Nicolas Faysse
email: faysse@cirad.fr

Léna Aguilhon
email: lena.aguilhon@hotmail.fr

Kassirin Phiboon
email: kassirinp@gmail.com

Man Purotaganon
email: purotaganon@gmail.com

Mainly farming…but what's next? The future of irrigated farms in Thailand

Keywords: ageing farmers, farming households, irrigation schemes, rice, Thailand

Introduction

Rural inhabitants in East and Southeast Asian countries increasingly obtain their income from off-farm sources. This is the case in low, medium and high income countries in the region [START_REF] Haggblade | The rural non-farm economy: Prospects for growth and poverty reduction[END_REF][START_REF] Rigg | The puzzle of East and Southeast Asia's persistent smallholder[END_REF] and is taking place not only thanks to increased opportunities in non-agricultural sectors but also because of the difficulty of maintaining or increasing incomes from farming. Many studies describe such processes in situations where farm characteristics and the environment in which farms evolve limit the prospects for obtaining an income, these being small size, lack of irrigation water, or limited market access [START_REF] Fishman | Patterns of migration, water scarcity and caste in rural northern Gujarat[END_REF][START_REF] Hu | Economic drivers of contemporary smallholder agriculture in a transitional economy: A case study of Hu Village from southwest China[END_REF][START_REF] Pritchard | How does the ownership of land affect household livelihood pathways under conditions of deagrarianization?'Hanging in','stepping up'and 'stepping out'in two north Indian villages[END_REF].

Far fewer studies have investigated the extent to which better endowed farms in East and Southeast Asia, in particular larger farms and farms with access to irrigation, are on the same pathway towards a diminished role of agriculture as a source of income in farming families. What is happening on these farms needs to be analysed to understand the evolution of the agricultural sector in these countries as a whole, especially as irrigated areas usually play a major role in supplying inputs to agricultural value chains and in supporting food security at national level. This topic is particularly relevant in Thailand, where the average farm is quite big (3.1 ha, according to the 2013 agricultural census) compared with other countries in East and Southeast Asia [START_REF] Rigg | The puzzle of East and Southeast Asia's persistent smallholder[END_REF]. Several studies have underlined the intensity and rapidity of the decline in the economic role of agriculture in farming households with limited access to land and irrigation water in Thailand. [START_REF] Gödecke | Rural-urban transformation and village economy in emerging market economies during economic crisis: empirical evidence from Thailand[END_REF], [START_REF] Nilsen | Remittances and development: the impact of remittances on livelihood security[END_REF], [START_REF] Rigg | Joining the dots of agrarian change in Asia: A 25 year view from Thailand[END_REF] and [START_REF] Rigg | Who will tend the farm? Interrogating the ageing Asian farmer[END_REF] investigated agrarian changes in villages in the Northern and Northeast Regions, where farming is mostly rainfed and where the average farm (between 1.9 and 2.3 ha in these studies) is smaller than the national average.

The image that emerges from these studies can be outlined as follows. First, ageing of the farming population is even faster than at national scale. In the villages studied by [START_REF] Rigg | Joining the dots of agrarian change in Asia: A 25 year view from Thailand[END_REF], the average age of people whose main activity was farming increased from 36 in 1983 to 55 in 2008. Second, young people are moving out of the villages. [START_REF] Gödecke | Rural-urban transformation and village economy in emerging market economies during economic crisis: empirical evidence from Thailand[END_REF] and [START_REF] Nilsen | Remittances and development: the impact of remittances on livelihood security[END_REF] identified a wide gap in the age pyramid at village level, as most people aged between 20 and 40 had moved to cities to find work. Third, household members increasingly find opportunities to work in factories and still come home every day [START_REF] Rigg | Reconfiguring rural spaces and remaking rural lives in central Thailand[END_REF]Shirai and Rambo, 2017;Shirai et al., 2017).

All these changes have reduced the availability of family labour, and farming households consequently increasingly choose farming systems and practices that require less family labour, e.g., planting trees, mechanisation or the use of paid labour [START_REF] Formoso | Are Thai Peasants still Farmers? The Socioeconomic Transformation of Two Villages of Northeastern Thailand[END_REF][START_REF] Podhisita | Household Dynamics, the Capitalist Economy, and Agricultural Change in Rural Thailand[END_REF]. In areas located not far from the frontiers of Thailand, hired labourers often come from neighbouring countries [START_REF] Barney | Land, livelihoods, and remittances: A political ecology of youth out-migration across the Lao-Thai Mekong border[END_REF][START_REF] Rungmanee | Unravelling the dynamics of border crossing and rural-to-rural-to-urban mobility in the Northeastern Thai-Lao Borderlands[END_REF]. These changes in the organisation of farming households (in terms of spatial structure and labour) have enabled them to adapt to the constraints and opportunities in both urban and rural areas. However, most of these changes reflect a trend towards less intensive farming [START_REF] Rigg | More than rural: textures of Thailand's agrarian transformation[END_REF].

More generally, the increasing labour constraints can limit farmers' capacity to or interest in testing and implementing more productive or more environmentally sustainable farming practices [START_REF] Bhandari | Impact of demographic transformation on future rice farming in Asia[END_REF][START_REF] Phastraporn | Analysis of Farm Structures and Farm Management Practices as Drivers of Adoption of Sustainable Land Management Practices in the Northeast Region of Thailand[END_REF]. This description of farm dynamics is representative of what is happening to the majority of the farms in these regions. Nevertheless, in rainfed areas of the North and Northeastern Regions of Thailand, some farms are actively engaged in changes involving the intensive use of family labour [START_REF] Piotrowski | Farming systems and rural out-migration in Nang Rong, Thailand, and Chitwan Valley, Nepal[END_REF][START_REF] Plews-Ogan | Polyculture, autonomy, and community: the pursuit of sustainability in a northern Thai farming village[END_REF]. Moreover, macro indicators do not show that the agricultural sector has become "dormant". Thailand remains a major producer and exporter of agricultural products (Thailand Board of Investment, 2017). Many farms successfully access high-value markets [START_REF] Kersting | New institutional arrangements and standard adoption: evidence from small-scale fruit and vegetable farmers in Thailand[END_REF] and powerful agro-industries have emerged [START_REF] Briones | Investigating the structures of agricultural trade industry in developing countries[END_REF]. The contribution of agriculture to the growth of Thailand's domestic product has not changed much over the past two decades (from 9.1% in 1996 to 8.6% in 2016, according to the World Bank, 2018). However, there have been few recent studies of agricultural dynamics in areas better endowed with resources in Thailand. [START_REF] Formoso | Are Thai Peasants still Farmers? The Socioeconomic Transformation of Two Villages of Northeastern Thailand[END_REF] studied rice farms with access to irrigation in the Northeast Region and reported that agriculture was still the main income-generating activity of several farms but did not detail the characteristics of these farms. By contrast, [START_REF] Rigg | More than rural: textures of Thailand's agrarian transformation[END_REF] reported that in a village located in an irrigated area of the Central Region, almost all the villagers surveyed said farming was no longer their main occupation.

The present study focuses on irrigated areas of central Thailand. Its aim was to understand whether the engagement of members of farm households in farming has declined in a similar way to that described in areas of Thailand where farms have limited access to land and water. Taking into account the diversity in the size and types of production of farms in the study area, our analysis addresses three issues: (i) how farming systems have adapted to key constraints and changes in the environment and within the farms, thus enabling -or not -households to earn their livelihood farming; (ii) what are the future prospects of these farms, especially in terms of the engagement of family members in farming; and (iii) to what extent ongoing policies and local initiatives to support agriculture help farming households deal with prevailing constraints and thus help sustain their engagement in farming.

Methodology

Study area

The study was conducted in the Bang Pakong River delta. This area belongs to a broader zone around Bangkok which also includes the deltas of the Mae Klong and Chao Phraya Rivers. These delta areas are not clearly defined in hydrological terms. This zone represents the largest irrigated area in Thailand and is mainly dedicated to growing rice. Intensive shrimp farming in coastal areas around Bangkok started in the 1980s [START_REF] Szuster | Environment and Livelihoods in Tropical Coastal Zones: Managing Agriculture-Fishery-Aquaculture Conflicts[END_REF], but faced a series of crises in the 1990s and in the 2000s, in particular because of diseases. This activity later recovered and expanded thanks to the development of new production techniques and to the introduction of shrimp species capable of adapting to low salinity levels [START_REF] Lebel | Innovation cycles, niches and sustainability in the shrimp aquaculture industry in Thailand[END_REF]. This enabled the extension of shrimp breeding to inland areas. Today, shrimps are the main agricultural product in the downstream part of the Bang Pakong River Basin [START_REF] Seekao | Key factors affecting the flood vulnerability and adaptation of the shrimp farming sector in Thailand[END_REF].

The main role of the Ministry of Agriculture and Cooperatives in this zone is to manage water, i.e. to provide irrigation water in the dry season and address flood problems in the rainy season. Four main national agricultural policies have been implemented in the delta region around Bangkok in the past three decades. The first involved a series of schemes to support rice prices on the domestic market but this support stopped almost completely after the military coup in 2015 [START_REF] Ricks | Public Choice, Institutional Change, and Rural Subsidies: Politics and the Price of Rice in Thailand[END_REF].

Second, reduction of the extent of land under rice and the promotion of other crops were declared national objectives in the Fourth National Plan (1977Plan ( -1981) ) and were strongly reaffirmed in the Seventh National Plan (1992Plan ( -1996) ) because of the low profitability of rice farming and because of water shortages [START_REF] Sirisup | Government policy and farmers' decision making: The agricultural diversification programme for the Chao Phraya River Basin (1993-95) revisited. Thailand's rice bowl: Perspectives on social and agricultural change in the[END_REF][START_REF] Srimanee | The fruit and vegetable marketing chains in Thailand: policy impacts and implications[END_REF]. A major diversification programme was implemented in the Chao Phraya River Basin from 1993 to 1999, but had limited results, the main causes being floods, labour shortages and difficulties related to the marketing of non-rice products [START_REF] Sirisup | Government policy and farmers' decision making: The agricultural diversification programme for the Chao Phraya River Basin (1993-95) revisited. Thailand's rice bowl: Perspectives on social and agricultural change in the[END_REF].

Third, from 2000 on, the Ministry of Agriculture and Cooperatives promoted an approach aimed at developing a "self-sufficiency economy" for small-scale farms [START_REF] Egery | Economic risks in the agricultural sectors of emerging economies: Smallholder perspectives of projects based on Thailand's Philosophy of Sufficiency Economy[END_REF]. According to this approach, small-scale farmers should avoid intensive monocropping (related to contract farming, for instance). Rather, small-scale farmers should produce both for home consumption and for the market, they should produce multiple crops, and use limited amounts of pesticides and chemical fertilizers.

Fourth, in 2015, the government announced a new policy that was almost completely opposed to previous ones. This policy aimed at helping small-scale farms improve the production and marketing of one crop (or animal). Groups of farmers were invited to work together in "large-scale schemes" and in partnership with public organisations to reduce production costs thanks to economies of scale, to increase yields and negotiate better prices. In the rice sector, the official objective was to reduce production costs by 20% and increase farm sales by 20% (Department of Agricultural Extension, 2016). This was to be achieved thanks to training, enhanced collective action between farmers and improved connection with markets (e.g., certification or contracting with agro-industries).

The main river in Prachinburi Province is the Prachinburi River, which becomes the Bang Pakong River after the confluence with the Nakhon Nayok River. The study areas are four irrigated zones that receive water from the Prachinburi and Bang Pakong Rivers (Figure 1). These four zones were selected because they include the main farming systems in the downstream part of the Prachinburi River basin. Farmers in Bang Pla Ra Subdistrict concentrate on fish and shrimp farming and farmers in Bang Taen Subdistrict on rice and fish farming. In the two other zones, farmers concentrate on rice production. Many farmers in the Dong Krathong Yam Subdistrict have purchased agricultural machinery, such as a tractor, and farm relatively large areas (more than 13 ha). Farmers in Bang Kung Subdistrict farm much smaller areas. Each study area receives irrigation water through a network of canals connected to the Prachinburi and Bang Pakong Rivers. The pumps that pump water from the rivers into the canals are operated by water user associations in Bang Kung, Bang Pla Ra and Dong Krathong Yam Subdistricts and by the subdistrict local administration in Bang Taen Subdistrict.

Analytical framework

We characterised farming systems and investigated how the farms had adapted to the constraints they faced, especially those related to water resources, agricultural equipment and labour. The future prospects of the farms were delineated using two indicators: the farmers' own plans for the future and interest expressed by possible successors in taking over the farm. Preliminary interviews showed that in many farming households, farming was the main activity of at least one member. Thus, we analysed whether farm incomes were sufficient for potential successors to be interested in taking over the farm as their main activity. Possible successors (particularly the farmer's own children) often compare the income they expect from farming with the income they could get from non-farming activities. The economic criterion concerning annual net income is clearly only one among many other criteria they use to decide whether to take over the farm or not. Other criteria include opportunities to increase their income in the future, income uncertainty, quality of life, the possibility to send the children to highquality schools, the amount of physical effort required, and autonomy in decision making [START_REF] Ruiz Salvago | The engagement in farming of rural young people in Thailand: present involvement, futures plans and hopes[END_REF].

The minimum wage for a full-time job in Thailand is approximately 8,000 baht1 per month (Thai National Wage Committee, 2016). Working in factories may involve renting a room or daily transport, at a cost of approximately 1,500 baht per month. Thus, working in factories may provide a net income of 6,500 baht per month. We consequently defined an economic threshold of 78,000 bath (approximatively 2,450 US$) net income per year as the minimum amount that possible successors would want before accepting to take over the farm, and to work on the farm as their main incomegenerating activity. This economic threshold is a very rough approximation, first because of the wide range of opportunities to obtain a non-farming income and of the variability of the cost of living. Second, farms with different characteristics do not require the same amount of labour and a more detailed analysis would involve calculating net income per unit of labour time.

Data collection and analysis

Twenty-seven farmers were interviewed in each of the four areas, giving a total of 108 farmers (43% of whom were women). We interviewed the farm holder or, if the farm was run by a couple, one of them.

The farms were chosen from lists of farmers provided by farmers' groups (e.g., the water users' association) to ensure diversity in terms of farm size, agricultural activities and the location of the farm within the irrigated areas. Interviews first focused on farm characteristics and family structure and second, on production costs and benefits in 2016. Third, farmers were asked if they had previously faced problems of insufficient irrigation water, brackish water or floods, and if so, what they had done to tackle them. Finally, farmers were asked about their plans in the future (in approximately 5 years) and whether they had already identified a successor within the family to take over their farm. Ten staff members of the offices of the Ministry of Agriculture and Cooperatives in Prachinburi Province were also interviewed to understand the policies and local initiatives implemented in our study areas to support farming activities. The interviews were conducted in 2017.

Farm net incomes were calculated as the difference between gross sales and yearly production costs, but did not account for past investments in agricultural equipment, since our focus was on the net income that a successor would expect if he or she took over the farm as it was. Neither did the assessment of production costs include family labour. We calculated the net annual income for each farm based on what each farm produced in 2016 including the possible cost of renting in land.

We compared net farm incomes with the above-mentioned economic threshold in two ways. First, we assumed the farm could be run by only one family member: the farm was considered economically attractive for possible successors if the net farm income was above this threshold. Second, we considered the number of family members working on the farm as declared in the survey (without accounting for how much time these members actually spent farming). In this case, we compared the net farm income with the economic threshold calculated at 78,000 baht per year multiplied by the number of family members engaged in farming. The farm was considered economically attractive for possible successors if the income generated was high enough to ensure that all members engaged in farming would be better off than working in factories.

Results

Types of farms

Before the 1990s, farmers located in the study areas only produced rice. They grew one rice crop per year, from approximately June to November. In the early 2000s, farmers started producing two rice crops per year: a rainy season rice from May to August and a dry season rice from November to February. Irrigation of rice is complementary in the rainy season but indispensable in the dry season.

Shrimp farming also developed in Bang Taen and Bang Pla Ra Subdistricts in the 1990s. One shrimp production cycle lasts four months (one month for preparation of the pond and three months for production per se), so three shrimp production cycles per year are possible. The length of the fish production cycle varies between 8 and 12 months. All the farmers in Bang Pla Ra Subdistrict interviewed had completely stopped rice farming, and at the end of the 2000s, they had shifted from producing shrimp alone to producing shrimp and fish bred together in the same ponds.

Four main types of farms were identified based on their agricultural production and equipment (Table 1). The first type groups farmers in Bang Pla Ra Subdistrict who bred fish and shrimp together in the same ponds. These farmers owned most of the land they used for fish and shrimp production. The second type groups eight farmers in Bang Taen Subdistrict who produced both rice and shrimp. The third type groups farmers in Bang Taen and Dong Krathong Yam Subdistricts who produced rice and had invested in a four-wheel tractor, and in rare cases also in a harvester. These farmers had purchased a tractor to reduce their dependence on service providers, e.g., for deep ploughing. The fourth type groups farmers in Bang Taen, Dong Krathong Yam and Bang Kung Subdistricts who mainly produced rice and had not invested in either a tractor or a harvester. They owned only a small tiller. Their average farm size was less than half the average size of the third type of farms. Some rice farmers grew other crops or had fishponds, but in a very small area and mainly for home consumption.

Farmers who grew rice had increased their farmed area in the past two decades mainly by renting in land. Rented land for rice production represented approximately half their farmed land. Farmers could generally not afford to buy land as the cost (which varied significantly but was approximately 600,000 baht per ha in Dong Krathong Yam) was very high compared to average net profit to be made from rice farming.

Among the interviewees, 74% farmed full time. For 75% of the remaining farmers who had other income-generating activities, such as being head of the village or running a shop, farming represented the main income-generating activity. In other words, in 94% of the households, farming was the main income-generating activity for at least one member of the household. In 41% of the cases, only one family member was involved in farming, in 47%, two were involved, and in 12% of cases, three or more members were involved. In 15% of farms (mostly belonging to Types 1, 2 and 3), the farmers' children aged less than 40, were also involved in farming.

According to the 2013 Thai agricultural census, at national level: 64.2% of farms cultivate less than 3.2 ha and can be considered as small-scale 2 , 31.1% farm between 3.2 and 9.6 ha and can be considered as medium-scale, and 4.7% of farms cultivate more than 9.6 ha, and can be considered as large-scale (National Statistical Office of Thailand, 2013). Among the farms we surveyed, 21% farmed less than 3.2 ha (13% only produced rice and 8% fish or shrimp), 55% farmed between 3.2 and 9.6 ha, and 25% farmed more than 9.6 ha. Thus, most of the farms we surveyed can be considered as medium to large scale.

Adaptation to constraints

Most of the farms we surveyed had adapted their farming practices to brackish water, floods, lack of labour or lack of agricultural equipment. Concerning brackish water, 52% of the farmers we interviewed said that the water in the river near their farm was sometimes brackish in the dry season. These farmers were generally located in downstream areas, Bang Taen and Bang Pla Ra Subdistricts. In their opinion, the occurrence of brackish water in the river had become increasingly frequent in the dry season over the past 15 years, especially in March and April. This was due to increased pumping because farmers had started producing dry season rice. As a result, seawater intruded inland over a much greater distance from the estuary.

At the individual level, rice farmers had adapted by growing short-duration rice varieties, which can be harvested before March. Fish and shrimp farmers had dug ponds to store water. At collective level, in February, the water users' associations pump water into canals to store it for later use when the water in the river becomes brackish. When salinity in the river reaches approximately 1 g/l, the gates connecting the canals to the river are closed and no more water is pumped into canals usually until June. As the gates are closed, if not enough water is stored in the canals, the farmers may face water shortages during this period. Thanks to these adaptive measures, only 11% of the farmers interviewed considered that the occurrence of brackish water affected crop yields or the production of fish and shrimp.

Second, floods occur frequently in the study areas in October and November. In Bang Taen, Dong Krathong Yam and Bang Kung Subdistricts, farmers made sure they harvested rice or completed a shrimp or fish production cycle before the flood period. In Bang Pla Ra Subdistrict, fish and shrimp farmers had installed nets along the edges of the ponds to make sure the fish and shrimp could not escape from the ponds during flooding. Farmers organised in groups (usually three to four members) had also collectively built small dykes around the ponds. Flooding was also managed collectively in Bang Taen Subdistrict, as the pumps operated by the subdistrict local administration, which were used to pump water into the canals in the dry season, were also used to pump flood water back into the river. Thanks to these adaptive measures, the farmers said they were usually not affected by floods.

Third, almost all the rice farmers outsourced part of or all their agricultural operations. In the study area, rice production involves five main activities: ploughing, sowing, spraying chemicals, applying fertilizers and harvesting. Among the 81 farmers who grew rice, 63 did not do the deep ploughing themselves, and 78 did not harvest themselves, mostly because they did not have the necessary machinery.

Approximately two thirds of the rice farmers also paid labourers to sow seeds, spray chemicals and apply fertilizers. The reasons given were: 1) lack of available family labour during periods of high labour needs; 2) health risks associated with the spraying of pesticides; and 3) the farmers' old age. This had consequences for profits since paying for hired labour and renting machines with their operators represented 54% of rice production costs (not including the cost of renting in land). Thus, on farms which only produced rice, only one person was engaged in full-time farming, while the other family members helped occasionally, for instance, with sowing.

By contrast, farmers engaged in fish and shrimp farming or combined rice and shrimp farming generally did the breeding themselves and only hired labourers to harvest the fish and shrimp at the end of each production cycle. They were also significantly younger than the farmers who only produced rice (p < 0.001). The average number of family members working on rice farms with no agricultural machinery was lower than in the three other types (Table 4) both because of the outsourcing of agricultural activities and because they farmed less land than rice farms with machinery.

Future prospects of the farms

Farmers involved in the most profitable activities (shrimp farming or combined fish and shrimp farming)

generally either planned to invest in their farming systems or had no major plans to change their systems because they were generally satisfied with them at the times of the interview (Table 1). Almost none of the farmers who only produced rice (Types 3 and 4 in Table 1) planned to intensify or expand their farming system. The advanced age of many of these farmers contributed to their lack of interest in changing their farming systems. Moreover, they considered that rice production had limited prospects for development due to low rice prices (and the government discourse claiming there would be no further subsidies for rice) and lack of identified opportunities for a major improvement in rice farming practices.

In particular, rice farmers who had invested in agricultural machinery did not mention a plan to expand their rice cropped area. Another reason for them not to expand rice cultivation was that they considered that they did not have the necessary labour force to do so.

Instead of expanding rice cropped areas, rice farmers who aimed to change their farming systems (41% of farmers who only produced rice) planned to diversify by growing other crops such as vegetables, planting orchards, or fish farming. None of the farmers who only produced rice were interested in shrimp farming because of the high investment costs required, lack of knowledge of the production techniques and markets, and because they considered shrimp farming to be risky, both in terms of diseases and in terms of market prices.

Forty-seven percent of rice farmers had no future plans because they considered their scope for change to be limited. Indeed, two main types of constraints do limit opportunities for change, in particular planting orchards or growing vegetables. The first constraint was the occurrence of brackish water and floods. Farmers could attempt to avoid flooding by building dykes and they could attempt to deal with brackish water by digging ponds in which fresh water would be stored. However, these investments were costly, and neither was guaranteed to solve the problems of brackish water or floods. Moreover, such costly investments were insecure on land that was rented in by the farmer, and 14 out of the 27 interviewed farmers in Bang Kung Subdistrict owned no land. Among the 73 farmers who only produced rice, only six had started planting an orchard or growing vegetables on very small areas.

Table 1 shows the farmers' own assessment of the chances that someone in their family would take over the farm. The percentage of farmers who already knew there would be no successor in their family was low among farmers engaged in shrimp farming or combined fish and shrimp farming (respectively, 15% and 0%). Rice farmers who had invested in agricultural machinery were also likely to have identified a successor (only four of the 22 farmers who farmed more than 9 ha had no identified successor). By contrast, 48% of rice farmers who had no machinery were sure that no-one in their family would take over their farm, most said their children were not interested.

In 2016, average yields of rice farms were 4.2 t/ha for both rainy season and dry season rice, giving an average net profit of 15,700 baht (i.e., approximatively US$490) per ha per year. If the farmers rented in land, the average net profit dropped to 8,350 baht per ha. The average net income for shrimp production was much higher: 108,000 baht/ha in 2016. Combined fish and shrimp production was between the two with an average net profit of 75,000 baht/ha in 2016. The profit had previously been higher, but by 2017, the sales price of fish had been declining for several years.

Table 2 compares net farm incomes with the economic threshold defined in the methods section. The net income of most Type 1, 2 and 3 farms was above the threshold when only one farming family member was considered, or when the number of family members actually involved in farming in 2017 was taken into consideration. Moreover, most Type 1, 2 and 3 farms that were under the threshold when considering the number of family members actually involved in farming may still be considered as being able to provide sufficient incomes for one person farming fulltime. For the six fish and shrimp farms which were under the threshold when considering all farming members but not when considering one member, the ratio of farmed area to the number of farming family members was of 0.6 to 0.8 ha per person. In practice, 66% of farmers we interviewed who were engaged in combined fish and shrimp breeding farmed more than 1.6 ha per person. This means that these farms could probably be managed by one person alone, and that they can thus be considered as above the economic threshold in terms of economic attractivity for possible successors. The same goes for rice farmers who owned agricultural machinery. The income of six of these farms was above the threshold when only one person was considered, but not when the number of family members actually involved in farming in 2017 was used for the calculations. For these six farms, the ratio of farmed area to the number of farming family member was 3 to 6 ha per person. However, the ratio of 47% of the rice farmers who had machinery was more than 6 ha per person. In contrast with the situation of fish and shrimp farmers and rice farmers who owned machinery, the income of more than two thirds of rice farmers with no machinery was below the threshold.

Interpreting the differences in economic profitability reveals similarities with the one based on identifying possible successors. Among the farmers who already had identified a successor, 63% were above the threshold (taking one farmer into account), whereas only 36% of those who had no successor were above this threshold. Rice farmers who cultivated a relatively larger area were generally more able to buy a tractor. However, the purchase of a tractor did not only reflect farm size: it also reflected farmers' willingness to invest in their farm in order to reduce the cost of outsourcing agricultural work and to have more freedom of choice in deciding when to do the work. Some farmers who farmed a relatively small area had also invested in a tractor. Conversely, the absence of a tractor was only one factor among others (farmer's ageing, lack of an identified successor and small farm) which when combined, weakened rice farms.

Hereafter, we use the term "vulnerable rice farms" to refer to Type 4 farms, to avoid focusing on the absence of agricultural machinery.

Agricultural policies and local initiatives

The support provided to farmers by the Ministry of Agriculture and Cooperatives differed considerably depending on the topic: water issues, agricultural production and marketing, and the increasing age of farmers. There was active support for dealing with water issues in the study areas, in particular, the construction of the Naruebodindrachinta Reservoir in the upstream part of the Prachinburi River Basin. distributed tree seedlings and fingerlings to some farmers in the subdistricts in our study areas. However, none of farmers we interviewed had benefitted from such a programme.

Two "large-scale schemes" focused on rice production started in Bang Taen and Bang Kung Subdistricts in 2017. The farmers involved in these two schemes received rice seeds, they attended training sessions (e.g., on rice cultivation techniques and integrated pest management) and the soil of their farm was analysed. However, there was no initiative concerning marketing because of the low quality of the rice they produced. A "large-scale scheme" was also implemented in Bang Pla Ra Subdistrict in 2017, which focused on fish and shrimp production. A market was built so farmers could contact more middlemen, hopefully leading to increased competition between the latter.

However, the successful implementation of proposed "large-scale schemes" involving rice farms faced major challenges. First, these schemes aim to bring about major changes in farming practices and to promote collective action between farmers to jointly negotiate prices of both agricultural inputs and produce. However, many of the farmers with vulnerable rice farms we interviewed who were taking part in the large-scale rice schemes were already old and, especially in Bang Kung Subdistrict, they had no hope of finding a successor within their family. These farmers are likely to have limited interest in undertaking the major changes in their practices that would be required to decrease production costs by 20% and increase their sales by 20%. Second, the activities proposed in the framework of the two "largescale schemes" focusing on rice may not fully match the priorities of many rice farmers, since half of them declared that their goal was to stop rice mono-cropping and to diversify. Finally, the offices of the Ministry of Agriculture and Cooperatives in Prachinburi Province had done almost nothing to deal with the issue of helping young people to start farming (see also [START_REF] Phiboon | Support programmes and the diversity of young farmers in Thailand: a good match?[END_REF].

Concerning local initiatives, thanks to support provided by a company in the framework of a Corporate Social Responsibility initiative, in 2014, a group of farmers in Bang Taen Subdistrict began producing and marketing organic rice (Faysse and Phiboon, in press). This group included both farmers mainly aiming to increase profitability and farmers mainly aiming to produce rice for home consumption.

Discussion

Mainly farming…until now

The image that emerges from the study of irrigated farms in Prachinburi differs from the one of farms with limited access to land and water in other areas of Thailand in several ways. Much more labour is required by these farms than by the small-scale rainfed farms of the Northeast and North Regions: rice farmers grow two rice crops and often on a much larger area, and fish and shrimp breeding requires daily care. However, most of these farms also brought in sufficient income for at least one household member to farm as his or her main activity. The economic threshold used here would not make much sense in farms where household members dedicate limited time to farming, as documented in many cases in the Northeast and North Regions. In the present case, where farming was the main activity of almost all the interviewees, and the only activity for two thirds of them, it provided an interpretation of differences between farms that largely agrees with differences in the way farm holders saw the future of their farms.

What is more, the average age of fish and shrimp farmers in the present survey was below national average and, on several farms, young family members were also engaged in farming. Higher farm incomes were linked to younger age and higher farmers' assessment of the possibility that a family member would take over the farm in the future. As reported by [START_REF] Zagata | Deconstructing the 'young farmer problem in Europe': Towards a research agenda[END_REF] and [START_REF] Davidova | Subsistence farming, incomes, and agricultural livelihoods in the new member states of the European Union[END_REF] in Europe, one of the key drivers of the processes of ageing farming population and limited installation of young farmers is the income that can be obtained from farming. There is less shortage of young people willing to become farmers when incomes from farming are comparable to incomes young people can obtain from non-farming activities.

Nevertheless, the sustainability of vulnerable rice farms in our study areas appears to be compromised. [START_REF] Kasem | Crop diversification in Thailand: Status, determinants, and effects on income and use of inputs[END_REF] and [START_REF] Sirisup | Government policy and farmers' decision making: The agricultural diversification programme for the Chao Phraya River Basin (1993-95) revisited. Thailand's rice bowl: Perspectives on social and agricultural change in the[END_REF] already identified the constraints facing farms in the delta area around Bangkok, such as lack of fresh irrigation water or shortage of labour.

Compared to these two studies, which took place eight and 16 years ago, the role of an ageing population in rice farms has become of key importance. What is more, the authors of those studies identified the constraints separately, whereas in the farms surveyed here, these constraints had become much more interrelated.

Figure 2 shows the interrelations between water resources, the farming system and farm characteristics for the vulnerable rice farms. These interrelations have created a vicious circle of limited profitability, which threatens the sustainability of these rice farms. The vicious circle increasingly discourages farmers from changing their practices and, in the words of [START_REF] Dorward | Hanging in, stepping up and stepping out: livelihood aspirations and strategies of the poor[END_REF] from "stepping in" to intensify their farming systems.

Uncertain futures

There is still no clear indication of how farms in Thailand with limited access to land and water will evolve in the future, as up to now the adaptive strategies implemented by farm holders have made it possible to put major agrarian changes "on hold" [START_REF] Rigg | More farmers, less farming? Understanding the truncated agrarian transition in Thailand[END_REF]. At a broader level, [START_REF] Rigg | The puzzle of East and Southeast Asia's persistent smallholder[END_REF] proposed four scenarios for the evolution of smallholders in Asia. The first is a business-as-usual scenario in which smallholders remain in rural areas because of the absence of alternative opportunities.

The second one amounts to the disappearance of smallholders and a shift towards farms.

This would resemble what took place in most of Western Europe in the second part of the 20 th century, whereby the agricultural land of farms for which no successor had been found was taken over by remaining farmers, leading to a continuous increase in farm size [START_REF] Vidal | Thirty years of agriculture in Europe. Farm numbers declining as farms grow in size[END_REF]. The third scenario concerns an increase in smallholders' political power, leading to public policies providing substantial support and protection for smallholder farmers. The fourth scenario corresponds to a move towards households continuing to mix farming and non-farm income-generating activities (both locally and thanks to migration). This would prolong the dynamics currently observed on rainfed rice farms in the Northern and Northeast Regions of Thailand.

The first three scenarios proposed by [START_REF] Rigg | The puzzle of East and Southeast Asia's persistent smallholder[END_REF] do not appear to correspond to the possible future of rice farms in our study areas, at least not in the coming decade. The lack of expected successors for most of the vulnerable rice farms may limit the possibility of a shift towards the first scenario ("remaining smallholders by default"). Concerning the second scenario ("shift towards large-scale farms"), rice farmers who had invested in agricultural machinery did not express any interest in increasing their farmed area, at least using current farm production techniques. Options for increased mechanization of rice production may exist in the future but were not yet present in the area at the time of the survey. Concerning the third scenario ("policies protecting smallholders"), there is no hint of willingness on the part of the government to strongly support smallholder farmers' access to national and international markets, especially after the last scheme to support rice prices was seriously criticized [START_REF] Ricks | Public Choice, Institutional Change, and Rural Subsidies: Politics and the Price of Rice in Thailand[END_REF].

The fourth scenario (mixing of farming and non-farming income-generating activities) may take place but it would require notable changes in farming systems, since rice farmers are already engaged in the time-consuming activity of growing two rice crops a year, and on larger areas than the ones generally farmed in the Northern and Northeast regions of Thailand. Such a scenario may involve reducing the intensity of farming or leaving land unfarmed.

The need for comprehensive approaches in Thailand and other newly industrialised Southeast Asian countries

As already pointed out at national level [START_REF] Faysse | Dwindling or thriving? Making sense of the diversity of agricultural and rural dynamics in Thailand[END_REF], Thai agricultural policies do not appear to take the diversity of farming situations in the study areas fully into account. They do not distinguish between:

(i) currently profitable farming systems which -for the moment -are sustainable at farm level (and for which "large-scale schemes" may be beneficial), and (ii) farming systems which have entered a vicious circle of limited profitability and for which policies such as the "large-scale schemes" alone do not appear to be sufficient to interrupt the vicious circle in which they are trapped. In the short term, public policies could provide support to help rice farms adapt to existing constraints, while taking the diversity of their situations into account. The support provided to organic farming in Bang Taen is a promising example as it provides an opportunity to farmers aiming for increased profitability and to farmers aiming to increase rice production for home consumption. In the longer term, the sustainability of the agricultural sector in the rice production zone will probably not be achieved through limited adjustments, rather, a transformation of farming systems is required [START_REF] Darnhofer | Assessing a farm's sustainability: insights from resilience thinking[END_REF].

Farms in irrigated areas of Malaysia, Indonesia, the Philippines and Vietnam are usually much smaller than the farms in our study area: generally ranging between 0.5 to 3 ha [START_REF] Man | Off-farm employment participation among paddy farmers in the Muda Agricultural Development Authority and Kemasin Semerak granary areas of Malaysia[END_REF][START_REF] Bosma | Factors affecting farmers' adoption of integrated rice-fish farming systems in the Mekong delta, Vietnam[END_REF][START_REF] Mariano | Factors influencing farmers' adoption of modern rice technologies and good management practices in the Philippines[END_REF][START_REF] Nathan | Livelihood Strategies and Household Income of a Paddy Farming Community in Northwest Selangor, Malaysia[END_REF][START_REF] Antriyandarti | Constraints of farm size enlargement in the rice sector of Central Java: A case study[END_REF]. Studies in these irrigated areas mention some aspects of a similar "vicious circle" that could limit the capacities of farms to evolve in the future. In these areas, farmers' frequent engagement in non-farming activities has been reported [START_REF] Lorenzen | Disintegration, formalisation or reinvention? Contemplating the future of Balinese irrigated rice societies[END_REF][START_REF] Moya | Changes in Rice Farming in the Philippines: Insights from five decades of a household-level survey[END_REF][START_REF] Nathan | Distributional effects of non-farm incomes in a Malaysian rice bowl[END_REF]. The lack of interest of young people in engaging in farming was also mentioned, albeit often based on limited quantitative data [START_REF] Moya | Changes in Rice Farming in the Philippines: Insights from five decades of a household-level survey[END_REF][START_REF] Ngah | Socio Economic Transformation of Rice Cultivation Area in Malaysia: A Case of Two Villages in Sabak Bernam[END_REF][START_REF] Susilowati | Attracting the young generation to engage in agriculture[END_REF].

This vicious circle could become a major obstacle to the implementation of public programmes to increase rice productivity and production (e.g., in Malaysia, [START_REF] Davidson | Stagnating yields, unyielding profits: The political economy of Malaysia's rice sector[END_REF]. Like in the cases studied in Thailand, programmes that propose a marginal increase in profits from farming may not be sufficient to break the vicious circle. In order to find pathways towards more sustainable farming systems, there is a need for comprehensive approaches tackling economic and environmental issues at the same time as the problem of supporting new generations of farmers. The latter type of support is still incipient in newly industrialised countries of Asia (FFCT-RDA, 2014) but increasingly merits deliberation.

Conclusion

Almost all irrigated farms surveyed in the present study provided sufficient income to enable at least one household member to farm as his or her main activity. Apart from this shared trait, the situation of the farms varied widely from being economically sound to very fragile. Moreover, these farms evolve in an environment marked by heavy constraints, particularly in terms of access to irrigation water, flooding and marketing. This limits their capacity to adapt to ongoing agricultural and non-agricultural changes. In rice production areas, up to now, access to irrigation water has enabled farmers to adapt to the increasingly low profitability of rice farming, as did the expansion of non-farming activities in the Northeast Region of Thailand. However, the future of rice farms (both the smaller and the larger ones) is uncertain.

Irrigated areas in newly industrialised countries of Asia (e.g., the "granaries" in Malaysia, the delta area around Bangkok in Thailand, the Mekong River delta in Vietnam) have been described as the "rice bowls" of these countries. The present study shows that the sustainability of rice production can be very fragile even when the farms are relatively large according to Southeast Asian standards. If these systems are to continue playing an active role in national agricultural production and to help achieve national food security, there is a need for new ways of thinking about the future of these areas. Sustainable agricultural systems will likely involve tackling issues such as farm size, the engagement of young farmers, and types of agricultural production, as these "rice bowls" are likely to contain more than rice in the future.

Figure 1 .

 1 Figure 1. Location of the four subdistricts studied

  It started operating in 2016 and played a role both in limiting the occurrence of flooding and, by releasing stored water, in reducing salinity in the dry season. Local offices of the Ministry of Agriculture and Cooperatives made some attempts to improve the relations between farmers and other actors of agricultural value chains. Farmers could attend training courses on agricultural practices and, in the framework of the "self-sufficiency economy" programme, the Ministry of Agriculture and Cooperatives

Figure 2 .

 2 Figure 2. Constraints to changes in vulnerable rice farms towards more profitable farming

Table 1 .

 1 Farm types

	Farm type

Table 2 .

 2 Proportion of farms above the economic threshold of attractivity for possible successors

		1. Fish and	2. Rice and	3. Rice and	4. Rice, no
		shrimp farming	shrimp	machinery	machinery
	Considering one family member
		96%	100%	84%	31%
	farming full time
	Taking the number of family
	members farming at the time of the	74%	100%	53%	28%
	survey into account

In May

2018, 1 US dollar = 31.8 baht.

The Office of Agricultural Economics of Thailand (2013) in fact considers that small-scale farmers farm less than 2.4 ha. However, the 2013 agricultural census does not provide figures corresponding to this threshold.

This work was supported by the Agence Nationale de la Recherche (French National Agency for Research) as part of the DOUBT project.


Van-Thuan Hoang

Ndiaw Goumballa

Thi-Loi Dao

Tran Duc

Anh Ly

Laetitia Ninove

Stéphane Ranque

Didier Raoult

Philippe Parola

Cheikh Sokhna

Vincent Pommier De Santi

Philippe Gautret

Respiratory and gastrointestinal infections at the 2017 Grand Magal de Touba, Senegal: a prospective cohort survey

Keywords: Respiratory tract infections, gastrointestinal infection, PCR, Grand Magal, Touba, pilgrims

Background:

The Grand Magal of Touba is the largest Muslim pilgrimage in Senegal with a potential for infectious disease transmission.

Methods: Clinical follow-up, adherence to preventive measures and qPCR-based respiratory and gastrointestinal pathogens carriage pre-and post-Magal, were assessed.

Introduction

The Grand Magal is at once a religious ceremony and a festival. About 4-5 million Mourid participate to the celebration each year, coming from across Senegal and the surrounding countries, as well as from countries outside Africa, making this event the largest Muslim religious mass gathering in West-Africa. The two central events of the Magal are visits to the Great Mosque of Touba, which involves a partial circumambulation of the mosque, and to the mausoleum of Cheikh Ahmadou Bamba. Pilgrims also visit the mausoleums of several other important Mouride leaders who were descendants of the Cheikh. The Mosque area is a secluded place surrounded by walls, within the city. The access to the Mosque area is allowed to everyone (including tourists) but flows are regulated by security staffs. In addition, pilgrims visit places in Touba that are associated with the holy life of the Cheikh, including the "Well of Mercy," a spring which sacred water is reputed to be able to heal all sorts of illnesses and misfortune. A visit to the central library of Touba which contains the writings of the Cheikh and other influential Mouride theologians, and to the Mouride University are among the other places visited by pilgrims. Finally, pilgrims visit their personal Mouride spiritual guides, or Marabouts who receive their followers in their personal residence in the city. Recitation of the Koran and spiritual introspection complete these religious activities. During the Grand Magal period, in addition to the religious celebrations, intense cultural activity takes place including conferences, seminaries, and debates between representatives of various Muslims communities from Senegal and from the diaspora. Recitation of poems by Ahmadou Bamba, and collective hymn-singing sessions are organized at night, in the streets, under large open tents. Informally, pilgrims also visit Touba's large temporary marketplace, one of the biggest in the country where a wide range of products can be found with prices lower than those of any other market in Senegal.

During this period, pilgrims are accommodated in private housing structures since there are no hotels in Touba. These houses can be residences of local inhabitants, where family members living in different parts of Senegal or who have emigrated outside the country, come together during the Magal period, or Marabout houses with a capacity that can be up to hundreds of individuals. Many pilgrims sleep on carpets, on the floor, into the houses or on outside terraces.

Food is prepared collectively by family members or by Marabout followers. Slaughtering of animals is mostly done in the streets, in front of housing structures. Different community associations of Mouride disciples (dahiras) are responsible for feeding the pilgrims through free provision of food in the streets and along the roads to Touba. The Senegalese government also provides some technical support.

Medical care is provided free of charge during the Grand Magal. Most of the available local public medical infrastructures are involved in the medical preparation, surveillance and response during the event [START_REF] Sokhna | Communicable and non-communicable disease risks at the Grand Magal of Touba: The largest mass gathering in Senegal[END_REF]. As an example, three tertiary care and four secondary care hospitals (total bed capacity of 481) and about 300 primary healthcare centers and 50 private structures in Touba and surrounding cities were mobilized in 2015. The vast majority of the medical staffs taking care of patients during the Grand Magal are nurses, midwives and volunteer community health agents. Overall, 78 medical doctors were mobilized during the Grand Magal 2015, many of them coming from Dakar to temporarily reinforce the local staff.

Based on the registers of consultations carried out in the public health structures of the region, we evaluated the number and the profile of morbidity observed during the pilgrimage of 2015 among 32,229 in and out-patients [START_REF] Sokhna | Communicable and non-communicable disease risks at the Grand Magal of Touba: The largest mass gathering in Senegal[END_REF]. The most frequent complaints were fatigue (12%) followed by trauma (11%) and heatstroke (11%). Infectious diseases have also been highly reported, including febrile systemic illnesses (5%) and rapid-test confirmed malaria (3%), diarrheal diseases (5%), respiratory tract infection symptoms (5%) and ear, nose and throat infection symptoms (5%). Microbiological investigation of these infections was not conducted in most cases.

The objective of the present preliminary descriptive study was to evaluate the prevalence of respiratory and gastrointestinal symptoms and the carriage of pathogens commonly associated with these symptoms among pilgrims before and after their stay in Touba.

Materials and methods

The complementary figure 1 details the procedure of this study.

Study population

A convenience sample of pilgrims participating in the Grand Magal 2017 was surveyed by a longitudinal prospective cohort study that was conducted from November 4 th to November 23 rd , 2017. Inhabitants of two villages: Dielmo (13°43' 22.07'' N, 16°24'40.09'' W) and Ndiop (13°41'08.01''N, 16°23'01.01'' W), located in Fatick region, South Senegal were included.

Villages are divided in concessions where individuals from a same family live in close contact. The population in the villages was 991 (510 Ndiop and 481 Dielmo) in 2017, including about 50% Mourides, part of whom did not travel to Touba because of limited financial resources. All pilgrims participating to the 2017 Magal in these villages were invited to participate in our study and were identified by the nurses in charge of the primary health care centers in both villages. At inclusion, the pilgrims were questioned using a standardized questionnaire. This questionnaire addressed demographics, chronic medical conditions and vaccination status against influenza. In Touba, pilgrims were housed in different concrete houses; three groups in three family houses and others in different Marabout houses. Health issues occurring during and after the Magal, were recorded by a nurse who travelled with the group of pilgrims. Housing location in Touba and use of preventive measures (face mask, disposable handkerchiefs, hand washing with soap hand disinfectant) were investigated by questionnaires during the stay in Touba. The consumption of antibiotics was also documented through post-travel questionnaires. Influenza like illness (ILI) was defined as the association of cough, sore throat and fever [START_REF] Rashid | Influenza and the Hajj: defining influenza-like illness clinically[END_REF]. Diarrhea was defined by at least three loose or liquid stools per day.

Sample collection

The procedure included systematic throat, nasal and stool swabs, 1-3 days before departing from the villages (pre-Magal specimens) and 3-6 days following return (post-Magal specimens). Respiratory samples were collected with commercial rigid cotton-tipped swab applicators (Medical Wire & Equipment, Wiltshire, UK) that were inserted in the anterior nose or in the oro-pharynx, and then placed in viral transport media (Sigma Virocult ® ).

Participants provided stools samples in sterile containers. Investigators secondary collected small amounts of stools using swab applicators, placed in viral transport media (Sigma Virocult ® ). This standard procedure was previously explained to the pilgrims by the investigators. Swabs were kept at 4°C before being transported to the Dakar laboratory for storage in a -80 °C freezer within 48 hours of collection and subsequently transferred to Marseille on dry ice for being processed.

Identification of respiratory and gastrointestinal pathogens

Respiratory specimens

The EZ1 Advanced XL (Qiagen, Hilden, German) with the Virus Mini Kit v2.0 (Qiagen) was used for the DNA and RNA extraction from the respiratory samples according to the recommendation of the manufacturer. All quantitative real-time PCR were performed using a C1000 Touch™ Thermal Cycle (Bio-Rad, Hercules, CA, USA). Positive results of bacteria or virus amplification were defined as those with a cycle threshold (CT) value ≤35. Negative control (PCR mix) and positive control (DNA from bacterial strain or RNA from viral strain) were included in each run.

Identification of respiratory virus

Human coronavirus (HCoV) and human para-influenza virus (HPIV) were detected by onestep duplex quantitative RT-PCR amplifications of HCoV/ HPIV-R Gene Kit (REF: 71-045, Biomérieux, Marcy l'Etoile, France), according to the manufacturer's recommendations. The Multiplex RNA Virus Master Kit (Roche Diagnostics, France) was used to detect influenza A, influenza B, human rhinovirus, human enterovirus, metapneumovirus, respiratory syncytial virus, adenovirus and internal controls MS2 phage by one-step simplex real-time quantitative RT-PCR amplifications [START_REF] Ninove | RNA and DNA bacteriophages as molecular diagnosis controls in clinical virology: a comprehensive study of more than 45,000 routine PCR tests[END_REF].

Identification of respiratory bacteria

Real-time PCR amplifications were carried out by using LightCycler ® 480 Probes Master kit (Roche diagnostics, France) according to the manufacturer's recommendations. The SDD gene of Haemophilus influenzae, phoE gene of Klebsiella pneumoniae, nucA gene of Staphylococcus aureus, lytA gene of Streptococcus pneumoniae [START_REF] Memish | Mass gathering and globalization of respiratory pathogens during the 2013 Hajj[END_REF], P1 gene of Mycoplasma pneumoniae [START_REF] Cohen-Bacrie | Revolutionizing clinical microbiology laboratory organization in hospitals with in situ pointof-care[END_REF], ctrA gene of Neisseria meningitidis [START_REF] Vuong | Development of Real-Time PCR Methods for the Detection of Bacterial Meningitis Pathogens without DNA Extraction[END_REF] and Toxin gene of Bordetella pertussis [START_REF] Appelt | Polyphasic analysis of a middle ages coprolite microbiota, Belgium[END_REF] were amplified with internal DNA extraction controls T4, as previously described.

Gastrointestinal specimens

Stool swabs were centrifuged at 4000 x g for 10 min. The RNA were extracted from 200µL clear supernatant using the EZ1 Advanced XL (Qiagen, Hilden, German) with the Virus Mini Kit v2.0 (Qiagen) according to the manufacturer's recommendation.

The DNA was extracted by semi-automated extraction. 200µL of rectal swabs was added to 350 µL of G2 lysis buffer (Qiagen) and glass powder in a tube, then disrupted in a FastPrep BIO 101 apparatus (Qbiogene, Strasbourg, France) at maximum power for 40s. The incubation was at 100°C for 10 min to allow for complete lysis. Then, the tubes were centrifuged at 10,000g for 1 min. Subsequently, 200 µL of supernatant was collected in other tubes and enzymatically digested using 20 µL of proteinase K (20 mg/mL, Qiagen), and incubated overnight at 56 °C. The automated procedure using the EZ1 Advanced XL (Qiagen, Hilden, German) with the DNA Tissue Kit (Qiagen) according to the manufacturer's recommendation [START_REF] Menu | Evaluation of two DNA extraction methods for the PCR-based detection of eukaryotic enteric pathogens in fecal samples[END_REF].

Identification of gastrointestinal virus

The Multiplex RNA Virus Master Kit (Roche Diagnosis, France) was used for detecting hepatitis A and E virus, adenovirus, rotavirus, norovirus, astrovirus and internal controls MS2 phage by one-step simplex real-time quantitative RT-PCR amplifications [START_REF] Jiang | Simultaneous detection of five enteric viruses associated with gastroenteritis by use of a PCR assay: a single real-time multiplex reaction and its clinical application[END_REF][START_REF] Gerber | Comparison of Real-Time Reverse Transcriptase PCR Assays for Detection of Swine Hepatitis E Virus in Fecal Samples[END_REF][START_REF] Jothikumar | Development and Evaluation of a Broadly Reactive TaqMan Assay for Rapid Detection of Hepatitis A Virus[END_REF].

Identification of gastrointestinal bacteria and parasites

Real-time PCR amplifications were carried out using the LightCycler ® 480 Probes Master kit (Roche diagnostics, France) according to the manufacturer's recommendations. The mapA gene of Campylobacter jejuni, ipaH gene of Shigella spp/EIEC (enteroinvasive Escherichia coli) [START_REF] Van Lint | Evaluation of a real-time multiplex PCR for the simultaneous detection of Campylobacter jejuni, Salmonella spp., Shigella spp./EIEC, and Yersinia enterocolitica in fecal samples[END_REF], gene invA of Salmonella spp, gene stx1 and stx2 of enterohemorrhagic E. coli, EAF and eae gene of enteropathogenic E. coli (EPEC) and pCVD432 gene of enteroaggregative E. coli (EAEC) [START_REF] Hardegen | A set of novel multiplex Taqman real-time PCRs for the detection of diarrhoeagenic Escherichia coli and its use in determining the prevalence of EPEC and EAEC in a university hospital[END_REF] were amplified with internal DNA extraction controls TISS. The 18S gene was used to detect Entamoeba histolytica and Giardia lamblia. Finally, gene Hsp70 was amplified to test Cryptosporidium spp. [START_REF] Menu | Evaluation of two DNA extraction methods for the PCR-based detection of eukaryotic enteric pathogens in fecal samples[END_REF].

All quantitative real-time PCR to detect respiratory and gastrointestinal pathogens were performed using a C1000 Touch™ Thermal Cycle (Bio-Rad, Hercules, CA, USA). Negative control (PCR mix) and positive control (DNA from bacterial strain or RNA from viral strain) were included in each run. A cycle threshold (CT) value ≤35 was used to assess positive results of bacteria or virus amplification.

Statistical analysis

Pearson's chi-square or Fisher's exact tests were used for statistical analyses. The acquisition of respiratory and gastrointestinal pathogens was defined as negative before travel and positive when returning from Touba. Prevalence of respiratory and gastrointestinal pathogens carriage before and after the Grand Magal, were compared using the McNemar's Test.

Percentages and comparisons were carried out using STATA 11.1 (Copyright 2009 StataCorp LP, http://www.stata.com). A p value of ≤0.05 was considered significant.

Ethics

Pilgrims were invited to participate on a voluntary basis. Participants (or their parents when minors) were asked to sign a written consent form. The protocol was approved by the National Ethic Committee for Health Research in Senegal (SEN17/62). It was performed in accordance with the good clinical practices recommended by the Declaration of Helsinki and its amendments.

Results

Study population

A total of 123 pilgrims agreed to participate to the survey. Among them, 110 participated to the Grand Magal and fully completed the study and 13 participants cancelled their trip to Touba after inclusion in the study. Most participants (61.8%) were from family groups from 8 different main concessions including 4 or more persons per concession participating to the Magal, while 38.2% remaining participants traveled in small groups from a same concession with 3 persons (2.7%) or 2 persons (18.2%) or alone (17.3%) (Figure 1). Forty-eight pilgrims were male (43.6%) and 62 female (56.4%) with a gender ratio of 0.77. The median age was 20 years (min = 8 months, max = 75 years, interquartile (15, 31 years)). Twenty-nine (26.4%) participants were children <15 years and 5 (4.5%) pilgrims were over 60 years of age. Most participants were from N'Diop village (90/110, 81.8%). Chronic respiratory disease was the most common comorbidity (8.2%) (Table 1).

The duration of the stay in Touba was short (3 days) and most of pilgrims (86.4%) were housed in 7 different locations with some overlapping between concessions (Figure 1).

Regarding preventive measures, 46.4% of pilgrims reported washing their hands more often than usual during the Grand Magal, 63.6% used hand gel frequently. 32.3% and 2.8% pilgrims reported using frequently disposable handkerchiefs and face mask, respectively during the pilgrimage. Only one pilgrim was vaccinated against influenza (Table 2).

Clinical features and detection of respiratory and gastrointestinal pathogens

Respiratory symptoms

During the study period 46 (41.8%) pilgrims reported at least one respiratory symptom with most individuals having the onset of symptoms during their stay in Touba (20.0%) or soon after returning (10.9%). Only 7 participants (6.4%) reported suffering from respiratory symptoms before traveling to Touba. Median time between arrival in Touba and onset of symptoms was 3 days. Rhinitis was the most frequent symptom (30.0%), followed by cough (24.6%), sore throat (10.0%), expectoration (4.6%) and voice failure (4.6%). However, 10.0% ill pilgrims reported fever and 1.8% ILI. Only 2.7% received antibiotics for respiratory tract infection and none of the participants was hospitalized. A total of 42/46 (91.3%) individuals were still symptomatic on returning to Ndiop and Dielmo.

Pre-and post-Magal nasopharyngeal swabs were collected from all 110 and 108 (98.2%) participants, respectively. The most common virus detected was human rhinovirus (18.2%) and human coronavirus (18.2%), followed by adenovirus (7.3%) and influenza B virus (2.7%) (Table 4). The global carriage of bacteria was high, ranging from 34.5% for S. pneumoniae to 77.3% for H. influenzae. The prevalence of rhinoviruses, coronavirus and adenovirus increased post-Magal with acquisition of 13.0, 16.7 and 4.6% respectively. This increase was statistically significant for coronaviruses, p = 0.0001. Carriage of S. pneumoniae, S. aureus and K. pneumoniae decreased following a participation to the Magal, while that of H. influenzae significantly increased, p = 0.03. Despite the overall decrease in bacterial carriage, the acquisition of bacteria ranged from 3.7% for S. pneumoniae to 26.9% for H. influenzae (Table 3). We found no significant difference in the prevalence of respiratory symptoms and in the acquisition of respiratory pathogens according to concession and housing location in Touba (supplementary Table S1 andS2).

At total of 16 (14.6%) pilgrims reported gastrointestinal symptoms mostly during their stay in Touba (7.3%) or soon after returning (3.6%). Only 4 participants (3.6%) reported suffering gastrointestinal symptoms before traveling to Touba. Vomiting was the most frequent symptoms (9.1%) followed by diarrhea (4.6%), constipation (1.8%) and nausea (0.9%). None of participants was hospitalized and only 2/110 (1.8%) received antibiotic for gastrointestinal symptoms. A total of 7/16 (43.8%) of the pilgrims were still symptomatic upon their return to the villages. Sixty (54.5%) participants provided stool sample pre-and 69 (62.7%) post-Magal, with 45 (40.9%) paired specimens collected. Most common viruses were adenovirus (9.5%) and norovirus (2.4%). 10.7% individuals tested positive for G. lamblia. The global carriage of bacteria was high ranging from 1.2% for C. jejuni to 78.6% for EAEC. Of note, 8.3% of all participants were positive for T. whipplei. Acquisition of gastrointestinal viruses and parasites was low, while bacterial acquisition ranged from 2.2% for C. jejuni to 33.3% for EPEC (Table 4).

Discussion

Religious mass gatherings like the Hajj pilgrimage in Mecca, Saudi Arabia have been associated with outbreaks of gastrointestinal infections, respiratory infections and meningitis [START_REF] Abubakar | Global perspectives for prevention of infectious diseases associated with mass gatherings[END_REF], mostly due to crowding conditions favoring the inter-human transmission of pathogens.

The Grand Magal pilgrimage in Touba Senegal qualifies for the WHO mass gathering definition [START_REF]B2BC5AB159FB1E?sequence=1[END_REF]. This is the first report addressing the morbidity in a cohort of pilgrims at the Grand Magal. Publications about Grand Magal associated diseases are scarce. A cholera outbreak involving 12,135 patients in the Grand Magal area occurred in 2004-2006, with a total of 29,556 cases reported over an 18-month in the country [START_REF] Manga | Cholera in Senegal from 2004 to 2006: lessons learned from successive outbreaks[END_REF]. In 2018, a dengue outbreak was associated to the Grand Magal [START_REF] Diagne | Dengue Epidemic in Touba, Senegal: Implications for the Grand Magal Pilgrimage for Travelers[END_REF][START_REF] Sokhna | The Grand Magal of Touba in the time of a dengue outbreak in Senegal[END_REF]. As described in the introduction, our group provided overall figures of syndromic surveillance data during the 2015 Grand Magal.

The most frequent reasons for consultation were trauma, followed by fatigue and heatstroke.

Infectious diseases were also prevalent with, notably, a high rate of febrile systemic illnesses and malaria, diarrheal diseases, and respiratory tract infections [START_REF] Sokhna | Communicable and non-communicable disease risks at the Grand Magal of Touba: The largest mass gathering in Senegal[END_REF].

In our study, the population was characterized by the young age of participants with 26.4% children and only few elderly pilgrims, in marked contrast with the characteristics of Hajj pilgrims [START_REF] Memish | Hajj: infectious disease surveillance and control[END_REF]. Indeed, the Grand Magal is a familial event and many adult pilgrims travel with their children. As a consequence of the young age of participants, the prevalence of chronic conditions was low, as opposed to Hajj pilgrims [START_REF] Memish | Hajj: infectious disease surveillance and control[END_REF][START_REF] Pane | Causes of mortality for Indonesian Hajj Pilgrims: comparison between routine death certificate and verbal autopsy findings[END_REF][START_REF] Khan | Morbidity and mortality amongst Indian Hajj pilgrims: A 3-year experience of Indian Hajj medical mission in mass-gathering medicine[END_REF][START_REF] Ahmed | Health risks at the Hajj[END_REF][START_REF] Al-Tawfiq | Expected immunizations and health protection for Hajj and Umrah 2018 -An overview[END_REF]. Also, in comparison with the Hajj pilgrimage, where pilgrims stay in Saudi Arabia for around 3 weeks [START_REF] Memish | Hajj: infectious disease surveillance and control[END_REF], we note that the duration of stay in Touba during the Grand Magal is shorter (3 days) (Table 5).

The vaccination rate against influenza was dramatically low. The use of face masks was rare, while 2/3 of pilgrims declared using hand sanitizer. The overall prevalence of respiratory symptoms was high, affecting 42% participants and a 4.8 fold increase was observed following the participation to the Grand Magal. This result is in line with studies conducted at the Hajj, where 50-93% pilgrims presented respiratory symptoms [START_REF] Hoang | Infectious Diseases and Mass Gatherings[END_REF]. Gastrointestinal symptoms were less frequent, affecting 15% individuals, but three times more frequent after participation in Hajj. Overall, these symptoms were relatively mild leading to a low proportion of antibiotic consumption (12.5% ill pilgrims) and no pilgrim was hospitalized. However, 91.3% and 43.8% of pilgrims still had respiratory and gastrointestinal symptoms, respectively when they returned home, which can be a source of infection for their family members. Acquisition of respiratory viruses and H. influenzae at the Grand Magal was common, as observed in the setting of the Hajj pilgrimage [START_REF] Hoang | Infectious Diseases and Mass Gatherings[END_REF]. We found no evidence for increased transmission of respiratory infections between individuals from a same concession or from a same housing location in Touba which suggests that respiratory infections may have resulted from contacts with the overall population in Touba in overcrowding areas, in and around the Mosque rather than from intra-familiar or intra-domiciliar transmission. Our survey has several limitations, including its small sample size and the fact that most pilgrims came from a single village. Also, the short time between inclusion and post-Magal questionnaire administration and testing makes it difficult to establish a formal link between symptoms and pathogen acquisition and pilgrimage participation. Another limitation is that we did not investigate Mycobacterium tuberculosis prevalence in our study. However, given the long incubation time of tuberculosis and the short duration of stay of pilgrims in Touba, PCR-based detection of M. tuberculosis in relation to the event would not have been feasible.

Finally, the proportion of participant who provided paired samples of stool specimen was low.

Further study including larger numbers of pilgrims are needed to investigate potential risk factors for respiratory and gastrointestinal infections at the Grand Magal. Nevertheless, this preliminary study confirms that Grand Magal pilgrims are likely to be exposed to communicable disease risk, as observed in other pilgrimage settings, despite the relatively short duration of the event.

287 Figure 1 :

 2871 Figure 1: Distribution of pilgrims according to concession in villages and to housing location in Touba

Table 1 :

 1 Characteristics of the population

	Variables

Table 3 :

 3 Prevalence of respiratory pathogens

	Respiratory pathogens	Pre-and/or post-travel N = 110 n %	Acquisition N = 108 n %	Pre-travel N = 110 n %	Post-travel N = 108 n %	P* (Post-travel versus pre-travel)
	Respiratory virus
	Influenza A	0	0	0	0	0	0	0	0	NA
	Influenza B	3	2.7	1	0.9	2	1.8	1	0.9	0.56
	Metapneumovirus	0	0	0	0	0	0	0	0	NA
	Respiratory syncytial virus	0	0	0	0	0	0	0	0	NA
	Human rhinovirus	20	18.2	14	13.0	6	5.5	14	13.0	0.07
	Enterovirus	0	0	0	0	0	0	0	0	NA
	Adenovirus	8	7.3	5	4.6	3	2.7	6	5.6	0.25
	Coronavirus	20	18.2	18	16.7	2	1.8	19	17.6	0.0001
	Coronavirus HKU1	0	0	0	0	0	0	0	0	NA
	Coronavirus 229E	4	3.6	3	2.8	1	0.9	3	2.8	0.32
	Coronavirus NL63	10	9.1	9	8.3	1	0.9	10	9.3	0.003
	Coronavirus OC43	9	8.2	9	8.3	0	0	9	8.3	0.003
	Parainfluenza virus	0	0	0	0	0	0	0	0	NA
	Respiratory bacteria
	Staphylococcus aureus	80	72.7	15	13.9	65	59.1	50	46.3	0.03
	Streptococcus pneumoniae	38	34.5	4	3.7	34	30.9	22	20.4	0.01
	Haemophilus influenzae	85	77.3	29	26.9	56	50.9	69	63.9	0.03
	Klebsiella pneumoniae	66	60.0	7	6.5	59	53.6	30	27.8	<0.0001
	Neisseria meningitidis	0	0	0	0	0	0	0	0	NA
	Bordetella pertussis	0	0	0	0	0	0	0	0	NA

Table 4 :

 4 Prevalence of gastrointestinal pathogens

	Gastrointestinal pathogens	Pre-and/or post-travel N = 84	Acquisition N = 45	Pre-travel N = 60	Post-travel N = 69	P* (Post-travel versus pre-
		n	%	n	%	n	%	n	%	travel)
	Gastrointestinal virus
	Hepatitis A virus	0	0	0	0	0	0	0	0	NA
	Hepatitis C virus	0	0	0	0	0	0	0	0	NA
	Adenovirus	8	9.5	2	4.4	6	10.0	3	4.3	0.56
	Astrovirus	0	0	0	0	0	0	0	0	NA
	Rotavirus	0	0	0	0	0	0	0	0	NA
	Norovirus	2	2.4	1	2.2	0	0	2	2.9	0.32
	Gastrointestinal bacteria
	Entamoeba histolytica	0	0	0	0	0	0	0	0	NA
	Giardia lamblia	9	10.7	1	2.2	8	13.3	2	2.9	0.18
	Cryptosporidium spp	0	0	0	0	0	0	0	0	NA
	Salmonella	5	6.0	1	2.2	1	1.5	4	5.8	1
	Shigella/EIEC	10	11.9	2	4.4	5	8.3	9	13.0	0.16
	EHEC	29	34.5	8	17.8	10	16.7	25	36.2	0.13
	EPEC	52	61.9	15	33.3	25	41.7	38	55.1	0.22
	EAEC	66	78.6	11	24.4	40	66.7	50	72.5	0.13
	Campylobacter jejuni	1	1.2	1	2.2	0	0	1	1.5	0.32
	Tropheryma whipplei	7	8.3	0	0	6	10.0	6	8.7	1
	(*) McNemar's test on 45 paired sample

Table 5 .

 5 Main characteristics of the Grand Magal in comparison with the Hajj pilgrimage[START_REF] Sokhna | Communicable and non-communicable disease risks at the Grand Magal of Touba: The largest mass gathering in Senegal[END_REF][START_REF] Sokhna | The Grand Magal of Touba in the time of a dengue outbreak in Senegal[END_REF][START_REF] Memish | Hajj: infectious disease surveillance and control[END_REF][START_REF] Pane | Causes of mortality for Indonesian Hajj Pilgrims: comparison between routine death certificate and verbal autopsy findings[END_REF][START_REF] Khan | Morbidity and mortality amongst Indian Hajj pilgrims: A 3-year experience of Indian Hajj medical mission in mass-gathering medicine[END_REF][START_REF] Ahmed | Health risks at the Hajj[END_REF][START_REF] Al-Tawfiq | Expected immunizations and health protection for Hajj and Umrah 2018 -An overview[END_REF]

	The Grand Magal pilgrimage	The Hajj pilgrimage

Funding

This study was supported by the Institut Hospitalo-Universitaire (IHU) Méditerranée Infection, the National Research Agency under the program « Investissements d'avenir », reference ANR-10-IAHU-03, the Région Provence Alpes Côte d'Azur and European funding FEDER PRIMI.