Human immunodeficiency virus (HIV) is a retrovirus that infects the cells of the immune system. If left untreated, it can severely impair the immune system’s ability to respond to infections and other diseases.

There are two types of HIV: HIV-1 and HIV-2. While their names may be similar, they’re actually two distinct lineages of virus.

Below, we’ll explore the similarities and differences between HIV-1 and HIV-2, the risks associated with them, and whether it’s possible to have both at the same time.

HIV-1 is the predominant type of HIV worldwide. In fact, it’s estimated that HIV-1 makes up 95 percent of all HIV cases worldwide.

Let’s dig deeper into HIV-1 and what you need to know.

What is HIV-1?

Both types of HIV evolved from primate viruses. The genetic ancestors of HIV-1 are viruses from chimpanzees. It’s believed that these viruses made their way to humans when hunters came into contact with the blood of these animals.

HIV-1 is divided into four different groups: M, N, O, and P. Each group is believed to have come from a separate primate-to-human transmission event.

Group M accounts for the majority of HIV cases worldwide. It’s further divided into nine subtypes (A, B, C, D, F, G, H, J, and K). The rate of these subtypes varies depending on your location.

Subtype C is the most common HIV-1 subtype worldwide. It makes up about 46.6 percent of HIV-1 cases. However, subtype B is the most common HIV-1 subtype in the United States.

HIV-1 subtypes can also combine to create hybrid viruses by a process called recombination. This can happen if a person contracts a second subtype of HIV-1. These combination or recombinant viruses can potentially be transmitted to others.

What are the symptoms of HIV-1?

It’s possible that some people may experience flu-like symptoms 2 to 4 weeks after contracting HIV-1. This is called acute HIV. Its possible symptoms can include:

These symptoms may last for days or weeks before going away. After acute symptoms pass, a person living with HIV may not experience additional symptoms for many years.

This period is referred to as latency. Even though there are no symptoms during latency, when left untreated, HIV-1 still continues to damage the immune system.

How is HIV-1 transmitted?

A person can contract HIV-1 when bodily fluids containing the virus come into direct contact with their blood or with mucous membranes, such as the penis, vagina, or rectum. Bodily fluids that may transmit HIV include:

  • blood
  • semen and pre-seminal fluid (pre-cum)
  • vaginal fluids
  • anal fluids
  • breast milk

According to the Centers for Disease Control and Prevention (CDC), the most common ways that HIV-1 is transmitted include:

  • anal or vaginal sex without a condom or other barrier method
  • sharing injection drug needles
  • during pregnancy, delivery, or breastfeeding

Other less common ways that HIV-1 can be transmitted include:

  • oral sex
  • deep, open mouth kissing
  • occupational exposures, such as needlesticks or other sharps injuries
  • tattoos or piercings that are done using shared or improperly sterilized equipment
  • bites that break the skin
  • blood transfusions, blood products, or organ transplants

How does HIV-1 progress?

There are three different phases of HIV-1 progression. Let’s look at each one in a little more detail:

  1. Acute HIV infection. This is the period shortly after a person contracts HIV-1. A high number of HIV-1 particles can be found in the blood. Flu-like symptoms may be present.
  2. Latent or chronic HIV infection. At this stage, the infection has become chronic. The amount of virus in the blood (viral load) is lower, and symptoms aren’t present. The length of this stage can vary.
  3. Acquired immunodeficiency syndrome (AIDS). In this stage, the immune system has been severely weakened and viral load is high. There is an increased risk of severe opportunistic infections.

How is HIV-1 diagnosed?

There are a variety of tests that can detect HIV-1. These are typically done using a sample of blood and can include:

  • Antigen/antibody tests. These tests detect antibodies to HIV and the presence of a viral protein called p24.
  • Antibody tests. These tests detect the presence of HIV antibodies.
  • Nucleic acid tests. These tests can detect the presence of viral genetic material in a blood sample. They can both diagnose HIV and determine viral load.

It’s important to note that each type of test has a different window period. This is the amount of time between contracting HIV and when a test can accurately detect it.

How is HIV-1 treated?

After HIV-1 is diagnosed, a healthcare professional will perform several additional tests that can then help develop a treatment plan. These include:

  • Viral load test. Also called an HIV nucleic acid amplification test (NAAT or NAT) or HIV RNA test, this test determines how much virus is present in the blood.
  • CD4 count. CD4 cells are the immune system cells that HIV infects and destroys. Also called a CD4 count test, this test measures how many of these cells are present in the blood.
  • Drug resistance testing. Some strains of HIV-1 may be resistant to certain types of antiretroviral drugs. This test helps detect mutations that are known to lead to drug resistance.

Antiretroviral drugs treat HIV-1. There are many types of antiretroviral drugs available. Generally speaking, they all work by disrupting the virus’s ability to infect cells and make more of itself (replicate).

Taking antiretroviral drugs each day works to keep viral load low and even undetectable. This means that the virus cannot continue to harm the immune system and cannot be passed on to anyone else.

HIV-2 is less common than HIV-1 worldwide. It occurs most often in western Africa, where it’s estimated that 1 to 2 million people are currently living with the virus.

While HIV-2 has been reported in the United States, it’s still rare. For example, between the years of 2010 and 2017, HIV-2 accounted for less than 0.1 percent of new HIV diagnoses in the United States.

Let’s examine the different aspects of HIV-2 in more detail.

What is HIV-2?

HIV-2 evolved from viruses found in the sooty mangabey monkey. It’s believed to have been passed to humans in much the same way as HIV-1, through hunters coming into contact with the blood of animals with the virus.

As we mentioned earlier, HIV-1 and HIV-2 are quite different from each other. On a genetic level, it’s estimated that HIV-2 is more than 55 percent different than HIV-1.

Like HIV-1, HIV-2 is divided into groups. There are nine groups of HIV-2, lettered A through I. However, it’s believed that only viruses from group A and D are currently circulating in humans.

Unlike HIV-1, there are no HIV-2 subtypes.

How is HIV-2 transmitted?

The ways that HIV-2 is and isn’t transmitted are generally the same as HIV-1. However, HIV-2 has been observed to be less transmissible than HIV-1.

For example, research has found that HIV-2 has a fivefold lower rate of sexual transmission and a 20- to 30-fold lower rate of transmission during pregnancy, delivery, or breastfeeding.

This may be due to the fact that, when compared with HIV-1, people living with HIV-2 generally have lower levels of HIV-2 particles present in the blood. When less virus is found in the blood, the virus is harder to transmit.

What are the symptoms of HIV-2?

The symptoms of HIV-1 and HIV-2 are generally similar. The progression of HIV-2 is different than that of HIV-1, though.

How does HIV-2 progress?

HIV-2 can progress through the same three stages as HIV-1. However, the length of these stages may be different.

People living with HIV-2 can have a longer latency period (stage 2) that can last 10 years or more. However, HIV-2 can still eventually progress to AIDS (stage 3) if antiretroviral therapy isn’t received.

How is HIV-2 diagnosed?

The same types of tests used to detect HIV-1 can detect HIV-2. However, it’s important to note that, due to the differences between the viruses, a test that’s specifically designed for HIV-1 may not detect HIV-2.

The current CDC recommendations are that a person first be tested using an antigen/antibody test that detects p24 as well as antibodies to HIV-1 and HIV-2.

If test results are positive, another test is performed to differentiate between HIV-1 and HIV-2.

It’s important to know whether someone has contracted HIV-1 or HIV-2 because this information can have an impact on treatment options.

How is HIV-2 treated?

When a person receives a diagnosis of HIV-2, a healthcare professional will perform tests to assess viral load and CD4 count.

While there isn’t a test approved by the Food and Drug Administration (FDA) for HIV-2 viral load, certain testing facilities can perform these tests.

Like with HIV-1, antiretroviral drugs also treat HIV-2, but treatment plans must be carefully considered. This is because HIV-2 is resistant to some types of antiretroviral drugs, such as:

It’s possible to have both HIV-1 and HIV-2. However, since HIV-2 is much less common than HIV-1 worldwide, dual infections are generally rare.

In western Africa, where HIV-2 is more common, it’s estimated that the rate of having both HIV-1 and HIV-2 can be up to 3.2 percent.

It’s possible that having both viruses may slow the progression of disease. Indeed, some studies have found that progression is slower in people who have contracted both viruses than in those who have contracted HIV-1 alone.

However, a 2014 study found no difference in outcome between people who have contracted both viruses and people who had contracted HIV-1 alone. Overall, further research is needed to learn more.

People living with HIV-1 and HIV-2 can have an increased risk for certain health conditions.

Infections

It’s possible that people living with HIV may contract other pathogens as well. Two of the most common are tuberculosis and viral hepatitis.

Tuberculosis is a bacterial disease that affects the lungs but may also spread to other areas of the body. While tuberculosis is treatable, it’s still one of the leading causes of death worldwide for people living with HIV.

Several types of viruses can cause viral hepatitis, which can lead to liver damage. Two types of viral hepatitis that can commonly occur in people living with HIV are hepatitis B and hepatitis C. Both types are treatable with medication.

Opportunistic infections can also occur in people living with HIV. These are infections that happen more frequently in people who have a weakened immune system. Some examples of common opportunistic infections are:

Opportunistic infections are generally less common now due to advances in HIV treatment. That’s why taking antiretroviral drugs each day as directed is very important.

Cancer

People living with HIV can have an increased risk for developing certain types of cancers. These include:

Like opportunistic infections, taking antiretroviral drugs as prescribed can reduce the risk of developing some of these cancers. Additionally, vaccination can protect against hepatitis B and HPV.

Other chronic health conditions

Even when HIV is managed using antiretroviral drugs, it can still place a lot of stress on the body. Because of this, people living with HIV can be at risk for a variety of chronic health conditions, including:

The outlook for people living with HIV has greatly improved since the virus was first identified. Many people with HIV live long, healthy lives.

Antiretroviral therapy is essential to this. These medications can reduce a person’s viral load to undetectable levels, helping prevent further damage to the immune system and lowering the risk of transmission.

A 2020 study evaluated the life expectancy of 39,000 people living with HIV who had access to antiretroviral drugs. Researchers found that, overall, the life expectancy of these people was similar to that of people without HIV.

People living with HIV can still be at risk for various chronic health conditions. Because of this, treatment not only focuses on reducing viral load, but also on preventing and managing chronic health conditions, should they occur.

There’s currently no vaccine for HIV. However, scientists are currently hard at work to develop one.

In the meantime, there are a variety of effective ways to prevent contracting HIV:

  • Use barrier methods. Using condoms or other barrier methods during sex can help prevent HIV transmission
  • Get tested for HIV and other sexually transmitted infections (STIs). Knowing HIV and STI status can help prevent transmission of these infections. Encourage sexual partners to get tested as well.
  • Take pre-exposure prophylaxis (PrEP). PrEP is a daily medication that sexual partners of someone living with HIV can take to reduce their risk of contracting the virus.
  • Don’t share needles. If you use injection drugs, don’t share needles or other equipment.
  • Use post-exposure prophylaxis (PEP), if necessary. PEP is a medication that people without HIV can take if they may have been exposed to HIV. It’s effective when taken within 72 hours of exposure.

There are actually two different types of HIV: HIV-1 and HIV-2. These viruses are very different from each other on a genetic level and represent two distinct primate-to-human transmission events.

HIV-1 is the most common type of HIV worldwide. HIV-2 is much less common worldwide, but is more common in western Africa.

While HIV-1 and HIV-2 cause a similar disease and are transmitted in the same way, there are some important differences. For example, HIV-2 is transmitted less efficiently, may progress more slowly, and is resistant to some types of antiretroviral drugs.

Regardless of the type of virus, it’s important that people living with HIV receive antiretroviral therapy to reduce the level of virus in their body. Through using antiretroviral drugs, many people with HIV live long, healthy lives.