Toxoplasma
encephalitis in immunocompromised patients results from reactivation of previously acquired (
latent) infection. The aim of the study is to assess the antigenaemia and antibody response to Toxoplasma gondii in human immunodeficiency virus (HIV)-infected patients to determine the best marker for early diagnosis of
toxoplasmosis in such patients. Indirect
enzyme-linked
immunosorbent assay (ELISA) for detection of
IgG,
IgM and
IgA anti-toxoplasma
antibodies and double-sandwich ELISA for toxoplasma
antigen is carried out in serum samples collected from 100 HIV seropositive patients and 75 controls. Toxoplasma-specific
IgG,
IgM and
IgA antibody response and antigenaemia were detected in 12%, 6%, 7% and 14% of HIV-infected patients, respectively. On retrospective analysis of 14 patients with antigenaemia only one had central nervous system (CNS) symptoms attributable to toxoplasma
infection. In this patient, the CD4+ cell count was below 50/microL and none of the specific
immunoglobulin isotype responses could be detected. The patient showed clinical improvement following specific
chemotherapy for
toxoplasmosis. In 25 HIV-negative and anti-toxoplasma
IgG antibody-positive controls,
IgM was detected in two (8%),
IgA in five (20%) and antigenaemia in 10 (40%), while 50 HIV seronegative healthy controls were negative for both
antigen and antibody responses. The study indicates that detection of toxoplasma
antigen in addition to
IgG antibody response may prove to be a useful
indicator in the early diagnosis of reactivated
toxoplasmosis in HIV/
AIDS patients.