In their effort to get ahead of the disease, the collaboration took a close look at the habitat that supports the worms’ intermediate host — a small snail of the Biomphalaria species that lives in the Senegal River and its tributaries. They found that a common aquatic plant called Ceratophyllum demersum — also known as hornwort — can hold up to 99% of these snails, with which they have a mutualistic relationship.
Exacerbated by fertilizer runoff from agricultural operations farther upstream, c. demersum and other aquatic plants tend to proliferate in local waterways, which impedes access for daily activities such as cooking, irrigation and washing clothes.
For their experiment, the researchers conducted a three-year randomized control trial in 16 communities, to see if and how much nuisance vegetation removal in about half of the communities would affect the presence of the snails. They measured baseline infection rates, administered antiparasitic drugs, removed the vegetation and then measured reinfection rates in more than 1,400 schoolchildren. In total, the research teams took out an estimated 430 metric tons (wet) of aquatic vegetation from water access points.
“In our randomized controlled trial, control sites — places where we didn’t remove submerged vegetation from water access points — had 124% higher intestinal schistosoma reinfection rates,” López-Carr said. In addition to lowered infection rates where they removed the vegetation, the researchers found that the removed material could be used to feed livestock, or turned into compost for growing crops, lowering costs dramatically and increasing yields for local farmers.