Trichobilharzia is the largest genus within the family Schistosomatidae, covering over 40 species of avian parasites To clarify the existing confusion in the systematics of the genus, we recommend combining knowledge of life cycles and developmental stages, snail/bird hosts, cytogenetical and molecular data together with morphological criteria for the characterization of particular species The high specificity of Trichobilharzia for the intermediate host is a likely reflection of the ability to avoid the internal defence of specific snails The spectrum of final hosts (birds) seems to be much wider The infection of birds--trichobilharziasis--may lead to considerable tissue injuries, caused by eggs of the parasite or migration of immature/mature worms through the body Most Trichobilharzia (visceral species) migrate through the viscera of the host, but nasal species display a neurotropic mode of migration Due to a low specificity of penetrating cercariae, mammals (including humans) can be attacked This leads to cercarial dermatitis, predominantly in sensitized hosts Experimental infections indicate that Trichobilharzia never mature in an incompatible (mammalian) host However, not all cercariae and schistosomula are necessarily trapped and eliminated in the skin, and parasites may migrate throughout the viscera and the nervous system of mammals These findings suggest that the pathogenicity of Trichobilharzia may have been underestimated in the past and health risks associated with trichobilharziasis need to be studied further

Biology of the schistosome genus Trichobilharzia.

The following list, compiled during my tenure of a grant given by the Nuffield Foundation to the Wildfowl Trust, Slimbridge, Gloucestershire, records species of Protozoa, helminths and Arthropoda found in anatid birds, either by the authors of the papers listed in the References, or by others to whose work these authors refer. It will be seen that there are, after the names of all the parasites, numbers which indicate, by reference to the corresponding numbers in the References, the authors and publications in which the species concerned are recorded. Thus Cotylurus brevis (142, 145*) means that this trematode was recorded from Aix galericulata, the Mandarin Duck, by Dubois (1953) and that Dubois & Rausch (1950a) reported an experimental infection of this duck with it.

A list of the parasitic protozoa, helminths and arthropoda recorded from species of the family Anatidae (ducks, geese and swans).

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.

Avian Schistosomes and Outbreaks of Cercarial Dermatitis

The life-cycle of Trichobilharzia australis n.sp. from northern Australia is outlined and the morphology of each stage described. Adult worms occur in the nasal blood vessels of the black duck (Anas superciliosa Gmelin, 1789). Cercariae develop in a lymnaeid snail, Austropeplea vinosa (Adams & Angus, 1864) (= Lymnaea lessoni Deshayes in part).

The life-cycle and morphology of Trichobilharzia australis n.sp. (Digenea: Schistosomatidae) from the nasal blood vessels of the black duck (Anas superciliosa) in Australia, with a review of the genus Trichobilharzia

SUMMARY 1. Birds and snails are suitable hosts for many parasites, including helminths in general and trematodes in particular. Among trematodes, members of the family Schistosomatidae with two-host life cycles (snails as intermediate hosts and birds as definitive hosts) are successful and abundant pathogens. Their transmission between birds and snails in nature can be influenced by many abiotic and biotic factors. 2. In snails, the prevalence of schistosome infections and production of cercariae can be influenced by host immunological susceptibility ⁄ physiological suitability, snail age ⁄ size, interspecific competition of trematode larvae, etc. Schistosomes are able to survive in overwintering snails, serving as a source of infection in spring. 3. Birds may also differ in susceptibility to and prevalence rates of schistosome infections. They are long-range vectors of schistosomes. 4. Climate changes influence behaviour of migratory birds, lead to shifts in season- or temperature-dependent processes in snails and schistosomes, and influence the frequency of schistosome transmission and intensity of infection. Also, eutrophication can increase the growth of snail populations and transmission of bird schistosomes. 5. Dispersal of bird schistosomes to new regions and an increased availability (local abundance) of the snail hosts, together with the use of new water reservoirs (e.g., in higher latitudes) for recreational purposes, may contribute to a higher number of outbreaks of cercarial dermatitis.

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Papers

Studies on dermatitis-producing schistosomes in the Pacific Northwest, with special reference to Trichobilharzia oregonensis.