Abstract
Blastocystis sp. is a common intestinal parasite infecting humans and a wide range of animals worldwide. It exhibits an extensive genetic diversity and 17 subtypes (STs) have thus far been identified in mammalian and avian hosts. Since several STs are common to humans and animals, it was proposed that a proportion of human infections may result from zoonotic transmission. However, the contribution of each animal source to human infection remains to be clarified. Therefore, the aim of this study was to expand our knowledge of the epidemiology and host specificity of this parasite by performing the largest epidemiological survey ever conducted in animal groups in terms of numbers of species screened. A total of 307 stool samples from 161 mammalian and non-mammalian species in two French zoos were screened by real-time PCR for the presence of Blastocystis sp. Overall, 32.2% of the animal samples and 37.9% of the species tested were shown to be infected with the parasite. A total of 111 animal Blastocystis sp. isolates were subtyped, and 11 of the 17 mammalian and avian STs as well as additional STs previously identified in reptiles and insects were found with a varying prevalence according to animal groups. These data were combined with those obtained from previous surveys to evaluate the potential risk of zoonotic transmission of Blastocystis sp. through the comparison of ST distribution between human and animal hosts. This suggests that non-human primates, artiodactyls and birds may serve as reservoirs for human infection, especially in animal handlers. In contrast, other mammals such as carnivores, and non-mammalian groups including reptiles and insects, do not seem to represent significant sources of Blastocystis sp. infection in humans. In further studies, more intensive sampling and screening of potential new animal hosts will reinforce these statements and expand our understanding of the circulation of Blastocystis sp. in animal and human populations.
Highlights
Blastocystis sp. is an enteric protist with a worldwide distribution belonging to the group Stramenopiles and currently identified as one of the most common single-celled eukaryotes found in human stool samples [1,2,3]
This was not the conclusion of an epidemiological study conducted at a zoo of Kuala Lumpur, Malaysia, in which a total of 197 stool samples from 16 species of primates, 21 species of hoofed mammals and 9 feline species were tested for the presence of intestinal parasites, with only 2 samples collected from 2 primate species being described as positive for Blastocystis sp. [40]
By combining our molecular data with data obtained in previous surveys and comparing the summarized overall ST distribution between animals and humans, it appears that non-human primates (NHPs) and artiodactyls, especially livestock, could represent potential reservoirs of zoonotic transmission of Blastocystis sp. (Fig 2)
Summary
Blastocystis sp. is an enteric protist with a worldwide distribution belonging to the group Stramenopiles and currently identified as one of the most common single-celled eukaryotes found in human stool samples [1,2,3]. A recent study even showed a prevalence of 100% in a cohort of children living in a rural area of Senegal [7]. Such a high prevalence of Blastocystis sp. Clearly raises the question of the impact of this parasite in human health. Much current data suggests that this parasite should be associated with non-specific gastrointestinal symptoms including diarrhea, abdominal pain, and vomiting [1], and is suspected to be linked to irritable bowel syndrome [13] and urticaria [15]
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