Strategy for diagnosis of Toxoplasma gondii in stereotactic brain biopsies

The colloidal gold method using polyclonal antitoxoplasma antibodies was used to detect Toxoplasma organisms in stereotactic brain biopsies of patients with AIDS. For comparison, conventional histologic staining and additional other immunohistochemical methods were also studied in the same cases. Compared to the other stains, a reliable diagnosis of Toxoplasma gondii could be established with the colloidal gold method in all patients investigated. This method was highly specific and sensitive and stained both the encysted and the tachyzoite forms of the organism. Stronger contrast of the single parasite and better identification is possible if it is applied together with silver enhancement. Conventional staining and immunohistochemical peroxidase techniques are not advantageous, because they allow a diagnosis only by observation of the rare pseudocysts and not by free parasites in tissue, so the colloidal gold method appears to be the preferred method for a rapid diagnosis of cerebral toxoplasmosis, especially in cases where only small amounts of tissue can be obtained.