Toxoplasma

Abstract

Toxoplasmosis is a zoonotic infection caused by the protozoon Toxoplasma gondii affecting animals worldwide. T. gondii has a facultative heteroxenous life cycle with felids as definitive hosts and a wide range of mammalian and avian species as intermediate hosts. Infectious stages are oocysts present in felid feces, bradyzoites forming tissue cysts, and tachyzoites. While two major clonal lineages (type II and III) dominate clinical and natural isolates in Europe and North America, other parts of the world, like Brazil and Argentina, are dominated by non-clonal or other clonal T. gondii lineages, representing a greater genetic diversity. Different animal species show a variable degree of susceptibility to T. gondii infection and to the development of clinical signs. Humans are considered susceptible, and about one third of the human population in the world is estimated to be infected. Toxoplasmosis is an important abortive disease in small ruminants. It is mainly asymptomatic in cattle and chicken, but the latter is an epidemiological sentinel, and isolation of viable parasites from this source is frequent. Infected pigs can show reproductive failure, and, in addition, their tissues are considered, together with infected small ruminant tissues, a relevant source of human infection. Cats and dogs can show neuromuscular disease mainly associated with other immunosuppressive conditions, such as viral infections. Some species like New World monkeys, lemurs, Pallas’ cats, slender-tailed meerkats, and some Australian marsupials are highly susceptible to fatal generalized toxoplasmosis. General control measures are presented, focusing on the prevention of human toxoplasmosis.