Human Immunodeficiency Virus Type 2

Guideline and Commentary

John G. Bartlett, MD


June 06, 2012

In This Article

Natural History and Epidemiology

HIV-1 and HIV-2 are closely related retroviruses of the same genus (Lentiviridae) and share the same modes of transmission. Both types are considered to have arisen from the introduction of simian immunodeficiency virus into the human population, although they derive from different primate simian immunodeficiency viruses: HIV-2 from SIVsm (sooty mangabey) and HIV-1 from SIVcpz (chimpanzee).

HIV-2 is present throughout West Africa, with the highest prevalence in its area of origin, Guinea-Bissau, where, in 1990, 8% of adults and 20% of persons over 40 years of age were infected.[12,13] HIV-2 has been reported in Portugal and France, as well as countries with colonial ties to these nations (Angola, Mozambique, Brazil, and parts of India), due to large West African immigrant populations and/or long histories of commerce and other ties to West Africa.

HIV-1/HIV-2 Co-Infection

HIV-1/HIV-2 co-infection in West Africa is increasing, particularly in border countries between West and East Africa.[13] In the United States, co-infection has also been reported. Among the 166 cases of HIV-2 reported by the CDC, 19 patients (11%) tested positive for possible HIV-1/HIV-2 co-infection. However, the extent of HIV-1/HIV-2 co-infection within the entire patient population could not be assessed due to incomplete HIV-1 testing results for some individuals.[3]

The dynamics of interaction between HIV-1 and HIV-2 have been a matter of controversy for decades,[14,15,16,17] and expertise in the area of HIV-1/HIV-2 co-infection remains limited. One study suggested that mortality rates were higher among HIV-1/HIV-2 co-infected individuals than HIV-1 mono-infected individuals,[17] but this may be dependent on which infection occurred first. Over time, HIV-1 seems to outcompete HIV-2 as the primary virus behind disease progression in HIV-1/HIV-2 co-infected persons. Data also suggest that the mortality associated with HIV-1/HIV-2 co-infection is dependent on CD4 count and is higher than in HIV-2 mono-infected individuals matched for disease stage.[18]

HIV-1/HIV-2 co-infection is difficult to diagnose due to the cross-reactivity of antibodies, as well as viral antigens, making treatment decisions based on co-infection difficult to determine. Genetic sequence verification of both viral sequences should be encouraged for diagnosis of HIV-1/HIV-2 co-infection. See the section entitled HIV-2 Screening and Diagnosis for guidance on the tests that are best designed to differentiate between HIV-1 and HIV-2.


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