Photo courtesy of UCSB
In August 2003, thousands of bathers were diagnosed with cercarial dermatitis after swimming in a geothermally heated brook in Landmannalaugar, Iceland. The number of cercariae in the water and cases of cercarial dermatitis decreased during the winter months. However, the following August cases of cercarial dermatitis reappeared in the area though the prevalence of snails shedding Trichobilharzia cercariae never exceeded 1%. The rapid increase of cercariae in the water were in actuality caused by a breeding mallard female and its ducklings, which were raised on the bathing site during the summer. All the ducklings had nasal- and visceral Trichobilharzia infections. As a result emerging miracidia infected snails that in turn started shedding the cercariae that caused cercarial dermatitis in the bathers. In future years this rapid increase of cercariae could be avoided if ducklings are not allowed to have access to the bathing site and the adjacent brook.
A biology teacher reported to the Kiel Department of Dermatology in June 2000 after he had developed itchy skin lesions on his hands and forearms the previous day about five hours subsequent to cleaning the cold water aquarium of the school at which he worked. The aquarium contained fish and a water snail of the species L. stagnalis, which he had collected a week earlier from the shores of a lake near the school. The patient displayed multiple erythematous papules and papulopustules on his forearms. Further examination revealed a broadened epithelium, subepidermal oedema and a perivascular lymphohistiocytic infiltrate. The snail was removed from the aquarium and transferred to a water-filled Petri dish. Following stimulation with heat and light the snail released thousands of cercariae, which were identified by microscopic analysis as belonging to the species Trichobilharzia ocellata.
A 63-year-old woman developed a pruritic exanthema on her extremities after an hour of work in her garden pond in Planegg, Southern Bavaria. As the appropriate vectors (ducks and snails) were present, doctors were able to make a tentative diagnosis of cercarial dermatitis. Cercarial dermatitis appears worldwide, but in Central Europe the disease is often not recognized.