Schistosomiasis in Returned Travelers
ABSTRACT & COMMENTARY
By Philip R Fischer, MD, DTM&H
Professor of Pediatrics, Department of Pediatric and Adolescent, Medicine, Mayo Clinic, Rochester, MN.
Dr. Fischer reports no financial relationships in this field of study.
SYNOPSIS: Ten of 19 members of an Israeli tour group chose to swim in the high-altitude fresh water of a crater lake in western Uganda. All 10 (and none of the 9 non-swimmers in the group) developed acute schistosomiasis with headache (10 of 10), fever (9 of 10), eosinophilia (9 of 10), and cough (8 of 10) three to seven weeks after the exposure.
SOURCE: Lachish T, et al. High rate of schistosomiasis in travelers after a brief exposure to the high-altitude nyinambuga crater lake, Uganda. Clin Infect Dis 2013;57:1461-4.
It is estimated that 90% of the world's cases of schistosomiasis occur in Africa. The infection results from exposure of human skin to cercarial forms of Schistosoma in fresh water where snail intermediate hosts live. For travelers, Lake Victoria and Lake Malawi are known to pose particular risk.
An 18-year-old presented for care with three weeks of headache, intermittent fever, and weakness (with a one week history of cough and diarrhea) six weeks after he returned from an organized tour in Uganda. There, he had gone swimming for 15 minutes in Lake Nyinambuga, a volcanic crater lake in Western Uganda. His peripheral blood had 9730 eosinophils per microliter (55% of the total white blood cell count).
All nine of the 18-year-old's companions who swam in the lake (mean exposure time estimated to be 22 minutes) and none of the nine non-swimmers on the tour developed similar symptoms. All had headache, nine had fever, nine had eosinophilia (mean count 2690), nine had weakness, eight had cough, seven had neck pain, and six had pruritus. All affected travelers had positive Schistosoma serology by ELISA testing.
Five of the ten afflicted travelers received steroids for symptomatic relief, and all were treated with praziquantel three months after the exposure.
Schistosoma parasites cause three sorts of problems for people. First, schistosomes, especially the avian parasite species, can cause an itchy rash (cercarial dermatitis) immediately following exposure of human skin to infested water. For bird parasites, this is a "dead end" infection that is not established in humans. The itch can be bothersome for two to 10 days. This condition occurs in many areas of the world, and the intensity of symptoms relates to the intensity of exposure and the host's history of previous sensitizing exposures.1 Second, acute schistosomiasis (sometimes called Katayama fever), as seen in the Israeli travelers reported by Lachish and colleagues, occurs two to eight weeks after exposure to human schistosomes as eggs stimulate an allergic-type response. Third, the life-threatening risk of schistosomiasis comes much later when chronic infection has led to portal hypertension (such as with S. mansoni) or urinary disease (with S. haematobium). There are often no warning symptoms of these chronic infections.
What should an infectious disease physician do?
If someone presents with a past history of cercarial dermatitis, they could be advised to either wear skin-covering swimwear or apply DEET (diethyl-meta-toluamide insecticide) cream prior to subsequent exposure to potentially contaminated fresh water. Neither of these measures is fully protective, but symptoms might be moderated by decreasing the degree of contact between skin and cercariae.
During pre-travel consultations, travelers can be warned of the risk of freshwater exposure in Schistosoma-endemic areas of Africa. As pointed out by the Israeli travelers' experience, infection can occur even with relatively brief exposure and in areas at high altitude (more than 1400 meters above sea level) where infection has not previously been reported.2 One approach is to prohibit all freshwater contact during the trip, but many travelers would prefer to take the risk of infection as a trade-off for the pleasure of swimming in a volcanic crater or water-skiing in Lake Malawi.3 Vigorous towel drying after exposure may be helpful. Travelers should at least be warned that if they choose to have skin contact with freshwater in a potentially risky area, they should present for testing three months after the trip (by which time a serologic response to infection would be expected to be present) with treatment given in the event of positive results.
Treatment can, of course, be offered to symptomatic patients. Cercarial dermatitis is usually treated with antihistaminics. Steroids may be given orally for severe symptoms of acute schistosomiasis. Anti-parasitic treatment is ineffective for these early stages of infection.4,5 For established infection (as seen by positive serology three or more months after exposure), praziquantel is given in multiple doses on a single day (with the dose varying with the weight of the patient and the specific infecting Schistosoma species).6 The chronic consequences, such as portal hypertension, are incompletely reversible; early treatment after an infection-causing exposure is important.
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