Sessions

Cercarial dermatitis is a parasitic skin condition associated with exposure to natural freshwater environments. In humans, it is most commonly caused by the cercariae of avian schistosomes. During their life cycle, freshwater snails serve as intermediate hosts and release infective cercariae into the surrounding water. The occurrence of these schistosomes in recreational waters may be of both public health and epidemiological significance; however, cases of cercarial dermatitis currently remain largely unrecognised in Hungary. The aim of our study was to investigate whether avian schistosomes potentially capable of causing cercarial dermatitis could be detected in Hungarian recreational waters, either directly in water samples or in potentially infected snails. Sampling sites were selected at Lake Balaton beaches where symptoms suggestive of cercarial dermatitis had been reported. Several methodological approaches were applied to determine which method might be most suitable for routine environmental surveillance.Snails and water samples were collected from five recreational bathing sites at Lake Balaton. Water samples were concentrated by membrane filtration. Cercarial shedding of the collected snails was monitored by stereomicroscopy for seven days. DNA was isolated from snails positive for cercarial shedding, as well as from membrane-filtered concentrates of shed cercariae and water samples. The presence of avian schistosome DNA was investigated using dPCR. The primer–probe set targeted a conserved region of the 18S rDNA of members of the family Schistosomatidae. It was therefore primarily suitable for the detection of schistosomes, but did not allow unequivocal identification of the genus Trichobilharzia or differentiation between individual species. Cercarial shedding was observed in 4% of the collected snails. On preliminary stereomicroscopic examination, the shed cercariae were morphologically consistent with schistosome cercariae. Six snail samples and ten cercarial samples were analysed by dPCR, of which four (66%) and three (30%), respectively, tested positive. Of the five water samples examined, one was weak positive and two yielded ambiguous results. Overall, the presence of avian schistosomes was demonstrated by at least one detection method at three sampling sites. Our findings confirm that avian schistosomes capable of causing cercarial dermatitis are present in Hungary, as it has been demonstrated in several other European countries. The scarcity of recognised cases is likely attributable to limited awareness of the condition among both the affected individuals and healthcare professionals, who may not consider cercarial dermatitis as a possible diagnosis. Based on our results, approaches based on the examination of snails appear to be more suitable for identifying at-risk locations than direct examination of water samples. However, further studies involving a larger number of sampling sites are required to confirm these findings.