Investigation of an outbreak of cercarial dermatitis

Abstract

We present the investigation of an outbreak of cercarial dermatitis that occurred in a recreational-tourist lake in the Quebec City region (Canada) in the summer of 1999. A case-reporting form was sent to 450 families likely to have activities that would bring them in contact with the lake's water. The snails were characterized and the prevalence of their infestation by schistosomes was investigated. In total, 63 episodes consistent with cercarial dermatitis were reported. Sixty-nine percent of the cases occurred from swimming at the same beach. This location was the one where the only population of snails in the lake was identified. Shoreline residents were informed that they should not feed waterfowl, and a clean-up of the snail population was done at the start of the following summer. There were no cases of cercarial dermatitis at this site the following summer.

Avian Schistosomes and Outbreaks of Cercarial Dermatitis

“…For example, longer exposure in water increases cercarial penetration via frequent water visits and more time spent in shallow water (4,(304)(305)(306). While gender does not influence the risk of infection (4,304,305,307), some studies found a higher risk among children of less than 15 years of age, since they tend to spend more time in shallow water (280,308,309). There are rare cases of nonsensitive individuals that may be due to host desensitization (310) or individual nonsusceptibility/nonattractivity to cercariae (4,311).…”

“…Locally, the highest risk of infection usually occurs in shallow, warm, and vegetation-rich shore areas, where the snails accumulate and release cercariae (308,309). Cercariae of avian schistosomes are concentrated just beneath the water surface (see the information on host finding), so swimming in deeper water may reduce the infection probability (280).…”

“…Most cases of cercarial dermatitis correlate with high air and water temperatures during the summer months, when schistosome development in snails is amplified and emission rates of cercariae are stimulated by sunlight (4,11,279,280,304,305,309,314). Production can reach several thousands of cercariae/snail/day (169,300,315), and these emission rates may even counterbalance the loss of cercarial capability to survive and infect hosts at high temperatures (see above).…”

“…In addition, after repeated exposures, some snails may become resistant to copper sulfate or avoid the treatment by burrowing into the mud (322,323). Manual collection of snails (309,324) or destruction of their habitats by local removal of littoral vegetation (2) represents a less harmful approach to snail control. Large-scale destruction of snail populations by use of heavy machines along the shores of Annecy Lake (France) and Cultus Lake (Canada) led to substantial reductions of cercarial dermatitis (2).…”

Prevalence of schistosome induced cercarial dermatitis in north of Iran

“…The age groups were classified in 7 levels and each level was 10 years younger than the next. There were 338 people in age groups of [10][11][12][13][14][15][16][17][18][19] years old, 565 people (24.5%) in the group of 20-29 years old, 459 people in the age group of 30-39 years old, 427 people in age group of 40-49 years old, 507 people in the age group of 50-59 years old, 9 people in the age group of 60-69 years old and 5 people in age group of more than 70 years old. From the vocational point of view, the people under study were divided into 5 job groups which are: householders, clerks, farmers, university or school students, other vocations and self-employments.…”