Five species of the flatworm or blood flukes, also known as schistosomes, cause the main forms of human bilharzia or schistosomiasis.
Five species of the flatworm or blood flukes, also known as schistosomes, cause the main forms of human bilharzia or schistosomiasis. They are:
A person gets bilharzia when his/her skin comes into contact with contaminated fresh water. The parasites enter the skin, then migrate through the body to the blood vessels of the lungs and liver. From there they may advance to the veins around the bowel or bladder. The worms will lay eggs which can either be passed in the urine or faeces, or remain in the tissues in the human host. Eggs that remain in the host are usually found in the liver (S. mansoni) or the bladder (S. haematobium).
Infected people can infect fresh water if they urinate or defecate in it.
This will start a new cycle of infection when contaminated water is used in ordinary daily activities such as washing, bathing and swimming or professional activities (also see Course).
Cause About 600 million people are at risk of becoming infected with this parasitic disease, the underlying causes of which include the following:
In chronic bilhazia, it is the body’s reaction to the worm’s eggs, laid in the liver, intestine or bladder, that causes the symptoms associated with bilharzia. Eggs are rarely found in the brain.
Blood in the urine is a clear indication of urinary bilharzia, and is the commonest symptom of this type of bilharzia. In the case of intestinal bilharzia, symptoms may initially be so atypical that diagnosis is difficult. If left untreated, these symptoms can lead to serious complications of the liver and spleen.
Blood in the urine is a clear indication of urinary bilharzia. In the case of intestinal bilharzia, symptoms may initially be so atypical that diagnosis is difficult. If left untreated, these symptoms can lead to serious complications of the liver and spleen.
Prevalence The disease commonly affects the following people:
When the new parasites have entered a person’s skin (it can happen in a few seconds), they migrate to the blood vessels of the lungs. From there they migrate to the blood vessels of the liver and intestines (Schistosoma mansoni) and bladder (Schistosoma haematobium). Bilharzia continues its life cycle in the blood vessels of the intestines (in the case of intestinal bilharzia) or the bladder (in the case of urinary bilharzia) of the victim.
In 30 to 45 days a cerceriae is transformed into a long worm. The female worms lay between 200 and 2 000 eggs per day over an average of five years. It is the eggs and not the worm that cause the damage to the bladder, intestines and other vital organs, such as the liver. The body's reaction to the eggs in the liver can cause fibrosis in the liver, which in turn causes enlargement of the spleen, and dilation of some of the blood vessels, especially in the base of the oesophagus.
Risk factors You may get infected with bilharzia if: