Toxoplasma gondii is an obligate intracellular protozoan parasite that infects most species of warm-blooded animals, including humans. Toxoplasmosis is primarily acquired by ingestion of undercooked, infected meat; via oocysts from fecally contaminated hands, food and water; and maternally through transplacental transmission. In addition, transmission associated with organ transplantation and during blood transfusion has been reported, although the risk of transmission through blood transfusion is extremely low.
Acquired infection with Toxoplasma gondii in healthy individuals is commonly asymptomatic, however 10-20 % of patients with acute infection may develop lymphadenopathy . Severe infections can occur in AIDS patients and adults immunocompromised by cancer chemotherapy or transplant recipients receiving immunosuppressive treatment. These infections can be fatal. Toxoplasmic encephalitis is the most common presentation and is the most frequent cause of focal central nervous system lesions in AIDS patients.
Primary infection during pregnancy can result in transplacental transmission of the parasite resulting in congenital infection. The risk of congenital infection is lowest (10-25%) if acute maternal infection occurs during the first trimester and highest (60-90%) if it occurs during the third trimester. Severity of congenital infection is greatest when maternal infection is acquired early during pregnancy. Common outcomes of congenital
toxoplasmosis include chorioretinitis, intracranial calcifications and hydrocephalus. The majority of infants infected later in pregnancy are asymptomatic at birth, with sequelae occurring later in life.
Early treatment after prenatal diagnosis of Toxoplasma gondii infection has been shown to reduce the frequency and severity of congenital toxoplasmosis6. Serological tests can be used to identify seronegative women who then should be monitored during pregnancy.
The presence of IgG antibodies to Toxoplasma gondii indicates that infection has occurred but does not distinguish between recent and past infection. IgM antibodies are detected in individuals with a recently acquired infection, but antibodies may persist for up to 18 months post-infection. To differentiate between a recently acquired and a past infection, IgM and IgG positive specimens should be tested for IgG avidity. A high avidity index for IgG antibodies is a strong indication that an infection took place more than 4 months ago.
Manufacturer’s Reagent package insert, Architect Toxo IgG, November 2014, Abbott Laboratories, MAX-Planck-Ring 65205 Wiesbaden, Germany.