Bilharzia is caused by the Schistosoma-parasite, a worm that is spread by fresh water contaminated with the parasites. The disease affects the lungs, liver, spleen, bladder and intestine. The aquatic snails carry the parasite in asexual life stage developmental stage. The control of bilharzia often happens using chemical management. With medicines (praziquantel) it is possible to combat the mature worm.
But medicine is often expensive and out of reach for the poor Africans in the countries below the Sahara, where bilharzia occurs most. To prevent the spread of the parasite a more structural approach is needed. Biological control of aquatic snails is such an option. Monde researched the possibilities to reduce the host. Without snails the parasite cannot reproduce. Early this week Monde successfully defended her thesis about this approach.
Cichlids are the natural predators of snails. But for biological control they are less suitable because the fish are the most available source of protein for poor people. Monde researched (in the lab) the use of Australian red claw crayfish, an introduced species that is widely spread in African waters, and a crossbred catfish. Both species were found to feed the host snails, only their efficiency decreased by the presence of alternative food.
The efficiency of the catfish and the crayfish is also related to water pollution. Endosulfan, a forbidden but still widely used insecticide, was found to reduce the success of the biological control. Monde: ‘The predators are more sensitive for endosulfan than their prey. Therefore, this type of control will not work in waters with high levels of pesticides.’
Yet she is convinced that the method has potential. ‘It is a matter of customization. In some areas it will work, and in some it won’t. But the circumstances need to be taken into consideration. My research shows that the method is viable. And it is cheap.’