Trematodes Trichobilharzia spp

Swimmers' itch or cercarial dermatitis is endemic in northern Europe (see Chapter 22). The disease is caused by the penetration of the skin by cercaria of non-human schistosomes (often Trichobilharzia spp. and Bilharziellapolonica) with birds and rodents as primary hosts. The penetration of cercariae into the skin produces a short-lived dermatitis or even urticarial and vesicular eruptions in the case of heavy and repeated exposures. It is a problem mainly during warm summer months when the number of cases increase drastically due to bathing in shallow lakes containing high levels of cercariae and in some coastal areas where the salt level is low. The distribution is not well understood but it is often focal, and 50% of 248 Swedish districts reported problems with swimmers' itch during the summer of 1999 (Cecilia Thors, personal communication). Cases of swimmers' itch have also been reported from Norway (Thune 1994).

Nematodes Ascaris

Ascaris infections are found in the northern part of Europe as well as in the rest of the world, but the incidence of indigenous infections is not well defined. There are indications that most of the individuals have contracted the infection outside the Nordic countries, but 35 cases of indigenous Ascaris were reported in Denmark in 1997 (Petersen 1998). An outbreak of ascariasis, probably due to imported vegetables, has been reported from Finland (Raisanen et al. 1985).

Asymptomatic carriers

Pinworm or Enterobius vermicularis is the most common human helminth infection. Indeed, the Guinness Book of Records claims that it is the second most-common human infection, after the common cold. Interestingly, the prevalence is higher in temperate than in tropical climates and it is more common in developed than in underdeveloped countries.

In Finland, 344 children were studied for the presence of pinworm and 5.2% of the children were found positive (Kyr├│nseppa 1993), while two studies in Swedish children showed higher prevalence figures of 27 (Kjellberg and Heyman 1993) and 21% (Herrstr├│m et al. 1997). The latter study showed that more children than previously known, are asymptotic carriers (36/41 positive children) and that finger sucking is strongly associated with a positive tape-test.

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