Toxoplasmosis is a common infection caused by the protozoan Toxoplasma gondii (T. gondii).1 The infection is mainly acquired by ingestion of food or water contaminated by cat feces or by undercooked meat from infected animals.1 During primary infection healthy individuals generally have mild symptoms or show no signs of the disease. However, if primary infection occurs during pregnancy it can result in severe damage to the fetus.1
The risk of transmitting the infection to the fetus increases if the infection is acquired later in the pregnancy, but the risk of fetal damage is highest when the infection is acquired early in pregnancy.1 Early treatment in acute infection during pregnancy can prevent or ameliorate congenital damage1. The diagnosis of T. gondii infection usually starts with the detection of anti-Toxoplasma IgG and IgM antibodies. The presence of Toxo IgM antibodies is presumptive of an acute, recent or reactivated Toxoplasma infection.
The diagnosis of acute acquired infection during pregnancy is established by a seroconversion or a significant rise in antibody titres (IgG and/or IgM) in serial samples.
Toxoplasma IgG avidity test is performed to date the infection.2 The antibodies produced during the primary response have a lower avidity than those produced during the non-primary response, hence a high avidity performed early in gestation suggests that infection has taken place more than 4 months ago and rules out a recent primary acute infection2. However, no clinical interpretation can be deduced from a low or grey-zone avidity result.