Projet Crevette
A mature West African prawn at the village water point protecting children from schistosomiasis.
Humans catch schistosomiasis in shallow water. Water parasite larvae are spread by tiny aquatic snails into the water, and the larva can directly penetrate human skin anywhere on the body. Fortunately, this native prawn hunts and eats aquatic snails.
P Projet-Crevette's objective is to eliminate the transmission of the fourth largest global disease, human Schistosomiasis. By restoriing a native species, we can permanently interrupt the life cycle of the parasite, improve water quality, and sustain the results through a village-based prawn fishery.
In the Senegal River, the local prawn today is almost extinct. In the 1980s, the Diama Dam was constructed in Senegal to prevent saltwater from back flowing into agricultural lands. Shortly after the dam was constructed, there was an unexpected outbreak of human Schistosomiasis in villages upriver of the dam — with a globally unprecedented velocity of transmission.
Why? A migratory prawn lost access to its saltwater breeding ground, and virtually disappeared in two years. This prawn is the natural predator of the snails that harbor the Schistosome parasite. Without Pa predator, the snail population simply exploded, and so did schistosomiasis.
Unexpected consequences of changes to the ecosystem. Just as mosquitoes carry malaria, small aquatic snails are the carriers for Schistosomiasis. Without natural snail control, the disease infected up to 90% of the population in many villages. Women and children, who spend the most time in the water washing clothes and dishes, are at highest risk of infection. Thus, the disease has disproportionately impacted the most vulnerable. While the disease can be treated with an efficient de-worming drug, the treatment does not prevent re-infection. People become infected again with larvae penetrating their skin... just as soon as they go back in the water.
Our mission is to restore the prawn population in the lower Senegal River basin to its original size before the dam was built. Prawns living at their pre-dam population size can cut the transmission of schistosomiasis. Assisted by more aggressive snail-eaters at the hot spots, they can halt transmission. We started a prawn hatchery in late 2011 with an interim goal of producing 20,000 fingerlings per month in 2014, and even larger crops thereafter, that can be sold to village cooperatives. The prawns, in turn, reach market size in six months. On the local fishmarket, these giant river prawns sell for five times the price of fish. So an active cycle of prawn rearing at the village beaches can guarantee the sustainability of vector control for human schistosomiasis. Medical interventions remain essential to complete the picture of eliminating the disease, but we have already reached the point where people with schistosomiasis can be treated individually instead of through mass drug campaigns. Vector control with individual therapy is far less costly, and the prawns present an economic opportunity for the afflicted community.
Our greatest achievement to-date is the creation of a large, disease-free water point in the village of Lampsar, Senegal, a place known and written about since World War II as a high velocity transmission site for both forms of human schistosomiasis. This water point serves several hundred people a day, and is the village's swimming area for hundreds of children.
The water point at Lampsar, Senegal on a winter afternoon, February 2013.