Outrunning the risks of ‘river fever’
Schistosomiasis infects millions of people each year. Researchers at Stanford and in Senegal are working to reduce disease transmission in rice paddies, make food systems more productive and sustainable, and boost local economies – with the help of fish.
Although schistosomiasis has afflicted Africa since the time of the Egyptian pharaohs, it remains poorly controlled, with progress toward elimination moving at an agonizing pace, according to Giulio De Leo.
A professor of oceans and of Earth system science at the Stanford Doerr School of Sustainability, De Leo studies a global hotspot of the tropical disease along the shores of the Senegal River in West Africa.
People contract schistosomiasis when they step into water contaminated with the parasite’s larvae, which can burrow into the skin, enter the bloodstream, and then migrate to the liver, where they mature into adults. Adult parasites lay eggs in the veins of the bladder or intestine that eventually exit the body in urine or feces, respectively.
Without adequate sanitation, these excreted eggs can hatch in freshwater and infect freshwater snails, where the parasite clones itself. Multiple larvae then leave the snail to re-enter the water, where they often encounter a human host, and the cycle begins again. Thus, the parasite needs both humans and snails to survive.
Over 800 million people worldwide risk contracting the disease, also known as “river fever,” and 250 million – mostly schoolchildren – require treatment each year for symptoms of diarrhea, abdominal pain, and an array of chronic health complications. Despite effective medical treatments, reinfection rates remain high due to inadequate water sanitation.
De Leo, who is also an affiliate at the Center for Human and Planetary Health in the Stanford Woods Institute for the Environment and co-lead of the Center’s Disease Ecology in a Changing World program, has spent a decade testing ways to track schistosomiasis hotspots and reduce transmission risk by leveraging natural predators of snails. With an international team, he’s now piloting an intervention. By introducing native fish species that prey on snails into irrigated fields, the researchers aim to interrupt the parasite’s life cycle.
De Leo applied for a grant from the Stanford Sustainability Accelerator, based at the Doerr School of Sustainability, to fund a pilot study that would help 70 farmers in Senegal integrate fish aquaculture into their rice paddies and train them in fish husbandry and harvesting. The grant also supports project contributors from the Station d’Innovation Aquacole, the Research Center for Economic and Social Development, and the Department of Agricultural Sciences, Aquaculture, and Food Technologies at the Université Gaston Berger in Senegal, as well as the University of Notre Dame and Cornell University in the U.S.
A previous trial with a different snail predator, African river prawns, came up short because “prawns are escape artists,” says De Leo. Keeping them in enclosures where local villagers access water for daily chores proved challenging.
De Leo and the team brainstormed options that don’t require building enclosures. They refocused their efforts on integrating fish aquaculture into rice agriculture, which is rapidly expanding in Africa to feed a population projected to reach 2.5 billion by 2050.
Fish aquaculture could play a key role in supplying nutritious, sustainable protein to Africa in the coming decades, since it typically has a smaller carbon footprint and requires less land and fresh water than beef, pork, and poultry. The researchers recognized that integrating fish into rice farming could generate more food and value from the freshwater already used to flood fields.
De Leo’s project partners have found that snails in rice fields and adjacent irrigation canals make schistosomiasis an occupational hazard for rice farmers in the Senegal River Basin and have proposed introducing local snail-eating fish as a solution.
For their pilot study, De Leo’s team selected the African catfish, a voracious snail predator that can be raised in rice paddies, where it fertilizes the soil with its droppings. With the Accelerator’s support, the team has prepared robust contingency plans.
“The real world is always more complex than we envision,” said De Leo. “The Accelerator pushed us to plan for policy and technology risks and provided a framework to explore a range of intervention alternatives, including the type and depth of ditches that we need to dig to protect fish from the hottest hours of the day.”
The ditches also shield fish from predators, allowing them to grow large enough to be sold for a profit.
Another risk concerns limited institutional support for smallholder farmers, who grow the majority of rice in Africa. The project team approached organizations such as the global research partnership AfricaRice to strengthen farming operations and improve rice paddy management.
“The Accelerator is helping us test that this approach can work for people and the environment,” said De Leo. Early results are promising: fewer snails, higher rice yields, and rising incomes. The team also estimates that farmers can recoup their capital investments within a year. “With the guidance of our partners in Senegal, we’re demonstrating a proof of concept to scale adoption.”
Learn more about the Farming Innovation for Sustainable Health (FISH) project team and pilot study.
Other Accelerator project team members include Roz Naylor, who is the William Wrigley Professor Emerita, a professor (emeritus) of environmental social sciences and (by courtesy) of economics, and the founding director of the Center on Food Security and the Environment, which is a joint effort of the Freeman Spogli Institute for International Studies and the Stanford Woods Institute for the Environment, where Naylor is also a senior fellow (emeritus); Talya Shragai, a research and program manager at the Disease Ecology in a Changing World program at the Center for Human and Planetary Health in the Stanford Woods Institute for the Environment; Andrew Chamberlin, a researcher in the Oceans Department; Ao Yu, a doctoral student in the Earth System Science Department; and Poppy Brittingham, a doctoral student in the Oceans Department. De Leo is also a member of Stanford Bio-X, a fellow of the Center for Innovation in Global Health, and a faculty affiliate of Stanford HAI and the King Center on Global Development.
The Stanford Woods Institute for the Environment funded earlier studies focused on prawns through an Environmental Ventures Project (EVP) seed grant.
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