What Is Human Immunodeficiency Virus?

Human immunodeficiency virus (HIV) is the virus that causes HIV infection, which can develop into acquired immune deficiency syndrome (AIDS). Over time, HIV wears down the immune system by destroying the CD4 (T) cells that fight disease and infection. Ultimately, people infected with HIV can become very sick from opportunistic infections (viruses, bacteria, fungi and parasites that don’t usually affect healthy people).

There is currently no cure for HIV or AIDS, but there are medications that can make the immune system stronger and treat infections effectively. People who receive treatment can live full lives with HIV for many years.

Without treatment, people with HIV pass through three phases:

  • Stage 1–Acute HIV infection: In the first month after infection with HIV, some people may experience flu-like symptoms, as the body responds to the virus. They are very contagious at this point.
  • Stage 2–Clinical latency (HIV dormant): For a period of months or years, patients infected with HIV may be symptom-free. They can still infect others with the virus during this stage.
  • Stage 3–AIDS: Eventually, the immune system isn’t strong enough and a patient may get severe opportunistic illnesses. Without treatment, people with AIDS live an average of about three years.

It’s estimated that more than 1.1 million Americans have HIV, and about 15 percent of those people don’t know that they have the virus. Nearly 40,000 people are diagnosed with HIV in the United States each year, but the number has been declining over the last several years. Globally, nearly 40 million people have HIV, but that number continues to grow each year.