BLASTOCYSTIS IN COMPANION ANIMALS

摘要

The genus Blastocystis is a complex grouping of enteric protozoa commonly detected in a broad variety of species, including most mammals, many avian species, reptiles and amphibians. Phylogenetically, Blastocystis is a member of the Stramenopiles (phylum Heterokonta), an extremely diverse and complex phylum of predominantly algal genera. This organism is one of the most common gastrointestinal parasites of human beings, with reported prevalence rates ranging from 5% in some western countries to >76%in some parts of the developing world. Originally, species were named on the basis of the host organism (i.e. Blastocystis hominis, B. ratti), however it is now well recognized that there is no single species that infects only humans (or any other host organism), and the entire group of organisms is now identified as genus Blastocystis with numbered subtypes, these subtypes being determined by small subunit ribosomal DNA (SSU-rDNA) gene sequences. At the time of writing there are at least 14 known subtypes of Blastocystis identifiable on the basis of SSU-rDNA sequences.In addition to the remarkable genetic diversity within this genus, there is a high degree of morphologic variation, with vacuolar, "granular", amoeboid, and cystic forms identified. Any subtype from any host organism may be identified in any of the morphologic forms, although the amoeboid form is thought to be closely linked to disease in humans. Transmission is thought to be predominantly fecal-oral; there is also some evidence for water-borne transmission. The high prevalence rates reported from human beings in the developing world likely reflect differences in public sanitary infrastructure, closer exposure to open sewers, and closer exposure to animal waste than in the developed world.