HIV-2 Diagnosis and Viral Load Measurements

Abstract

Human immunodeficiency virus type 2 (HIV-2), a member of the Retroviridae, represents a related but distinct group of infections to HIV-1, the global agent of acquired immunodeficiency syndrome (AIDS). While HIV-2 bears similarity to HIV-1, it represents a separate genetic, virologic, and epidemiologic entity of viruses with marked differences in natural history and disease associations (▶HIV Prevention in the Correctional System). Accurate, reliable diagnosis of HIV-2 infections is important not only from an individual perspective but when considering wider epidemiological and clinical consequences of HIV-2. Differences in HIV-2 biology impact on diagnostic approaches to detect HIV-2, either as monotypic infections or simultaneous dual HIV-1 and HIV-2 infections. From the initial identification of HIV-2 in the mid-1980s, the disease course and relative pathogenicity of HIV-2 have been much debated although a clearer picture has emerged (▶Natural histroy and clinical features of HIV-2 infection). HIV-2 is recognized as being less pathogenic than HIV-1, the majority of HIV-2 infections presenting as long-term nonprogressors (LTNP), with up to 80 % of all HIV-2 infections falling into this category (de Silva et al. 2008). However, HIV-2 clearly can have severe consequences for a significant minority of individuals leading to profound immunological dysfunction, morbidity, and mortality. Hence, accurate diagnosis of HIV-2 infections is important to ensure blood donations remain HIV-2-free. Similar principles to HIV-1 diagnosis apply, including electron microscopy, direct virus isolation, detection of virus antigens, demonstration of virus-specific antibodies, or identification of components of the viral genome. However, only a proportion may be considered appropriate for HIV-2 diagnosis due to the differing biology of HIV-2 in vivo compared to HIV-1. In practice, serological detection with sensitive and specific anti-HIV-2 or HIV-2 antigen detection assays provide a frontline laboratory diagnosis, enriched and augmented by the application of molecular techniques for genome detection. HIV-2 presents a number of particular challenges when effecting a reliable diagnosis, stemming from its evolutionary origins and entry into human populations. One important consideration when identifying diagnostic approaches to virus infection is knowledge of the range and spectrum of the infecting agent; HIV-2 viruses are no exception. Such considerations need to be taken into account when developing diagnostic strategies for HIV-2.