Prevalence of Blastocystis in Shelter-Resident and Client-Owned Companion Animals in the US Pacific Northwest

Domestic dogs and cats are commonly infected with a variety of protozoan enteric parasites, including Blastocystis spp. In addition, there is growing interest in Blastocystis as a potential enteric pathogen, and the possible role of domestic and in-contact animals as reservoirs for human infection. Domestic animals in shelter environments are commonly recognized to be at higher risk for carriage of enteropathogens. The purpose of this study was to determine the frequency of infection of shelter-resident and client-owned domestic dogs and cats with Blastocystis spp in the Pacific Northwest region of the USA. Fecal samples were collected from 103 shelter-resident dogs, 105 shelter-resident cats, 51 client-owned dogs and 52 client-owned cats. Blastocystis were detected and subtypes assigned using a nested PCR based on small subunit ribosomal DNA sequences. Shelter-resident animals were significantly more likely to test positive for Blastocystis (P<0.05 for dogs, P = 0.009 for cats). Sequence analysis indicated that shelter-resident animals were carrying a variety of Blastocystis subtypes. No relationship was seen between Blastocystis carriage and the presence of gastrointestinal disease signs in either dogs or cats. These data suggest that, as previously reported for other enteric pathogens, shelter-resident companion animals are a higher risk for carriage of Blastocystis spp. The lack of relationship between Blastocystis carriage and intestinal disease in shelter-resident animals suggests that this organism is unlikely to be a major enteric pathogen in these species.