introduction of Lumpy Skin Disease into France through imports of cattle[END_REF]. These previous studies can serve as a basis for further modelling development.

The third and the fourth most important drivers were related to the risk of showing no clinical sign and silent spread during infection and post infection (D1-5) and as consequence, the difficulty to detect the emergence (D3-7). The disease is expressed only in the most susceptible animals [START_REF] Liénard | A longitudinal study of Besnoitia besnoiti infections and seasonal abundance of Stomoxys calcitrans in a dairy cattle farm of southwest France[END_REF][START_REF] Gollnick | Naturally acquired bovine besnoitiosis: Disease frequency, risk and outcome in an endemically infected beef herd[END_REF][START_REF] Taylor | Stable Fly (Stomoxys calcitrans, Muscidae)[END_REF]. In the chronic phase, cutaneous lesions and patognomnic scleral cysts may be helpful for diagnosis and also surveillance. However, many animals are sub-clinically infected with low parasite loads and they may act as parasite carriers which can only be diagnosed by serological tools [START_REF] Frey | Chronic bovine besnoitiosis: Intra-organ parasite distribution, parasite loads and parasite-associated lesions in subclinical cases[END_REF]. In endemic areas, clinical cases are observed between 1-10% of the new infections but between 15-20% in the case of B. besnoiti infections in areas where the disease is emerging [START_REF] Jacquiet | Bovine besnoitiosis: Epidemiological and clinical aspects[END_REF]. Moreover, during the first weeks following infection, acutely infected animals may be difficult to be clinically diagnosed due to non-specific signs [START_REF] Duvallet | Other vector-borne parasitic diseases: Animal helminthiases, bovine besnoitiosis and malaria[END_REF]. In addition, several other diseases should be considered in the differential diagnosis according to the stage of the BB such as malignant catarrhal fever, bovine granulocytic ehrlichiosis, bluetongue, bovine respiratory disease, photosensitization, scabies or zinc deficiency [START_REF] Alzieu | La besnoitiose bovine: Actualités physio-pathogéniques, cliniques et épidémiologiques[END_REF]. Indeed, clinical surveillance of BB is not fully efficient, and it is essential to carry out confirmatory laboratory tests [START_REF] Duvallet | Other vector-borne parasitic diseases: Animal helminthiases, bovine besnoitiosis and malaria[END_REF]. There is no formal gold standard test for BB but four tests are frequently used to confirm a clinical suspicion of BB: rtPCR and serological tests (IFAT, ELISA and WB). For WB, the sensitivity (Se) and specificity (Sp) are close to 100%. The Se and Sp of the IFAT are close to 100% and 95%, respectively. Depending on the ELISA used, their Se and Sp are generally > 97% and >93%, respectively [START_REF] García-Lunar | An Inter-Laboratory Comparative Study of Serological Tools Employed in the Diagnosis of Besnoitia besnoiti Infection in Bovines[END_REF]. The Se and Sp of the rtPCR are around 90% and >99% [START_REF] Schares | Quantitative real time polymerase chain reaction assays for the sensitive detection of Besnoitia besnoiti infection in cattle[END_REF]. A previous study recommended also a mandatory active surveillance system via a systematic analysis of all imported animals originating from areas at risk [START_REF] Delooz | Emergence of Besnoitia besnoiti in Belgium[END_REF]. Research is recommended to develop more commercial accurate laboratory assays and decision-making trees able to help the diagnostic of BB.

The fifth most important driver was the existence of vectors and their potential spread (D1-7). The knowledge of different species of blood-sucking insects in a country, their distribution and frequency over time, and the time-period during which vectors remain infectious after a blood meal on an infected animal [START_REF] Liénard | Development of a protocol testing the ability of Stomoxys calcitrans (Linnaeus, 1758) (Diptera: Muscidae) to transmit Besnoitia besnoiti (Henry, 1913) (Apicomplexa: Sarcocystidae)[END_REF][START_REF] Bigalke | New concepts on the epidemiological features of bovine besnoitiosis as determined by laboratory and field investigations[END_REF][START_REF] Sharif | Assessment of persistence of Besnoitia besnoiti (Henry, 1913) bradyzoites in Stomoxys calcitrans (Diptera: Muscidae)[END_REF] are of prime importance to develop QIRA modelling [START_REF] Saegerman | Risk of introduction of lumpy skin disease in France by the import of vectors in animal trucks[END_REF][START_REF] Saegerman | Risk of introduction of Lumpy Skin Disease into France through imports of cattle[END_REF]. In addition, due to the presence of mechanical vectors of BB (i.e., S. calcitrans and tabanids) in Europe, the seasonality of BB was previously reported as playing a major role in disease epidemiology [START_REF] Salem | Susceptibility of two European strains of Stomoxys calcitrans (L.) to cypermethrin, deltamethrin, fenvalerate, lambda-cyhalothrin, permethrin and phoxim[END_REF]. The inclusion of seasonality should be valuable for further development of a QIRA modelling.

The sixth most important driver was geographic proximity between a specific nonendemic country and a specific endemic country of origin (D2-2). This driver is related to the third and the fourth ones because if a disease is notifiable, it is easier to secure the trade. Threat analysis and QIRA modelling should be appropriate responses to deal with this driver [START_REF] Saegerman | Risk of introduction of lumpy skin disease in France by the import of vectors in animal trucks[END_REF][START_REF] Saegerman | Risk of introduction of Lumpy Skin Disease into France through imports of cattle[END_REF].

The seventh most important driver is related to the animal density of farms with extensive (small holders with a few animals) versus intensive farming (D4-3). Density of farms is a driver of spread of a disease, especially if mechanical vectors are present and if these vectors are able to transmit parasites for few hours after their last (interrupted) blood meal on infected cattle [START_REF] Sharif | Assessment of persistence of Besnoitia besnoiti (Henry, 1913) bradyzoites in Stomoxys calcitrans (Diptera: Muscidae)[END_REF].

The eighth most important driver is the last reported case of the disease in Europe (D2-3). This driver can be related to the fact that BB is currently not a reportable disease in most of the affected countries. Several criteria to include a disease as reportable exist among which the most important is its zoonotic character (that was not the case for BB according to [START_REF]Scientific statement on Bovine besnoitiosis[END_REF]) and its significant health impacts, taking into account the occurrence and severity of the clinical signs, including direct production losses and mortality [START_REF] Oie | Terrestrial Animal Health Code. Criteria for the Inclusion of Diseases, Infections and Infestations in the OIE list[END_REF]. Despite several papers reporting economic concerns related to BB (e.g., [START_REF] Cortes | A review on bovine besnoitiosis: A disease with economic impact in herd health management, caused by Besnoitia besnoiti (Franco and Borges)[END_REF][START_REF] Delooz | Emergence of Besnoitia besnoiti in Belgium[END_REF]), factual data on the burden of the disease and its translation to monetary losses are completely lacking [START_REF]Scientific statement on Bovine besnoitiosis[END_REF]. We strongly recommend estimating the economic burden of BB in order to convince policy makers to take action (or not) whether to include BB as a notifiable disease based on factual data.

The ninth most important driver was related to the mode of transmission of the pathogen (D1-8). There is evidence that several biting insects can mechanically transmit B. besnoiti [START_REF] Alzieu | La besnoitiose bovine: Actualités épidémiologiques et diagnostiques[END_REF][START_REF] Liénard | A longitudinal study of Besnoitia besnoiti infections and seasonal abundance of Stomoxys calcitrans in a dairy cattle farm of southwest France[END_REF][START_REF] Liénard | Development of a protocol testing the ability of Stomoxys calcitrans (Linnaeus, 1758) (Diptera: Muscidae) to transmit Besnoitia besnoiti (Henry, 1913) (Apicomplexa: Sarcocystidae)[END_REF][START_REF] Bigalke | New concepts on the epidemiological features of bovine besnoitiosis as determined by laboratory and field investigations[END_REF] but the entire life cycle remains unknown and especially the definitive host [START_REF] Cortes | Besnoitiosis in bulls in Portugal[END_REF]. The intra-herd transmission of BB is generally intense but weak between herds [START_REF] Waap | Prevalence and geographic distribution of Besnoitia besnoiti infection in cattle herds in Portugal[END_REF]. However, no information of the basic reproductive number for BB is known. Currently, in Europe, there is no strong evidence of the role of the wildlife in BB [START_REF] Waap | Serological survey of Toxoplasma gondii and Besnoitia besnoiti in a wildlife conservation area in southern Portugal[END_REF][START_REF] Gutierrez-Exposito | The role of wild ruminants as reservoirs of Besnoitia besnoiti infection in cattle[END_REF]. More studies are needed.

The tenth most important driver was related to the problem of the ability of preventive/control measures to stop the disease from entering the country or spreading (D2-1). Recent studies recommended the awareness of decision-makers about the need for an appropriate prevention and control policy, law enforcement and the implementation of necessary measures to avoid BB becoming endemic in non-endemic countries [START_REF] Delooz | Emergence of Besnoitia besnoiti in Belgium[END_REF][START_REF] Humblet | Integrated Management of Blood-Feeding Arthropods in Veterinary Teaching Facilities-Part 1: Overview of Haematophagous Arthropods of Interest in North-Western Europe[END_REF][START_REF] Humblet | Integrated Management of Blood-Feeding Arthropods in Veterinary Teaching Facilities-Part 2: Overview of Control Methods against Adults and Immature Stages[END_REF][START_REF] Humblet | Integrated Management of Blood-Feeding Arthropods in Veterinary Teaching Facilities-Part 3: Proposal for a Coherent and Affordable Control Plan[END_REF]. As biosecurity measures, a quarantine and a systematic screening of all imported animals originating from areas at risk can be proposed [START_REF] Delooz | Emergence of Besnoitia besnoiti in Belgium[END_REF]. In addition, in South Africa and Israel, live-attenuated vaccines were used [START_REF]Scientific statement on Bovine besnoitiosis[END_REF]. Other valuable preventive/control measures should be identified using networking permitting sharing of information and experiences between researchers/veterinarians and literature search, especially systematic review and meta-analyses and using an evidenced-based approach.

As an example of a recent advance, real-time PCR on skin biopsies permitted the detection of super-spreaders in BB [1] and identification/elimination of these super-spreaders contribute to disease control in heavily infected herds. The control of stable flies can be difficult by the development of insecticide resistance [START_REF] Tainchum | Phenotypic susceptibility to pyrethroids and organophosphate of wild Stomoxys calcitrans (Diptera: Muscidae) populations in southwestern France[END_REF] and nothing is known about the eventual resistance of horseflies to insecticides (or even their effectiveness). In addition, the lack of repellents with long lasting activity in livestock hampers ecto-parasite control. Moreover, regular treatments are not feasible in extensive husbandry systems.

Considering the European spread in time and space of the BB, the importance of live-animal trade between European countries (endemic versus non-endemic), the fact that notification of the disease is currently not mandatory, the large proportion of sub-clinically infected animals (but at risk), the need for affordable confirmatory tests, and the climatic changes that affect and alter the habitats and population dynamics of vectors, the BB is becoming a concern and needs more collective efforts to limit its spread and its impacts.

Materials and Methods

The methodology followed in this expert elicitation of knowledge is the same as previously published [START_REF] Bianchini | Prioritization of livestock transboundary diseases in Belgium using a multicriteria decision analysis tool based on drivers of emergence[END_REF][START_REF] Saegerman | First expert elicitation of knowledge on drivers of emergence of influenza D in Europe[END_REF] for other emerging diseases but is adapted for BB. For transparency, the method is detailed below.

Species Included

The objective was to prioritize the drivers of BB in Europe.

Questionnaire Design

To determine the main drivers of BB emergence, a questionnaire was used. A driver was defined as a factor that has the potential to directly or indirectly precipitate ("drive") or lead to the emergence of BB in cattle. A former questionnaire made to rank (re-)emergence of animal diseases based on drivers [START_REF] Bianchini | Prioritization of livestock transboundary diseases in Belgium using a multicriteria decision analysis tool based on drivers of emergence[END_REF] was adjusted for bovine besnoitiosis in cattle. These were formatted in an Excel ® (Microsoft, Redmond, WA, USA, 2016) file with one spreadsheet per domain, each domain harbouring its respective drivers. Each driver had a score with its definition, which could range from 0 to 4 or 1 to 4 and an intra driver weight point. A last spreadsheet was added, in which the 8 domains were listed, with an inter-domain weight.

Expert Elicitation on Drivers Used to Assess the Emergence of Bovine Besnoitiosis in Europe

An expert elicitation of knowledge was conducted, which consisted of gathering the opinion of people with recognized scientific expertise and/or experience in the field of BB in cattle (Appendix A). For guidance purposes, an explanatory letter accompanied the questionnaire that each expert had to fill out (Appendix C). Each expert was contacted personally and responded individually to the questionnaire. Data generated by the elicitation were based on the individual values provided by experts in order to capture the degree of variability of experts' knowledge. The elicitation was performed in one month.

Scoring and Weighting System

The elicited experts were asked to provide three types of information. First, they were asked to score the drivers (as established in Appendix B). For each driver, the higher the score, the higher the driver's chance to contribute to the emergence of BB in cattle. Uncertainty score was not asked due to lack of evidence-based data on BB in cattle at this stage. Secondly, experts were requested to weight each driver within a specific domain (intra-domain weight). This relative weight was determined using the Las Vegas technique [START_REF] Gore | Biostatistics and the Medical Research Council[END_REF]. Briefly, experts were given a number of points to be distributed between the drivers according to their importance in the specific domain. If all the drivers of a given domain had been considered as equivalent by experts, each of them would have received the same score. Lastly, the relative importance of each domain was subsequently weighted by experts (inter-domain weight).

Calculation of an Overall Weighted Score for Each Driver and Ranking Process

To obtain the overall score per driver, an aggregation method that combined the two types of weighting (i.e., the intra-and inter-domain) was used. First, the driver score (coefficients attributed by experts) was standardized by dividing it by the number of possibilities. Indeed, some drivers were allocated coefficients from 0 to 4 (5 possibilities) and others from 1 to 4 (4 possibilities). Afterwards, this standardized score was multiplied by the intra-domain weight and the inter-domain weight, as given by the expert. These results led to an overall weighted score for each driver and per expert:

OWSDri = SDri × WDri × WDoj (1)
In this formula, OWSDri = overall weighted score for a specific driver; SDri = standardized score for a specific driver; WDri = intra-domain weight for a specific driver; WDoj = inter-domain weight for a specific driver included in a specific domain. Further-more, all drivers were ranked based on the median overall weighted score obtained for each driver and taking into account the answers of all the experts who answered the questionnaire. The statistical difference of the median, depending on the specific driver or the group of drivers considered, was assessed through a non-parametric Kruskal-Wallis equality-of-populations rank test (State SE 14.2; StataCorp, College Station, TX, USA).

Cluster Analysis

A cluster analysis was carried out using a regression tree analysis (Salford Predictive Modeler ® , Version 8.2, Salford Systems, San Diego, CA, USA). The median overall weighted score (median OWSDri) being a continuous variable, the aim was to obtain groups of drivers with minimal within-group variance, with comparable likelihood to play a role in the emergence of BB in cattle. In addition, the statistical difference between medians after grouping drivers in clusters was assessed using a non-parametric Kruskal-Wallis equalityof-populations rank test. Indeed, each driver was characterized by a median (based on all experts' answers), then drivers were grouped. The test allowed highlighting of potential significant differences between groups, in terms of driver medians, after clustering.

Sensitivity Analysis to Test the Robustness of the Expert Elicitation

In order to identify whether the ranking of BB drivers of emergence was influenced by the choice of experts, a sensitivity analysis was performed on the top five and top seven drivers. First, we started by ranking the drivers using the obtained median OWSDri. Second, an expert was excluded from the analysis and the ranking of the drivers was carried out using the same methodology as previously described. This was done expert by expert. Third, we counted the number of changes in the ranking, for each driver, only considering changes equal or more than one rank. These results were confirmed using a Kruskal-Wallis equality-of-populations rank test on experts.

Conclusions

Since scientific knowledge on drivers of emergence of BB in cattle is still incomplete and associated uncertainty is high, expert elicitation of knowledge and multi-criteria decision analysis, in addition with clustering and sensitivity analyses, allowed the identification of seven drivers of more importance on which to focus on future studies. The transport of live cattle asymptomatic carriers seems to be a key factor of introduction and spread of BB. Indeed, further quantitative import risk assessment and estimation of economic burden of BB are highly recommended. This expert elicitation of knowledge should be also refined in the coming years when more evidence data will be available. In this case, addition of an uncertainty index should be recommended during elicitation. The present methodology could be applied to other emerging animal diseases. The application of this methodology to a specific disease also allows highlighting or not the need for more investigations. The disease can be present in zoo animals, but it is not known to have been transmitted from zoo animals to livestock

Score 2 Low:

The disease can enter a zoo (e.g., with introduction of an infected exotic animal) but only accidental transmissions of the disease from zoo animals to livestock have been reported. Hence, zoos have a low effect on the (re)emergence of the disease in livestock of your country

Score 3 Moderate:

The disease can enter a zoo and be present in zoo animals but it needs a vector (biological/mechanical) for its transmission into livestock. Therefore, zoos have a moderate effect on the (re)emergence of the disease your country

Score 4

High: Disease can be introduced to a zoo via an infected imported animal, zoo animals can carry the disease that can easily jump to livestock animals Table A2. Cont.

D6_2

The Negligible: there is a negligible probability of disease (re)emerging in livestock because of an increase in populations of endemic/migrating wild birds.

Score 2

Low: there is a low probability of the disease (re)emerging and spreading through increased populations of endemic/migrating wild birds. Disease has spread from the endemic/migrating wild birds but only accidentally or under exceptional circumstances Score 3 Moderate: there is a moderate probability of disease being introduced and spread through increased populations of endemic/migrating wild birds. They are hosts and in close contact with domestic livestock (i.e., poultry farms) may spread the disease

Score 4

High: there is a high probability for a disease to (re)emerge through increased populations of wild/migrating birds. These are hosts or reservoirs of the disease

Figure 1 .

 1 Figure 1. Boxplot of the relative importance of the eight domains of bovine besnoitiosis in cattle (N = 11 experts). Legend: The solid bold line represents the median of the score distribution between the different experts; the solid lines below and above each rectangle represent, respectively, the first and the third quartiles; adjacent lines to the whiskers represent the limits of the 95% confidence interval; small circles represent outside values. The eight domains of drivers are: D1, pathogen/disease characteristics; D2, distance of outbreaks (spatial-temporal scales); D3, ability to monitor, treat and control the disease; D4, European farm characteristics; D5, changes in climate conditions; D6, wildlife interface; D7, human activity; and D8, economic and trade activities.

Figure 2 .

 2 Figure 2. Ranking of the median overall weighted score for each potential driver of bovine besnoitiosis in cattle. (Boxplot based on 11 experts). Legend: the X-Axis represents the drivers with the following codification: D1 to D8 refer to the eight domains of drivers and D1_1 to D8_9 refer to a specific driver (for the codification, see Appendix B), small circles represent outside values. The relation to Figure 3 was provided by the group named as having, respectively, "more importance" and "less importance" in bovine besnoitiosis emergence.

Figure 3 .

 3 Figure 3. Aggregation of drivers of bovine besnoitiosis in cattle using the score, into two homogenous groups using a regression tree analysis. Legend: N, number; Average, average score; SD, standard deviation; D1 to D8 refer to the eight domains of drivers and D1_1 to D8_9 refer to a specific driver (for the codification, see Appendix B).

  Using the following algorithms on 12 December 2021 (((bovine besnoitiosis [Title/Abstract]) OR (Besnoitia besnoiti [Title/Abstract]) OR (B. besnoiti [Title/Abstract])) AND (cattle [Title/Abstract]) AND (Europe [Title/Abstract])), search strings were conducted in PubMed (US National Library of Medicine, National Institutes of Health). The results of the search (N = 47 articles from 2009 through 2021) showed that three review paper were produced; other papers were related to field/epidemiological surveys (N = 20), biology studies (N = 10), diagnosis (N = 8), experimental studies (N = 3), treatments (N = 2), and vectors (N = 1).

  Fifty drivers were established and classified in eight different domains (Appendix B). The domains (D) were: (D1) disease/pathogen characteristics (N = 9 drivers); (D2) distance of Europe (spatial-temporal scales) (N = 3 drivers); (D3) ability to monitor, treat and control the disease (N = 7 drivers); (D4) Farm/European characteristics (N = 7 drivers); (D5) changes in climatic conditions (N = 3 drivers); (D6) wildlife interface (N = 6 drivers); (D7) human activities (N = 6 drivers); and (D8) economic and trade activities (N = 9 drivers).

Appendix A .

 . Profile of Experts Involved in the Elicitation of Knowledge (N = 11)

  The infected animal does not show any pathognomonic clinical sign(s); farmer is reluctant to declare/notify any abnormality Number of drivers = 7, hence 70 points to be distributed within this domain for the intra-domain weighing Domain D4. Farm/European characteristics. D4_1 Mono species farms-One single farmed animal (e.g., only bovines) or multi species farms (farms with more than one species e.g., goats and bovines in the same farm/land/premises) the type of farm does not influence in any form (re)emergence of the disease among the livestock population Score 2 Low: mono or multi species farm has a low effect on the risk of disease to emerge or re-emerge Score 3 Moderate: the type or types of farmed animals has a moderate effect on the emergence of the disease in your country Score 4 High: the type of farmed animals has a high influence for the disease to emerge and spread in your countryTable A2. Cont. D4_6 Proximity of livestock farm to wildlife and wildlife reservoirs of disease e.g., contact with wild or feral birds and animals which have been scavenging on landfill sites that contain Disease (re)emergence from wildlife and wildlife reservoir never reported Score 2 Low: Disease (re)emergence from wildlife and wildlife reservoir rarely reported Score 3 Moderate: Disease (re)emergence from wildlife and wildlife reservoir is documented regularly Score 4 High: wildlife is a reservoir for the disease and the main source of infection for livestock D4_7 Changes of land use, e.g., field fragmentation, creation of barriers, Changes in land use have a negligible effect on the (re)emergence of pathogen/disease Score 2 Low: changes in land use have a low effect on the (re)emergence of the disease/pathogen but need other factors (e.g., land use changes combined with higher winter temperatures) Score 3 Moderate: land use changes increases the availability of vectors or increases the pathogen's survival. Also empty land can create a suitable environment for certain wildlife carrying the disease (e.g., migratory birds)Score 4 High: land use changes are one of the main drivers for pathogen or its vectors Number of drivers = 7, hence 70 points to be distributed within this domain for the intra-domain weighing Domain D5. Changes in Climatic Conditions D5_1 Influence of annual rainfall in the survival and transmission of the pathogen/Pathogen survival and mode of transmission of the disease are not influenced by increased rainfall Score 2 Low: pathogen survival and mode of transmission of the disease are slightly influenced by increased rainfall Score 3 Moderate: pathogen survival and mode of transmission of the disease are moderately influenced by increased rainfall Score 4 High: pathogen survival and mode of transmission of the disease are highly influenced by increased rainfall Table A2. Cont. D5_2 Influence of annual humidity in the survival and transmission of the pathogen/Pathogen survival and mode of transmission of the disease are not influenced by increased humidity Score 2 Low: pathogen survival and mode of transmission of the disease are slightly influenced by increased humidity Score 3 Moderate: pathogen survival and mode of transmission of the disease are moderately influenced by increased humidity Score 4 High: pathogen survival and mode of transmission of the disease are highly influenced by increased humidity D5_3 Influence of annual temperature in the survival and transmission of the pathogen/Pathogen survival and mode of transmission of the disease are not influenced by increased temperature Score 2 Low: pathogen survival and mode of transmission of the disease are slightly influenced by increased temperature Score 3 Moderate: pathogen survival and mode of transmission of the disease are moderately influenced by increased temperature Score 4 High: pathogen survival and mode of transmission of the disease are highly influenced by increased temperature Number of drivers = 3, hence 30 points to be distributed within this domain for the intra-domain weighing

  the disease has never (re)emerged from the narrowing of the farm-wild interface Score 2 Low: the disease has a low probability to (re)emerge via the livestock farm-forest interface. The disease has been known to (re)emerge from the wild bush but very rarely Score 3 Moderate: the disease has a moderate probability of (re)emergence via the farm/wildlife interface. Barriers ( natural or artificial) are needed to keep the disease/pathogen (re)emerging in livestock Score 4 High: there is a high probability for the disease to (re)emerge via the farm/forest interface. Barriers (natural or artificial) separating farms from natural forests are ineffective D6_3 Increase of autochthons (indigenous animal) wild mammals in Europe and neighbouring countries Score 0 Not applicable: disease has not been reported in wildlife Score 1 Negligible: the increase the autochthonous mammals population does not affect the risk of the diseases to (re)emergence Score 2 Low: The slight increase of autochthonous mammals can slightly increase the probably of the disease emerging Score 3 Moderate: The increase of wild mammals has been associated with the re-emergence of the disease Score 4 High: The increase of wild mammals is the only factor associated with outbreaks of the disease in livestock D6_4 Increase in endemic/migrating populations of wild birds Score 0 Not applicable: Wild/migrating birds are not a reservoir of the disease Score 1

  re)emergence of the disease by terrestrial movements of wildlife has only been suspected but never confirmedScore 2Low: There is a low probability for the disease to (re)emerge and spread through transboundary movements of terrestrial wildlifeScore 3Moderate: There is a moderate probability for the disease to (re)emerge and spread through transboundary movements of terrestrial wildlifeScore 4High: There is a high probability for the disease to (re)emerge and spread through transboundary movements of terrestrial wildlife. These are host and may spread/carry the disease along Number of drivers = 6, hence 60 points to be distributed within this domain for the intra-domain weighing the movement of tourism is a negligible driver on the emergence or re-emergence of the disease Score 2 Low: tourism increase has a low driver of the (re)emergence of the disease Score 3 Moderate: tourism increase has a moderate driver for the (re)emergence of the disease. Biosecurity measures are enough to stop the entering of the pathogenScore 4High: tourist movement is a high driver on the (re)emergence of a disease. Tourists are highly likely to bring the disease into your country in their belongings and biosecurity measures are insufficient to stop the pathogen

D8_6

  Most likely influence of increased (il)legal imports of non-animal products such as tires, wood, furniture from EU member states for the disease/pathogen to (re)emerge in your countryScoreScoreNegligible: (il)legal movements of live animals (livestock, pets, horses etc) from Third countries have a negligible influence on the pathogen/disease (re)emergence in your countryScoreLow: (il)legal movements of live animals (livestock, pets, horses etc) from Third countries have a low influence on the pathogen/disease (re)emergence in your country Score Moderate: (il)legal movements of live animals (livestock, pets, horses etc) from Third countries have a moderate influence on the pathogen/disease (re)emergence in your country Score High: (il)legal movements of live animals (livestock, pets, horses etc) from Third countries have a high influence on the pathogen/disease (re)emergence in your country. D8_7 Most likely influence of (il)legal movements of live animals (livestock, pets, horses etc) from Third countries for the disease to (re)emerge in your country Score Score Negligible: (il)legal movements of live animals (livestock, pets, horses etc) from Third countries have a negligible influence on the pathogen/disease (re)emergence in your country Score Low: (il)legal movements of live animals (livestock, pets, horses etc) from Third countries have a low influence on the pathogen/disease (re)emergence in your country Score Moderate: (il)legal movements of live animals (livestock, pets, horses etc) from Third countries have a moderate influence on the pathogen/disease (re)emergence in your country Score High: (il)legal movements of live animals (livestock, pets, horses etc) from Third countries have a high influence on the pathogen/disease (re)emergence in your country Table A2. Cont. D8_8 Most likely influence of increased imports of animal sub-products such as skin, meat and edible products from Third countries, for the disease to (re)emerge in your Increased imports of animal subproducts such as skin, meat and edible products from Third countries have a negligible influence on the pathogen/disease (re)emergence in your country Score 2 Low: Increased imports of animal subproducts such as skin, meat and edible products from Third countries have a low influence on the pathogen/disease (re)emergence in your country Score 3 Moderate: Increased imports of animal subproducts such as skin, meat and edible products from Third countries have a moderate influence on the pathogen/disease (re)emergence in your country Score 4 High: Increased imports of animal subproducts such as skin, meat and edible products from Third countries have a high influence on the pathogen/disease (re)emergence in your country D8_9 Most likely influence of increased (il)legal imports of non-animal products such as tires, wood, furniture from Third countries, for the disease to (re)emerge in your increased (il)legal imports of non-animal products such as tires, wood, furniture from Third countries have a negligible influence on the pathogen/disease (re)emergence in your country Score 2 Low: increased (il)legal imports of non-animal products such as tires, wood, furniture from Third countries have a low influence on the pathogen/disease (re)emergence in your country Score 3 Moderate: increased (il)legal imports of non-animal products such as tires, wood, furniture from Third countries have a moderate influence on the pathogen/disease (re)emergence in your country Score 4 High: increased (il)legal imports of non-animal products such as tires, wood, furniture from Third countries have a high influence on the pathogen/disease (re)emergence in your country Number of drivers = 9, hence 90 points to be distributed within this domain for the intra-domain weighing

Table A1 .

 A1 Profile of experts involved in the elicitation of knowledge (N = 11).

	Last Name	First Name	Gender	Institution	Country	Field of Expertise
	Álvarez-García	Gema	Female	Complutense University of Madrid	Spain	Animal health: Parasitology and parasitic diseases
	Alzieu	Jean-Pierre	Male	Veterinary Laboratory of the department of Ariège	France	Animal parasitology
				Regional Association for
	Delooz	Laurent	Male	Animal Registration	Belgium	Animal disease epidemiology
				and Health
	Evrard	Julien	Male	Regional Association for Animal Registration and Health	Belgium	Animal disease project management
				Department of Veterinary
	Gentile	Arcangelo	Male	Medical Sciences, University	Italy	Bovine internal medicine
				of Bologna
	Houtain	Jean-Yves	Male	ARSIA	Belgium	Animal disease management
	Jacquiet	Philippe	Male	Ecole Nationale Vétérinaire de Toulouse	France	Parasitology, parasitic diseases, applied zoology and tropical parasitology
	Gazzonis	Alessia Libera	Female	Università degli Studi di Milano	Italy	Veterinary parasitology, parasitic diseases
	Liénard	Emmanuel	Male	Ecole Nationale Vétérinaire de Toulouse	France	Parasitology, parasitic diseases and applied zoology
	Schares	Gedeon	Male	Friedrich-Loeffler-Institut	Germany	Animal health
	Villa	Luca	Male	Università degli Studi di Milano	Italy	Veterinary parasitology, parasitic diseases

Table A2 .

 A2 Cont. Animals only are infected by direct close contact with other infected animals and vertical transmission

	D1_8	Transmission of the pathogen
		Score 0
		Score 1 Low: Score 2 Moderate: transmission by direct and indirect contact only (e.g., through vehicles, clothes, instruments) or non-flying vector (e.g., ticks)
		Score 3	High: Exclusively vector transmission by flying vectors (e.g., culicoides, mosquitoes)
		Score 4	Very high: more than three modes of transmission and/or airborne transmission
	D1_9	Environmental persistence
		Score 0	Null: pathogen does not survive in the environment
		Score 1

Low: only anecdotal isolation of the pathogen from the environment has been recorded

Score 2

Moderate: The survival of the agent in the environment is limited (only temporary) and it's dependent on certain environmental conditions such as humidity, temperature, rainfall, etc.

Score 3 High:

The survival of the agent in the environment is limited (only temporary) and NOT dependent on certain environmental conditions such as humidity, temperature, rainfall, etc.

Score 4

Very high: agent naturally surviving in the environment (soil, water) and organic materials were it has a long term-survival Number of drivers = 9, hence 90 points to be distributed within this domain for the intra-domain weighing Domain D2.

Distance to Europe D2_1 Current incidence (cases)/prevalence of the disease in the world Score 0 Score 1 Pathogen

		Score 3	Disease was reported/present in the African continent
		Score 4	Disease was reported in countries of the Mediterranean Basin, Middle East and the Russian Federation
	D2_2	European geographic proximity of the pathogen/disease to Europe
		Score 0
		Score 1	Disease has never been present in Europe
		Score 2	Disease has been reported in Europe in the past but is currently exotic.

has been reported only in the countries of the Australasia (Australia, New Zealand, New Guinea and Neighbouring Pacific Islands) region

Score 2

Disease was reported in countries of the Americas, Caribbean and Asia (excluding the Russian Federation)

Score 3

Disease is currently present in at least one European country which is NOT bordering your country

Score 4

Diseases is currently present in at least one of the countries bordering your country

Table A2 .

 A2 Cont.

	D2_3	To your knowledge when was the disease last reported in Europe
		Score	More than 20 years ago
		Score	More than 10 years ago
		Score	More than 5 years ago
		Score	More than 1 year ago
		Score	Currently present in Europe
	Number of drivers = 3, hence 30 points to be distributed within this domain for the intra-domain weighing
	Domain D3.

Ability to Monitor, Treat and Control the Disease D3_1 Ability of preventive/control measures to stop the disease from entering the country or spreading (containment of the epidemic/pandemic), excluding treatment, vaccination and vector

  Absence; no vaccine available on the market for a use in the species considered in the study, no experimental vaccine either

	D3_2	Vaccine availability
		Score
		Score	Very high: Commercialized vaccine available on a global scale (worldwide)
		Score	High: Local/mono-species vaccine available at a regional/national scale and/or for a targeted species (not systematically available for a global fight plan)
		Score	Low: Experimental vaccine, not commercialized to date; severe adverse reaction when applied; limited protector effect
		Score	Very low:

(s)/reservoir(s) control Score Score Very High: Sanitary certificate; effective traceability of animals and by-products; effective disinfection measures; no contact between domestic and wild animals; effective biosecurity measures Score High: No sanitary certificate; effective traceability of animals and by-products; effective disinfection measures; limited or incomplete possibilities to restrict contacts between domestic and wild animals; effective biosecurity measures Score Low: No sanitary certificate; incomplete traceability of animals and by-products; ineffective disinfection measures; incomplete restriction of contacts between domestic and wild animals; ineffective biosecurity measures Score Very low: No sanitary certificate; no traceability of animals and by-products; ineffective disinfection measures; impossibility to restrict contact between farms or between domestic and wild animals; biosecurity measures totally ineffective

Table A2 .

 A2 Cont.

	D3_3	Control of reservoir(s) and/or vector(s)
		Score 0	Null: No vector-borne transmission and/or no reservoir(s) known to date
		Score 1	Very high: Effective. Limited reservoir(s) with limited geographical repartition, easy-to-identify; high scientific knowledge on vector(s)/reservoir(s); effective fighting measures
		Score 2	High: Limited reservoir(s)/vector(s) with limited geographical repartition; easy-to-identify, high scientific knowledge on vector(s)/reservoir(s); effective fighting measures but not applicable at a large scale; limited fighting measures
		Score 3

Low: Numerous reservoirs vectors identified with limited geographical repartition; hard to identify. Lack of scientific knowledge on vector(s)/reservoir(s). Fighting measures are poorly effective-resistances and/or negative impact on environment;

Score 4

Very low: Numerous Vector(s)/reservoir(s)identified with wide geographic distribution; hard to identify, absence of scientific knowledge on vector(s)/reservoir(s); no effective fighting measure against vector(s) (no active molecule, resistance to measures applied)

D3_4 Availability and quality of diagnostic tools in your country

Score 0 Score 1 Very High: Field test(s) available and easy to use, with highly discriminating sensitivity and specificity Score 2 High: Tests used in local/regional laboratories by not in the field Score 3 Low: tests only used in specialized laboratories/national reference laboratory Score 4 Very Low: no diagnostic tools available to date

D3_5 Disease is currently under surveillance overseas (OIE, EU) Score 0 Score 1 Very high: Generalized

  Surveillance only in some EU member states (because they had cases of the disease) and only in some non-EU countries (not a disease reported in any international organisations) Absence of surveillance of the pathogen in all EU member countries and worldwide

	Score 2	High: Surveillance of the pathogen only EU member states
	Score 3 Low: Score 4 Very low:

surveillance implemented by all EU Member States and worldwide surveillance (i.e. OIE reported)

Table A2 .

 A2 Cont. Knowledge on eradication procedures but have never had to implement an eradication program in your country

	D3_6	Eradication experience in other countries and/or your country
		Score 0
		Score 1	Very high: Previous experience on eradication has been applied, fast and successfully
		Score 2	High: Previous experience on eradicating the disease but with some setbacks in the process
		Score 3 Low: Score 4 Very low: It is a novel disease, first time countries are faced with a new disease to eradicate
	D3_7	Detection of emergence-e.g.

, difficulties for the farmer/veterinarian to declare the disease or clinical signs not so evident Score 0 Score 1 Very high

: Disease is easily detected with clinically signs and farmers are aware of the disease and willing to notify it as soon as possible it Score 2 High: Disease is easily detected by the clinical signs but farmers don't have sufficient knowledge/awareness nor interest to notify it Score 3 Moderate: Disease is not as easily detect by the clinical signs and farmers don't have sufficient knowledge/awareness nor interest to notify

Table A2 .

 A2 Cont. disease is present in hunted wildlife and birds and only accidental cases have been reported in livestock that have (re)emerged because of hunting. The risk of the disease/pathogen of (re)emerging in livestock due to hunting activities is practically null disease is present in hunted wildlife and birds and hunting is one of the main modes of transmission of the disease to livestock

	D6_5	Hunting Activities: hunted animals can be brought back to where livestock is present
		Score 0
		Score 1	Negligible: The risk of the disease/pathogen of (re)emerging in livestock due to hunting activities is practically null
		Score 2 Low: Score 3 Moderate: disease is present in hunted wildlife and birds but a certain control is established by the hunter
	Score 4 High: D6_6 Transboundary movements of terrestrial wildlife from other countries
		Score 0	Not applicable: Disease is not carried by terrestrial wildlife

Table A2 .

 A2 Cont. the disease is currently present in countries where more immigrants come from and pathogen highly likely to enter through, clothes, shoes and or possession, but the current biosecurity measures in place are able to prevent the emergence of the disease in your countryScore 4High: the immigration movement has a high effect as a driver on the emergence or re-emergence of disease in your country. Disease is highly likely to emerge using this route as biosecurity measures are not enough to avoid emergence of the disease

	D7_2	Human Immigration
		Score 0
		Score 1	Negligible: the immigration movements are a negligible driver of the disease (re)emergence in your country
		Score 2	Low: the immigration movements are a low driver of the disease (re)emergence in your country
		Score 3	Moderate:

D7_3 Transport movements: more specifically commercial flights, commercial transport by ships, cars or military (excluding transport vehicles of live animals) Score 0 Score 1 Negligible: the

  role of commercial movements as a driver on the (re)emergence of the disease in your country is negligibleScore 2Low: the role of commercial movements as a driver on the (re)emergence of the disease in your country is low. It is easily preventable by implementing biosecurity measures

	Score 3	Moderate: the role of commercial movements as a driver on the (re)emergence of a disease in your country is moderate. Disease can be prevented if biosecurity measures are tightened
	Score 4	High: the role of commercial movements as a driver on the (re)emergence of a disease in your country is high. Disease is hard to control via the current biosecurity measures
	D7_4

Transport vehicles of live animals Score 0 Score 1 Negligible: the

  role of transport vehicles of live animals as a driver for the (re)emergence of the disease in your country is negligibleScore 2Low: the role of transport vehicles of live animals as a driver for the (re)emergence of the disease in your country is low the role of transport vehicles of live animals as a driver for (re)emergence of the disease in your country is high

	Score 3	Moderate: the role of transport vehicles of live animals as a driver for (re)emergence of the disease in your country is moderate
	Score 4	High:

Table A2 .

 A2 Cont. the role of bioterrorism as a driver for a disease to (re)emerge is low: agent is available and easy to handle by professionals and labs but has a low spreadScore 3Moderate: the role of bioterrorism as a driver for a disease to (re)emerge is moderate: agent available and easy to handle by professionals and labs and rapidly spreadsScore 4High: the role of bioterrorism as a driver for a disease to (re)emerge is high: Agent is available and easy to handle by individuals and rapidly spreads

	D7_5	Bioterrorism potential
		Score 0
		Score 1	Negligible: the role of bioterrorism as a driver for a disease to (re)emerge is negligible: agent is available but difficult to handle or has a low potential of spread or generates few economic consequences
		Score 2	Low:

D7_6 Inadvertent release of an exotic infectious agent from a containment facility e.g., Laboratory Score 0 Score 1 Negligible

	Score 4	High: pathogen is handled in a risk 3 or 4 laboratory (BSL3 or BSL4) in the country. It can leave the facility if the correct biosecurity measures are not implemented correctly and easily spread to livestock
	Number of drivers = 6, hence 60 points to be distributed within this domain for the intra-domain weighing
	Domain D8.

: the pathogen is not currently present in any laboratory

Score 2

Low: the pathogen is present in a containment facility but its release is very unlikely as it is very easily contained

Score 3

Moderate: the pathogen is present in a containment facility and its release can occur as not easily contained

Economic and Trade Activities D8_1 Decrease of resources allocated to the disease surveillance Score 0 Score 1 Negligible: resources

  allocated to the disease surveillance have no effect on the (re)emergence of the disease in your country Disease has never been under surveillance resources allocated to the disease surveillance have a low effect on the (re)emergence of the disease in your country Disease has been under surveillance in the past and no change has happened after surveillance has been stopped resources allocated to the disease surveillance have a moderate effect on the (re)emergence of the disease in your country Disease is under passive surveillance (reported only when observed) but with no need to further increase its surveillance resources allocated to the disease surveillance have a high effect on the (re)emergence of the disease in your country Disease needs to be under active and passive surveillance as its (re)emergence can easily occur, therefore if its surveillance decreases it's highly likely to (re)emerge

	Score 2 Low: Score 3 Medium: Score 4 High:

Table A2 .

 A2 Cont.

	D8_2	Modification of the disease status (i.e.,

reportable disease becoming not reportable) or change in screening frequency due to a reduced national budget Score 0 Score 1 Negligible: modification

  of the disease status due to a reduced national budget has a negligible effect on the (re) emergence of the disease in your country modification of the disease status due to a reduced national budget has a low effect on the (re) emergence of the disease in your country modification of the disease status due to a reduced national budget has a moderate effect on the (re) emergence of the disease in your country modification of the disease status due to a reduced national budget has a high effect on the (re) emergence of the disease in your country

	Score 2 Low: Score 3 Moderate: Score 4 High:

D8_3 Decrease of resources allocated to the implementation of biosecurity measures at border controls (e.g., harbors or airports) Score 0 Score 1 Negligible: decreasing

  the resources allocated to the implementation of biosecurity measures has a negligible effect on the (re)emergence of the disease in your country.

Disease has never been detected in the past in a harbor or airport

Score 2

Low: decreasing the resources allocated to the implementation of biosecurity measures has a low effect on the (re)emergence of the disease in your country. The disease has been suspected to have entered other countries because of deficient biosecurity at border controls Score 3 Medium: decreasing the resources allocated to the implementation of biosecurity measures has a moderate effect on the (re)emergence of the disease in your country. The disease has been introduced in other countries because of deficient biosecurity at border controls

Score 4

High: decreasing the resources allocated to the implementation of biosecurity measures highly increases the risk of (re)emergence of the disease in your country. In the past, the disease has been introduced in other countries and in your country because of deficient biosecurity at border controls

D8_4 Most likely influence of (il)legal movements of live animals (livestock, pets, horses etc) from neighbouring/European Union member states (MS) for the disease to (re)emerge in your country Score 0

  (il)legal movements (livestock, pets, horses etc.) from neighbouring/European Union MS have a high influence on the pathogen/disease (re)emergence in your country

	Score 1	Negligible: (il)legal movements of live animals (livestock, pets, horses etc) from neighbouring/European Union MS have a negligible influence on the pathogen/disease (re)emergence in your country
	Score 2	Low: (il)legal movements (livestock, pets, horses etc) from neighbouring/European Union MS have a low influence on the pathogen/disease (re)emergence in your country
	Score 3	Moderate: (il)legal movements (livestock, pets, horses etc) from neighbouring/European Union MS have a moderate influence on the pathogen/disease (re)emergence in your country
	Score 4	High:

Table A2 .

 A2 Cont.

	D8_5	Most likely influence

of (il)legal movements of pets from Third countries for the disease to (re)emerge in Europe Score Score Negligible: increased

  (il)legal imports of animal subproducts such as skin, meat and edible products from EU member states have a negligible influence on the pathogen/disease (re)emergence in your countryScoreLow: increased (il)legal imports of animal subproducts such as skin, meat and edible products from EU member states have a low influence on the pathogen/disease (re)emergence in your countryScoreModerate: increased (il)legal imports of animal subproducts such as skin, meat and edible products from EU member states have a moderate influence on the pathogen/disease (re)emergence in your countryScoreHigh: increased (il)legal imports of animal subproducts such as skin, meat and edible products from EU member states have a high influence on the pathogen/disease (re)emergence in your country

Acknowledgments:

The authors thank all experts who participated to this study. Their names can be found in Appendix A.

Funding: This research received no external funding.

Institutional Review Board Statement: Not applicable.

Informed Consent Statement: Not applicable.

Data Availability Statement:

The data that support the findings of this study are available from the corresponding author upon request.

Author Contributions: C.S. and J.B. organized the elicitation of experts. J.E., J.-Y.H., L.D., J.-P.A., G.S., E.L., P.J., L.V., G.Á.-G., A.L.G. and A.G. were elicited as recognized experts in the field of bovine besnoitiosis. C.S. analyzed the data. C.S. drafted the manuscript, while S.E.M. reviewed and edited it for clarity. C.S. and J.B. contributed to the study design. All authors have read and agreed to the published version of the manuscript.

Conflicts of Interest:

The authors declare no conflict of interest.

Appendix B. Domains with Each Defined Driver and Their Respective Defined Scores

Table A2. Domains with each defined driver and their respective defined scores (Adapted form [START_REF] Gentile | Evidence for bovine besnoitiosis being endemic in Italy-First in vitro isolation of Besnoitia besnoiti from cattle born in Italy[END_REF]).

Domain D1. Disease/Pathogen Characteristics

D1_1

Current Knowledge of the Pathogen.

Score 0 Score 1 Very high: deep scientific knowledge on the pathogen, extensive scientific literature available on its biology (transmission mode, knowledge on vector(s), infectivity, etc.)

Score 2

High: detailed scientific knowledge on the pathogen but conflicting scientific results; some elements of the pathogen's biology are still not elucidated

Score 3

Moderate: limited scientific knowledge on the pathogen agent because it is still under characterization; pathogen recently discovered/isolated but belonging to a well-known and studied family of pathogens; the pathogen is characterized by multiple variants not characterized yet

Score 4

Low: lack of scientific knowledge on the pathogen (multiplication, infectivity, incubation period, transmission mode, etc.); pathogen agent recently discovered and emerging Guidance letter for the expert elicitation.

D1_2

Ranking criteria of emerging bovine besnoitiosis in Belgium (Experts' opinion) Dear Colleague

This special request is related to the emergence of bovine besnoitiosis in Belgium.

The objective of the present study is to understand more the drivers of emergence of the bovine besnoitiosis in Belgium. The questionnaire was prepared in order to present different criteria of interest and summarized in a total of 50 drivers. For each driver, scores are given with a corresponding definition. Drivers are grouped by category (N = 8), each category in one spreadsheet. After the scoring the weight of each driver for a specific category of drivers and for each category are performed.

Objective of the questionnaire

We would like your expert opinion on the drivers of emerging bovine besnoitiosis in Europe.

Hence, to answer on the basis of "how likely is it for bovine besnoitiosis in Belgium in response to the different drivers".

How to fill the questionnaire

In the attached Excel Questionnaire, there are 9 Spreadsheets. The first 8 correspond to the 8 categories of drivers and the 9th to the Intra-category weighing.

Actions to be done:

1)

Score and balance each driver within each category of drivers:

Please give a score according to what you estimate is the importance of each driver in the (re)-emergence of specific disease(s).

After the scoring, please balance each driver for each category of drivers. Balancing the criteria will rely on the distribution of points between the different proposed criteria under each category. The total number of points to be distributed among the drivers is specified for each category (each spreadsheet). e.g., category pathogen characteristics total 90 points; distance of outbreaks (spatial-temporal scales) a total of 30 points to be distributed.

2)

Intra-category weighing: The last step of the process will consist in the distribution of 80 points between the 8 categories of criteria (Pathogen characteristics, distance of outbreaks, etc.). This is on the 9th spreadsheet. The distribution will depend on which is believed to be the strongest category of drivers.

As an expert in the field, your collaboration will help us a lot for the good course of the project.

Thank you in advance for your collaboration and for the time spent in filling the file before the Date.

For any question, not hesitate to contact claude.saegerman@uliege.be


T Zhou

M L Locatelli

L Laudebat

P Bidan

FEM simulation based study of electric field reduction by linear and nonlinear resistive solution for HV power module under switching operation

The development of wide band gap semiconductor devices, in answer to the increase in the voltage level and the power density of power electronics converters, requires the development of new solutions for their electrical insulation systems, especially for the electric field reduction in power modules. The introduction of a resistive material within the encapsulation system, either as an added surface layer, or using the encapsulating bulk material, is one solution reported. In most cases, the related studies have been made by observing the steady state of an excitation in time domain. However, the isolation system in power modules is exposed to Pulsed Width Modulation (PWM) signals with a high switching speed. In this study, we investigate the resistive solution in the transient regime with a high slew rate voltage pulse excitation, close to realistic switching signals endured by the new semiconductor power devices (exhibiting dV/dt up to 100 kV/µs).

I. INTRODUCTION

The development of new semiconductor materials for power devices, particularly silicon carbide (SiC) and gallium nitride (GaN), leads to a new generation of wide band gap semiconductor power modules. The integration of SiC (or GaN) chips is a promising solution for reducing the size and the weight of the converters, thanks to faster switching speeds (up to 100 kV/μs), higher operating voltages and temperatures. The highest blocking voltage of commercial Si IGBT is 6.5 kV, whereas 15 kV SiC IGBT has already been developed [START_REF] Kadavelugu | Characterization of 15 kV SiC n-IGBT and its application considerations for high power converters[END_REF][START_REF] Madhusoodhanan | Solid-State Transformer and MV Grid Tie Applications Enabled by 15 kV SiC IGBTs and 10 kV SiC MOSFETs Based Multilevel Converters[END_REF], and even higher blocking voltages are expected in the future. A higher operating voltage level will further enhance the risk of partial discharges (PD) occurrence, which is one of the main causes of aging, degrading the electrical insulation reliability and which can lead to permanent failures such as material dielectric breakdown. In fact, in power modules, the highest electric fields may occur at the edges of the metallization of the ceramic substrate where the ceramic, the metallization and the encapsulating silicone gel are joining, so called triple points (TP) [START_REF] Frey | Electric field investigation in high voltage power modules using finite element simulations and partial discharge measurements[END_REF]. Hence, there is a maximum probability of PD at TP. In this regard, the electric field control at TP in order to limit PD is needed for future high voltage power modules. Methods to control the electric field E and protect the device by ameliorating the geometrical designs [START_REF] Hourdequin | Metallized ceramic substrate with mesa structure for voltage ramp-up of power modules[END_REF][START_REF] Reynes | Protruding ceramic substrates for high voltage packaging of wide bandgap semiconductors[END_REF] or adding some new parts in critical area [START_REF] Bayer | Enhancement of the partial discharge inception voltage of DBCs by adjusting the permittivity of the encapsulation[END_REF][START_REF] Bayer | Stacking of Insulating Substrates and a Field Plate to Increase the PDIV for High Voltage Power Modules[END_REF][START_REF] Donzel | Nonlinear resistive electric field control for power electronic modules[END_REF] have been proposed. The use of a bridging resistive surface layer, which connects the high voltage electrode and the ground potential [START_REF] Mitic | IGBT module technology with high partial discharge resistance[END_REF][START_REF] Tousi | Combined geometrical techniques and applying nonlinear field dependent conductivity layers to address the high electric field stress issue in high voltage high-density wide bandgap power modules[END_REF], is regarded as an effective field control method. The high electrical stress is reduced by a conduction current flowing through the layer. The resistive layer material can be a linear or nonlinear material. Here, 'linear' means that the electrical conductivity is independent on the electric field and 'nonlinear' means a field dependent conductivity (FDC). FDC dielectrics could be developed by adding nonlinear fillers into an insulating matrix. According to relation [START_REF] Kadavelugu | Characterization of 15 kV SiC n-IGBT and its application considerations for high power converters[END_REF], their electrical conductivity 𝜎 equals to 𝜎 ! at low E, and then exhibits an exponential increase when E is greater than a threshold value [START_REF] Christen | Nonlinear resistive electric field grading part 1: Theory and simulation[END_REF]. The threshold value (E " ) and the nonlinearity exponent (α) can be adjusted by choosing the particle type, size, surface treatment, shape and volume concentration [START_REF] Lin | A varistor-polymer composite with nonlinear electrical-thermal switching properties[END_REF][START_REF] Yang | Grading electric field in high voltage insulation using composite materials[END_REF].

𝜎(𝐸) = 𝜎 ! (1 + * |𝐸| 𝐸 # , $%& ) (1)
On the other hand, a faster voltage switching speed also brings a more severe electrical stress on the insulation system, especially at TP. In this aspect, some studies showed that the behavior of PD in IGBT module embedded in liquid encapsulation is quite different under not only different wave forms (sinusoidal or square) but also different slew rates (dV/dt). PD inception voltage (PDIV) of the tested sample is 18 kV under a 50 Hz sinusoidal voltage, 14 kV for a 400 μs-rise time bipolar square voltage and 8 kV for a 100 ns-rise time unipolar positive/negative square voltage [START_REF] Abdelmalik | Influence of fast rise voltage and pressure on partial discharges in liquid embedded power electronics[END_REF].

Although some previous researchers have studied the electric field reduction effectiveness of a linear resistive layer applied at the metallization edge [START_REF] Frey | Electric field investigation in high voltage power modules using finite element simulations and partial discharge measurements[END_REF][START_REF] Mitic | IGBT module technology with high partial discharge resistance[END_REF] and the performance of a nonlinear layer under different wave forms [START_REF] Donzel | Nonlinear resistive electric field control for power electronic modules[END_REF][START_REF] Tousi | Combined geometrical techniques and applying nonlinear field dependent conductivity layers to address the high electric field stress issue in high voltage high-density wide bandgap power modules[END_REF][START_REF] Tousi | The Effect of Type of Voltage (Sinusoidal and Square Waveform) and the Frequency on the Performance of Nonlinear Field-Dependent Conductivity Coatings for Electric Field Control in Power Electronic Modules[END_REF][START_REF] Huang | Mitigation measures of the electric field in the medium-voltage power module: Effect of voltage types and recommendations for designers[END_REF], few studies focus on the electric field control in the transient state under high slew rates (of the order of 100 kV/μs) as allowed by the switching speed of SiC MOSFET devices [START_REF] Das | 10 kV, 120 a SiC half H-bridge power MOSFET modules suitable for high frequency, medium voltage applications[END_REF]. In this study, we analyze the effectiveness of the resistive layer field reduction method under a high slew rate by numerical simulations.

In the first section, our study aims to simulate the module insulation system while using a linear resistive layer. The results in the transient state show that the field reduction depends both on the properties of the layer and on the slew rate of the applied voltage. In the second section, the effect of a FDC layer with different parameter sets under a high slew rate are evaluated. A tradeoff between the field reduction control and the thermal management is also discussed at the end.

II. LINEAR RESISTIVE LAYER

A. Description of the simulation method By using finite element method (FEM) simulation, one can obtain the electric field inside the power module which cannot be measured by the experiment. In fact, one can evaluate the effect of the insulating material properties, the geometry design, under different excitations, on the electric field distribution in the transient state. Our numerical simulation is carried out with COMSOL Multiphysics in time domain.

The simulated geometry is based on a direct bonded copper (DBC) aluminum nitride (AlN) ceramic substrate, as scheduled on Fig. 1 (a). It consists of a 2 mm thick metallized ceramic substrate with two metal electrodes placed 2 mm apart, which are covered by a 0.1 mm thick resistive layer. A step voltage excitation with a slew rate k (in kV/μs) from 0 V at 0 s to 20 kV is applied to the upper left electrode. The upper right bottom electrodes are regarded as the ground (0 V) potential. The DBC-AlN substrate is encapsulated by silicone gel. The permittivity and the electrical conductivity of AlN ceramic and silicone gel are shown in table I. We assume that relative permittivity er and the electrical conductivity s of the resistive layer could be modified. In particular, assuming the layer properties equal to the silicone gel ones means the structure is regarded as a standard structure without layer. It should be noted that all the results of the simulation not only depend on the mesh, but also on the geometry such as the thickness of the layer and the substrate, the shape of the metallization edge... Mathematically, the electric field at TP is infinite. In order to observe mesh independent field values, the maximum mesh size is set to 5 μm at critical areas, and the maximum electric field values Emax are finding out along measurement lines 1 and 2 in the gel with a distance of 15 μm from the layer/gel boundary, and along measurement line 3 in the ceramic as shown in Fig. 1 (b).

B. Electric Field Simulation without resistive layer

Fig. 2 (a) shows the time evolution of the maximum electric field up to long times (3000 s) when the system is under a step excitation, for two voltage slew rates k. The electric field keeps strengthening until the steady state has been reached. According to the steady-state solver, the maximum field is 66.87 kV/mm in AlN and 75.39 kV/mm in gel when the system is stabilized. It should be noted that the electric field distribution under a step excitation in steady state is independent on the slew rate.

The velocity of the field strengthening process depends on the dielectric time constants t = e0er/s (e0 vacuum permittivity) of the materials in the insulating system where tAlN and tgel being far greater than the voltage rise time, such k values have almost no effect on the electric field at the end of the ramp in this module standard insulation system configuration (Fig. 2 (b)).

C. Electric Field Simulation with a Linear Resistive Layer

In order to reduce the electrical stress, a linear resistive layer connecting the electrodes is implemented in the system. The evolutions of the maximum electric field in AlN, for different layer conductivities, and for 10 kV/μs and 100 kV/μs slew rates (er_layer = 2 in these simulations) are shown in Fig. 3 (in AlN) and Fig. 4 (in gel).

With the resistive layer, the local electrical stress can be reduced, thanks to the current flowing through the layer, compared to the case without resistive layer (as reported above Fig. 2). Moreover, it should be noted that the transient time electric field is further reduced only if the layer conductivity is great enough. Indeed, the velocity of the reduction process depends on the time constant tlayer of the layer. Hence, the peak value found at the end of voltage ramp in each case arises as a result of the competition between the voltage increase (electric field enhancing which depends on the slew rate k) and the electric field reduction velocity (depends on the time constant tlayer). Moreover, as pointed in Fig. 3 and Fig. 4, the peak value increases when the slew rate increases from 10 to 100 kV/μs. In order to keep the same performance of the electric field reduction at transient state, the conductivity of the layer should be increased 10 times while the slew rate increases 10 times.

Since the relative permittivity influences the layer time constant tlayer (tlayer is proportional to the layer permittivity), Fig. 5 shows also the electric field evolution with different layer permittivity values for two layer conductivity values and for k = 100 kV/μs. When the layer conductivity is quite low (equals to 10 -4 S/m), the transient field peak value decreases significantly while the layer permittivity increases. In this situation, the evolution of the field in transient state depends on the ratio of the layer permittivity and the substrate permittivity.

On the opposite, for a high enough layer conductivity, the system turning into the steady state faster and the field reduction almost depends mainly on the layer conductivity (for the same geometry). Hence, the variation of the layer permittivity almost has no effect on the transient field peak value when the layer conductivity is as high as 10 -2 S/m in Fig. 5.

In conclusion in the case of a linear resistive layer implementation, it has been shown that in order to well control the electric field reduction both in steady state and in transient state under a high slew rate excitation, a high enough layer electrical conductivity is required. However, the resistive current flowing in such a layer is proportional to the layer conductivity. For the future power modules including new fast switching devices, conductivities as high as discussed above (10 -2 S/m) would generate a large amount of leakage current within the electric system, and lead to a further increase in the module temperature. A field grading conductivity layer, which can auto adapt its property under a high field increase, has been proposed as a smart solution to reduce the electrical stress without leading to excessive leakage current. In the next section, the simulations with a FDC dielectric layer will be discussed.

III. FDC NONLINEAR RESISTIVE LAYER

Here it is considered that a nonlinear resistive layer connecting the electrodes is implemented in the simulated structure, with a dielectric permittivity er of 12, and an electrical conductivity 𝜎(𝐸) described by equation ( 1), assuming s0 = 10 -13 S/m, and different threshold (E " ) and nonlinear exponent (α) values. Simulations are performed for a step excitation with a slew rate k of 100 kV/μs. Fig. 6 shows the maximum electric field time evolution in the substrate during the transient state for all the given cases. At the beginning of the voltage supply, inducing low field values (E < Eb), the FDC layer exhibits a constant conductivity, so the field increase rates are the same in all cases. Then, as discussed before, a higher conductivity (for lower Eb and E > Eb) leads to a faster electric field limitation caused by a higher resistive current. Finally, a more nonlinear behaviour (for higher a value) turns to the steady state faster. Consequently, the effect on field reduction is more significant with a lower E " or higher α.

In the given geometry, a FDC layer with E " = 2 kV/mm and α = 15 allows to achieve the same performance of field reduction as a linear layer with a constant 𝜎 as high as 10 -2 S/m, in transient state under a k = 100 kV/μs step excitation. Fig. 7(b) allows to compare these two cases, representing the distribution of the electric field along the layer/substrate boundary at different times. The FDC layer can allow to achieve almost the same Emax reduction in the system as with the constant high conductivity layer (except at the beginning of the voltage rise (red curve, t = 0.1 µs) where the constant layer has a better efficiency, but where the latter is not high yet).

Besides the maximum field reduction aspect, both linear and nonlinear solutions need to be compared from the induced leakage current and power losses points of view. To estimate the leakage current flowing out the simulated structure, a 10 mm-depth of the 2-D geometry has been supposed. The time evolution of the resulting currents for the linear case (𝜎 = 10 -2 S/m) and two nonlinear cases are shown in Fig. 8(a). The resistive leakage current (as observable after the voltage rising stage, when t > 0.2 µs) is reduced by about 10 times by implementing a FDC layer with E " = 2 kV/mm and α = 15 compared to the linear layer. Fig. 7(a) also allows to notice the significative impact on the current of α parameter for the same Eb parameter. This illustrates the superiority of the nonlinear solution, allowing to adjust the same field reduction efficiency as the linear solution while monitoring acceptable leakage currents through the external system. However, these currents leading to power losses and an internal heating of the layer, the latter should be considered carefully as well during the design optimization process. The loss density can be calculated from the scalar product between the current density and the field at each node. Although lower total power losses are generated, it can be noticed that a higher local power density level may be

IV. CONCLUSION

The integration of new SiC components in high power modules allows higher blocking voltage and faster switching speed which lead to more severe electrical stress in their insulation system. A resistive layer is an effective method to reduce the electric field strength at triple points within the insulating system. The studied simulations showed that the field reduction effect in the transient state is the result of the competition between the field increase speed (which depends on the excitation slew rate) and the relative permittivity as well as the electrical conductivity of the layer. Under an excitation with a voltage slew rate as high as 100 kV/μs, an extreme high conductivity material should be used in the resistive layer to reduce efficiently the field both in transient and steady states. By using a FDC layer, the same electric field reduction can be achieved, with a well-optimized field dependency of the conductivity. The field is then reduced in the critical areas without a prohibitive increase in the current through the module. An important local concentration of the generated losses by Joule effect in these zones appears, which will require to add a thermal analysis to the entire system design optimization.

  Fig. 1. (a) Schema of the simulated geometry. (b) Zoom at TP, representing the lines used to determine Emax values in gel and ceramic. Also the simulated electrical field (kV/mm) distribution near TP in a standard structure is shown. k=10kV/7s Emax in gel k=10kV/7s Emax in AlN k=100kV/7s Emax in gel k=100kV/7s

Fig. 2 .Fig. 3 .

 23 Fig. 2. (a) Evolution of max. electric field without layer from 0 to 3000 s, and (b) from 0 to 5 μs

Fig. 4 .Fig. 5 .

 45 Fig. 4. Evolution of Emax in gel for different layer conductivities under a step excitation with two different slew rates

Fig. 6 .

 6 Fig. 6. Evolution of maximum electric field with FDC layer in AlN under the step excitation with k =100 kV/μs