Giardiasis of domestic animals and its zoonotic significance: A review

Giardiasis is the most common waterborne parasitic intestinal infection ofboth animals and humans worldwide, and it leads to significant morbidity and mortality in animals, particularly in young aged group like calves in the developing and developed world. It is a zoonotic infectious disease where animals are considered as sources of infection for humans through consumption of water and food contaminated with cysts of Giardia. Giardia species differ significantly in host range, with G. duodenalis having the broadest host range and greatest public health significance. Giardia duodenalis has eight different assemblages A through H. The disease Causes gastro intestinal disturbance, gall bladder colic and jaundice. Malabsorption and maldigestion mainly result from a diffuse shortening of epithelial microvillus. Giardia duodenalis (synonyms intestinalis, lamblia) is a flagellate binucleated protozoan, and it has two morphological forms: cysts and trophozoites. The life cycle of Giardia is direct, and the infective stage of the parasite, the cyst, is encysted when released into the feces and is immediately infectious. Trophozoites are pear-shaped, binucleate, multi-flagellated parasite forms and are the disease causing stage and colonize the upper small intestine, where they adhere to the epithelial surface and proliferate by binary fission. Infected animals, contaminated water and feed are main sources of infection. Age of animals, season of the year, area, housing, feeding, management practices are usually considered as risk factors for the occurrence of giardiasis. The infection can be transmitted by the fecal-oral route, or through contaminated food and water. To survive within the intestine, Giardia undergoes antigenic variation and few virulent factors have been identified to be responsible for the infection. These include ventral adhesive disc proteins and surface lectins, the four pairs of flagella which allow for movement and variant surface proteins. The clearance of Giardia from a host requires both innate and adaptive immunity effector mechanisms. The infection can be diagnosed by examining fecal specimens using different coproscopic techniques, serological tests and by molecular analysis. Restricting animals from surface water during periods of high cyst shedding may reduce watershed contamination. Health education on personal and environmental hygiene would help in reducing the occurrence of the infection. This review work tries to gather information on giardiasis of domestic animals with respect to its epidemiology, host immune responses, pathophysiology, distribution and its public health importance.