Madagascar is one of the poorest countries in the world. Many people lack sufficient dietary protein and stunting affects 50% of children nationally. The country has one of the world’s highest rates of schistosomiasis (a devastating disease of poverty). Political instability has made control programmes difficult and infection rates are increasing. Up-to-date information is patchy, but the best estimates suggest at least 11 million Malagasy people were infected in 2011.
In 2018, Malagasy biologist Ranja Andriantsoa noticed that, although the range of the invasive marbled crayfish and schistosomiasis in Madagascar overlap, the snails which are the obligate intermediate host of the schistosome parasites do not seem to co-occur with the crayfish – an observation which we hypothesize may be the result of predation by marbled crayfish on snails.
Marbled crayfish are widely eaten in Madagascar and informal observations also suggest they may be playing an important role in the diet of children, as they can be collected and eaten during play.
Conservationists have raised concern about potential impacts on endemic freshwater biodiversity (especially the endemic crayfish Astacoides), although so far almost nothing is known about the impacts of this invasive species on endemic crayfish in Madagascar.
There is increasing awareness (mostly based on research by our US-based team members) that snail predation by crustaceans can interrupt the life cycle of the parasites that cause schistosomiasis. For example, a decade of research in Senegal has shown that extirpation of native prawns after dam building reduced predation pressure on snails and increased the transmission of schistosomiasis. The spread of marbled crayfish in Madagascar provides a natural experiment to better understand the ecology of schistosomiasis transmission, which may inform potential solutions.