Clinical Information

Toxoplasma gondii is an intracellular protozoan parasite that chronically infects 10% or more of the adult population in the United States. Transmission may occur by ingestion of undercooked meat containing cysts, by direct contact with the feces of an infected cat excreting infectious oocysts, and vertically through the placenta. Accurate diagnosis is crucial because of the different therapeutic options.

Serology is the traditional method for diagnosing toxoplasmosis and ascertaining the previous exposure history of the host.(1) Active toxoplasmosis is suggested by the presence of IgM antibodies, but elevated anti-IgM titers are often absent in immunocompromised patients. In addition, elevated IgM can persist from an acute infection that may have occurred as long ago as 1 year. Serologic results may also be unreliable or challenging to interpret in immunocompromised patients and in suspected intrauterine infection.

Detection of Toxoplasma gondii DNA by PCR has proven to be a rapid and reliable alternative or supportive method for the diagnosis of toxoplasmosis. When performed on blood, it may detect circulating parasite DNA and thus confirm or support the results of serologic testing. PCR testing on peripheral blood has been used successfully to detect cases of ocular toxoplasmosis(2) as well as invasive disease in allogeneic stem cell recipients.(3,4)