Known transmission sites in Africa include Lake Victoria (Uganda), the Nile (Egypt, Uganda), the Crater Lakes (Uganda), Lake Kivu (Rwanda), Lake Muhazi (Rwanda), the Congo River (DRC), Lake Tanganyika (DRC, Tanzania, Burundi), the Omo River (Ethiopia), the Dogon Valley (Mali), Lake Malawi (Malawi), rivers in Madagascar and the Zambezi River (Zambia, Zimbabwe), see maps below.
In Asia, the Mekong River (Laos) and rivers in the Philippines are known sites of transmission. North-eastern Brazil (in the region surrounding Fortaleza) is also a transmission area.
Very recently, more than a hundred cases of schistosomiasis were reported in South-eastern Corsica, following water contact in the Cavu River.
The risk of Bilharzia is greatest in stagnant water (such as in reservoirs), but infection can also occur in rivers (large or small, fast-flowing or slow-flowing). Some people become infected after a single, brief exposure, whilst others do not become infected even after swimming for several hours. Factors that can influence an infection include the individual's susceptibility to this infectious disease, the location and the season in which the freshwater contact takes place.
The disease usually presents with flu-like symptoms, but it is also possible to become infected and not develop any symptoms initially. In rare cases, severe complications can occur within the first months after exposure (blood in the urine, paralysis) and these individuals should contact a doctor immediately.
There is no prophylactic medication or vaccine. It is therefore best to avoid bathing or swimming in freshwater. Undergoing treatment after bathing in water that is possibly contaminated (as has been proposed in some countries), without a correct diagnosis and proper monitoring, can be dangerous and is absolutely not recommended. If no symptoms occur, a test can be performed three months after any exposure. Blood, urine and stool samples will be collected (microscopy, serology and eosinophilia). If an individual does develop symptoms, the tests can be performed at an earlier stage.
The Institute of Tropical Medicine in Antwerp has developed new testing methods (PCR tests on blood, urine and stool samples) and hopes to be able to detect more cases of schistosomiasis more quickly. These tests are not yet used in the routine.
- Global distribution of schistosomiasis
- Schistosomiasis in travelers: main sources of infection
- www.who.int/ith, chapter "Disease distribution maps"
- Maps per country
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