"This research project would not have happened had we not had buy-in and trust from the farmers we worked with," Emily Selland told CG about an effort in Senegal that showed integration of native fish into watery rice fields might curb schistosomiasis risks, which may be affected by climate shifts.
One of the world's most prevalent and under-addressed diseases may have a new foe: fish.
A research project along the Senegal River basin pitted two species of fish against the freshwater snails known to carry the parasite that causes the "dominant form of schistosomiasis in the region," according to a news release.
The researchers, whose study was published in Nature Sustainability last month, found that when native Nile tilapia and African bonytongue were introduced or restored to rice fields in rural Senegal, freshwater snail populations declined.
Native fish swimming through the intentionally flooded fields where rice is grown may suppress the parasite-carrying mollusks by feeding on them or by outcompeting them for resources. This could be especially good news for rice farmers and their families, who may face increased risks of schistosomiasis.
Although this study did not measure immediate impacts on infection rates, the researchers noted that combining animal husbandry and rice cultivation may offer multiple benefits that could support well-being.
"From a health perspective, this research is the tip of the iceberg," Emily Selland, the lead author of the study and a graduate student in the Rohr Laboratory of Ecology and Public Health at the University of Notre Dame in Indiana, told CG via email.
In addition to Notre Dame, partners in the effort included collaborators from the Station d'Innovation Aquacole in Senegal, the Université Gaston Berger in Senegal, the Research Center for Economic and Social Development in Dakar, Stanford University, Cornell University, and the University of California.
Selland said the study, which also examined data from a recent survey to understand links between children's schistosomiasis infections and household participation in rice farming, "is not a direct measure of infection risk in rice fields, but combined with our ecological data, it points toward real human impact of rice-fish farming and snail control in these fields."
While some progress has been made, by some estimates, schistosomiasis affects more than 200 million people, the vast majority of whom live in Africa. The disease can cause intestinal problems, organ damage, and even death, according to the World Health Organization. Other complications can include an increased risk of bladder cancer and, in children, anemia.
Genital forms of the disease — female genital schistosomiasis (FGS) and male genital schistosomiasis (MGS) — can also pose sexual and reproductive health concerns, including genital lesions, bleeding, and pain. According to the Global Schistosomiasis Alliance, FGS can also "greatly increase the risk of HIV and cervical cancer, and can cause infertility and miscarriage." Ectopic pregnancy is another potential complication that can be life-threatening.
Schistosomiasis predominantly affects tropical and subtropical locations and communities with inequitable access to sanitation infrastructure and clean water. In addition to infection risks from snails that release parasites into the water, transmission can occur when water becomes contaminated with urine or feces from an infected person.
Since shifts in rainfall and flooding can exacerbate water contamination and expand freshwater snail habitats, some scientists have been examining the potential for human-induced climate change to affect infection rates.
"Rising temperatures, changing rainfall patterns, floods, and droughts can all affect the freshwater snails that transmit the disease," Kwame Kumi Asare told CG. Asare is the lead author of a review on the subject published last year in the International Journal of Environmental Research and Public Health and a Senior Research Fellow at the University of Cape Coast, Ghana.
Asare noted that the climate-linked impacts on schistosomiasis may vary. For example, heavy rains and floods might increase risks in "new geographic areas that were previously considered low-risk or non-endemic, while some regions that become too hot or dry for snail survival could experience reduced transmission."
To better understand the implications of these changing conditions and because FGS in particular is often underdiagnosed, Asare said there is an urgent need for additional research, including a closer look at a range of gendered risks.
"Climate conditions that expand snail habitats, prolong transmission seasons, or increase human contact with infested water may indirectly contribute to greater exposure among females, especially in communities where women and girls are responsible for water collection, washing, irrigation activities, or other water-related tasks," Asare said.
Selland's work is set to play a part in broadening knowledge about the disease.
To conduct the rice-fish integration study, she and other researchers worked with farmers to integrate the Nile tilapia and African bonytongue into their rice fields.
"This research project would not have happened had we not had buy-in and trust from the farmers we worked with. It is because of their enthusiasm, feedback, and support that this research was a success," said Selland, who highlighted partners at the Station d'Innovation Aquacole in Saint-Louis, Senegal, not only for their study co-authorship but also their work in nurturing relationships with the farming community.
"It has been truly wonderful to have farmers open to working with us multiple years in a row, which speaks to their commitment and support."
It may also speak to the potential for combined rice-fish cultivation to strengthen crops while adding fish to local food systems and economies.
According to the study in Nature, the integration of the native fish "improved soil nutrients and boosted rice yields by >25% with a net benefit of US$1,805-3,415." The addition of these fish to the ecosystem also meant another food source and potential earnings.
"That introduces a potential new income stream, but also additional tasks, for households," Selland told CG. "I hope that the ways in which this innovation affects social systems and gender dynamics are something that our group and others continue to pay attention to and gather better information on in the future."
According to the International Fund for Agricultural Development, women already produce 80% of the food in Senegal, where they play major roles in rice farming and processing. Innovations such as solar-powered irrigation and methods for reducing water usage in farming may also help to improve the resilience of rice production, food security, and local economies.
Selland says further areas of investigation could include evaluating how best to scale up the aquaculture industry by making young fish more available to farmers or better supporting farmers in raising fish from that early stage themselves. There is also room to explore the impact of additional native fish species on these rice-fish systems. Further development and relationship-building among communities, policymakers, and research groups could help scale the research to other countries facing endemic schistosomiasis as well.
Meanwhile, cross-sectoral efforts continue to advance the treatment and prevention of the disease, with stakeholders working to improve access to sanitation infrastructure and researchers developing vaccines.
Asare also called for "stronger surveillance and climate-informed disease forecasting to identify emerging hotspots early."
In its 2021-2030 roadmap for neglected tropical diseases, the WHO set the goal of eliminating schistosomiasis as a public health problem by 2030.
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