What are HIV and AIDS?
The human immunodeficiency virus (HIV) is the virus that causes AIDS. HIV attacks the immune system by destroying CD4 positive (CD4+) T cells, a type of white blood cell that is vital to fighting off infection. The destruction of these cells leaves people infected with HIV vulnerable to other infections, diseases and other complications.

The acquired immunodeficiency syndrome (AIDS) is the final stage of HIV infection. A person infected with HIV is diagnosed with AIDS when he or she has one or more opportunistic infections, such as pneumonia or tuberculosis, and has a dangerously low number of CD4+ T cells (less than 200 cells per cubic millimeter of blood).

How HIV Causes AIDS
HIV destroys CD4 positive (CD4+) T cells, which are white blood cells crucial to maintaining the function of the human immune system. As HIV attacks these cells, the person infected with the virus is less equipped to fight off infection and disease, ultimately resulting in the development of AIDS.

Most people who are infected with HIV can carry the virus for years before developing any serious symptoms. But over time, HIV levels increase in the blood while the number of CD4+ T cells decline. Antiretroviral medicines can help reduce the amount of virus in the body, preserve CD4+ T cells and dramatically slow the destruction of the immune system.

People who are not infected with HIV and generally are in good health have roughly 800 to 1,200 CD4+ T cells per cubic millimeter (mm3) of blood. Some people who have been diagnosed with AIDS have fewer than 50 CD4+ T cells in their entire body.
Learn More

• More on How HIV Causes AIDS

• The HIV-AIDS Connection

• The Evidence That HIV Causes AIDS

• The Relationship Between HIV and AIDS

• HIV/AIDS Connection Resources and Links

Symptoms

Early Symptoms
In the initial stages of HIV infection, most people will have very few, if any, symptoms. Within a month or two after infection, individuals may experience a flu-like illness, including:

• Fever

• Headache

• Tiredness

• Enlarged lymph nodes in the neck and groin area

These symptoms usually disappear within a week to a month and are often mistaken for another viral infection, such as influenza (flu). However, during this period people are highly infectious because HIV is present in large quantities in genital fluids and blood. Some people infected with HIV may experience more severe symptoms initially or a longer duration of clinical symptoms, while others may remain symptom-free for 10 years or more.

Later Symptoms
During the late stages of HIV infection, the virus severely weakens the immune system, and people infected with the virus may experience the following symptoms:

• Rapid weight loss

• Recurring fever or profuse night sweats

• Extreme and unexplained fatigue

• Prolonged swelling of the lymph glands in the armpits, groin or neck

• Diarrhea that lasts for more than a week

• Sores of the mouth, anus or genitals

• Pneumonia

• Red, brown, pink or purplish blotches on or under the skin or inside the mouth, nose or eyelids

•  Memory loss, depression and other neurological disorders.

Each of these symptoms can be related to other illnesses. The only way to determine if you are infected with HIV is to get tested.

Treatment of HIV Infection
In the early 1980s when the HIV/AIDS epidemic began, people with AIDS were not likely to live longer than a few years.

Today, there are 31 antiretroviral drugs (ARVs) approved by the U.S. Food and Drug Administration (FDA) to treat HIV infection. These treatments do not cure people of HIV or AIDS. Rather, they suppress the virus, even to undetectable levels, but they do not completely eliminate HIV from the body. By suppressing the amount of virus in the body, people infected with HIV can now lead longer and healthier lives. However, they can still transmit the virus and must continuously take antiretroviral drugs in order to maintain their health quality.