Skírnisson Karl, Kolarova Libusa
Institute for Experimental Pathology, University of Iceland, Keldur v/Vesturlandsveg, 112 Reykjavík, Iceland.
Laeknabladid. 2005 Oct;91(10):729-36.
Swimmer's itch (SI) or human cercarial dermatitis is caused by free-swimming larvae of bird parasites of the family Schistosomatidae (Trematoda) which have penetrated thorough the skin. Sometimes, mainly during first infections, the larvae do not cause any symptoms but if trapped by the immune system of the host each larva causes a maculopapular eruption. So far, five bird schistosome species have been reported in Iceland. Cercariae are shed by the freshwater snail Radix peregra but adults live in anseriform birds; one nasal Trichobilharzia species occurs in the nasal cavity of mallards, two visceral species have been found in veins of whooper swans and a visceral species has been found in greylag goose and in mallards, respectively. Experiments have shown that developing schistosomulae are able to survive for days or even weeks in mammals. Long term pathologic effects on the host are unknown. During the second half of August 2003 thousands of bathers got SI in a slowly streaming brook with geothermally heated groundwater in Landmannalaugar, the most frequently visited area in the interior of Iceland. The number of cercariae in the water and SI cases decreased until October but still in December and in late winter 2004 SI cases were reported. In August 2004 SI again started in the area but the density of cercariae in the water seemed to be less than in the previous year. The prevalence of snails shedding Trichobilharzia cercariae on the bathing site never exceeded 1%. The rapid increase of cercariae in the water by the middle of August in 2003 and 2004 were caused by a breeding mallard female and its ducklings which were raised on the bathing site during summer. All the ducklings had nasal- and visceral Trichobilharzia infections which they must have acquired soon after hatching. Three weeks later the adult worms could have started egg-laying. Consequently, emerging miracidia infected the snails which finally started shedding the cercariae by middle of August in 2003 and 2004. 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. Retrospective enquiries suggest that some visitors have occasionally got SI after bathing in the brook in preceding decades. Low number of papules, however, indicates a low density of cercariae in the water.
游泳者皮疹（SI）或人类尾蚴性皮炎是由裂体科（吸虫纲）鸟类寄生虫的自由游动幼虫穿透皮肤引起的。有时，主要是在初次感染时，幼虫不会引起任何症状，但如果被宿主的免疫系统捕获，每个幼虫都会引起斑丘疹。到目前为止，冰岛已报告了五种鸟类血吸虫物种。尾蚴由淡水螺Radix peregra排出，但成虫生活在雁形目鸟类中；一种鼻腔毛毕吸虫物种存在于绿头鸭的鼻腔中，两种内脏物种分别在大天鹅的静脉中被发现，还有一种内脏物种分别在灰雁和绿头鸭中被发现。实验表明，发育中的童虫能够在哺乳动物体内存活数天甚至数周。对宿主的长期病理影响尚不清楚。2003年8月下旬，在冰岛内陆最常被光顾的兰德曼纳劳卡，数千名沐浴者在一条缓慢流淌、有地热加热地下水的小溪中感染了游泳者皮疹。水中尾蚴数量和游泳者皮疹病例数一直减少到10月，但在12月以及2004年冬末仍有游泳者皮疹病例报告。2004年8月，该地区再次出现游泳者皮疹，但水中尾蚴密度似乎低于前一年。在沐浴地点排出毛毕吸虫尾蚴的蜗牛患病率从未超过1%。2003年和2004年8月中旬水中尾蚴的迅速增加是由一只在夏季在沐浴地点饲养的绿头鸭母鸭及其小鸭引起的。所有小鸭都感染了鼻腔和内脏毛毕吸虫，它们一定是在孵化后不久就感染了。三周后，成虫可能开始产卵。因此，孵化出的毛蚴感染了蜗牛，最终蜗牛在2003年和2004年8月中旬开始排出尾蚴。如果不允许小鸭进入沐浴地点和相邻的小溪，在未来几年中可以避免尾蚴的这种迅速增加。回顾性调查表明，在过去几十年中，一些游客偶尔在这条小溪中沐浴后会感染游泳者皮疹。然而，丘疹数量较少表明水中尾蚴密度较低。
