To reduce human infections, control the snails

Schistosomiasis (also known as billharzia) is a parasitic flatworm that infects a quarter of a billion people worldwide, mostly in tropical countries. If left untreated, it causes chronic pain and diseases of the liver and kidney, and kills up to 200,000 people annually. In recent years, control of the disease has focused on mass-treating humans with a drug called praziquantel, instead of reducing the prevalence of snails that are a required part of the parasite’s life cycle. A new study now shows a strong relation between elimination of┬áschistosomiasis and control of the snails, instead of using drug treatments that are unable to prevent reinfection when people enter streams and lakes containing the parasite-infested snails. For example, in 1994 Japan completely eliminated┬áschistosomiasis from their entire country through a sustained snail control effort, while some countries relying purely on drug treatment of humans have seen little reduction in disease prevalence. The scientists authoring the study, which include SAFS professor Chelsea Wood, urge a rethink in global strategy that focuses more on snail control to reduce the disease burden of schistosomiasis. The work appears in the journal Trends in Parasitology.

Human-to-snail infection is from eggs in human urine and feces released into water bodies; while snail-to-human transmission occurs when humans enter snail-infested waters. Control of the disease occurs through (a) human drug treatment, (b) chemicals killing snails, (c) natural snail enemies, (d) modifying snail habitats, (e) genetic control through gene drives, and (f) traps, repellants and other novel strategies.
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