Schistosomiasis Schistosomiasis, an infection estimated to occur worldwide among some 200 million people, is caused by ‘flukes’ whose complex life cycles utilize specific fresh water snail species as intermediate hosts. Infected snails release large numbers of minute free-swimming larvae which are capable of penetrating the unbroken skin of the humans. Even brief exposures to contaminated water can result in infection. Most exposure to schistosomiasis is in travel to endemic areas of Africa, however the disease also occurs in the Caribbean, South America and Asia. Those at greatest risk are travellers who engage in wading or swimming in fresh water in areas where poor sanitation and appropriate snail hosts are present, such as Lake Malawi. Bathing with contaminated fresh water can also transmit infection. Human schistosomiasis cannot be acquired by wading or swimming in salt water (oceans or seas).
The disease Signs of acute infection can occur a few weeks after exposure to infected water, but most acute infections cause no symptoms. The most common acute symptoms are: fever, lack of appetite, weight loss, abdominal pain, weakness, headaches, joint and muscle pain, diarrhoea, nausea, and cough. Rarely, the central nervous system can be involved to produce seizures or transverse myelitis as a result of mass lesions of the brain or spinal cord. Chronic infections can cause disease of the lung, liver, intestines, and/or bladder. Many people who develop chronic infections can recall no symptoms of acute infection.
Prevention Since there is no practical way for the traveller to distinguish infested from non-infested water, fresh water swimming in rural areas of endemic countries should be avoided. In such areas heating bathing water to 50° C (122° F) for 5 minutes or treating it with iodine or chlorine in a manner similar to the precautions recommended for preparing drinking water will destroy larvae and make the water safe. Swimming in adequately chlorinated swimming pools is virtually always safe, even in endemic countries. Filtering water with paper coffee filters may also be effective in removing larvae from bathing water. If these measures are not feasible, allowing bathing water to stand for 3 days is advisable since larvae rarely survive longer than 48 hours. Vigorous towel drying after accidental water exposure has been suggested as a way to remove larvae in the process of skin penetration, however it is far safer to avoid contact with contaminated water in the first place.
Testing and Treatment Diagnosis of infection is usually confirmed by serological (blood) studies or by finding schistosome eggs on microscopic examination of stool and urine. Schistosome eggs may be found as soon as 6-8 weeks after exposure. Upon return from foreign travel, if you think you may have been exposed to schistosome-infected fresh water, be sure to see a physician to undergo screening tests. Individuals who have participated in activities which expose them to Schistosomiasis should also seek follow up at least 3 months after exposure for retesting if initial results are negative. Safe and effective oral drugs are available for the treatment of schistosomiasis.