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Schistosomiasis in Travelers
Abstract & Commentary
By Philip R. Fischer, MD, DTM&H
Dr. Fischer is Professor of Pediatrics, Department of Pediatric & Adolescent Medicine, Mayo Clinic, Rochester, MN
Dr. Fischer reports no financial relationship to this field of study.
Synopsis: Schistosomiasis is a potential problem for international travelers, especially adventure travelers involved in water sports; it is also encountered in migrants to developed countries. Diagnosis is made using urine and stool microscopy or serologic testing. Praziquantel is the medication of choice for effective therapy.
Source: Clerinx J, Van Gompel A. Schistosomiasis in travellers and migrants. Trav Med Infect Dis 2011;9:6-24.
Tropical Medicine Specialists Jan Clerinx and Alfons Van Gompel from Belgium provide a practical review of current knowledge about schistosomiasis as it relates to travelers and migrants, including good images of parasite lifestyle, maps, parasite eggs, and 223 references. Overall, about 83% of imported schistosomiasis originates from Africa. The severity of symptoms depends upon the intensity of the infection, the individual's immune responses and the pre-treatment duration of the infection.
Non-immune travelers may present an itchy, papular rash soon after the skin is penetrated by the cercarial form of the parasites; penetration may take up to 72 hours. This "swimmers' itch" occurs with human schistosome infections as well as with the abortive non-infecting contact of animal schistosomes with human skin.
Acute schistosomiasis, still sometimes referred to as Katayama fever, is a systemic hypersensitivity reaction directed toward the maturing parasites; it usually occurs 3 weeks to 3 months after initial infection. Patients may have fever, cough, abdominal discomfort, and sometimes an urticarial rash.
The presentations for chronic schistosomiasis vary between parasite species. Schistosoma haematobium causes a granulomatous inflammation within the bladder and ureteral walls and patients may present with dysuria and hematuria. S. mansoni infection in the intestinal tract has been associated with abdominal discomfort and fecal blood loss, but most infected patients have no intestinal symptoms. Portal hypertension results from long-term infection with S. mansoni, S. japonicum, and S. mekongi. Neuroschistosomiasis results from the "ectopic" migration of adult worm pairs into small cerebral or spinal vessels with a secondary destructive eosinophilic granulomatous immune response to ova.
Schistosoma infection is best documented by finding ova in either urine or feces, but not all infections are heavy enough to produce detectable excretion of eggs. Antibody tests are very useful, but seroconversion is not assured until 2 or more months after infection. Antigen tests show some promise.
Praziquantel (single dose of 40 mg/kg) is the most cost-effective and widely used medication for treatment of schistosomiasis. Corticosteroids are helpful in acute schistosomiasis, but dosing regimens have not been well studied. They may also be combined with praziquantel treatment in the management of travelers with neuroschistosomiasis. Artemisinin derivatives are being evaluated and might prove adequately effective.
Travel medicine practitioners must confront the issue of schistosomiasis during pre-travel consultations when they give advice about fresh-water contact occurring in many areas of Africa. Again, they must deal with schistosomiasis on seeing returned travelers inquiring as to whether the returnees are asymptomatic or had pruritus after water contact, unexplained itchiness or fever, perhaps with respiratory and intestinal symptoms associated with headache and eosinophilia. In reviewing the topic of schistosomiasis, Clerinx and Van Gompel have provided us with a useful resource.
Additional new information has become available to guide travel medicine practitioners in caring for people who might come in contact with fresh water in schistosomiasis-endemic areas. Several new reports remind physicians of the frequency of schistosomal infections and, thus, the importance of appropriate testing and treatment.
In May, Verani and colleagues reported on a cross-sectional survey of children in Kenya. While anti-schistosomiasis efforts had previously been directed at older children, Verani found that 14% of 1-year-olds were already infected and that 90% of children were infected by age 10 years.1 All travelers, even very young ones, should either avoid contact with fresh water in schistosomiasis-endemic areas or ensure good post-exposure testing and/or treatment.
At the International Society of Travel Medicine (ISTM) meetings in Boston this May, several studies reported new information on schistosomiasis. First, 7% of 132 Dutch travelers (median age 25, median duration of trip 12 weeks, 47% backpackers) were found to have schistosomiasis-positive serology. Just 2 (of 9) had had symptoms of acute schistosomiasis; the others had no symptoms suggestive of schistosomiasis.2 Second, a group of 29 Irish school children visited Uganda for a cultural experience that included some lake, river, and waterfall exposure. Two of the returned students developed illness that prompted blood counts to be done and had significant eosinophilia (19% and 51%). Twenty of the 29 tested children were seropositive for schistosomiasis. In retrospect, 8 of the children had had symptoms suggestive of Katayama fever, and only 6 had been totally asymptomatic.3 Finally, Belgian groups of 9 and 7 travelers visited the Dogon Valley in Mali for an adventurous vacation.4,5 All 9 in one group (each of whom had experienced cercarial dermatitis, 1 of whom developed terminal hematuria) and 1 of 7 in the other group developed positive schistosomiasis tests.
During a symposium on "Water-Related Hazards" at the May 2011 ISTM meetings, Eli Schwartz of Israel noted that more water-related infections arise via skin contact than by ingestion. In some groups of adventure travelers who acquire schistosomiasis, the attack rate is frequently near 100%; most cases in travelers are from Africa, although schistosomiasis has emerged as a problem among river rafters in Laos. Most travelers with schistosomiasis experience acute schistosomiasis, and only about 7% present with cercarial dermatitis. Marc Mendelson from South Africa discussed common challenges in managing schistosomiasis. He pointed out that early post-exposure praziquantel is not effective in preventing disease; the use of DEET prior to water contact and vigorous toweling after exposure can partially prevent infection from getting established. Acute schistosomiasis occurs 1-12 weeks after exposure, and symptoms that arise are mostly from a hypersensitivity reactions to migrating larvae rather than from new ova that are laid 4 or more weeks after cercarial contact; thus, corticosteroids would be more useful in acute schistosomiasis treatment than would be praziquantel, which is effective for established infections, 3 months or more after the exposure. Interestingly, mefloquine is somewhat effective against juvenile forms of schistosomiasis. Diagnostic tests are helpful, but sensitivities vary with the stage of infection. Schistosomiasis also has been linked to false-positive HIV test results and false-positive tests for some malaria antibodies. Eosinophilia can persist for up to a year after effective treatment of schistosomiasis. Even with advanced disease, treatment does help reduce hepatic fibrosis and splenomegaly.
Clearly, schistosomiasis should be of concern to travelers, especially adventurous travelers who are wading, splashing, swimming, or boating in fresh water in regions where schistosomiasis is endemic. Whether symptomatic or not, patients with such exposures can be tested and/or treated following their travels.