Swimmer’s Itch: Incidence and Risk Factors

Abstract

Swimmer's itch (cercarial dermatitis) affects people engaged in open-water activities. We report incidence and risk factors for a US lake. Water exposures and swimmer's itch experience were reported daily for riparian household residents and guests at Douglas Lake, Michigan, in July 2000. Incidence of swimmer's itch was 6.8 episodes per 100 water exposure days. Positive risks were (1) exposures in shallow water and in areas with onshore winds and (2) more days of lake use in July. Further epidemiological studies will help public health agencies address this bothersome problem at recreational lakes.

Avian Schistosomes and Outbreaks of Cercarial Dermatitis

“…Cercarial dermatitis develops as a result of sensitization of the human immune system (232,260), and repeated exposures to cercariae influence the occurrence and intensity of subsequent infections. 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).…”

“…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).…”

“…accumulate in vegetation-free areas, on stones or muddy sediments; and physid snails prefer detritus as a source of food (312,313). In addition, cercariae of avian schistosomes can be transported by wind and water currents for several kilometers (2,304,305). Therefore, taking the local situation into account is essential for risk assessment, because conditions unsuitable for one snail species may provide an ideal habitat for another.…”

“…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).…”

“…This is usually attributed to the peak activity of the preferred definitive hosts. Thus, Trichobilharzia and some other genera infecting aquatic birds leave the snail host during the light period of the day, mainly in the morning hours (2,4,280,305). Increased illumination, temperature, and snail locomotory activity trigger cercarial emergence (169,211,316,317).…”