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Cercarial Dermatitis among Bathers in California; Katayama Syndrome among Travelers to Ethiopia

Cercarial dermatitis--California: In late August 1981, four persons sought medical attention for dermatitis after swimming or wading in a cove of the Mad River at Camp Bauer in Humboldt County, California, 10 miles from the Pacific coast. Subsequent investigation uncovered 12 additional cases later diagnosed as cercarial dermatitis. Interviews with 14 patients revealed that all were exposed between August 29 and September 2, and that the most common complaint was pruritis occurring within 1H hours after water contact. Discomfort ranged from moderate to severe. In a few persons, pruritis persisted several days; those patients were treated with antipruritics.

These clinical reports led to a search for evidence of parasites at the site of exposure, a 100-yard stretch of beach bordering a large pool of sluggishly moving water. Snails of the genus Physa were noted in the pool's shallows. They were taken to the Humboldt County Health Department laboratory, where furcocercous cercariae were observed emerging from snails held in dishes of water. As a control measure, authorities posted warning signs on the beach.

Katayama syndrome--Ethiopia: On January 11, 1982, a physician in Gunnison, Colorado, requested diagnostic advice for a patient with a history of intermittent fever, cough, lethargy, and myalgias associated with an absolute eosinophilia. The patient had been ill for 5 weeks, with onset of illness on December 6, 1981, one week after he returned from rafting the Omo River in Ethiopia. Preliminary investigation revealed that, among eleven travelers, five had similar illnesses--four with fever and eosinophilia and one with malaise and eosinophilia. Onset dates ranged from December 6 to December 21. All five patients had sought medical care in December 1981, but various diagnostic evaluations, including thick blood film examination, serology for malaria and schistosomiasis, and stool examination for ova and parasites, had not provided a diagnosis.

Katayama syndrome (acute schistosomiasis) was suspected, and stool, urine, and serum specimens taken between January 10 and February 10, 1982, were examined from 10 of 11 travelers; the eleventh traveler had similar but independent evaluation in Sweden in early January. At least three 1-gram stool samples from each of nine patients were processed by the modified Ritchie concentration technique (MRCT). Formal-ether concentrations were done on single stool specimens from the other two. All symptomatically ill travelers and one asymptomatic one had Schistosoma mansoni eggs in their stools, with counts ranging from three to 15 eggs/gram of stool. The five remaining asymptomatic travelers had no eggs on examination of the entire sediment from at least 3 grams of stool. All egg-positive persons had positive IFA tests for schistosomiasis, while all egg-negative persons had negative tests. Those with proven S. mansoni were treated with a single dose of oxamniquine (30 mg/kg). Repeat stool examinations (at least 3 gm by the MRCT) 1 month post-treatment were negative. Concurrently, five of six patients who initially had negative tests were retested and remained egg- and IFA-negative.

The rafting trip had begun on November 7, 1981. In addition to occasional contact with the Omo River, the travelers often bathed in tributary streams entering the Omo canyon. They iodinated drinking water and most iodinated shower water, especially during the latter part of the trip. They were aware of the risk of contracting schistosomiasis from the lower stretches of river and particularly from the Mui River, where their trip ended on November 26; consequently, they iodinated all Mui River water used for bathing or drinking. Thereafter they avoided any contact with untreated natural waters.

A survey of the entire group revealed no specific mode or site of exposure. Among multiple bathing sites, three pools were used by all infected travelers, as well as by some uninfected ones. Those who towel-dried had a reduced likelihood of infection, but that was not statistically significant; and one person who repeatedly towel-dried was infected. Reported by J Philpot, J Tarr, MD, Gunnison, R Hopkins, MD, State Epidemiologist, Colorado State Dept of Health; G Dean, MD, Wichita Falls, Texas; T Humphry, MD, Arcata, K Sherman MPH, W Stricklind, M Thibeau, P Anderson, MD, Humboldt-Del Norte County Health Dept, G Grodhaus, MA, SB Werner, MD, California Dept of Health Svcs; Field Svcs Div, Epidemiology Program Office, Helminthic Diseases Br, Div Parasitic Diseases, CDC.

Editorial Note

Editorial Note: Schistosome life cycles are characterized by asexual reproduction in an extremely restricted range of snails (intermediate host) and sexual reproduction (oviposition) in a restricted range of vertebrates (definitive host). Vertebrates become infected when free-swimming furcocercous (fork-tailed) cercariae emerge from snails and penetrate the skin, losing their tails and becoming schistosomula (juvenile worms).

Man was not a suitable, definitive host in the first outbreak, and the schistosomula died in the skin, initiating cercarial dermatitis (schistosome dermatitis, swimmer's itch, clam digger's itch, sea bather's itch). Many species of schistosomes throughout the world may produce this syndrome, including some parasites of sea birds and marine snails. Usually, onset of pruritic, papular rash occurs within a few hours after bathing and may be preceded by a stinging sensation just after exposure. Symptoms are probably due to the host's reaction to the dead and dying schistosomula and may persist for several days but always resolve spontaneously. Treatment with antihistamines or antipruritics may provide relief.

Katayama syndrome (acute schistosomiasis), as described in the second outbreak, resulted from infection by S. mansoni of man, an appropriate host. The syndrome usually occurs with primary infections by S. mansoni and S. japonicum but has been reported with heavy secondary infections by these two species and, rarely, with primary S. hematobium infections. After single-source exposures, incubation ranges from 2 to 10 weeks; onset of illness corresponds to late maturation of juvenile worms and onset of oviposition (at 4-6 weeks). Since egg excretion in the stool is further delayed, a parasitologic diagnosis of early Katayama syndrome is virtually impossible in all but the few cases with delayed onset.

As with chronic schistosomiasis, severity of Katayama syndrome parallels worm burden (1). Unlike chronic schistosomiasis, symptoms often occur with very light infections. Thus, a sensitive stool-concentration technique, such as the MRCT, with examination of the entire sediment from at least 1 gram of stool, is recommended to confirm the diagnosis. While safe and effective schistosomocidal drugs are now available, they lack evaluation in prepatent schistosomiasis.

In the cercarial dermatitis outbreak, the demonstration of infected snails at the suspected site of exposure was convincing evidence for that diagnosis, as well as for incrimination of the river as the first source of that type of documented in California. In the Katayama syndrome outbreak, no specific site of infection could be determined. However, natural pools in stream beds used for swimming or bathing have been incriminated previously as sites of infection in Africa and other endemic areas (2). In addition to such pools in tributary streams, shallows without appreciable flow in the Omo River may have harbored infected snails; water from the main current of the river is a highly improbable source.

The Katayama syndrome outbreak is by no means unique. The waters of the Mui River were implicated as the source for two previous outbreaks among game park visitors (3), and CDC has received anecdotal reports of infected river-rafters from other trips.

Preventive measures for both syndromes are aimed at preventing penetration by cercariae. Avoiding potentially infected water (including drinking water), although entirely effective, may not be practical. Iodinating (1 part per million for 30 minutes), chlorinating, or heating the water kills the cercariae. Frequent towel drying is effective, but because Katayama syndrome requires only a small worm load, this practice could reduce symptomology without completely preventing disease. Molluscicides are too expensive to be practical, except in the most frequently visited and infected water-contact sites. With the increasing popularity of rafting on African rivers and the unavoidable water contact, in addition to other exposures of tourists to endemic areas, physicians should suspect acute schistosomiasis when they obtain typical clinical evidence and compatible exposure histories. In the United States (except in Puerto Rico), there are no suitable snail hosts for human schistosomes; therefore, only cercarial dermatitis may be acquired.


  1. Hiatt RA, Sotomayor ZR, Sanchez G, Zambrana M, Knight WB. Factors in the pathogenesis of acute schistosomiasis mansoni. J Infect Dis 1979;139:659-66.

  2. Clarke VdeV, Warburton B, Blair, DM. The Katayama syndrome: report on an outbreak in Rhodesia. Cent Afr J Med 1970;16:123-6.

  3. Zuidema PJ. The Katayama syndrome; an outbreak in Dutch tourists in the Omo National Park, Ethiopia. Trop Geogr Med 1981;33:30-5.

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