Abstract
Toxoplasma gondii is a zoonotic protozoan parasite that can cause morbidity and mortality in humans, domestic animals, and terrestrial and aquatic wildlife. The environmentally robust oocyst stage of T. gondii is fundamentally critical to the parasite's success, both in terms of its worldwide distribution as well as the extensive range of infected intermediate hosts. Despite the limited definitive host species (domestic and wild felids), infections have been reported on every continent, and in terrestrial as well as aquatic environments. The remarkable resistance of the oocyst wall enables dissemination of T. gondii through watersheds and ecosystems, and long-term persistence in diverse foods such as shellfish and fresh produce. Here, we review the key attributes of oocyst biophysical properties that confer their ability to disseminate and survive in the environment, as well as the epidemiological dynamics of oocyst sources including domestic and wild felids. This manuscript further provides a comprehensive review of the pathways by which T. gondii oocysts can infect animals and people through the environment, including in contaminated foods, water or soil. We conclude by identifying critical control points for reducing risk of exposure to oocysts as well as opportunities for future synergies and new directions for research aimed at reducing the burden of oocyst-borne toxoplasmosis in humans, domestic animals, and wildlife.
Highlights
Biology Commons, Immunology and Infectious Disease Commons, Medical Sciences Commons, Veterinary Microbiology and Immunobiology Commons, and the Veterinary Pathology and Pathobiology Commons
Domestic cats fed by humans or scavenging from foods discarded by people as well as wild felids that consume fewer, larger prey animals or prey species with lower prevalence of T. gondii infection may have lower risk of repeat shedding and lower observed infection and oocyst shedding prevalences (Afonso et al, 2007; VanWormer et al, 2013b)
The epidemiologic importance of whether human toxoplasmosis is transmitted by oocysts or tissue cysts was debated even before the life cycle was determined in the 1970s (Jackson and Hutchison, 1989)
Summary
Toxoplasma gondii is an apicomplexan protozoan parasite that infects birds and mammals, including humans (Dubey and Beattie, 1988). New methods that can discriminate the route of T. gondii acquisition have demonstrated that, in some populations, a significant proportion of infections are caused by oocyst ingestion (Hill et al, 2011). Despite these findings, mainstream thinking in exposure mitigation for both humans and animals often neglects a comprehensive understanding and management of factors that are important to reducing the risk of exposure to oocysts. This review aims to (i) summarize critical aspects of oocyst biology, environmental resistance, and felid dynamics of oocyst shedding; (ii) review the importance of oocyst-borne infections in human and animal populations; (iii) synthesize current knowledge on oocyst contamination of water, soil, fresh produce and seafoods; and (iv) identify critical gaps in current knowledge where further research and collaborative efforts should be directed to reduce T. gondii infections in animals and humans
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