ABSTRACT
G. lamblia (G. intestinalis, G. duodenalis) is a common cause of water-borne diarrheal disease worldwide, afflicting almost all vertebrates, including humans. The taxonomy of Giardia at the species level is still debated and unresolved, because of the limited distinguishing morphologic features between species. Three groups (assemblages) comprising six species based on ultra - structural variation identified by scanning electron microscopy have been considered; only one, G. lamblia of the intestinalis group, has been recovered from a variety of mammals including humans, livestock and companion animals. On the basis of host of origin, 41 Giardia species have been described. Although isolates of G. lamblia are morphologically similar, distinct host-adapted genotypes have been identified within G. lamblia.
