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Quick Facts

Human Immunodeficiency Virus (HIV) Infection and AIDS

By The Manual's Editorial Staff,

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What is the human immunodeficiency virus?

The human immunodeficiency virus (HIV) is a type of virus called a retrovirus. It causes AIDS (acquired immunodeficiency syndrome), which is life-threatening.

HIV is called an immunodeficiency virus because it weakens (causes deficiency) of your immune system. Your immune system helps defends you against infection and cancer.

HIV infection weakens your immune system because it kills certain types of white blood cells called CD4 lymphocytes. Without enough CD4 lymphocytes, you're more likely to get certain infections and cancers.

  • HIV infection weakens your body's defenses against certain infections and cancers

  • There's no cure for HIV, but HIV medicines make a big difference in slowing down the virus

  • Without treatment, HIV causes AIDS

  • Starting HIV medicines as soon as you can may help you avoid AIDS-related problems

  • People don’t die from HIV itself, but from complications of the infections and cancers they get

  • Practicing safe sex, not sharing needles, and not getting other people's blood on you help prevent HIV infection

What is AIDS?

AIDS is acquired immunodeficiency syndrome. Not everyone with HIV infection has AIDS. You have AIDS when you have HIV infection along with either:

  • A very low number of CD4 lymphocytes

  • Certain infections and cancers

There are many infections and cancers that define AIDS. Some common ones include:

People with AIDS often have severe weight loss—this is called "AIDS wasting."

What causes HIV infection?

When the HIV virus takes over a CD4 lymphocyte, it makes many copies of itself before killing the CD4 cell. Those copies then take over other CD4 lymphocytes, which make even more copies. This cycle continues until there are billions of HIV in your body.

You can be infected with HIV from contact with the body fluids of an infected person, especially:

  • Blood

  • Semen

  • Vaginal fluids

  • Breast milk

It’s rare to get infected from someone's tears, urine, or saliva. These fluids carry the virus but in smaller amounts.

  • You can get HIV by having unprotected sex with an infected person

  • You can get HIV by sharing needles with an infected person

  • Children can get HIV from infected mothers during pregnancy, childbirth, and breastfeeding

  • But you can’t get HIV by touching, holding, or being near someone with HIV

What are the symptoms of HIV?

Many people have no symptoms right away. Within 1 to 4 weeks after getting HIV, you may have symptoms like:

  • Fever

  • Rash

  • Lumps in your neck, under your arms, or in your groin—the lumps are swollen lymph nodes, tiny bean-shaped organs that help your body fight infection

  • Feeling weak and tired

These symptoms last 3 to 14 days. After these go away, you may have few or no symptoms for years.

Later on, if you aren't treated, your weakened immune system has trouble protecting you from infections. You'll have different symptoms depending on what infection you get. For example, with a lung infection, you may have a cough and trouble breathing. With an infection in your esophagus, you may have pain when you swallow. An infection in your intestines will cause diarrhea and weight loss.

How can doctors tell if I have HIV?

Doctors first do a simple screening test on your blood or saliva (spit). If the screening test shows signs of HIV, doctors do other blood tests to tell for sure.

If you have HIV infection, doctors measure the amount of HIV in your blood.

  • This amount is called the viral load

The viral load is an important number for you and your doctor. A high viral load is bad. It means there's a lot of virus in your body and your immune system is very weak. A low viral load is good. It usually means your treatment is working.

Doctors also regularly do blood tests to see how many CD4 cells you have.

  • This is called your CD4 count

A high CD4 count means your immune system is strong. A low CD4 count means your immune system is getting weaker. A low CD4 count may mean your drugs have stopped working or you aren't taking them. The drugs may stop working because the virus has developed resistance to them. When your CD4 count gets very low, you may have to take medicine to prevent infections.

Knowing you have HIV is important because getting treatment can help you live longer, be healthier, and not pass on the virus to other people.

How do doctors treat HIV?

Doctors can’t cure your HIV, but they can use HIV medicines, called antiretroviral drugs, to slow down the infection:

  • Antiretroviral drugs stop HIV from copying itself and lower the amount of HIV in your blood

  • You usually take 3 or more different HIV medicines because HIV medicines work best in groups

  • Often several medicines are put into one tablet, so you don't have to take as many pills

  • HIV medicines must be taken for life

  • If you stop taking the medicine, even for a short time, the HIV can come back

If you take your medicine exactly as the doctor prescribes, you can live a long time with HIV infection.

Doctors may give you other medicines to:

  • Prevent other infections, such as thrush and pneumonia

  • Help with side effects, such as weakness and weight loss

Make sure all of your doctors know which HIV medicines you’re taking before they give you any other medicines.

How can I prevent HIV?

You can prevent HIV by practicing safe sex and not sharing needles.

  • Use a latex condom during sex and use the condom correctly so it's less likely to leak or break

  • Don’t use petroleum jelly or another oil-based lube with condoms because it can weaken them

  • Get tested for HIV and ask your partner to get tested too before ever having any type of sex together

  • Don’t share needles or syringes with anyone

  • Wear latex gloves if you might come into contact with the blood or other body fluids of another person

  • If you're pregnant, get an HIV test so your doctor can start you on medicine to prevent your baby from getting infected

You can also take HIV medicines before being exposed to HIV. But the medicines are expensive and are usually only prescribed for people with a high risk of infection, such as people who have a partner with HIV.

If you already have HIV, you can prevent the spread of infection to other people by practicing safe sex and not sharing needles.

There isn't yet a vaccine to prevent HIV infection.

Where can I learn more about HIV?