Prevalence rates in dogs varies but it is commonly reported in 5 - 15% of dogs in routine epidemiological surveys. Seasonal increases in prevalence are usual during the winter and summer months.
Species which are pathogenic to dogs include:
- Giardia duodenalis assemblage A & B - mainly human-to-human, but also seen in dogs and cats
- Giardia duodenalis assemblage C - mainly dogs
- Giardia duodenalis assemblage D - mainly dogs
- Giardia duodenalis assemblage D - mainly ungulates (cattle, sheep, horses, pigs, goats)
Other species such as G. lamblia, G. intestinalis, and G. enterica primarily infect humans.
The distinction of assemblages is usually determined by analysis of the glutamate dehydrogenase locus, a distinction which has importance since assemblages A & B are usually zoonotic and have been commonly detected in dogs and cats living in households.
The life cycle is relatively direct, with dogs ingesting cysts in soil contaminated with feces from other dogs, cats or humans.
Under proteolytic activation by gastric acids, cysts release the flagellate protozoa (trophozoites), which eventually reside in the mucosal surfaces of the small intestine, attaching to the brush border. They multiply by binary fission and trophozoites consequently encyst in the small or large intestine and pass in the feces. Transmission occurs by the fecal-oral route. Prepatent period is usually 1 - 2 weeks. Infections are usually associated with kenneled dogs.
Clinical signs are usually mild acute diarrhea. As is observed in cats, chronic, intermitten diarrhea can be observed in kennels, and steatorrhea is not uncommon.
Diagnosis is based on light microscopic visualization of cysts, or ELISA detection of Giardia antigens. Speciation requires PCR assays.
A differential diagnosis must include other endoparasites and exocrine pancreatic insufficiency.
Treatment is relatively effective with fenbendazole, albendazole, ronidazole, metronidazole or secnidazole. However, elimination of the organism is usually unsuccessful in large kennels and sporadic outbreaks are regularly observed.
Drug treatment combined with the disinfection of the environment and shampooing of the dogs is often effective at reducing Giardia cyst excretion.
- Scoop on Pets
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