Regarding the Zoonotic Transmission of Giardia duodenalis Infection

Giardia duodenalis, a member of the genus Giardia, is a common intestinal protozoan parasite in humans and some farm, companion, and wild animals. Due to the uniform morphology of the parasites sampled from a wide range of hosts, the taxonomy of the genus Giardia has been the subject of debate for more than a century. The confusion generated by this controversy, and the technological limitations to carry out the necessary research to clarify the matter, led to an insufficient understanding of the epidemiology of the infection, mainly in aspects related to host specificity and zoonotic transmission. The results of molecular and epidemiological studies conducted over the last four decades, which are reviewed in this paper, allow us to conclude that zoonotic transmission of Giardia duodenalis infection is possible. Concurrently, these findings suggest that most Giardia infections are host-specific, rendering zoonotic transmission relatively uncommon. Nevertheless, from a public health perspective, such transmission remains a critical concern for vulnerable groups, particularly children and immunocompromised individuals. In these populations, even infrequent zoonotic events can lead to severe clinical outcomes, including chronic diarrhea, malabsorption, and failure to thrive.