The relevance of Giardia infections in veterinary medicine

Worldwide prevalence studies indicate a high prevalence of Giardia in domestic animals, mainly in livestock and in companion animals. In mammals, Giardia duodenalis is the most prevalent species. Phylogenetic analysis revealed that G. duodenalis is in fact a species complex, comprising 7 so-called assemblages (assemblage A to G). Some of these assemblages are host-specific and others are zoonotic. In domestic animals, infections with only one assemblage are most often reported, and to a lesser extent mixed infections. Untill recently, most research on Giardia in domestic animals has been inspired by the concern for zoonotic transmission, and not from a veterinary prespective. Despite the high prevalence and the alleged pathogenicity, Giardia is often neglected as a pathogen in veterinary medicine. This is mainly due to the vagueness of the clinical symptoms, ranging from growth retardation and ill thrift to more overt symptoms, such as acute or chronic diarrhea. Although several clinical studies do indicate an association between Giardia infection and clinical signs, other studies report the presence of Giardia trofozoites or cysts in fecal samples from apparently healthy animals. Whether there is a difference in clinical outcome when animals are infected with one particular assemblage or another or with multiple assemblages has not yet been determined, and certainly warrants further studies. At present, only fenbendazole/febantel is registered in dogs for the treatment of Giardia. Several other chemotherapeutics are efficacious, but none are registered. Whether chemotherapeutic treatment is useful in the prevention of infection is uncertain, and additional hygienic or management measures seem to be needed