Bilharzia, or “snail fever,” is a disease caused by a parasitic worm. The worm, or fluke, has several different species. It affects the intestines and the urinary system preferentially, but because it lives in the blood vessels, it can harm other systems in the body too.
The World Health Organization (WHO) describe bilharzia — now mostly known as schistosomiasis — as both an acute and chronic disease. Symptoms appear as the body reacts to the parasite’s presence, but complications can persist long-term.
The disease can affect different parts of the body, including the lungs, the nervous system, and the brain. The area of damage will depend on the species of parasite.
Bilharzia is not usually fatal immediately, but it is a chronic illness that can seriously damage the internal organs. In children, it can lead to reduced growth and problems with cognitive development.
Some types of bilharzia can affect birds and mammals, such as water buffalo.
Transmission: How do you get it?
Schistosomiasis or bilharzia is passed on by a parasite that is present in fresh water in some places.
According to the WHO, the infection starts when a person comes into direct contact with fresh water where certain types of water snail carry the worm.
The parasites enter the body when a person is swimming, washing, or paddling in contaminated water. They can also become infected by drinking the water or eating food that a person has washed in untreated water.
The infective form of the fluke is known as cercariae. The cercariae emerge from the snails, pass through a person’s skin when they are in the water, and develop into adult worms that live in the individual’s blood.
Depending on the type of worm, bilharzia can affect:
the urinary system, increasing the risk of bladder cancer
the spinal cord
The infection cycle of the parasite begins when the worm’s eggs enter fresh water through the feces and urine of humans who already have the infection.
The eggs hatch in the water, releasing tiny larvae, and the larvae reproduce inside the water snails.
After they have infected water snails, the worm’s cercariae, are released. The cercariae can survive for up to 48 hours.
The cercariae can penetrate human skin and enter the bloodstream. There, they travel through the blood vessels of the lungs and liver, and then to the veins around the bowel and bladder.
After some weeks, the worms are mature. They mate and start producing eggs. These eggs pass through the walls of the bladder, the intestine, or both. Eventually, they leave the body through urine or feces. At this point, the cycle starts again.
A person with schistosomiasis cannot pass it on to another person. Humans only become infected through contaminated water where the snails are living.
A fever and a rash are symptoms of bilharzia.