Giardiasis in dogs and cats: update on epidemiology and public health significance

Molecular data have defined seven genetic Assemblages of Giardia duodenalis, named A–G. Humans are infected with Assemblages A and B, dogs primarily with C and D, and cats with F. Assemblage A has been subclassified into subtypes A-I to A-IV: A-I has been reported in humans and animals, A-II in humans, and A-III and IV exclusively in animals. Assemblage B has broad host specificity infecting humans and animals. Recently, small numbers of dogs and cats have been reported to also carry Assemblages A-I or B. Because these genotypes are found primarily in humans, and no comprehensive studies to address zoonotic transmission of G. duodenalis are yet available, the potential role of dogs and cats cannot be conclusively excluded.