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Abstract

More than 600 million people are infected with the nematode Strongyloides stercoralis. Also non-human primates, dogs and cats were described as natural hosts. For mor than 100 years it is controversially discussed if the S. stercoralis in these animals is really the same species as the one in humans and if these animals serve as a reservoir for zoonotic human strongyloidiasis. This discussion was predominantly based on epidemiology and on biological differences such as different preferences for one of the three life cycles these parasites can undergo or the infection potential in experimental infections. Recently, molecular/genomic investigations of wild populations of S. stercoralis added new insights. Our lab has been involved in such studies in Cambodia, China, Thailand, Iran and Bangladesh. Based on the "classic" literature and the molecular/genomic studies by us and others I will argue that: a) Dogs can carry S. stercoralis indistinguishable from the ones in humans and should be considered a putative source for zoonotic infection. While zoonotic infection may be epidemiologically relevant in certain settings, it appears unlikely that strongyloidiasis is normally a zoonosis. b) dogs also carry genomically distinct types (species) of Strongyloides that are not normally found in humans. A case of introgression of a "human and dog type" mitochondrial genome into the "dog only type" population argues for occasional intermixing. c) Even within human derived S. stercoralis there is high within-species genetic diversity. This, along with biological differences, suggest that S. stercoralis in humans might also be a complex of closely related species or subspecies with possibly different pathogenetic potential. In order to further investigate this and to study biological differences, controlled experiments are desirable. This requires that different isolates are in laboratory culture. I will present our progress towards establishing a collection of S. stercoralis isolates.