Bilharzia (also known as schistosomiasis) is a parasitic disease caused by tiny worms called schistosomes that drill through human skin in fresh water and damage organs ranging from the liver to the brain. It affects about 200m people, particularly in Africa, and kills more than 10,000 a year. Many victims are children; the parasites stunt both physical growth and cognitive abilities, damaging personal prospects and dragging down the economies of already poor countries.
Schistosomes alternate between two hosts: mammals (including humans) and aquatic snails. Breaking the snail link breaks the cycle, but attempts to do so with molluscicides have had limited success.
A study published in PLOS Neglected Tropical Diseases by Roland Proud of St Andrews University and colleagues found that restocking Tanzania's Lake Victoria with catfish sharply reduced bilharzia transmission. Catfish populations in the lake had crashed owing to overfishing and the introduction of Nile perch, a predatory species that wreaks havoc on native fish.
The researchers bred 50,000 catfish fingerlings and released them at three sites on the lake's Tanzanian shore. After three months, snail populations had declined by 57% at stocked sites and the number of parasite eggs in local children's faeces dropped by 55%, while control sites showed no change.
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