Schistosomiasis

Schistosomiasis, also known as bilharzia (bill-HAR-zi-a), is a tropical disease caused by a microscopic worm or “fluke”. It is a “neglected tropical disease” - one which causes substantial illness in a large number of people globally.

Infective stages called “cercariae” can penetrate skin that is exposed to infected water, usually in fresh water lakes and rivers. Part of its life cycle takes place in snails at the water’s edge. The fluke develops in the infected person and can cause problems over time. The worm eggs are responsible for organ damage. 

More than 240 million people are infected with schistosomiasis world-wide. Most human infections are caused by Schistosoma mansoni, Schistosoma haematobium and Schistosoma japonicum. S. Mansoni is found in Africa, South America and some Caribbean islands. S. Haematobium is found in Africa and the Middle East and S. Japonicum is found in Asia.

Early on, schistosomiasis is usually without symptoms. Occasionally there is an itchy rash or asthma-like cough soon after infection. Diagnosis is made by a blood test or checking the urine or stools for eggs, which can be identified from 6 to 8 weeks after exposure in an infected waterway. The blood test can take 12 weeks to become positive after the water exposure.

Chronic infection can lead to serious damage in the liver, lungs, urinary tract and even spinal cord. This is mostly seen in locals such as lake fishers who get heavy and repeated infections with no treatment.

There is no vaccine currently available, but the disease can be treated.

The risk of exposure can be high in some travellers.

Apart from long term residents in Africa and humanitarian workers, the trans-African traveller, particularly those on truck safaris through Malawi are most at risk.

Other areas of risk include:

• Africa: Sub-Saharan region, Egypt and Sudan
• South America: Brazil, Suriname, Venezuela
• Caribbean: Dominican Republic, Guadeloupe, Martinique, St Lucia
• Middle East: Iran, Iraq, Saudi Arabia, Yemen
• Southeast Asia and southern China

Surveillance data for 14 years (1997 to 2010) identified 1,465 cases of imported schistosomiasis. The cases fell into 3 main groups: non-European immigrants (51%), European travellers (33%), and long-term expatriates (16%). Most cases (95%) had returned from Africa and very few had received pre-travel advice. High risk areas to European travellers included Lake Malawi, Lake Victoria and the Dogon county in Mali, all popular tourist areas.

Travellers should avoid freshwater exposure in areas of risk, however, this is easier said than done. Even a brief exposure to contaminated fresh water such as crossing a stream can result in infection (the ocean is not a risk, nor are chlorinated pools).

Untreated piped water coming from infected lakes, rivers or canals may be infected. Heating water to at least 50ºC for 5 minutes can disinfect the water, as can storing it in a holding tank for a few days. Areas of fast flowing water are safer than still water bodies. Reedy areas at the edges are the riskiest. If you must swim in a suspect area, dry off vigorously with a towel afterwards and get a check-up about three months later (sooner if you get symptoms).