Schistosomiasis is caused by several species of parasitic flatworm or blood flukes, known as schistosomes. Transmission occurs by skin contact with freshwater contaminated with the larval forms of schistosomes . Within days of being infected, some people develop a rash or itchy skin where the larvae has entered the body. Within 1-2 months of infection, fever, chills, cough and muscle ache may occur. However, most people have no symptoms in the early phase of the infection. In chronic infections adult flukes live for many years in the veins of the host where they produce eggs, which cause damage to the organs in which they are deposited. This can cause disease in the liver, intestinal tract, bladder (including bladder cancer), kidneys, or lungs. Many persons with chronic infections recall no symptoms of acute infection.4,45,46
Transmission45,46 Schistosomiasis is transmitted by skin contact with freshwater contaminated with the larval forms of schistosomes (cercariae). These free-swimming larvae develop in water snails, which are infected as a result of eggs excreted in human urine or faeces. Even brief exposure to contaminated fresh water, such as wading, swimming, or bathing, can result in infection. This infection cannot be acquired by wading or swimming in salt water (oceans or seas).
Geographical distribution45 Schistosomiasis occurs in sub-Saharan Africa , the Arabian peninsula , Brazil , Suriname , Venezuela , China , in parts of Indonesia , the Philippines and eastern Mediterranean areas.
Risk for travellers45,46 Those at greatest risk are travellers who wade or swim in or bathe with freshwater in areas where poor sanitation and the appropriate snail hosts are present.
Because there is no practical way for the traveller to distinguish infested from noninfested water, travellers should avoid direct contact (swimming or wading) with fresh water in endemic areas. In case of accidental exposure, dry the skin vigorously to reduce penetration by larvae.
Avoid drinking, washing/bathing, or washing clothing in water that may contain larvae. Water can be treated to remove or inactivate cercariae by paper filtering, or use of iodine or chlorine. Thus swimming in adequately chlorinated swimming pools is virtually always safe, even in endemic countries.
Upon return from foreign travel, those who might have been exposed to infested fresh water should be advised to undergo screening tests.
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