Janani Ravikumar
Staff Writer
Armand Kuris, one of the world’s leading parasitologists and a zoology professor at the University of California, Santa Barbara, has developed a new approach to fighting the parasitic disease schistosomiasis along the Senegal River that could provide environmental and economic benefits, according to the UC Santa Barbara Current.
In 1986, the Diama Dam was constructed along the Senegal River between Senegal and Mauritania to improve irrigation and prevent upstream saltwater intrusion. Despite how beneficial this dam is for economic opportunity, it has also provided a source of fresh water that is ideal for snails that carry the parasite responsible for schistosomiasis.
According to the World Health Organization, people become infected with schistosomiasis when a larval form of the parasite—released by the snails—penetrates the skin upon contact with infested water. The larvae then develop into adult schistosomes, which live in the blood vessels where the females lay eggs. Some eggs are passed out of the body through urine or feces, while others become trapped in body tissue, causing damage to organs.
“Globally it affects 200 to 300 million people,” said Kuris, “making many of them very ill with anemia, liver and bladder dysfunction and reduced cognition, killing tens of thousands per year. So it’s a serious disease.”
There are two major forms of the disease: intestinal and urogenital. Intestinal schistosomiasis is characterized by abdominal pain, diarrhea, and blood in the stool. An accumulation of fluid in the peritoneal cavity and hypertension of abdominal blood vessels can result in liver and spleen enlargement in advanced cases. Urogenital schistosomiasis, on the other hand, is characterized by blood in urine and can result in fibrosis of the bladder and ureter, kidney damage, and bladder cancer in advanced stages. Neither form is immediately fatal and both disable more than they kill.
“Schistosomiasis is a big deal globally even if westerners and travelers are not at risk,” said U.S. Geological Survey marine ecologist Kevin Lafferty. “The parasites infect more than 200 million people per year, about the same as malaria, depending on the statistics you use.”
Fortunately, praziquantel, a drug that can rid patients of worms, is available, but it cannot reverse the damage already caused by the parasite and its eggs, and it cannot prevent reinfection.
“Less than half the people in Senegal who are at risk of schistosomiasis get the drugs they need,” said former UCSB postdoctoral researcher and Stanford Woods Institute ecologist Susan Sokolow in an interview with the UCSB Current. “It’s hard to treat everyone every year. And most go back into parasite-infected water the day after treatment because rural villages have no alternative water sources.”
According to Kuris and Lafferty, reintroducing prawns, predators of the parasite-carrying snails, could help curb schistosomiasis. In similar studies in Kenya conducted by Kuris, researchers first cured infected villagers of schistosomiasis with praziquantel and then introduced crayfish into the dam. A year and a half later, there were fewer snails in the river, and fewer people were infected.
“Drug resistance to the current drug praziquantel is happening in some places,” said Lafferty. “Researchers are seeking replacement drugs. But the nice thing about crayfish is that they can evolve as the system changes.”
With a $1.5 million grant from the National Science Foundation, Kuris and his researchers will continue to study the disease and investigate means to curb it. The grant will fund a multifaceted approach that includes drug treatments, reintroduction of the crayfish, surveys, monitoring, interviews, and experiments. In addition to the immediate effects on Senegal, the results of this study could apply to systems all over the world that involve the transmission of waterborne diseases.