The Fly Catchers of Senegal Making River Blindness a Relic of the Past

Ten kilometers from the border of Guinea, Saliou Toure sits on the bank of the fast flowing Gambia river for eleven hours. His facial expression is serious, his eyes are focused, and his slacks are meticulously rolled up, leaving his legs visible. With a quick hand motion, he traps a black fly in a glass tube as it lands on his leg. “We are careful and committed because flies can leave the other side of the border to come here,” he says. Toure is the leader of a team of four fly collectors from Yamoussa, Senegal; they were asked by the village chief to be volunteers in 2006.

For Toure and his team, the 2022 fly collection season was special—they received news from the national onchocerciasis elimination committee, that Senegal has interrupted transmission of onchocerciasis, becoming the second country on the African continent to reach this milestone.

The job of the fly collector is to capture thousands of small black flies into a glass tube. The glass tubes are sent to a lab to be tested for the presence of the parasite that causes onchocerciasis — a painful disfiguring disease that causes severe itching, rashes, and skin nodules. More than 205 million people worldwide are at risk of this disease, which can cause blindness if left untreated.

Support from the Reaching the Last Mile Fund (RLMF) enabled Senegal to collect and process more than 163,000 flies. The processing of these samples confirmed that the country will no longer require treatment in areas where onchocerciasis was previously endemic. “Long ago, we had the disease in the village and many people became blind, but right now there is no evidence of the disease in Yamoussa. We thank God now that there is no disease,” Toure proudly says.

“Basically, our work now is to watch and do everything so the disease doesn’t come back.“

Saliou Toure

Senegal is the second RLMF-supported country to interrupt transmission of onchocerciasis after Niger. While interruption in Niger was achieved through vector control and passive treatment with Mectizan during lymphatic filariasis (LF) MDA, Senegal is the first country in Africa to achieve interruption through the use of Mectizan alone—and was one of the first countries to utilize the generous Mectizan donation by Merck beginning in 1989.

“Basically, our work now is to watch and do everything so the disease doesn’t come back,” Toure says. Toure and his team will continue their work of catching flies for at least three more years. After three years with no signs of reemergence of the parasite within the black fly population, Senegal will submit an elimination dossier requesting certification of elimination by the World Health Organization (WHO). The RLMF is now working closely with the Senegal Ministry of Health and Social Action to plan and implement surveillance activities, including heightened surveillance in the important cross-border areas of Mali and Guinea where Toure and his team collect flies. This will minimize the risk of the disease coming back and make sure the decades of hard work will not be reversed.