HIV is a virus that attacks immune cells. Although HIV infections can’t be cured, they can be treated. These treatments can help prevent AIDS.
There are two types of HIV — HIV-1 and HIV-2. These two viruses share less than half of their genes and can work differently. HIV-1 and HIV-2 affect various groups of people, are diagnosed using dissimilar tests, and may require different treatments. Most people with HIV have HIV-1 infection.
About 19 out of 20 people with HIV infection worldwide have HIV-1. This virus is found throughout the world.
HIV-2 is most common in West African countries. It has also caused a small number of infections in people living in Europe, Asia, and South America. Only about 1 percent of people with HIV in the United States have the HIV-2 subtype.
In places where both viruses can occur, it is possible to have both HIV-1 and HIV-2 infections. These dual infections primarily occur in West Africa, where up to 1 out of 10 people with HIV have both viruses.
There are also other HIV subtypes. Group M is the most common type of HIV-1, which can also be broken down into additional subtypes. HIV-1 also includes groups N, O, and P. HIV-2 is divided into A and B subtypes. Sometimes, different subtypes can combine to form a brand-new subtype.
These different subtypes are more or less common in various parts of the world, but all HIV-1 subtypes and all HIV-2 subtypes are generally treated the same.
Both types of HIV are transmitted (spread) in similar ways, including through:
HIV-2 is less likely to spread through these methods. For example, untreated mothers with HIV-1 have a 15 percent to 30 percent chance of transmitting the virus to their child during pregnancy or birth. The risk is 1 percent to 2 percent for mothers with untreated HIV-2.
Both types of HIV lead to similar symptoms, although those with HIV-2 typically have a longer phase when they don’t have any symptoms.
In HIV’s early stages, people with HIV-1 or HIV-2 may experience:
Once these symptoms disappear, people will then enter the chronic or clinical latent stage of HIV. In this stage, the virus is within the CD4 cells (a type of white blood cell), but no symptoms appear.
Those with HIV-2 tend to stay in this chronic stage for about twice as long as those with HIV-1. These people are also more likely to have a lower viral load (fewer viral particles in the body), which means that their immune system may not be damaged as quickly or as severely. Their condition may take longer to progress to the third HIV stage, AIDS — if at all. In people living with AIDS, their immune systems can be very weak and they can develop serious infectious diseases.
People with AIDS have low CD4 counts and tend to have similar signs and symptoms regardless of whether they have HIV-1 or HIV-2.
Several types of tests are used to diagnose HIV, with some differences in the tests between the two HIV types.
Health experts from organizations such as the Centers for Disease Control and Prevention (CDC) recommend that HIV testing should ideally include a sequence of tests to look for both HIV-1 and HIV-2. They suggest that doctors first perform an HIV antigen/antibody test. This test can show whether a person’s blood contains pieces of the HIV-1 or HIV-2 viruses or antibodies (proteins made by the immune system to try to fight the virus) to one or both.
If this test result is positive, it indicates that someone may have HIV, and further testing is needed for confirmation. The CDC then recommends that labs perform an HIV-1/HIV-2 differentiation immunoassay. This can confirm the infection and distinguish between the two main virus types, showing whether there is HIV-1, HIV-2, or both. The differentiation assay may also suggest whether the antigen/antibody assay test result might have been false-positive, meaning there’s no HIV infection.
If the antigen/antibody assay test result is positive but the differentiation assay result is negative, further testing can rule out acute HIV infection. This is carried out by testing for HIV-1 genetic material (RNA) with a nucleic acid amplification test (NAAT). However, an HIV-2 NAAT is not routinely available to test for HIV-2, and further testing may be needed if a person is at risk for this infection.
Diagnosing HIV-1 and HIV-2 infection using the aforementioned testing sequence is recommended. If somone has only a strongly positive HIV-1 and/or HIV-2 NAAT result — showing a high amount of RNA or DNA in the blood — they may have an HIV-1 or HIV-2 infection and should undergo the other testing. A negative HIV-1 or HIV-2 NAAT result alone, however, is not adequate to rule out infection, as some people can have negative test results with this assay but still have active infection.
Doctors recommend that almost everyone with HIV infection take antiretroviral therapy (ART). This treatment blocks the virus from making more copies of itself, which helps the body keep the infection under control and reduces the risk of having HIV spread to other people. A dcotor may not recommend an HIV treatment if the person’s body is controlling the HIV well enough on its own and the HIV NAAT blood test result is negative or undetectable.
There are many types of ART that work very well for people with HIV-1. HIV-2 is resistant to certain ART types — enfuvirtide (Fuzeon) and a class of medications called non-nucleoside reverse transcriptase inhibitors. These medications will not work in people with HIV-2.
People with HIV-2 will be treated with other common types of ART medications, including integrase strand transfer inhibitors, nucleoside reverse transcriptase inhibitors, and protease inhibitors.
In people with HIV-1 or HIV-2, the virus may undergo additional gene changes that cause drug resistance. These individuals may have to switch their treatment regimens.
Because HIV-2 often leads to a lower viral load and has a slower disease progression (takes longer to transform into AIDS), it is often linked to a better outlook. A study of one group in West Africa, before the widespread availability of highly effective ART, showed that people with HIV-2 lived twice as long as those with HIV-1. However, HIV-2 can still lead to AIDS and be fatal, so treatment is still important.
The two types of HIV can sometimes lead to different sets of complications — problems that arise as a result of the infection. People with HIV-2 are less likely to develop Kaposi’s sarcoma, a type of cancer that causes tumors to form in the body’s soft tissues.
Vaccines teach your immune system to fight off certain types of germs, including viruses. Researchers are currently working on HIV vaccines that could help prevent infection.
Because the HIV-1 and HIV-2 viruses are not the same, they will likely require different vaccines. If HIV vaccines are developed, different ones may need to be used in various countries depending on which types of viruses are most common there.
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