Bilharzia, also known as Schistosomiasis is a parasitic infection caused by schistosomes or blood flukes. These are picked up by exposure to these organisms in freshwater, ie rivers, streams and lakes in endemic areas. The flukes cause illness in humans by producing inflammation and the mechanical obstruction of organs.

Schistosomiasis affects approximately 200 million people worldwide causing significant illness and in some cases death. In rural, tropical and semitropical areas different types cause different clinical pictures.

  • S.Japonicum endemic in the Philippines and the People's Republic of China
  • S.Mekongi endemic along the Mekong River valley
  • S.Mansoni endemic in the Middle East, Africa, eastern South America and parts of the Caribbean
  • S.haematobium endemic in the Middle East and Africa
The flukes penetrate your wet skin whilst you are immersed in freshwater inhabited by infected snails, which act as a host for the parasite. After infection, there follows a 4-6 week incubation period during which the schistosomal eggs migrate to the liver where they mature into male and female adults. They mate and then migrate to the veins in the lower abdomen. The different types migrate to different areas of the body which explains the variety of symptoms.

The eggs deposited by the female worms work their way through the walls of the organs (usually the intestines or the bladder) and are passed out of the body in the faeces or the urine.. When faeces or urine from infected humans are deposited into freshwater, the eggs hatch and infect snails thus completing the life cycle.

The adult worms can persist in the human host for decades and may not present as an illness for years, sometimes posing an interesting diagnostic problem for the doctor! In a minority of individuals symptoms present 4-6 weeks after infection with a severe feverish illness called Katayama fever. Symptoms include:

  • fever
  • headache
  • cough
  • urticaria
  • lymphadenopathy
Physical signs include a tender enlarged liver and spleen and blood tests may show a certain picture. This reaction is usually associated with S.japonicum and S.mansoni infections..

If you are still travelling and fall ill with an acute feverish illness, it would be wise to seek medical advice; whilst an acute illness with schistosomiasis is rare, you could have malaria.

Other, less serious symptoms sometimes seen during the early stages of infection include:

  • a short-lived, itchy rash 'swimmer's itch'
  • cystitis
  • diarrhoea
At one time, advice given to travellers was not to swim or paddle in Lake Malawi. Clearly avoidance of contact with the infected snails is one way to avoid infection, but it is now possible to screen people who may be at risk on their return to England.

If you know that you may have been at risk of infection, you must wait for 3 months after your last possible exposure, as the tests may not prove positive before this time. Then you should see your doctor who will arrange a blood test and also ask you to provide stool and urine specimens. The blood samples are sent to London for analysis and if the tests prove positive, you will be offered treatment as advised by the London School for Tropical Diseases.

Ref: The Travel & Tropical Medicine Manual Second Edition

Further information

This article published on
01 July 2005

Next review date 7/1/2013


Skin, hair and bones
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