Toxoplasmosis in HIV infection: An overview

Toxoplasma gondii is an obligate intracellular protozoan parasite presenting as a zoonotic infection distributed worldwide. In HIV-positive individuals, it causes severe opportunistic infections, which is of major public health concern as it results in physical and psychological disabilities. In healthy immunocompetent individuals, it causes asymptomatic chronic persistent infections, but in immunosuppressed patients, there is reactivation of the parasite if the CD4 counts fall below 200 cells/μl. The seroprevalence rates are variable in different geographic areas. The tissue cyst or oocyst is the infective form which enters by ingestion of contaminated meat and transform into tachyzoites and disseminate into blood stream. In immunocompetent persons due to cell-mediated immunity the parasite is transformed into tissue cyst resulting in life long chronic infection. In HIV-infected people opportunistic infection by T. gondii occurs due to depletion of CD4 cells, decreased production of cytokines and interferon gamma and impaired cytotoxic T-lymphocyte activity resulting in reactivation of latent infection. The diagnosis can be done by clinical, serological, radiological, histological or molecular methods, or by the combination of these. There is various treatment regimen including acute treatment, maintenance therapy should be given as the current anti T. gondii therapy cannot eradicate tissue cysts. In HIV patients, CD4 counts <100; cotrimoxazole, alternately dapsone + pyrimethamine can be given for 6 months. Hence, early diagnosis of T. gondii antibodies is important in all HIV-positive individuals to prevent complications of cerebral toxoplasmosis.