08-05-2025
Rare and deadly disease carried by African snails hits Europe
A rare but potentially deadly disease carried by African snails is spreading into Europe, scientists have warned.
Schistosomiasis is a parasitic infection caused by worms that naturally live in freshwater snails. The worms enter the human body by burrowing through the skin during contact with water in which the snails live – typically when people swim, paddle, or bathe in rivers and lakes.
Once largely confined to sub-Saharan Africa, the disease is now appearing in parts of Europe due to increased migration and tourism, according to researchers gathered at the Wellcome Trust last week.
More than 120 cases have been reported in Corsica since 2014, with evidence linking the cases to individuals from Senegal who most likely swam in local rivers and shed the worms through their urine, which subsequently infected snails in the area where they survived and multiplied.
Sporadic cases have also been reported in Spain and Portugal.
Adult worms can live inside the body and survive for decades. They lay thousands of eggs continuously every day and some go into the organs. These eggs are released by urine and faeces into water bodies, burrow into snails, and proliferate and left untreated can lead to bladder cancer, infertility, and severe organ damage.
'The particular snails which are responsible … are widespread in the southern Mediterranean region,' said Bonnie Webster, Principal Researcher at the Schistosome Snail Resource at the Natural History Museum. 'It was people travelling from Africa, particularly Senegal who imported the parasites. When it happens it's hard to control.'
'Once one snail is infected, they infect a whole population of snails which then infect a whole population of humans,' she added.
The disease is estimated to impact 240 million people, with 90 per cent of cases found in sub-Saharan Africa. There are 15,000 to 20,000 schistosomiasis-related deaths every year.
The spread of schistosomiasis, which is considered a neglected tropical disease (NTD), is also being driven by climate change, said Ms Webster.
'Climate change will cause huge changes in transmission which need to be understood,' she said. 'Some areas will become drier and other areas will become flooded creating new water bodies. This will lead to snails changing where they can be found and cause the prevalence of schistosomiasis to increase and spread leading to outbreaks in new locations.'
While cases are increasing in Europe, schistosomiasis mostly affects poor and rural communities in Africa – particularly agricultural and fishing communities.
Women doing domestic chores in infested water, such as washing clothes, are also at higher risk and can develop female genital schistosomiasis, a condition where the worms affect the reproductive system.
Inadequate hygiene and contact with infected water also make children especially vulnerable to infection.
There are two types of schistosomiasis – urogenital (the most prevalent form of the disease) and intestinal.
Urogenital schistosomiasis is when worms live in the veins and drain the pelvic organs. It can cause enlarged liver, blood in urine, miscarriages, kidney damage and bladder cancer, while intestinal schistosomiasis can cause abdominal pain, diarrhoea, and blood in the stool.
The first outbreak of schistosomiasis identified in Europe was in Portugal during the 1920s and was thought to have lasted 50 years, and was traced back to travellers from Angola.
The first person to acquire indigenous schistosomiasis in Europe was a 12-year-old German boy in Corsica in August 2013, who swam in the Cavu River on a family holiday.
Since then, more than 100 people who swam in the same river became infected.
The last case reported in Corsica was in 2019, although researchers suspect dozens of people may have contracted the infection undetected, given it can take years for symptoms to appear.
While there is a treatment for schistosomiasis – the drug praziquantil which works by paralysing the worms – there are critical shortages in large parts of Africa.
'The snowball effect that we're already seeing following the US aid funding cuts have had downstream effects with agencies abroad,' says Amaya Bustinduy, Clinical Professor of Global Paediatrics at the London School of Hygiene and Tropical Medicine.
'In Zambia, many laboratories working on diseases like HPV, NTDs and HIV have been shut down. We are just waiting to measure the impact.'
Ms Webster adds, 'Some diseases we've made really great progress with like schistosomiasis will start to reverse.'
The work on drug development is ongoing however there is concern that drug resistance is evolving.
Bustinduy says, 'It's only a matter of time for the disease to become drug resistant as we know there are genetic targets in the schistosomiasis parasite that are less susceptible to praziquantel. We need more studies.'
