New KU Leuven research shows that the risk of contracting schistosomiasis, an infectious disease caused by a parasitic flatworm, will increase considerably over the next century. Because of climate change, the freshwater snails that can transmit the parasite can now survive in various southern European countries. Researchers want to make people who go on holiday aware of the potential risks of taking a refreshing dive in a river or lake.
Schistosomiasis is a disease caused by parasitic worms that you can contract during swimming or taking a dip in contaminated freshwater. Most known cases are in Africa and parts of South America and Asia. The main symptoms are a rash, anaemia, severe abdominal pain, and blood in urine. There is no vaccine or preventive medication but the infection can be treated.
Schistosomiasis is a tropical disease caused by parasitic flatworms that are transmitted by freshwater snails (including the Bulinus truncatus snail). It is the second most common infectious disease (malaria at number one), with more than 200 million infections across the world. People can get infected by taking a dip or swimming in infected freshwater like rivers, ponds and lakes. Typical symptoms of the disease are a rash, anaemia, severe abdominal pain, and blood in urine or stools. If left untreated, the disease can lead to infertility, bladder cancer, liver fibrosis, or stunted growth and learning difficulties in young children.
Because of climate change, more and more tropical infectious diseases are introduced in Europe. Schistosomiasis has been found on the French island of Corsica since 2013, and more recently in Spanish Almería, but we don't know how far the disease could potentially spread.
Snails as guideline
Because the parasitic flatworms that cause schistosomiasis need the freshwater snail as a host, a team of biologists from KU Leuven, the Royal Museum for Central Africa and the University of Copenhagen studied the temperatures in which these snails can survive. 'We concluded that these snails can easily adapt to new circumstances, which would allow them to colonise new areas like Europe,' says Tim Maes, researcher at KU Leuven.
This data was combined with models that predict the European climate for the next century in order to estimate the future expansion of the snail's territory. This study showed that the climate in large areas of Spain, Portugal, France, Italy and Greece will become suitable for the survival of the freshwater snails over the next century. 'Other research has already shown that the parasite itself is able to survive in a temperate climate, but you need all three elements, snail, parasite and humans, to complete the infection circle. Travellers who bring the parasite from Africa to Europe do not present a large risk now, but because of climate change, in the future, the three elements will all be thriving in the European climate, allowing the infectious disease to spread,' explains Tine Huyse, researcher from KU Leuven and the Royal Museum for Central Africa.
Raising awareness for travellers and doctors
'In Belgium, for the time being, we do not expect the snails to be able to survive, but travellers coming back from a trip should be on the lookout for symptoms,' says Maes. 'For general practitioners, it is not always easy to think of schistosomiasis when tourists have not travelled outside of Europe, with all its consequences,' concludes Huyse.
