Scientists discover how terrifying cancer-causing parasitic worm can penetrate your body... without you feeling a thing

If a worm was trying to burrow into your skin, you'd be forgiven for thinking you'd feel it gnawing at your flesh—but scientists have identified how one wriggling parasite does so without you noticing. 

Schistosoma mansoni—also known as a blood fluke—is a 17mm-long flatworm which causes a chronic disease called intestinal schistosomiasis, which kills hundreds of thousands of people every year. 

It is the most prevalent parasite in humans—in 2021, the World Health Organisation estimated that there were 251.4 million people living with schistosomiasis across the globe—with the disease most widespread in Africa, parts of South America, the Caribbean, and the Middle East. 

Infection occurs during contact with infested water through activities like swimming, washing clothes, and fishing, when larvae—hosted in snails who have eaten eggs contained in infected human faeces—penetrate the skin.

Once inside, it releases thousands of eggs that can spread through the body infecting vital organs. 

A new mouse study by researchers at the Tulane School of Medicine explored why blood flukes don't cause pain or itching when it penetrates the skin. 

Their findings show that the worm—referred to in scientific circles as S. mansoni— causes a reduction in the activity of TRPV1+, a protein that sends signals the brain interprets as heat, pain, or itching. 

Surprisingly, this also means that the worm often evades detection by the immune system, unlike other bacteria or parasites that typically cause pain, itching, or rashes. 

However, while the discovery, published in The Journal of Immunology, is undeniably skin-crawling, researchers hope that it could have some medical benefit.

Study lead Dr. De'Broski R. Herbert, Professor of Immunology at Tulane School of Medicine, said that the worms could lead to new advances in pain medication, anti-inflammatories, and even preventative treatment against intestinal schistosomiasis

He said: 'If we identify and isolate the molecules used by [parasitic worms] to block TRPV1+ activation, it may present a novel alternative to current opioid-based treatments for reducing pain. 

'The molecules that block TRPV1+ could also be developed into therapeutics that reduce disease severity for individuals suffering from painful inflammatory conditions.'

In May, it was reported that the number of British travellers who have brought the parasite home with them had reached a record high.

Also called snail fever or bilharzia schistosomiasis, the infection can cause infertility, blindness, severe organ damage, and even bladder cancer if left untreated.

Scientists speaking at Wellcome Trust in London in May said while the disease was once confined to sub-Saharan Africa, it is now spreading in parts of southern Europe.

Outbreaks have been reported in the freshwater lakes and rivers of European holiday favourites like Spain, Portugal and parts of France.

Official UK Government data shows an increasing number of British travellers are also being infected.

The UK Health Security Agency recorded 123 cases in Britain in 2022, more than double the number tallied in the previous year and nearly triple the number recorded before the Covid pandemic.

Bonnie Webster, principal researcher at the Schistosome Snail Resource at the Natural History Museum, said the worm is believed to have reached Europe from African travellers.

'It was people travelling from Africa, particularly Senegal, who imported the parasites,' she said according to The Telegraph.

'Once one snail is infected, they infect a whole population of snails which then infect a whole population of humans.'

Experts believe importation by tourists, combined with climate change making European waters warmer and more hospitable for the worms, are behind a rise in infections on the continent.

However, as snail fever can be mistaken for host of other conditions, and sometimes cause no symptoms, many more people may be infected than official figures suggest.

Infected humans can contaminate freshwater sources with the worm by shedding eggs in their urine and faeces.

From there the worm infects a freshwater snail, where it grows to a size that enables it to infect a human.  

Infections can initially manifest as an itchy bumpy rash, colloquially known as 'swimmers itch'.

As the illness develops, symptoms include fever, more rashes, a cough, diarrhoea, muscle and joint pain, stomach ache and a general sense of being unwell.

These symptoms aren't caused by the worm itself but rather the body's reaction to it releasing thousands upon thousands of eggs.

Experts say snail fever is often misdiagnosed at this stage as the result of some other infection.

While the disease generally clears up on its own, patients are still at risk of long term health complications like organ damage as the parasite remains in their body.

In rare cases, the eggs can reach the brain and spinal cord where it can cause a host of serious health problems.

The NHS advises people who experience signs of infection, and who have been in an area where the worms are found, to contact their GP for advice.

Treatment for snail fever involves taking a drug called praziquantel which kills the worms.

People can reduce their risk of snail fever by avoiding swimming or paddling in fresh water as the worms cannot survive in the sea or in chlorinated swimming pools.