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Background Avian schistosomes are considered as main causative agents of human cercarial dermatitis (HCD) in Iran. The study was conducted to determine bird schistosomes in their final and intermediate hosts, in main wetlands of Mazandaran. Methods A total of 255 domestic and wild ducks were collected and the infection of nasal tissues of five ( Anas platyrhynchos domesticus , Aythya ferina, Cairina moschata, Anas platyrhynchos and Spatula clypeata ) species were analyzed using morphological techniques. Also, 1687 freshwater snails were collected and surveyed by cercarial shedding and crushing tests. Detection of HCD was performed for the presence of clinical symptoms of itching and maculopapular rashs by physical examination. Results Of 255 ducks, in 41 (16%) infection with nasal Trichibilarizia spp. were recognized by observing eggs and/or adult worms. The most infected ducks were Anas clypeata and Anas platyrhynchos domesticus . Overall, 0.17% of snails were infected with avian schistosomes. Also, clinical examination of 951 rice farmers revealed that 588 (61.82%) of them were suffered from HCD. Conclusion Our data suggest that domestic ducks could play a prominent role as a reservoir host for establishing life cycle of Trichobilharzia in the area. Also, existence of domestic reservoir ducks and suitable snail hosts in ponds and paddy fields of this area, climate conditions of the wetlands in Mazandaran leads to a high incidence of HCD.

BackgroundTrichobilharzia regenti (T. regenti) is an avian schistosomatid fluke species that causes human cercarial dermatitis (HCD) in areas of aquaculture in northern Iran. Understanding the phylogenetic relationships and genetic diversity of this thread‐like fluke will deepen our thoughtful of avian schistosomiasis epidemiology and lead to more effective HCD control in the region.ObjectivesTo determine the life cycle of nasal Trichobilharzia in aquatic birds as well as aquatic snails and also identify the haplotype diversity of the isolates in Mazandaran Province, northern Iran.MethodsIn the present study, adult or egg of Trichobilharzia isolated from aquatic birds as well as schistosomes cercariae isolated from aquatic snails in Mazandaran Province, northern Iran, belonged to the authors' previous research, were examined. Molecular studies and phylogenetic analysis were carried out on these schistosomes samples.ResultsThe phylogenetic analysis of the ITS1 and COX1 genes in isolated schistosomes revealed that all samples belong to the T. regenti clade. Remarkably, based on phylogenetic results, these schistosomes samples from Anas platyrhynchos domesticus, A. platyrhynchos, Spatula clypeata and Lymnaea stagnalis grouped together with previously sequenced samples from Iran (Trichobilharzia cf. regenti). Unlike the phylogenetic tree and haplotype network of COX1 gene, ITS1 did not show distinct clusters.ConclusionThis study completed the puzzle of the disease in Mazandaran Province by isolating and genotyping furkocercariae from L. stagnalis that was consistent with the isolated new genotype from ducks. For the first time in Iran, this confirmed the potential role of L. stagnalis snails in the transmission of the disease.