Temperature and light effects on Trichobilharzia szidati cercariae with implications for a risk analysis
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ta Veterinaria Scandinavica Open Access
RESEARCH
Temperature and light effects on Trichobilharzia szidati cercariae with implications for a risk analysis Azmi Al‑Jubury1* , Per Kania1, Anette Bygum2 and Kurt Buchmann1
Abstract Background: Cercarial dermatitis (swimmer’s itch) caused by bird schistosome cercariae, released from intermediate host snails, is a common disorder also at higher latitudes. Several cases were observed in the artificial Danish freshwa‑ ter Ringen Lake frequently used by the public for recreational purposes. The lake may serve as a model system when establishing a risk analysis for this zoonotic disease. In order to explain high risk periods we determined infection levels of intermediate host snails from early spring to late summer (March, June and August) and elucidated the effect of temperature and light on parasite shedding, behavior and life span. Results: Field studies revealed no shedding snails in March and June but in late summer the prevalence of Trichobilharzia szidati infection (in a sample of 226 pulmonate Lymnaea stagnalis snails) reached 10%. When investigated under laboratory conditions the cercarial shedding rate (number of cercariae shed per snail per day) was positively correlated to temperature raising from a mean of 3000 (SD 4000) at 7 °C to a mean of 44,000 (SD 30,000) at 27 °C). The cercarial life span was inversely correlated to temperature but the parasites remained active for up to 60 h at 20 °C indicating accumulation of cercariae in the lake during summer periods. Cercariae exhibited positive phototaxy sug‑ gesting a higher pathogen concentration in surface water of the lake during daytime when the public visits the lake. Conclusion: The only causative agent of cercarial dermatitis in Ringen Lake detected was T. szidati. The infection risk associated with aquatic activities is low during spring and early summer (March-June). In late summer the risk of infec‑ tion is high since the release, behavior and life span of the infective parasite larvae have optimal conditions. Keywords: Trichobilharzia, Bird schistosomes, Lymnaea stagnalis, Cercaria, Swimmer’s itch Background A series of schistosome species within the genus Trichobilharzia use birds (water fowl) as final hosts, carrying the adult stage, and pulmonate snails as intermediate hosts, shedding infective cercariae. These parasites are zoonotic as human may act as accidental host. The cercariae are the causative agent of cercarial dermatitis (swimmer’s itch), a skin rash provoked by penetration *Correspondence: [email protected] 1 Laboratory of Aquatic Pathobiology, Department of Veterinary and Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Stigbøjlen 7, 1870 Frederiksberg C, Denmark Full list of author information is available at the end of the article
of cercariae into the skin. Cercarial dermatitis has been recorded worldwide [1–4] including cold areas at northern latitudes e.g. Denmark [5–7], Norway [8], Sweden [9] and Iceland (geothermally heated water bodies) [2]. Ce
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