Photo courtesy of the City of Lynnwood
Cercerial dermatitis is a potential hazard worldwide, being absent only at the North and South Poles, wherever people share an aquatic environment with vertebrates and mollusks harboring the parasites. Although most often associated with fresh-water lakes, ponds, streams, irrigation ditches, and rice paddies, the condition can also be seen in salt water inhabited by the appropriate mollusk hosts. Therefore, the condition is seen in swimmers, duck hunters, fishermen, and in people whose occupations require water exposure such as clam diggers and rice farmers. In the US, it is endemic in numerous lakes in Michigan, Wisconsin, and Minnesota.
Photo courtesy of Mount Allison University
Two previous epidemiologic studies have evaluated water exposure, personal, and weather factors as risks for onset of cercarial dermatitis (Chamot et al., 1998; Lindblade, 1998). For bathers and swimmers, risks for swimmer's itch onset were based on more time spent in water, the time of day, past encounters with cercarial dermatitis, location (specific beaches had high rates), high barometric pressure, and high temperature (Chamot et al., 1998). Age, gender, and number of water entries on the selected day were not related to incidence. Also, farming or food production that requires flooded fields such as rice farming also may help cause cercarial dermatitis.