HIV-2

HIV-1 and HIV-2 are distinct retroviruses originating from two different primate species.¹ Transmission modes for both strains are the same, and infection with either strain can lead to the development of AIDS.²

However treatment strategies are different – NNRTIs are not active against HIV-2, a number of other drugs are less effective, and pregnancy should be managed differently.

The origin of HIV-2 is attributed to the sooty mangabey monkey. There are at least eight identified subtypes of HIV-2, but only subtypes A and B are commonly found. Although the majority of HIV-2 infections have been found in West Africa, the number of diagnosed cases in India is increasing. HIV-2 cases are also found in European countries with former colonial ties (particularly Portugal and France) to West Africa. Incidence of HIV-2 infection remains low in the UK (144 HIV-2 mono-infections and 22 HIV-1 and 2 dual infections).

A persistent lower viral load is one reason for a lower incidence rate and transmission risk in HIV-2 infection than is found in HIV-1.³

In general, after HIV-2 seroconversion, the viral load tends to remain low for a longer period than is typically found in HIV-1 infection. Approximately 5 to 15% of people infected with HIV-1 are considered to be long-term non-progressors versus 86 to 95% of people infected with HIV-2.⁴

The virulence of HIV-2 is considerably less than that of HIV-1, resulting in lower HIV-2 transmission rates, a slower course of infection, and delayed progression to AIDS.⁵ In the later stages of AIDS, HIV-2 infectiousness does increase, but for a shorter duration than is seen with HIV-1 infection.

An early prospective study of over 1100 infants born to HIV-1 and HIV-2 infected women showed that vertical transmission took place in 21% of the infants with HIV-1 infected mothers within the first 18 months while no transmission was seen in infants born to HIV-2 infected mothers.⁶

A study looking at a cohort of 250 women, almost equally divided between those with HIV-1 and HIV-2, found that over a period of four years, six of the HIV-2 infected women went on to acquire HIV-1 infection. In contrast, none of the women who originally tested positive for HIV-1 became reactive to HIV-2.⁷ This dispels the idea once held that persons with HIV-2 might have a protective benefit against acquiring HIV-1.

Testing for HIV-2 infection is covered in a later section.