Schistosomiasis and climate change

Schistosomiasis is a tropical and subtropical disease (fig 1) caused by infection with parasitic blood flukes of the genus Schistosoma (fig 2), which use freshwater snails as necessary intermediate hosts. The schistosomiasis pathology results mainly from inflammatory processes caused by parasites’ eggs in the human body, which may lead to several conditions such as abdominal pain, diarrhea, chronic anemia, cognitive impairment in children, growth stunting, infertility, a higher risk of contracting HIV in women, and death from liver failure or bladder cancer in cases of intense and chronic infection. These effects, combined with poverty and a lack of access to clean water, improved sanitation and hygiene make schistosomiasis one of the world’s most important, but also most neglected, human diseases. The intermediate host snails of schistosome parasites are poikilotherm—that is, their body temperature changes depending on the environment. As a result, reproduction, survival, and dispersal are strongly influenced by ambient temperature, as is parasite development inside the snail. Therefore, rising water temperatures and altered precipitation associated with climate change could considerably alter the distribution and abundance of the intermediate host snail and its schistosome parasites, resulting in a shift in disease dynamics and transmission to people. Assessing the impact of global warming and its compounded effect with change in land use are important challenges that will face global health soon. Predicting the effect of global climate change on schistosomiasis is a complex task,23 because how the disease responds to climate varies with the specific ecology of many different snails and parasite species (table 1) as well as the geographic context that may respond differently to rising temperatures and changes in precipitation (fig 1). We discuss potential effects of climate change on schistosomiasis, its interactions with other determinants of disease transmission, and considerations for schistosomiasis control and elimination in a changing world.