Our area of operation : the Senegal River valley

We work mainly in the lower Senegal River valley, in the Saint-Louis region. Here, water is both the primary resource and a source of disease, and environment, agriculture, economy and health are closely tied together. The stakes are very concrete: feeding people, protecting their health, and managing aquatic environments under heavy pressure.

A rural, agricultural and vulnerable region

The region’s population is largely rural and draws most of its income from farming, livestock and fishing. Poverty remains significant — around 37% of inhabitants (ANSD, EHCVM 2021-2022) — and mainly affects rural areas. Without reliable running water, many families use the river, ponds and canals every day for washing, bathing, dishes and watering livestock. This dependence on surface water is at the heart of the region’s health challenges.

Dam construction and the transformation of the environment

The Diama dam (completed in 1986), near the river mouth, was built to block saltwater intrusion and secure year-round freshwater, in order to develop irrigated agriculture in a drought-prone region. The lower valley duly became the country’s leading irrigated rice basin, supplying on the order of 35–40% of national rice production (DAPSA/SAED). But these works also deeply transformed the environment: permanent freshwater, lower salinity, more alkaline water, and a rapid expansion of irrigation canals and rice fields.

These changes created very favourable conditions for the freshwater snails (Bulinus, Biomphalaria) that host schistosomiasis parasites. At the same time, the dam blocked the migration of one of their natural predators, the local prawn Macrobrachium vollenhovenii, which breeds in the estuary (Sokolow et al., 2015). The spread of aquatic vegetation amplified the effect: some plants, such as Ceratophyllum, concentrate a large share of the snails, while others (Typha, reeds) slow the water flow and close off water access points.

A heavy burden of water-related diseases

The health consequences were rapid and lasting. Schistosomiasis, a neglected tropical disease, rose especially sharply: at Richard-Toll, an outbreak of intestinal schistosomiasis followed the dam coming into service, going from about 2% to over 70% of people infected within a year (Talla et al., 1990), while urinary schistosomiasis increased strongly (Southgate, 1997). The region remains one of the most affected in the world.

Beyond schistosomiasis, the region is also home to other water-related diseases, such as malaria, diarrhoeal diseases and dysentery, Rift Valley fever and lymphatic filariasis (Sow et al., 2002).

A One Health issue: people, animals and environment

These diseases illustrate a single principle: human health, animal health and the state of the environment are inseparable. Livestock share the same water points as people. Bovine schistosomiasis (linked to Schistosoma bovis) is widespread, and hybrid forms between human and cattle schistosomes (S. haematobium × S. bovis) have been detected in both snails and people (Webster et al., 2013).

Liver fluke disease (fasciolosis, caused by Fasciola gigantica) illustrates the same link: this parasite is also transmitted by freshwater snails, and cattle become infected while drinking or grazing at the water’s edge. It causes liver damage, stunted growth, lower milk yield and fertility, mortality and treatment costs — heavy losses for herders whose livelihoods depend on livestock.

Trends that intensify these stakes

Far from easing, these stakes are set to grow. To feed a fast-growing population, agriculture keeps expanding and intensifying — new hydro-agricultural schemes, more and more intensive rice growing — while pressure on water resources and climate change continue to reshape the environments. Yet agricultural expansion and the infrastructure that comes with it (dams, irrigation networks) are among the main drivers of infectious disease emergence: globally, they are associated with more than a quarter of the human diseases that have emerged since 1940, and more than half of those of animal origin (Rohr et al., 2019). And it is rural populations who bear the cost first, while the benefits of production go mainly to more distant consumers.

The relationship runs both ways: these diseases also weigh on agriculture and nutrition, by reducing people’s capacity to work and livestock productivity. But the close interrelation between health, environment and agriculture requires us to design solutions that address several of these challenges at once, rather than tackling them in isolation. Understanding and supporting these changes is a constant need, for health as much as for agriculture.