Chapter 37 : Human Immunodeficiency Viruses and Human T-lymphotropic Viruses

Abstract:

The human immunodeficiency viruses (HIV) and the human T-lymphotropic viruses (HTLV) originate from zoonotic transmission of ancestor retroviruses found in primates. HIV-1 and HIV-2 are the causative agents of AIDS; HTLV-1 causes adult T-cell leukemia/lymphoma and a broad spectrum of chronic inflammatory diseases, though only in few of those infected. The three principal questions in HIV diagnostics are (i) whether a person is HIV-infected and, if infected, (ii) with what exactly (viral properties) and (iii) how actively the virus is replicating (viral load). With regard to viral properties, identification of the virus type, i.e., HIV-1 or HIV-2, is essential for both the selection of a suitable viral load test for HIV RNA quantification in plasma and the decision with what to treat the patient. Answering these questions is important because current commercial viral load tests do not recognize HIV-2, and nonnucleoside reverse transcriptase inhibitors (NNRTI) are not effective against HIV-2 or group O viruses of HIV-1. Knowledge of preexisting viral mutations conferring resistance to antiretrovirals is another important point. As antiretroviral therapy is increasingly considered essential for all HIV infected persons, it is important to answer all relevant questions already at the timepoint of HIV diagnosis. Diagnosis of HTLV infection is performed accordingly, but with some important differences. HTLV never leads to viremia. Tests for viral RNA in plasma are thus useless, and all nucleic acid testing has to be performed on cells. The most important task is to differentiate between the pathogenic HTLV-1 and the virtually nonpathogenic HTLV-2.