Toxoplasma gondii

Clinical significance
Toxoplasma gondii is a widespread protozoan, a parasite of birds and mammals, that causes toxoplasmosis. Sexual reproduction of T. gondii occurs only in the cat’s intestine, producing oocysts that, once passed in the faeces, can be accidentally swallowed by humans or other animals, infecting them. In the cells of the infected host, the parasite multiplies asexually until the immune response manages to confine it within tissue cysts that persist for years, especially in the brain and muscles. Humans can therefore also become infected by eating raw or undercooked meat (usually lamb, pork or beef) containing tissue cysts. Toxoplasmosis can be passed from an infected mother to the fetus. A pregnant woman who is not immune to toxoplasmosis must therefore follow hygiene and dietary precautions throughout pregnancy, avoiding raw vegetables, raw meat and cured meats, and having her IgG and IgM antibody titres checked every month.
During acute infection, specific class M antibodies (IgM) rise, followed by IgG, which remain for life. If the serological picture is compatible with a recent or current infection, the avidity of the IgG antibodies must be measured to date the infection: if IgG avidity is high, the infection dates back at least four months before the sample was taken; if avidity is low, less than four months.