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Human immunodeficiency virus (HIV) is a virus that infects cells in the immune system. When HIV is not treated, it can cause the immune system to become severely weakened.

There are actually two types of HIV: HIV-1 and HIV-2. Of the two, HIV-1 is the most common. In fact, about 95 percent of people living with HIV around the world have HIV-1.

In this article, we’ll explore what you need to know about HIV-1, including how it’s treated and strategies for prevention.

HIV-1 is a type of retrovirus that originated from a similar virus in chimpanzees. It’s believed that this virus was passed to humans when they came into contact with the blood of chimpanzees they had hunted.

There are four groups of HIV-1: M, N, O, and P. The largest of these is group M, which is further divided into nine subtypes. Subtype B is the most common subtype in the United States. Subtype C is the most common worldwide.

Read this for more information about the four types and nine subtypes of HIV-1.

When a person contracts HIV-1, the virus begins to infect a specific type of immune cell called a CD4 cell. These cells are very important in helping coordinate the body’s immune response.

When HIV-1 isn’t treated with antiretroviral drugs, the virus continues to deplete the body’s CD4 cells. As this happens, it gets harder and harder for the immune system to deal with infections and certain types of cancer.

There are several tests that can diagnose HIV-1. These are most often done using a blood sample collected from a vein in the arm or through a finger prick:

  • Antibody tests. An antibody test detects antibodies to HIV. Antibodies are proteins that your immune system makes in response to foreign invaders, such as a HIV. Most HIV rapid or at-home tests are antibody tests.
  • Antigen/antibody tests. This type of test looks for antibodies to HIV as well as a viral protein called p24. It’s actually possible to detect p24 before antibodies develop.
  • Nucleic acid tests (NATs). A NAT detects the virus’s genetic material in a blood sample. It can also determine the amount of virus (viral load) in a person’s blood.

Each diagnostic test has a different window period. This is the time period between when a person was exposed to the virus and when the test can accurately detect it.

A healthcare professional will take a test’s window period into consideration during testing. It’s possible that a second test after the window period has passed will be necessary to confirm a negative result.

The Centers for Disease Control and Prevention (CDC) recommends using an antigen/antibody test for HIV diagnosis. If positive, this test is followed up with a confirmatory test to determine whether a person has HIV-1 or HIV-2.

HIV testing after diagnosis

Additional tests are performed both after a person receives an HIV-1 diagnosis and throughout their treatment. These include:

  • Viral load. The amount of virus in a person’s blood is called viral load. When HIV-1 isn’t treated, viral load will increase. In contrast, treatment with antiretroviral drugs can reduce viral load to undetectable levels.
  • CD4 count. A CD4 count looks at the number of CD4 cells in a blood sample. Decreasing levels of CD4 cells signal damage to the immune system.
  • Drug resistance testing. HIV-1 can become resistant to certain types of antiretroviral drugs. Because of this, drug resistance testing is performed to help inform which antiretroviral drugs can be used for treatment.

HIV is a viral infection. A person can contract HIV-1 when bodily fluids that contain the virus come into contact with their blood or with mucous membranes like those found in the genitals, anus, or mouth.

There are several bodily fluids that can transmit HIV-1. These include:

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

Some of the most common ways that HIV-1 is transmitted include:

  • through anal or vaginal sex without a condom
  • by reusing or sharing injection drug equipment
  • from a mother who’s not receiving antiretroviral therapy to a child during pregnancy, delivery, or through breastfeeding

There are also a few other less common ways that HIV-1 may be transmitted. These include:

  • oral sex
  • deep, open-mouth kissing
  • workplace exposures, such as accidental needlesticks or sharps injuries
  • receiving a blood transfusion or organ transplant
  • getting a tattoo or piercing with equipment that hasn’t been properly sterilized
  • human bites that break the skin

Ways that HIV cannot be transmitted

Now let’s take a quick look at some ways HIV-1 cannot be transmitted:

  • bodily fluids like sweat, tears, or saliva
  • casual contact, which can include:
    • shaking or holding hands
    • hugging
    • casual, close-mouthed kissing
  • sharing things like plates or eating utensils
  • using the same toilet seat as someone with HIV
  • contact with an object or surface that someone with HIV has touched, such as a doorknob, light switch, or faucet handle
  • sexual activities where bodily fluids aren’t exchanged
  • the bites of bugs like mosquitoes or ticks
  • through the air or through water
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The stages of HIV

HIV has three different stages. These are:

  1. Acute. This is the period shortly after a person contracts HIV-1. People in the acute stage have a high viral load and may experience flu-like symptoms.
  2. Chronic. During this stage, a person with HIV usually doesn’t experience symptoms. Even though no symptoms are present, the virus continues to damage the immune system if antiretroviral drugs aren’t used.
  3. Acquired immunodeficiency syndrome (AIDS). In this stage, the immune system is severely damaged. A person’s HIV has progressed to AIDS when CD4 count is below 200 cells per cubic millimeter or when they begin to have certain types of opportunistic infections.

HIV-1 treatment has progressed dramatically since the virus was first identified. Because of this, progression to AIDS is much less common now than it was earlier.

HIV-1 superinfection

It’s possible to contract two different strains of HIV-1. This is called a superinfection. In a superinfection, the new strain may become dominant, or both strains may coexist together.

Sometimes the new strain may have resistance to the antiretroviral drugs that a person is taking, making their current treatment less effective.

However, the CDC notes that superinfections that are difficult to treat are rare.

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There are many steps that a person can take to prevent contracting HIV-1. These include:

  • Using a condom. Using a condom during vaginal, anal, or oral sex can help prevent transmission of the virus during these activities.
  • Getting tested. Getting tested for HIV and other sexually transmitted infections (STIs) is a powerful tool for both detecting and treating these infections. Encourage sexual partners to get tested as well.
  • Not sharing needles. It’s important that injection drug users avoid sharing needles or injection drug equipment with others.
  • Taking pre-exposure prophylaxis (PrEP). PrEP is a daily medication that can be taken to help greatly lower the risk of contracting HIV through sex or by using injection drugs.
  • Using post-exposure prophylaxis (PEP). PEP is a medication that can be used in emergencies to prevent contracting HIV. To be effective, it needs to be started within 72 hours of possible exposure.

There’s currently no cure or vaccine for HIV-1. However, it can be managed through the use of antiretroviral drugs.

When these medications are taken daily as prescribed, viral load can become undetectable. This helps prevent the virus from causing further damage to the immune system. It also prevents transmission of the virus to others through sex.

What about reports of ‘cured’ people?

Only two people, Timothy Brown and Adam Castillejo, have been completely cured of HIV.

During treatment for acute myeloid leukemia, Brown received a bone marrow transplant from a donor who had a genetic mutation that leads to HIV resistance.

After the transplant, doctors could no longer detect HIV in Brown’s body. The exact reason why is still unknown.

Castillejo also received a bone marrow transplant, but to treat lymphoma. Like in Brown’s case, the donor had a genetic mutation that leads to HIV resistance.

Reports of other “cured” people may actually refer to long-term nonprogressors (LTNPs). While progression to AIDS is still possible without antiretroviral drugs, LTNPs are able to maintain stable viral loads and CD4 cell counts for long periods of time.

About 5 to 15 percent of people living with HIV are LTNPs. LTNPs can also be broken down further based off their viral load:

  • Viremic controllers are people who maintain a viral load at very low, but still detectable, levels.
  • Elite controllers are people who maintain viral load at undetectable levels. Elite controllers are very rare. It’s estimated that they make up less than 1 percent of people living with HIV.

There have also been reports of HIV-1 control in people who have previously taken antiretroviral drugs. These people are called post-treatment controllers and are also rare.

Scientists are studying these people to learn more about how they control viral load. This is because this information could help inform the development of a cure.

There are some behaviors that can raise the risk of contracting HIV-1. These include:

  • engaging in vaginal or anal sex without a condom
  • having another STI, such as gonorrhea, syphilis, or herpes
  • working in a job where occupational exposure to HIV may occur
  • receiving an unsafe or unsterile blood transfusion, organ transplant, or medical procedure

Some populations also have an increased risk for contracting HIV. According to information from the CDC, these groups make up the largest amount of new HIV diagnoses:

Some people experience flu-like symptoms about 2 to 4 weeks after contracting HIV-1. These symptoms can include:

It’s important to note that not everyone who contracts HIV will have symptoms. Because of this, some people may not be aware that they’re living with HIV. In fact, it’s estimated that 1 in 7 people who have HIV don’t know it.

HIV-1 treatment involves the daily use of antiretroviral drugs. These drugs work to prevent the virus from infecting new cells and making more of itself. When this happens, a person’s viral load can be greatly reduced.

There are several types of antiretroviral drugs. Each one works to target the virus in a different way:

HIV treatment typically involves the use of three or more antiretroviral drugs. Some of these drugs will be from different drug types to both better inhibit the virus and to prevent drug resistance.

Taking antiretroviral drugs daily as directed can reduce viral load to undetectable levels in 6 months or less. When this happens, there’s no risk of transmitting the virus to a sexual partner. This is called undetectable = untransmissible (U=U).

The outlook for people living with HIV-1 has greatly improved from when the virus was first identified. Now, people living with HIV-1 can live long, healthy lives.

Access to antiretroviral drugs is key to this improved outlook. This is because receiving antiretroviral therapy can both prevent HIV-1 from further harming the immune system and prevent the transmission of the virus to others.

A 2020 cohort study looked at 39,000 adults living with HIV who were taking antiretroviral drugs. It found that, overall, the life expectancy of these adults was similar to that of people without HIV.

HIV-1 is one of the two types of HIV. Worldwide, most people who are living with HIV have HIV-1. The virus can be broken down further into different groups and subtypes.

A person can contract HIV-1 when bodily fluids containing the virus come into contact with their blood or mucous membranes. Common ways this can happen are during sex without a condom and through sharing injection drug equipment.

HIV-1 infects immune cells called CD4 cells. When it’s not treated, the virus can gradually damage the immune system. The late stages of HIV-1 are characterized by low CD4 cell counts and opportunistic infections.

Various tests are available to help detect HIV-1. While there’s no cure for HIV-1, receiving prompt antiretroviral therapy can reduce the virus to undetectable levels and prevent damage to the immune system.

Read this article in Spanish.