Danger at the Dog Park? Enteropathogens Detected in Dogs Visiting Dog Parks

In a prospective study published in the Journal of Veterinary Internal Medicine, researchers identified enteropathogens in dogs visiting regional dog parks in Northern California.

Dog parks have become increasingly popular uses of green space in the United States. However, because of their high levels of environmental contamination, dog parks can be a source of zoonotic disease transmission. Dogs can harbor zoonotic enteropathogens, including Giardia and Cryptosporidium; these two parasites can persist in the environment for a long time, posing a public safety concern at dog parks.

Researchers analyzed dog owner-collected fresh fecal samples from 300 dogs visiting 1 of 3 regional dog parks (100 dogs/dog park) in Northern California between August and November of 2014. Fecal samples were collected during the dog park visits. Dog owners completed a questionnaire and scored their dogs’ fecal consistencies from 1 (hard, dry) to 6 (liquid); scores ≥ 4 were considered diarrheic for this study.

Each fecal sample was analyzed at a university laboratory (Parasitology Laboratory at University of California, Davis) and a veterinary commercial reference laboratory. The university laboratory used double centrifugation floatation and direct fluorescent antibody (DFA) testing to identify parasitic enteropathogens. DFA was used to detect Giardia and Cryptosporidium in samples with discordant results between detection methods (fecal floatation negative at the university laboratory and PCR positive at the reference laboratory).

The reference laboratory used single centrifugation floatation. Real time PCR was used to identify 11 parasitic, bacterial, and viral enteropathogens and toxin genes, including Giardia, Clostridium perfringens alpha toxin gene and enterotoxin gene (cpe), and canine parvovirus. DNA from PCR-positive Giardia samples underwent genotyping.

Of the 300 study dogs, 114 (38%) had ≥ 1 enteropathogens. Slightly under half (46%) of the 114 dogs had diarrhea, suggesting that, as the researchers noted, “positive results obtained for any of the enteropathogens do not prove disease causation.” Enteropathogen prevalence was not significantly different between the dog parks. Presence and absence of ≥ 1 enteropathogens, number of enteropathogens present, and previous intestinal parasite diagnosis were significantly and positively associated with increased fecal score. Age had a significant and negative correlation with fecal score and number of enteropathogens.

Most of the risk factors evaluated, including access to outdoor water sources other than the dog park, did not significantly influence fecal score or presence of ≥ 1 enteropathogens. However, one risk factor—frequency of dog park visits—was significantly and positively associated with increased fecal score.

The most frequently identified parasitic enteropathogens were Giardia (9%) and Cryptosporidium (5%); less frequently identified parasitic enteropathogens included Trichuris vulpis (1%) and Toxocara canis (0.3%). The presence of Giardia was significantly associated with younger age and increased fecal score. Researchers observed a significant difference in Giardia detection frequency between fecal floatation methods, and between DFA and reference laboratory fecal floatation and PCR results. Researchers also observed differences in Cryptosporidium detection frequency; all PCR-positive Cryptosporidium samples tested negative for Cryptosporidium on DFA.

Approximately 25% of study dogs had been dewormed within the past 6 months of the study. Interestingly, compared with dogs that had not been dewormed in the past 6 months, dewormed dogs were significantly more likely to have intestinal parasites. Parasites detected in the dewormed dogs included Giardia and Cryptosporidium. Researchers attributed this paradoxical finding to these parasites not being susceptible to the common deworming products.

Giardia samples undergoing genotyping contained dog-adapted assemblages C, D, or both. Researchers noted that “humans are primarily infected with [Giardia] assemblages A and B, and these have also been infrequently isolated from dogs, thus posing a potential zoonotic risk.”

Among the bacterial enteropathogens, Campylobacter and Salmonella were identified in 3% and 1% of samples, respectively; no dogs testing positive for either bacteria ate a raw food diet. Clostridium difficile TcdA and TcdB genes were present in 3% of samples; presence of these genes was not significantly associated with fecal score. Nearly 35% of samples contained C. perfringens alpha toxin gene or cpe. The quantity of C. perfringens alpha toxin gene (number of gene copies/gram of feces) was significantly, yet weakly, associated with fecal score; an association between quantity of cpe and fecal score was not statistically significant.

Among the viral enteropathogens, circovirus was most frequently identified (9%), followed by coronavirus (5%) and parvovirus (1%). Owners of parvovirus-positive dogs did not report signs of gastrointestinal upset. No samples tested positive for distemper virus.

Study limitations included the lack of Giardia ELISA testing and the limited use of DFA testing for Giardia.

To decrease the risk of zoonotic transmission from dogs at dog parks, researchers advised educating dog owners about this risk and discouraging dog park visits if a dog has diarrhea. Given the discrepancies in Giardia detection observed in this study, researchers suggested improving fecal floatation technique.

Dr. JoAnna Pendergrass received her doctorate in veterinary medicine from the Virginia-Maryland College of Veterinary Medicine. Following veterinary school, she completed a postdoctoral fellowship at Emory University’s Yerkes National Primate Research Center. Dr. Pendergrass is the founder and owner of JPen Communications, LLC.