What Is HIV-2?

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The human immunodeficiency virus (HIV) comes in two types: HIV-1 and HIV-2. HIV-2 was discovered in 1986—about five years after HIV-1 was found to be the virus behind acquired immune deficiency syndrome (AIDS). HIV-2 is mainly confined to western Africa.

While HIV-2 has some of the same characteristics as HIV-1, it differs in its origin, genetic makeup, distribution, virulence, and pathogenicity (ability to cause disease). It is also less responsive to certain antiretroviral drugs used to treat HIV.

Female scientist about to view a human sample under a microscope

Andrew Brookes / Getty Images

Origin

A zoonosis is an infectious disease that is transmissible from nonhuman animals to humans. Currently, there are more than 200 known types of zoonoses, which comprise a large percentage of new and existing diseases in humans.

Animal Connection

Both types of HIV are believed to have originated from animals:

  • HIV 1's zoonotic origins are thought to be linked to chimpanzees and gorillas.
  • HIV-2's zoonotic origins are thought to be linked to the sooty mangabey.

One of the major obstacles in creating a vaccine for HIV is that the virus has exceptionally high genetic variability. This means that not only are there two distinct genetic types of HIV, but there are numerous subtypes, some of which are more virulent or resistant to HIV drugs, making a cure a continual challenge.

Distribution

Of the estimated 38 million people worldwide living with HIV, approximately 1 to 2 million have HIV-2.

The bulk of HIV-2 infections are centered in West Africa, or in countries that have strong colonial or socioeconomic ties with West Africa, including:

  • France
  • Spain
  • Portugal

Other former Portuguese colonies have also reported significant numbers of HIV-2 infections, including:

  • Angola
  • Mozambique
  • Brazil
  • India

HIV is transmitted from someone with HIV to someone without the virus, through body fluids like:

  • Semen
  • Blood
  • Vaginal secretions
  • Breast milk

Common methods of transmission include unprotected vaginal and anal sex, and shared needles.

Over the last two decades, HIV-2 prevalence has declined in several West African countries like Senegal, Gambia, Cote D’Ivoire, Guinea-Bissau, but the reasons for this are unclear.

However, along with the declines, there has also been an increase in dual infections—where someone has HIV-1 and HIV-2—with some estimates suggesting that 15% of all HIV infections in West Africa involve both types.

Prevalence of HIV-2 in the United States

The first case of HIV-2 in the United States was reported in 1987. Currently, fewer than 1% of people in the United States with HIV have HIV-2.

Virulence and Pathogenicity

HIV-2 is typically far less virulent and tends to progress slower than HIV-1. Additionally, HIV-2 infection is associated with:

  • Lower viral loads
  • Slower declines in the CD4 count
  • Lower mortality rates

HIV-2 also has reduced sexual transmissibility and genital shedding compared to HIV-1.

Although people with HIV-2 can (and do) progress to AIDS, a significant number are elite controllers who do not experience the progression of the virus.

In recent years, increasing attention has been devoted to this subset of HIV-2-infected individuals, which has a larger proportion of long-term viral control than HIV-1. The idea is to use HIV-2 as a model for finding a functional cure against HIV.

Mother-to-Child Transmission of HIV-2

HIV-2 is more difficult to transmit perinatally than HIV-1. Although data on mother-to-child transmission of HIV-2 is incredibly sparse, it is thought to occur at a rate of approximately 0.6%.

Diagnosis

Currently, the Centers for Disease Control and Prevention (CDC) recommends that laboratories should conduct initial testing for HIV with a U.S. Food and Drug Administration (FDA)-approved antigen/antibody combination immunoassay that detects HIV-1 and HIV-2 antibodies.

The CDC also recommends the use of an HIV-1 p24 antigen to screen for established infection with HIV-1 or HIV-2, and for acute HIV-1 infection.

If a test is reactive, it's then followed by a supplemental test to differentiate between HIV-1 and HIV-2. Moreover, it's important to note that certain tests commonly used for HIV-1 testing—including the Western blot and HIV-1 RNA and DNA assays—do not reliably detect HIV-2 and may trigger a false-negative reading.

Test to Differentiate Between Two Types of HIV

The Multispot HIV-1/HIV-2 Rapid Test is currently the only FDA-approved test able to reliably differentiate between the two viruses. The test can also:

  • Detect circulating antibodies associated with HIV-1 and HIV-2 in human plasma and serum
  • Aid in the diagnosis of infection with HIV-1 and/or HIV-2.

Treatment

In order to prevent disease progression and transmission of HIV-2 to others, it is recommended that antiretroviral therapy starts at or soon after HIV-2 diagnosis.

While many of the antiretroviral drugs used to treat HIV-1 also work in people with HIV-2, that is not universally the case. For example, all non-nucleoside reverse transcriptase inhibitors (NNRTIs) and the fusion inhibitor enfuvirtide are ineffective in treating HIV-2.

At this point, the efficacy of the CCR5 inhibitor maraviroc is uncertain, while protease inhibitors have variable efficacy in people with HIV-2, with lopinavir and darunavir being the most useful.

NNRTIs aside, the first-line treatment approach of HIV-2 is similar to that of HIV-1 and typically consists of two nucleoside reverse transcriptase inhibitors (NRTIs) and one integrase strand transfer inhibitor (INSTI), such as:

  • bictegravir
  • dolutegravir
  • elvitegravir
  • raltegravir

Alternatively, the second option is two NRTIs plus a boosted protease inhibitor (darunavir or lopinavir).

People with HIV-2 who are taking antiretroviral therapy should undergo routine monitoring of quantitative HIV-2 levels, similar to what is done for people with HIV-1 in order to gauge their body's response to the medication.

Mortality Rates of People With HIV-2 on ART

Despite the reduced efficacy of certain HIV drugs, the mortality rate of people with HIV-2 on antiretroviral therapy is roughly half that of people with HIV-1 (64.2 per 100,000 versus 120.9 per 100,000).

A Word From Verywell

Before undergoing HIV testing, be sure to provide all relevant information about personal risk factors—including sexual history, shared needle use, and travel to or residence in West Africa—as these may be a crucial component in a possible diagnosis.

While getting any kind of testing for serious conditions like HIV can be stressful and unnerving, it's good to remind yourself that there are now several different effective treatment options that allow people with HIV to live nearly as long as those who have never been infected with the virus.

A functional cure for HIV remains elusive, but the research continues, including studies looking at how to use HIV-2 as a potential model for a cure.

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