In a recent study of intestinal parasites in dogs and cats in Australia, Giardia was found to be the most prevalent parasite in dogs. The aim of the current study was to determine the zoonotic significance of the Giardia and Cryptosporidium isolates recovered from dogs and cats by means of molecular tools. Of the successfully amplified isolates, all but one of the Giardia from dogs were either assemblage C and/or D, with one assemblage A. Of the amplified cat samples, all but one were assemblage F, with one assemblage D. The authors hypothesize that the lack of recovered zoonotic Giardia assemblages results from the low prevalence of Giardia in the human population. The Cryptosporidium recovered from dogs and cats was determined to be C canis and C felis, respectively, a finding that supports growing evidence that Cryptosporidium in companion animals is of limited public health significance to healthy people.

COMMENTARY: Further analysis of risk factors showed that dogs younger than 1 year were most likely to be infected with Giardia, a fact commonly observed in U.S. veterinary clinics. Although this report describes a reduced potential of zoonosis, other recent papers have described greater proportions of zoonotic Giardia assemblages in companion animals. Clinicians should continue to advise pet owners of the risk for zoonotic transmission of both parasites and of the serious health consequences of infection for immunocompromised individuals.

Determining the zoonotic significance of Giardia and Cryptosporidium in Australian dogs and cats. Palmer CS, Traub RJ, Robertson ID, et al. VET PARASITOL 154:142-147, 2008.