All it takes is a snail, a worm and some freshwater to become infected. Once you are, the disease could persist for decades -- and prove fatal.
The culprits come as a pair: freshwater snails harboring parasitic worms. Once released from the snails, the worms can burrow into the skin and deep inside the body of any human daring to enter its waters.
The infection at hand is 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 in their wake.
"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 majority of infected waters are found in Africa, particularly the continent's largest lake -- Lake Victoria -- where risk of infection is high. The challenge in controlling the disease is that people often don't develop symptoms for years, but can continue to transmit the infection.
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 versions of themselves now capable of burrowing back into human skin. On release back into the water they swim ready to, again, infect humans in their vicinity.
It's a perpetual cycle in which the parasites use both snails and humans to their advantage, manipulating both, to ensure the survival of their speciesAccording to WHO, 90% of those requiring treatment for schistosomiasis live in Africa, but most of them live around lake and river regions. The factor helping the disease persist, is poor sanitation
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 meant infections were controlled.
The same has not been true for populations surrounding the lakes of Africa, particularly Uganda where the highest burden now remains. The region's fishing and island communities rely on these lakes for their livelihood, making them hotspots for the disease.The idea is to treat everyone who is at risk as the cost of treating them is much lower than diagnosis and as symptoms can take years to emerge, most people don't know they're infected.