SAINT-LOUIS, SENEGAL —
Every year, more than 240 million people get a potentially deadly parasitic infection known as schistosomiasis, transmitted by fresh water snails. Infection rates have risen to as high as 80 percent in some parts of Africa, where communities often rely on rivers and lakes for bathing, cooking and other household chores. In Saint-Louis, Senegal, aid workers are using another indigenous species, the prawn, to keep parasite levels in check in local rivers.
In mid-morning, Coumba Ngiané washes a bucketful of family dishes and clothes.
She says the tap water is often cut off in the village, and so the women must come to the river to do laundry and bathe. She says when it gets hot, the children come here to cool off and play. People get sick, she says, and they know it is from the water but they can’t stay away.
Freshwater snails are the host for the microscopic parasite that gives you schistosomiasis. That parasite gets in the water and the larvae can enter your body through a cut, or even just the pores of your skin.
The larvae then lay eggs in the body, leading to diarrhea, abdominal pain and fever. It infects the intestines and if left untreated, can lead to organ failure and even death. In children, it can stunt growth and brain development.
There is treatment, but that won’t stop you from being re-infected the next time you enter the water.
The disease isn’t new to the Saint-Louis region of Senegal. But it got worse after the government built a dam on the Senegal River in 1986 to stop salt water from flowing onto farmers’ fields. The indigenous prawns that eat the snails that carry the parasite were nearly wiped out.
Amit Savaia, an Israeli prawn specialist currently working in the Saint-Louis area, said the prawns need to move from fresh water to salt water in order to breed.
“The dam that was built prevented them from migrating," said Savaia who is from Ben Gurion University. "So upstream [from] the dam, the prawns were almost sure extinct. And if the prawns are extinct, the snails have a very comfortable habitat to bloom and grow, and spread [schistosomiasis].”
Savaia says in some villages the rate of infection rose from less than 10 percent to more than 80 percent.
Now, “Projet Crevette,” or the “Prawn Project,” is trying to change that.
Every three months, the project releases between 50 and 100 prawns into enclosures at seven test sites in the area.
Project officer Nicolas Jouanard says the idea is to restore balance to the ecosystem.
“The idea with the prawns is that when they arrive they eat the snails that are in place and that are infected," said Jouanard. "You will get new snails because the prawns are not able to eat every snail, but the snails that you will have here will be small snails, a new generation of snails. So for them it will take time to be infected again. When they are young and small they cannot be infected.”
Scientists say dam construction has disrupted river ecosystems and increased schistosomiasis infection rates in several parts of the world, including China, Egypt and Ivory Coast, in recent decades.
The founder of the prawn project in Senegal, Elizabeth Huttinger, says their experiment with prawns is a first and the results of the 12-month testing phase are “very promising.”
“On the snail info, the very exciting thing is that there are no infected snails there anymore," said Huttinger. "But what is particularly interesting, is that the intensity of the infections at the prawn site are about 15 times lower than what they are at the control site.”
That means 15 times fewer people are getting sick in the areas where prawns have been re-introduced. And chronic infections are 40 times lower, as compared to the areas with no shrimp.
Because the dam is still in place, to keep the project going, researchers are teaching villagers at the test sites how to raise and breed prawns in plastic barrels full of fresh water and salt water. The villagers can then keep transferring prawns to the river to keep infection rates down.
Huttinger said they hope to replicate the project in other villages and, ultimately, apply the model worldwide.