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ARS Home » Northeast Area » Beltsville, Maryland (BARC) » Beltsville Agricultural Research Center » Animal Parasitic Diseases Laboratory » Research » Publications at this Location » Publication #360568

Research Project: Detection and Control of Foodborne Parasites for Food Safety

Location: Animal Parasitic Diseases Laboratory

Title: Are molecular tools clarifying or confusing our understanding of the public health threat from zoonotic enteric protozoa in wildlife?

item ROBERTSON, LUCY - Norwegian University Of Life Sciences
item CLARK, C. GRAHAM - London School Of Hygiene & Tropical Medicine
item DEBENHAM, JOHN - Norwegian University Of Life Sciences
item Dubey, Jitender
item KVAC, MARTIN - Biology Centre Of The Ascr Of The Czech Republic, Vvi
item LI, JANQIANG - Henan University
item PONCE-GORDO, FRANCISCO - Complutense University Of Madrid (UCM)
item RYAN, UNA - Murdoch University
item SCHARES, GEREON - Friedrich-Loeffler-institut
item SU, CHUNLEI - University Of Tennessee
item TSAOUSIS, ANASTASIOS - University Of Kent

Submitted to: International Journal for Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/31/2019
Publication Date: 2/13/2019
Publication URL:
Citation: Robertson, L.J., Clark, C., Debenham, J.J., Dubey, J.P., Kvac, M., Li, J., Ponce-Gordo, F., Ryan, U., Schares, G., Su, C., Tsaousis, A.D. 2019. Are molecular tools clarifying or confusing our understanding of the public health threat from zoonotic enteric protozoa in wildlife?. International Journal for Parasitology. 323-341.

Interpretive Summary: Toxoplasmosis, caused by the single celled parasite, Toxoplasma gondii, continues to be a public health problem worldwide. This parasite infects all warm-blooded hosts, including humans. It causes mental retardation and loss of vision in children, and abortion in livestock. The ingestion of food and water contaminated with resistant stage of the parasite, the oocyst, is a major mode of transmission of this parasite. Of all the hosts infected, only cats are known to excrete oocysts in feces. Cats can excrete millions of oocysts after eating an infected prey, such as a mouse or a bird. Oocysts can survive outdoors for months and they are highly infectious to humans. Wildlife plays plays an important role in the epidemiology of toxoplasmosis. This invited paper reviews zoonotic infections in wildlife, including toxoplasmosis. This paper by a team of international experts will be of interest to biologists and parasitologists, wildlife biologists, and public health workers.

Technical Abstract: Although it is accepted that emerging infectious diseases are frequently zoonoses, often originating in wildlife, enteric protozoa appear to be relatively minor contributors. When morphology determined by light microscopy was the only approach for identifying enteric protozoa, it was assumed that many of them could colonize multiple hosts and that all or several were probably zoonotic. However, the advent of molecular tools revealed genetic differences in morphologically identical enteric protozoa that colonized humans and other animals; thus, these were perhaps host specific. Nevertheless, some animals harboured parasites that were identical to those from human hosts at the few gene fragments investigated; thus, these were considered to have zoonotic potential. Later, more discriminatory tools again sub-divided some protozoa, while investigation of infection events indicated that some “host-specific” protozoa, could actually infect various hosts, circumstances permitting. We selected nine enteric protozoa and example wildlife hosts (Balantoides coli - wild boar; Blastocystis sp. - wild rodents; Cryptosporidium spp. - wild fish; Encephalitozoon spp. - wild birds; Entamoeba spp. - non-human primates; Enterocytozoon bieneusi - wild cervids; Giardia duodenalis - red foxes; Sarcocystis nesbitti - snakes; Toxoplasma gondii - bobcats) and reviewed how molecular tools have assisted our current understanding of their public health threat. Molecular tools have provided information about the possibility that enteric protozoa in wildlife may infect humans, and have suggested plausible transmission sources in specific cases or outbreaks. However, due to lack of discriminatory power, their use often indicates no more than the possible zoonotic character of a particular protozoan parasite. Molecular analyses, which should be as discriminatory as possible, are but one component of the toolbox, when trying to determine the potential public health impacts from enteric protozoa in wildlife.