The reservoirs and the modes of transmission of the most frequent microsporidial species in humans, Enterocytozoon bieneusi, are still unknown. We have examined fecal samples of 26 humans and 350 animals from 37 species to find 18 samples containing this parasite from humans, cats, pigs, cattle, and a llama. Genotypic characterization of the internal transcribed spacer of the rRNA gene resulted in 14 different genotypes, 6 of them previously undescribed. Phylogenetic analysis revealed the lack of a transmission barrier between E. bieneusi from humans and animals (cats, pigs, and cattle). Thus, E. bieneusi appears to be a zoonotic pathogen.Microsporidia are newly emerging pathogens of humans and animals. Due to the small size of their spores and uncharacteristic staining properties they are difficult to detect by light microscopy. As a consequence, Enterocytozoon bieneusi, the species now known to be the most frequent in microsporidial infections of humans, was not discovered until 1985 (5). It is now recognized as a true pathogen, causing diarrhea especially in immunocompromised patients (2, 19).E. bieneusi has recently been found in the feces of animals, including pigs, rhesus macaques, cats, and cattle (4,11,13,18). However, the potential reservoirs and the mode of transmission of this pathogen are still unknown. Traditional epidemiological studies to address the zoonotic potential of this pathogen, for example, case control studies to identify risk factors such as contact with certain animals, are hampered by the small number of diagnosed microsporidial infections. Experimental infections of humans are prohibited for ethical reasons.As an alternative, this problem could be solved by a differentiation of strains within this species and a comparison of the strains found in humans with those detected in animals. Unfortunately, because the spores of E. bieneusi strains are morphologically indistinguishable and since this species cannot be cultured, traditional morphological, biochemical, and immunological methods are unavailable for strain differentiation. Instead, a genotypic method has been described to differentiate characteristic genotypes of the internal transcribed spacer (ITS) of the rRNA gene (rDNA) (16).Before this report, 14 ITS genotypes were known from humans (5 genotypes), pigs (6 genotypes), a cat (1 genotype), and cattle (2 genotypes) (1, 13, 15-18), but since no identical ITS genotypes of E. bieneusi were found in humans and animals its zoonotic potential was controversially discussed. In this report we investigated diarrheal fecal samples of another 26 humans and 350 animals from 37 species. Molecular epidemiological analysis of these data now offers convincing evidence for a zoonotic potential of E. bieneusi. MATERIALS AND METHODSOrigin of stool and fecal samples. Fecal samples from 34 primates (26 humans, one chimpanzee, four gorillas, two baboons, and one mandrill), 122 carnivores (one mustelid, one polar bear, 60 cats, and 60 dogs), 147 even-toed ungulates (one wild boar, 50 domestic pigs, fo...

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The first and second internal transcribed spacers (ITS1, ITS2) as well as the intervening 5.8S coding region of the rRNA gene were characterized in eight Babesia canis isolates of differing geographic origin, vector specificity, and pathogenicity to dogs. The genotypes determined by sequencing segregated into three clearly separated groups close to or near the species level and correspond to the previously proposed subspecies B. canis canis, B. canis vogeli, and B. canis rossi. The three genotypes can be distinguished by Sau96I digestion of the polymerase chain reaction (PCR)-amplified rDNA target.

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