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S U M M A R YSchistosomes are digenean flukes, parasitic of birds, mammals and crocodiles. The family Schistosomatidae contains species of considerable medical and veterinary importance, which cause the disease schistosomiasis. Previous studies, both morphological and molecular, which have provided a good deal of information on the phylogenetics of this group, have been limited in the number of species investigated or the type or extent of molecular data used. This paper presents the most comprehensive phylogeny to date, based on the sequences of 3 genes, complete ribosomal small subunit rRNA and large ribosomal subunit rRNA, and mitochondrial cytochrome oxidase 1, sequenced from 30 taxa including at least 1 representative from 10 of the 13 known genera of the Schistosomatidae and 17 of the 20 recognized Schistosoma species. The phylogeny is examined using morphological characters, intermediate and definitive host associations and biogeography. Theories as to the origins and spread of Schistosoma are also explored. The principal findings are that Ornithobilharzia and Austrobilharzia form a sister group to the Schistosoma ; mammalian schistosomes appear paraphyletic and 2 Trichobilharzia species, T. ocellata and T. szidati, seem to be synonymous. The position of Orientobilharzia within the Schistosoma is confirmed, as is an Asian origin for the Schistosoma, followed by subsequent dispersal through India and Africa.

SUMMARY Cercarial dermatitis (swimmer's itch) is a condition caused by infective larvae (cercariae) of a species-rich group of mammalian and avian schistosomes. Over the last decade, it has been reported in areas that previously had few or no cases of dermatitis and is thus considered an emerging disease. It is obvious that avian schistosomes are responsible for the majority of reported dermatitis outbreaks around the world, and thus they are the primary focus of this review. Although they infect humans, they do not mature and usually die in the skin. Experimental infections of avian schistosomes in mice show that in previously exposed hosts, there is a strong skin immune reaction that kills the schistosome. However, penetration of larvae into naive mice can result in temporary migration from the skin. This is of particular interest because the worms are able to migrate to different organs, for example, the lungs in the case of visceral schistosomes and the central nervous system in the case of nasal schistosomes. The risk of such migration and accompanying disorders needs to be clarified for humans and animals of interest (e.g., dogs). Herein we compiled the most comprehensive review of the diversity, immunology, and epidemiology of avian schistosomes causing cercarial dermatitis.

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The development of nasal avian schistosomes of the genus Trichobilharzia in their final host is poorly known. Therefore, an experimental infection of ducklings (Anas platyrhynchos f. dom.) by T. regenti was performed. The infection resulted in leg paralysis and orientation/balance disorders of birds. The examination of the duck's spinal cord and brain confirmed the presence of developing parasites in pre-patent as well as patent periods. The absence of the worms in other tissues strongly supports our hypothesis that the parasite migrates through the central nervous system (CNS) to its final location in bird nasal mucosa. The injury level is probably dependent on number of parasites as well as yet unknown host factors. The affinity to the CNS seems to be high; also by exposure of experimental animals to low cercarial doses the growing worms in the CNS were found. In addition to the generally accepted view that bird schistosomes may cause cercarial dermatitis of mammals (including man), there is evidence of a partial development of T. regenti in mouse CNS; in certain cases leg paralysis was also recorded. Therefore, the pathogenesis spectrum caused by bird schistosomes in birds/mammals needs to be reconsidered.