Breaking news reports that agrochemicals that pollute our waters also increase the transmission of the parasite that causes schistosomiasis, also known as snail fever. The disease is caused by flatworms called schistosomes that are found in water contaminated from infected animal or human urine or feces. Symptoms of the disease include rash, itchy skin, fever, chills, cough, headache, belly pain, joint pain, and muscle aches; it can also leave lifelong liver and kidney damage.
In conducting an extensive literature review, the researchers analyzed the link between agrochemical concentrations and the schistosome life cycle. They found that even low concentrations of common pesticides increase rates of transmission. In the case of communities in the Senegal River Basin, they saw that the excess burden of disease due to agrochemical pollution was equivalent to disease caused by lead exposure, high sodium diets, and low physical activity.
The findings, published in the journal Lancet Planetary Health, show that the presence of agrochemicals enhances transmission of the worms by a) decimating aquatic predators that feed on the snails that carry the parasite, b) altering the composition of algae in the water, which snails feed on, and c) directly affecting the parasite itself. This news came as a surprise even to the researchers.
"We know that dam construction and irrigation expansion increase schistosomiasis transmission in low-income settings by disrupting freshwater ecosystems," said lead author Christopher Hoover, of UC Berkeley. "We were shocked by the strength of evidence we found also linking agrochemical pollution to the amplification of schistosomiasis transmission."
However, in the age of COVID-19, perhaps we should not be so surprised at the link between infectious diseases and environmental pollution.
"Environmental pollutants can increase our exposure and susceptibility to infectious diseases," said senior author Justin Remais, chair of the Division of Environmental Health Sciences at the UC Berkeley School of Public Health. "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."
Affecting hundreds of millions of people annually, schistosomiasis is the second most harmful parasitic disease, following malaria, in terms of its global impact on human health. "We need to develop policies that protect public health by limiting the amplification of schistosomiasis transmission by agrochemical pollution," Hoover said. "More than 90% of schistosomiasis cases occur in areas of sub-Saharan Africa, where agrochemical use is expanding. 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."
Sources: The Lancet Planetary Health, Science Daily
