The Challenge

In West Africa, the construction of the Diama Dam on the Senegal River in the 1980s was followed by a massive outbreak of schistosomiasis, a waterborne parasitic disease that causes debilitating symptoms in humans. The dam blocked the migration of freshwater prawns, predators of the snails that carry the parasite. Without prawns, the snail populations exploded, and so did the disease.

The changing distribution of fresh water and the loss of prawns upstream due to dam building has caused a rising burden of schistosomiasis in the developing world.

Our disease control approach is to restore natural snail predators (prawns) within the aquatic ecosystems where schistosomiasis has emerged, especially in managed ecosystems like irrigation schemes throughout the developing world where some of the highest parasite transmission sites exist today.

To achieve this, we formed The Upstream Alliance, a partnership among scientists and citizens on four continents, working together to reduce schistosomiasis. We are conducting research on the feasibility and long-term sustainability of restoring prawns to the waterways and developing a new prawn-farming enterprise for the health and well-being of local communities in West Africa.

The Approach

We are creating solutions to naturally reduce schistosomiasis, while helping to fight hunger and alleviate poverty. Our win-win approach relies on restoring natural ecological interactions to reduce disease and improve livelihoods. Our strong local partnerships and a dedication to economic and ecological sustainability have been key to success.

Sustainability Strategy

Besides their role as voracious predators of snails that carry schistosome parasites, freshwater prawns are also delicious. Prawns are safe to harvest and eat because they are dead-end hosts to the parasite. So, harvesting of prawns may generate a profit to sustain the intervention and ensure their presence beyond the life of any single grant or project.

But how do we restore prawns over the long-term in ecosystems where they have been excluded by dams, overfishing, or pesticide pollution?

Our long-range sustainability plan is to:
  1. Restore the migratory pathways of prawns (by building “prawn ladders” in dams)
  2. Reduce impacts on prawns’ natural populations (such as pesticide pollution)
  3. Encourage entrepreneurship via developing a sustainable prawn industry in rural locations subject to chronic schistosomiasis.
Meet the Scientists and Visit the Sites in this video from California Academy of Sciences:

People Involved


Mari, L., Gatto M., Ciddio, M., Dia, E.D., Sokolow, S.H., De Leo, G.A., Casagrandi, R. 2017. Big-data-driven modeling unveils country-wide drivers of endemic schistosomiasis.  Nature Scientific Reports. 7:489. 

Sokolow, S.H., Jones,I.J., Cords,O., Knight, A., Lund, A., Wood, C.L, Lafferty, K.D., Hoover, C.M., Collender, P.A., Remais, J., Lopez-Carr, D., Fisk, J., Kuris, A.M., De Leo, G.A. in press. Nearly 400 million people are at higher risk of schistosomiasis because dams block migration of snail-eating river prawns. Phil. Trans. R. Soc. B.

Garchitorena A., Sokolow S.H., Roche B., Ngonghala C.N., Jocque M., Lund A., Barry M., Mordecai E.A., Daily G.C., Jones J.H., Andrews J.R., Bendavid E., Luby S.P., LaBeaud A.D., Seetah K., Guégan J.F., Bonds M.H., De Leo G.A.  in press. Disease ecology, health and the environment: a framework to account for ecological and socio-economic drivers in the control of neglected tropical diseases. Phil. Trans. R. Soc. B.

Ciddio, M., Mari, L., Sokolow, S.H., De Leo, G.A., Casagrandi, R., Gatto, M. in press. The spatial spread of schistosomiasis: a multidimensional network model applied to Saint-Louis region, Senegal. Advances in Water Resources. 

Sokolow, S.H., Wood, C.L, Jones,I.J., Swartz,S.J., Lopez, M., Hsieh, M.H., Lafferty, K.D., Kuris, A.M., Rickards, C.G., De Leo, G.A. 2016. Global assessment of schistosomiasis control over the past century shows targeting the snail intermediate host works best. PLoSNTD. 10(7): e0004794.
Interactive website: 'A Century of Schistosomiasis Control'

Swartz, S.J.*, DeLeo, G.A., Wood, C.L., Sokolow, S.H. 2015. Infection with schistosome parasites in snails leads to increased predation by prawns: implications for human schistosomiasis control. Journal of Experimental Biology. 218(24):3962-3967.

Perez-Saez, J., Mari, L., Bertuzzo, E., Casagrandi, R., Sokolow, S.H., De Leo, G.A., Mande, T., Ceperley, N., Froehlich, J.M., Sou, M., Karambiri, H., Yacouba, H., Maiga, A., Gatto, M., Rinaldo, A. 2015. A theoretical analysis of the geography of schistosomiasis in Burkina Faso highlights the roles of human mobility and water resources development in disease transmission. PLoSNTD. 9(10): e0004127. doi:10.1371/journal. pntd.0004127

Sokolow, S.H., Huttinger, E., Jouanard, J., Hsieh, M., Lafferty, K.D., Kuris, A.M., Riveau, G., Senghor, S., Cheikh Thiam, C., N’Diaye, A., Faye, D.S., DeLeo, G. 2015. Reduced transmission of human schistosomiasis after restoration of a native river prawn that preys on the snail intermediate host. Proceedings of the National Academy of Sciences (PNAS). 112(31): 9650-9655.