HIV-2 Strain Overview

Three years after the emergence of the first cases of AIDS in the U.S., three scientists, Robert Gallo, Luc Montagnier, and Francoise Barre-Sinoussi, discovered the virus which caused this mysterious immune deficiency syndrome, HIV.

Several years later, a new strain was found in a man living in Africa, which has genetic variations far different than the one isolated in Europe and North America. As a result, the original virus was named HIV-1 while the newer strain was called HIV-2.

In biology, a strain is simply a genetic variation of an organism that makes it entirely unique. Similarities can exist but they are ultimately independent organisms. Demographically speaking, HIV-2 is a less common form of HIV with some subtle yet distinctive differences.

Colorized electron micrograph of HIV-1 virions (in yellow) budding from an infected CD4+ T-cell.
National Institute of Allergies and Infectious Diseases (NIAID)

How Are HIV-1 and HIV-2 Similar?

Despite differences in their genetic profile, HIV-1 and HIV-2 share the following similarities:

  • The modes of transmission are the same (sexual contact, blood-to-blood contact, mother-to-child transmission).
  • People infected with HIV-2 are subject to the same opportunistic infections as those infected with HIV-1.
  • HIV-1 and HIV-2 are treated with the same antiretroviral medications.
  • The same CD4 testing can be used to monitor HIV-1 and HIV-2 disease progression.

How Do HIV-1 and HIV-2 Differ?

There are also a number of key differences between HIV-1 and HIV-2.Among them:

  • HIV-2 appears to be less virulent, generally depleting the immune system at a slower rate than HIV-1.
  • People with HIV-2 tend to be less infectious in the early stage of the disease compared to those with HIV-1.
  • However, HIV-2 seems to be more infectious in the later stages of disease when the CD4 count had dropped below 200 cells/mL.
  • HIV-2 is typically constrained to certain parts of the world when compared to HIV-1 (although international travel has allowed for widening global distribution)
  • The viral load test used for HIV-1 is not as reliable for people with HIV-2 infection.
  • Some antiretroviral drugs may work less effectively for people with HIV-2 although this is more related to older-generation drugs than newer ones.

Where in the World Is HIV-2 Most Common?

HIV-2 is highly concentrated in West Africa countries such as Senegal, Nigeria, Ghana, and the Ivory Coast. In the past, few cases have been reported outside of these areas, but those numbers are quickly changing, particularly in HIV-2-prevalent countries popular with international travelers or those with a high influx of immigrants from HIV-2-prevalent countries.

Moreover, within both HIV-1 and HIV-2 are a number of groups, subtypes ("clades"), and sub-subtypes, which further increases the diversity of the virus. It is this diversity that makes HIV a "moving target" for researchers who struggle to create a vaccine able to treat all of the unique conformations of the virus.

There are currently eight HIV-2 groups, although only subtypes A and B are considered an epidemic. HIV-2 is believed to have crossed species from a type of SIV affecting the sooty mangabeys monkey directly to humans.

HIV-2 Group A is mainly seen in West Africa, although international travel has led to a small handful of documented cases in the U.S., Europe, Brazil, and India. By contrast, HIV-2 Group B has been confined to parts of West Africa.

By contrast, HIV-1 has four groups and numerous subtypes that predominate in different regions and different groups, including men who have sex with men and injecting drug users.

A Word From Verywell

In the past, the availability of HIV-2 testing assays was limited and only available by special request. In recent years, however, newer-generation combination tests (including the Alere Determine Combo) were released into the market, able to test not only for HIV-1 and HIV-2 but for HIV antibodies and antigens, as well.

Whether you test positive for HIV-1 and HIV-2, it is important that you always find a qualified HIV specialist who can help assess which treatment is best to treat your particular virus. This can be done with a blood test that can determine the genetic structure of your virus, as well as identifying the antigens specific to either HIV-1 or HIV-2.

The tests will outline the specific mutations that confer to drug resistance in the different types of HIV medications. By excluding the drugs that don't work and keeping those that do, you can be assured the best possible treatment outcome whatever the stage of infection.

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