Prevalence of Enteropathogens in Dogs Attending 3 Regional Dog Parks in Northern California

Hascall, K.L.; Kass, P.H.; Saksen, J.; Ahlmann, A.; Scorza, A.V.; Lappin, M.R.; Marks, S.L.

The relatively high number of dogs with false-negative Giardia PCR results at the commercial reference laboratory is concerning and could have occurred for several reasons. The presence of fecal inhibitors is plausible but was deemed unlikely because a positive internal amplification control was used in all samples and confirmed that no significant inhibitory activity remained in the nucleic acid. The internal sample quality control assessed by targeting a housekeeping gene also indicated good nucleic acid quality at both the gDNA and cDNA level. In addition, 2-fold dilutions of a select number of samples resulted in 1 Ct value weaker signals, confirming the absence of PCR inhibition. The high number of false-negative Giardia PCR results could have been a consequence of PCR test specificity. The Giardia PCR is highly specific for Giardia duodenalis based on the primer sets and does not pick up any other Giardia species, whereas fecal flotation or antibody-based Giardia detection tests are less discriminatory and more likely to detect nonclinically relevant species. In a dog park with a high density of dogs and their feces, combined with a high rodent and bird population, it is conceivable that nonclinical strains of Giardia are accumulated and occur in a high frequency of dogs that accidentally ingest these organisms, in the absence of overt infection. The high number of failed Giardia assemblage PCR tests, which is also Giardia duodenalis specific, could support the specificity aspect. This phenomenon would have to be tested specifically by characterizing Giardia strains by sequencing, which was not an objective of this study.