The potentially deadly disease schistosomiasis (commonly known as bilharzia), and carried by African snails, is spreading into Europe, scientists have warned.
A neglected tropical disease, it 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.
The Telegraph reports that once largely confined to sub-Saharan Africa, bilharzia 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 people 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 responsible for the urogenital form of the disease are widespread in the southern Mediterranean region,” said Dr Bonnie Webster, Principal Researcher at the Schistosome Snail Resource at the Natural History Museum.
“It was possible that people travelling between endemic areas of Africa and these Mediterranean regions led to the outbreak in Corsica. When it happens, it’s hard to control if people are continuously releasing eggs in their urine while swimming in natural pools.
“Once one snail is infected, they can infect a whole population of humans,” she added.
The disease is estimated to affect 240m people, with 90% of cases found in sub-Saharan Africa. There are 15 000 to 20 000 schistosomiasis-related deaths every year.
The spread of schistosomiasis is also being driven by climate change, said Webster.
“Climate change is likely to cause dramatic 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 where there is a lack of safe water and sanitation.”
While cases are increasing in Europe, bilharzia 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 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. It 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 have been 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.
Recent funding cuts to USAID are expected to worsen the problem, experts at Wellcome warned.
“The snowball effect that we’re already seeing since the US aid funding cuts have had downstream effects with agencies abroad,” said 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.”
There is also concern that drug resistance is evolving.
Bustinduy said: “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.”
The Telegraph article – Rare and deadly disease carried by African snails hits Europe (Open access)
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