Detecting Giardia: Clinical and Molecular Identification
Saleh, Meriam Naim
MetadataShow full item record
The protozoan parasite Giardia duodenalis (syn. G. lamblia, G. intestinalis) can cause diarrhea in humans, cats, dogs and other animals. Giardia duodenalis consists of eight assemblages (A-H) that are morphologically identical but genetically distinct. Assemblages C-H are generally species-specific, while A and B infect people and animals and are considered potentially zoonotic. Most canine and feline isolates belong to their respective species-specific assemblages, but isolates of assemblages A and B (predominantly found in humans) have also been recovered from dogs and cats. Diagnosis of infection has historically been by morphologic techniques (observing trophozoites on direct fecal smears or cysts on centrifugal zinc sulfate fecal flotations), and it is currently recommended to use morphologic techniques in conjunction with a sensitive and specific antigen test. Diagnosis is important for management of clinical giardiasis in cats and dogs and also to identify the assemblage present to determine its zoonotic potential. In my dissertation research I evaluated diagnostic techniques in use for companion animals, including centrifugal zinc sulfate fecal flotation, antigen tests optimized for use in dogs and cats, direct immunofluorescent assay (IFA), and Polymerase Chain Reaction (PCR). I showed that when compared to the reference IFA the veterinary optimized antigen tests performed similarly and had no statistically significant differences in sensitivity or specificity when combined with a centrifugal zinc sulfate fecal flotation test. Sensitivity and specificity by comparison to IFA was ≥ 82% and ≥ 90%, respectively, for all diagnostic tests evaluated in dogs and cats. When analyzed via Bayesian analysis sensitivity and specificity for all diagnostic tests was ≥83% and ≥95%, respectively. The Bayesian analysis also showed that using the direct immunofluorescent assay (IFA) as the reference test was supported. I also evaluated PCR as a molecular diagnostic technique to detect Giardia infections in dogs with soft stool or diarrhea (mimicking clinical signs of infection). I utilized both conventional and real time PCR assays and compared the results to the recommended method of diagnosis, the zinc sulfate fecal flotation combined with an immunoassay test. I found that agreement between PCR and microscopy combined with an immunoassay was poor to fair and varied depending on the molecular parameters and size of the DNA target underscoring the complexity of test evaluation and molecular diagnostics for Giardia. I also evaluated cats from a varied population (owned, shelter, feral) in Virginia to determine to what extent (if any) they were infected with potentially zoonotic assemblages of Giardia. The species-specific assemblage F was detected in 57% of the samples and assemblage A, which is considered potentially zoonotic, was recovered from 32% of the sampleI. In 11% both assemblages F and A were detected. We showed for the first time that cats in Virginia are infected with potentially zoonotic assemblages of Giardia.
- Doctoral Dissertations