Toxoplasmosis

Abstract

Toxoplasma gondii can infect all mammalian and avian species, with an estimated 1–3 billion of the world's human population currently infected. Toxoplasma oocysts shed in cat faeces can contaminate the environment, and common infection routes for humans are ingestion of oocysts directly from the environment or potentially on raw, unwashed vegetables and fruit, and consumption of viable tissue cysts in raw or undercooked meat. Toxoplasma infection in immunocompetent individuals is usually asymptomatic but presents as a self-limiting mild to moderate flu- or glandular fever-like illness in 10–20% of cases. Maternal infection acquired during pregnancy can be transmitted to the unborn child, causing congenital abnormality or fetal death. In immunosuppressed and immunodeficient people, acute infection or reactivation of parasites in latent tissue cysts from previously acquired infection can result in severe or life-threatening disease. Laboratory diagnosis relies primarily on testing for immunoglobulin (Ig) G, IgM and, in some cases, IgA, to assess infection status. IgG avidity testing can provide a more accurate estimate of duration of infection in pregnant mothers. Detection of active infection relies most commonly on nucleic acid amplification testing, while enhanced immunohistostaining can discriminate between latent and active forms of the parasite in affected tissues.