Immunoassay for Cerebral Toxoplasmosis Uses Parasite Antigens

By LabMedica International staff writers
Posted on 10 Nov 2011

Toxoplasma gondii excretory–secretory antigens (ESA) and a crude tachyzoite antigen were used to investigate cerebrospinal fluid (CSF) for active infection.

The parasite antigens were used in an enzyme-linked immunosorbent assay (ELISA) and immunoblotting to determine if anti-ESA antibodies were present in patients infected with human immunodeficiency virus (HIV).

Image: Colored transmission electron micrograph (TEM) of Toxoplasma gondii parasites (green), cause of toxoplasmosis (Photo courtesy of Moredun Scientific).

Scientists at the Instituto Adolfo Lutz (Sao Paulo, Brazil) tested CSF from 270 HIV-infected patients were analyzed and divided into three groups according to the presence or absence of active toxoplasmosis. In group I, there were 99 patients with cerebral toxoplasmosis; in group II, there were 112 patients with other opportunistic neurologic diseases and seropositive for toxoplasmosis; and in group III there were 59 patients with other opportunistic neurologic diseases and seronegative for toxoplasmosis.

There was a significantly different mean ELISA-relative values for CSF for group I which was at 7.0 and for group II where it was 3.9, when the crude tachyzoite antigen was used. Samples from groups I and II were reactive by immunoblotting, with similar intensities. In ESA-ELISA, the mean for group I was 9, and group II showed a mean value of 2.7, which was statistically different. Similar results were shown in immunoblotting where a CSF sample from group I reacted well with ESA, and the sample from a group II patient failed to do so. The mean ELISA-relative value of the control group (group III) was 0.5 for the first antigen and 0.4 for the second ESA-ELISA and/or immunoblotting.

The authors concluded that CSF samples could be used for the diagnosis of cerebral toxoplasmosis in association with clinical, serologic, and radiological information, thus providing a simple straightforward methodology, particularly suitable in countries with high prevalence of latent toxoplasmosis in the general population.

The study was published in September 2011, in the journal Diagnostic Microbiology and Infectious Diseases.

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Instituto Adolfo Lutz