All it takes is a snail, a worm and some freshwater to become infected. Once you are, the disease could persist for decades, and be deadly. The culprits are freshwater snails who harbour parasitic worms. Once released from the snails, the worms dig into the skin and deep inside the body of any human daring to enter its waters
The infection that results is called Schistosomiasis — also known as bilharzia — a chronic infection caused by parasitic Schistomosa worms that can live inside blood vessels for years on end causing fever, chills and inflammation.
How Does It Happen?
Inside the human body, female worms grow into adults and lay eggs that migrate through the body for release in faeces. If released into freshwater — through defecation in the water — they hatch and become ready to infect any freshwater snails in their path.
Once inside the snails, the young worms transform into adult worms now capable of burrowing back into human skin. On release back into the water they swim ready to, again, infect humans in their vicinity. The eggs of the parasites travel primarily to the intestine when inside humans for release, but while on this journey, they can become trapped in organs and the intestines, causing inflammation.
The characteristic symptom of the disease is a swollen abdomen.
Any freshwater which has these snails in them could be the cause of infection
says Alan Fenwick, Professor of Tropical Parasitology at Imperial College London.
The challenge in controlling the disease is that people often don’t develop symptoms for years, but can continue to transmit the infection. Infections primarily affect young children, and symptoms can take years to appear, making finding and treating those infected a challenge.
What Factors Are Responsible?
According to WHO, 90% of those requiring treatment for Schistosomiasis live in Africa, with most of them living around lake and river regions, where they carry out activities like swimming and fishing. People who have contact with these waters for their survival have the highest transmissions in the world, and usually have little to no immunity.
The factor helping the disease persist is poor sanitation, due to a lack of access to fresh water, safe water, and adequate sanitation. Hence, people who need to urinate and defecate tend to do so in the water, or on open ground, and then washed into the water body thus introducing the eggs which will then go on to infect snails.
Treatment and Prevention
Schistosomiasis was once worldwide and found commonly in parts of China and the Philippines, but large scale control programs, improved environments and greater sanitation facilities reduced the rate of infection.
The best way to curb the disease is to treat everyone in an area irrespective of whether they are infected or not infected, since the cost of treatment is much lower than that of diagnosis; and as symptoms can take years to emerge, most people don’t even know they are infected
This strategy is known as mass drug administration and is an approach used to control a range of infectious diseases including hookworm and elephantiasis.
“It isn’t necessarily 100% effective but it certainly is very effective indeed in that maybe 85 to 95% of the worms will be killed”, says Fenwick
