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Swimmer’s itch, also known as lake itch, duck itch, cercarial dermatitis, and schistosome cercarial dermatitis, is a short-term immune reaction occurring in the skin of humans that have been infected by water-borne schistosomatidae. Symptoms, which include itchy, raised papules, commonly occur within hours of infection and do not generally last more than a week. A number of different flatworm parasites in the family Schistosomatidae are what cause swimmer’s itch. These parasites use both freshwater snails and vertebrates as hosts in their parasitic life cycles. Mostly waterfowl are used as the vertebrate host. During one of their life stages, the larvae of the parasite, cercariae, leave the water snails and swim freely in the freshwater, attempting to encounter water birds. These larvae can accidentally come into contact with the skin of a swimmer. The cercaria penetrates the skin and dies in the skin immediately. The cercariae cannot infect humans, but they cause an inflammatory immune reaction. This reaction causes initially mildly itchy spots on the skin. Within hours, these spots become raised papules which are intensely itchy. Each papule corresponds to the penetration site of a single parasite. The schistosomatidae that give rise to swimmer’s itch should not to be confused with those of the genus ''Schistosoma'', which infect humans and cause the serious human disease schistosomiasis, or with larval stages of thimble jellyfish (''Linuche unguiculata''), which give rise to seabather's eruption. Seabather's eruption mostly occurs in salt water, on skin covered by clothing or hair, whereas swimmer's itch mostly occurs in freshwater, on uncovered skin. Since it was first described in Michigan in 1928, swimmer's itch has been reported from around the world. Some suggest incidence may be on the rise, although this may also be attributed to better monitoring. == Cause == The schistosomatidae genera most commonly associated with swimmer’s itch in humans are ''Trichobilharzia'' and ''Gigantobilharzia''. Trematodes in these groups normally complete their life cycles in water birds. However, swimmer’s itch can also be caused by schistosome parasites of non-avian vertebrates, such as ''Schistosomatium douthitti'', which infects snails and rodents. Other taxa reported to cause the reaction include ''Bilharziella polonica'' and ''Schistosoma bovis''. In marine habitats, especially along the coasts, swimmer’s itch can occur as well. In Australia, the so-called "pelican itch" is caused by cercariae of the genus ''Austrobilharzia'' employing marine gastropods of the genus ''Batillaria'' (''B. australis'') as intermediate hosts. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「swimmer's itch」の詳細全文を読む スポンサード リンク
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