A review on swimmer's itch and the occurrence of bird schistosomes in Iceland

Abstract

In the past decade, swimmer's itch (SI) has repeatedly occurred in people who have been wading or bathing in ponds or lakes in Iceland where water birds and snails are abundant. Some of the affected sites were warmed by geothermal activity, and others were not. A search for the causative agent of SI, ocellate furcocercariae that have been found in Iceland only in Radix peregra snails, revealed an average infection prevalence of 1.4% (n = 12,432). Locally, infection rates commonly exceeded 6%, the highest value observed being 24.5%. A search for adult schistosomes in visceral organs and the nasal cavities of 110 water birds belonging to the orders Gaviiformes, Podicipediformes and Anseriformes revealed eggs, miracidia or adult stages of at least seven previously identifiable schistosome species in four anseriform bird species. A previously unknown species of schistosome, Allobilharzia visceralis, was detected in whooper swans (Cygnus cygnus), and classified in a new genus. In mallards (Anas platyrhynchos) a nasal Trichobilharzia sp. and the visceral schistosome T. franki were identified. In red-breasted merganser (Mergus serrator), distinct egg types belonging to two species of the genus Trichobilharzia have been found. In grey-lag goose (Anser anser) two different egg types were also found - a large Trichobilharzia sp. and small eggs of a Dendritobilharzia sp. Additionally, unidentified cercariae, probably belonging to a previously undescribed genus were detected in R. peregra in Oslandsstjörn. Taken together, the data obtained by morphological examination of eggs and recent DNA sequencing results, indicate that at least eight species of bird schistosomes occur in Iceland.

Radix spp.: Identification of trematode intermediate hosts in the Czech Republic

“…Now it is re-confirmed that R. peregra, besides R. lagotis and R. labiata, can play a role as a vector of T. regenti; this is in agreement with the results from France (Jouet et al 2008). Interestingly, in Iceland, R. peregra represents the dominant snail species and hosts several schistosomes (Skírnisson et al 2009), showing that both the schistosomes and the snails can adapt to each other under specific local conditions.…”

Avian Schistosomes and Outbreaks of Cercarial Dermatitis

“…In North America and Europe, where most of the research has been focused, outbreaks occur in recreational ponds and reservoirs. These outbreaks have been reviewed extensively (7,8,70,71). Species of Trichobilharzia have been reported to cause dermatitis from other areas as well, such as Rwanda-Burundi (72), South Africa (73,74), New Zealand and Australia (75)(76)(77)(78)(79), Malaysia/Indonesia (80)(81)(82), Iran (65,(83)(84)(85)(86), United Arab Emirates (66), Thailand (87), and China (88,89) in the Eastern Hemisphere and Argentina (57,90,91), Chile (11), and El Salvador (92) in the Western Hemisphere.…”

“…For example, the accelerated growth of both snail and trematode larval populations (71) or changes in phenology of aquatic migratory birds to sedentary (268)(269)(270) can increase chances for outbreaks of cercarial dermatitis in both space and time.…”

“…Large snail populations with a high prevalence of avian schistosomes have been reported for several localities in Europe (71,(286)(287)(288), North America (289,290), and Australia (291). Usually, natural preserves support diverse and abundant populations of potential hosts of schistosomes, so these areas may serve as hot spots for outbreaks of cercarial dermatitis.…”

“…Production can reach several thousands of cercariae/snail/day (169,300,315), and these emission rates may even counterbalance the loss of cercarial capability to survive and infect hosts at high temperatures (see above). Irrespective of the season, outbreaks of cercarial dermatitis have been reported in geothermally heated lakes and ponds in Iceland (71). Time of day proved to be another risk factor.…”