Giardia duodenalis in humans and animals – Transmission and disease

Giardia duodenalis is a protozoan parasite infecting the upper intestinal tract of humans, as well as domestic and wild animals worldwide. Transmission of giardiasis occurs through the faecal-oral route, and may be either direct (i.e., person-to-person, animal-to-animal or zoonotic) or indirect (i.e., waterborne or foodborne). While asymptomatic infections are common in both humans and animals, a wide range of enteric symptoms have been reported, along with extra-intestinal and post-infectious complications. A definitive diagnosis of giardiasis is generally made by detection of cysts in stool specimens through microscopical examination of wet mounts, or through the use of permanent or fluorescent antibody stains. More recently, molecular methods have become popular for diagnosis and for testing environmental samples. Symptomatic giardiasis is often treated to reduce the duration of symptoms, to prevent complications, and to minimize transmission of the parasite to other hosts. Direct faecal-oral transmission of giardiasis can be largely controlled thorough improved hygiene and sanitation. In the case of waterborne transmission, a multiple barrier approach, including limiting access of people and animals to watersheds and reservoirs, and treatment using flocculation, filtration and disinfection, is necessary to minimize the risk. Since foodborne transmission is often associated with the consumption of fresh produce, a number of control measures can be taken during pre- and post-harvest, as well as at the food handler/consumer level to minimize the risk of contamination, or for removing or inactivating parasites. Good husbandry and farm management practices are important in controlling the spread of giardiasis in livestock and companion animals.