Prevalence and zoonotic potential of Giardia duodenalis in cattle and dogs

The main aims of the studies described in this thesis were to obtain prevalence information on Giardia duodenalis in cattle and dogs on Prince Edward Island, Canada, to genotype G. duodenalis-positive fecal samples to assess the zoonotic potential arising from infected cattle and dogs, and to compare diagnostic tests for the detection of G. duodenalis in bovine and canine feces.The significance of G. duodenalis and Cyptosporidium spp. In a bovine veterinary college teaching herd is described in Chapter 2. The mean G. duodenalis prevalence was 49%. Zoonotic Assemblage A and hoofed livestock-specific Assemblage E were identified in 43 and 57% of positive samples with successful 16S-rRNA sequencing. The presence of the zoonotic Assemblage A indicates a potential risk of infection for students and staff at this facility. In contrast, no Cryptosporidium spp. were found in these cows, suggesting that this herd posed a negligible risk of transmitting C. parvum infections to humans.Chapter 3 describes the prevalence and genotypes of G. duodenalis in cows and calves on Prince Edward Island. Giardia duodenalis prevalence was 38 and 51% in cows and calves, respectively. Giardia duodenalis was present in all dairy herds, in 9/10 beef herds and in 10/11 farms from which calves were sampled. Calves were infected with the zoonotic Assemblage A at 29% and the livestock Assemblage E at 71%, whereas 100% of the cows were infected with Assemblage E. Giardia duodenalis is highly prevalent in dairy and beef herds on Prince Edward Island and Assemblage A in calves is a potential public health concern.The performance of flow cytometry for the diagnosis of G. duodenalis in bovine feces compared to immunofluorescence microscopy was studied in Chapter 4 and demonstrated that flow cytometry did not perform as well as the immunofluorescence microscopy in the diagnosis of G. duodenalis in bovine feces. Several possible reasons for this outcome were identified and are discussed in that chapter.A G. duodenalis vaccine was evaluated in calves in Chapter 5. Serum antibody titers were significantly higher in vaccinated compared to non-vaccinated calves. Vaccinated calves tended to excrete more G. duodenalis cysts in their feces than non vaccinated calves. Despite a serological immune response following vaccination, this vaccine was not efficacious in preventing giardiasis in calves.The prevalence and genotypes of dogs from a local animal shelter, a local pet store and veterinary clinics on PEI were determined in Chapter 6. Giardia duodenalis was present in all three sources and highest in dogs from the pet store. The majority of isolates belonged to the host-adapted Assemblages D (41.5%) and C (19.5%). Zoonotic Assemblage A was isolated from 4.8% of dogs and mixed infections with zoonotic and host-adapted genotypes were found in 10% of dogs. A novel genetic sequence of an isolate belonging to Assemblage D was found in one dog. This study demonstrates that dogs on Prince Edward Island may be a potential source of human giardiasis.Chapter 7 describes the relative sensitivity and specificity of three diagnostic tests for G. duodenalis in canine feces compared to the immunofluorescence microscopy. The commonly used zinc-sulfate centrifugation flotation technique followed by microscopy was less sensitive (86%) than the immunofluorescence microscopy, but performed similar to the SNAP® Giardia test, which had a relative sensitivity of 90%. While the ProSpecT® test was the most sensitive test in this study (100%), it is not designed for dogs and somewhat more costly than the other tests. The SNAP® Giardia test may be favorable for use in veterinary clinics because it is fast and easy to perform.Source: Dissertation Abstracts International, Volume: 68-10, Section: B, page: 6530