Environmental management

Bilharzia


What is Bilharzia?

Bilharzia is a human disease caused by parasitic worms called Schistosomes. Over one billion humans are at risk worldwide and approximately 300 millions are infected. Bilharzia is common in the tropics where ponds, streams and irrigation canals harbor bilharzia-transmitting snails. Parasite larvae develop in snails from which they infect humans, their definitive host, in which they mature and reproduce.


Worms wriggling in your veins

Adult Schistosomes worms are about 1 cm long and hang out in mesenteric veins (the small veins that carry blood from the intestine to the liver). The worms feed on red blood cells and dissolved nutrients such as sugars and amino acids. This can cause anemia and decreased resistance to other diseases.
Schistosomes live in pairs, the male holding and protecting the female inside his ventral groove. Once paired, the two remain in constant copulation. The female lays hundreds of eggs each day, which find their way out of the human body through the urine or the faeces, depending on the species. The pathology is mostly caused by the large number of eggs becoming stuck in various body parts, in particular the liver (causing liver enlargement and malfunction) and the kidneys (causing kidney damage, detectable by blood in the urine).


Worms transmitted by snails

Schistosomes eggs are evacuated from the human body via faeces or urine. When sanitation is poor, they can reach rivers or lakes. They hatch into tiny swimming larvae called miracidia. These swim about until they locate a snail and bore into its body. Over a period of 3 to 4 weeks, miracidia develop into hundreds of sporocysts, which each produce thousands of cercariae, the next infective stage. A single snail can shed thousands of cercariae each day.


Can I catch Bilharzia from someone infected?

No - unless you are a snail !
Schistosomes must alternate between humans and snails to complete their life cycle. This means that Bilharzia can only caught from snails.
Under the tropics, any body of water containing vegetation could contain bilharzia-transmitting snails. Washing, swimming or paddling in that water therefore exposes you to infection by the parasite.


What are the symptoms?

In the case of urinary Bilharzia (found only in the Old World), the victim passes red urine, tinted by blood lost through the damaged kidneys. In some places such as Nigeria, this is actually seen as "coming of age", after which boys are considered men.

In the case of intestinal Bilharzia (Old and New World), blood may be passed in the faeces but is not often recognised.

Both types of Bilharzia cause anemia and fatigue. They are medically diagnosed by the presence of eggs in the urine or feaces.


Is there a vaccine?

Not yet, although many medical scientists are working on it. The problems involved in vaccine development are threefold:

The good news is that there is a readily available treatment. A drug called praziquantel is injected into the bloodstream and disrupts the parasite's tegument. The parasite is then destroyed.

Should you have personal medical questions about bilharzia, please contact consult your local specialist or the Center for Disease Control.

 


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