Giardiasis from a One Health Perspective

Abstract

The flagellated protozoan Giardia duodenalis is the etiologic agent of giardiasis, a very common gastrointestinal infection of mammals, including humans, with a global distribution. The clinical manifestations of giardiasis are quite variable, and range from the absence of symptoms to acute diarrhea, characterized by dehydration, abdominal pain, flatulence, nausea, vomiting, fatigue, and weight loss to chronic infection. There is considerable genetic variation within G. duodenalis, and eight major genetic groups, or assemblages, have been identified (assemblages A to H). Of these, assemblages A and B infect both humans and animals, whereas assemblages C to H are mostly host-specific, and rarely reported in humans. Multiple transmission routes are possible, including direct (person-to person, animal-to-person, and animal-to-animal), and indirect (through consumption of contaminated water and food) pathways. The increasing application of molecular techniques, from multi-locus typing up to whole genome analysis, showed that infection is highly prevalent in many animal species, yet zoonotic transmission contributes modestly to human giardiasis. Nevertheless, a few animal species (e.g., beavers) have been implicated in the transmission of Giardia to humans, particularly through contamination of water; well-conducted studies in epidemic settings may further clarify the role of animals. Water plays a very important role in the epidemiology of giardiasis, with widespread contamination of different water sources leading to waterborne outbreaks. To understand the complex epidemiology of giardiasis, a One Health approach is needed.