What is ‘snail fever,’ and why are pesticides allowing the parasites to spread easily?
New research shows that pesticides sprayed over agricultural lands can speed the spread of a debilitating, parasitic disease second only to malaria in terms of its impact on global health.
Schistosomiasis, also known as “snail fever,” affects more than 200 million people worldwide and comes from worms that live inside freshwater snails.
The study, published in the journal The Lancet Planetary Health, points to ongoing impacts of agricultural expansion and the need to understand its effects on human health in an effort to “control and eliminate” the disease.
“Environmental pollutants can increase our exposure and susceptibility to infectious diseases,” senior author of the study Justin Remais, chair of the division of environmental health sciences at the University of California, Berkeley, School of Public Health, said in a news release. “From dioxins decreasing resistance to influenza virus, to air pollutants increasing COVID-19 mortality, to arsenic impacting lower respiratory tract and enteric infections — research has shown that reducing pollution is an important way to protect populations from infectious diseases.”
In a review of 852 studies on the topic, the researchers found 144 experiments that linked pesticides to the parasites’ life cycle, then used a mathematical model to learn how concentrations of the agrochemicals influence infections in nearby human populations, according to the release.
The team found that pesticides such as atrazine, glyphosate and chlorpyrifos directly affect the survival of the parasite itself, kill organisms that eat the parasite-carrying snails, and modify the composition of algae in the water -- the snails’ main source of food, the release said.
And even small amounts of pesticides can increase transmission of the disease that begins when people come into contact with contaminated freshwater, the study found.
“If we can devise ways to maintain the agricultural benefits of these chemicals, while limiting their overuse in schistosomiasis-endemic areas, we could prevent additional harm to public health within communities that already experience a high and unacceptable burden of disease,” study lead author Christopher Hoover, a doctoral student of environmental health sciences at UC Berkeley, said in the release.
Although not found in the U.S., the parasite affects millions in South America, southern China, the Middle East, the Caribbean and most commonly in Africa, where about 90% of cases occur, Hoover said.
The infection can cause lifelong liver, kidney, lungs and intestine damage, and in rare cases, seizures, paralysis or spinal cord inflammation if eggs reach the brain or spine, according to the Centers for Disease Control and Prevention.
The disease can also cause anemia, malnutrition and learning disabilities in children, the agency said.
Sub-Saharan Africa is experiencing a boom in population density and agricultural expansion, suggesting pesticide pollution will become more common, according to the study. The researchers added that the benefits of farming may be outweighed by the harms of increased disease spread.
