Laboratory diagnosis of toxoplasmosis

Acute infection with Toxoplasma gondii is diagnosed by (i) detection of the parasite directly in patients' specimens using histological or immunological methods, (ii) isolation of T. gondii from blood, body fluids or tissue by inoculation in laboratory mice or on tissue culture cells, or (iii) serological methods for determination of a significant, T. gondii-specific, antibody titre rise or of T. gondii specific IgM (or IgA) antibody. Because of their high sensitivity, specificity and relative ease of performance, serological methods are preferentially used for diagnosis of T. gondii infection. The diagnosis of acute, postnatally-acquired, primary toxoplasmosis is usually established by serological methods and will in general present few problems. However, diagnosis of congenital infections and their late sequelae or of reactivation of a latent infection in immunocompromised patients is often more troublesome because of the absence of a significant antibody titre rise or the lack of specific IgM antibody. In these cases a combination of various methods may be required for definitive diagnosis of T. gondii infection.