The symptoms of HIV and AIDS vary, depending on the phase of infection.

Primary infection (Acute HIV)

Most people infected by HIV develop a flu-like illness within a month or two after the virus enters the body. This illness, known as primary or acute HIV infection, may last for a few weeks. Possible signs and symptoms include:

• Fever
• Headache
• Muscle aches and joint pain
• Rash
• Sore throat and painful mouth sores
• Swollen lymph glands, mainly on the neck

These symptoms can be so mild that you might not even notice them. However, the amount of virus in your bloodstream (viral load) is quite high at this time. As a result, the infection spreads more easily during primary infection than during the next stage.

Clinical latent infection (Chronic HIV)

In some people, persistent swelling of lymph nodes occurs during this stage. Otherwise, there are no specific signs and symptoms. HIV remains in the body and in infected white blood cells.

This stage of HIV infection generally lasts around 10 years if you're not receiving antiretroviral therapy. But sometimes, even with this treatment, it lasts for decades. Some people develop more severe disease much sooner.

Symptomatic HIV infection

As the virus continues to multiply and destroy your immune cells — the cells in your body that help fight off germs — you may develop mild infections or chronic signs and symptoms such as:

• Fever
• Fatigue
• Swollen lymph nodes — often one of the first signs of HIV infection
• Diarrhea
• Weight loss
• Oral yeast infection (thrush)
• Shingles (herpes zoster)

Progression to AIDS

Thanks to better antiviral treatments, most people with HIV in the U.S. today don't develop AIDS. Untreated, HIV typically turns into AIDS in about 10 years.

When AIDS occurs, your immune system has been severely damaged. You'll be more likely to develop opportunistic infections or opportunistic cancers — diseases that wouldn't usually trouble a person with a healthy immune system.

The signs and symptoms of some of these infections may include:

• Soaking night sweats
• Recurring fever
• Chronic diarrhea
• Persistent white spots or unusual lesions on your tongue or in your mouth
• Persistent, unexplained fatigue
• Weight loss
• Skin rashes or bumps

HIV is caused by a virus. It can spread through sexual contact or blood, or from mother to child during pregnancy, childbirth or breast-feeding.

How does HIV become AIDS?

HIV destroys CD4 T cells — white blood cells that play a large role in helping your body fight disease. The fewer CD4 T cells you have, the weaker your immune system becomes.

You can have an HIV infection for years before it turns into AIDS. AIDS is diagnosed when the CD4 T cell count falls below 200 or you have an AIDS-defining complication.

How HIV spreads

To become infected with HIV, infected blood, semen or vaginal secretions must enter your body. This can happen in several ways:

• By having sex. You may become infected if you have vaginal, anal or oral sex with an infected partner whose blood, semen or vaginal secretions enter your body. The virus can enter your body through mouth sores or small tears that sometimes develop in the rectum or vagina during sexual activity.
• From blood transfusions. In some cases, the virus may be transmitted through blood transfusions. American hospitals and blood banks now screen the blood supply for HIV antibodies, so this risk is very small.
• By sharing needles. Sharing contaminated intravenous drug paraphernalia (needles and syringes) puts you at high risk of HIV and other infectious diseases, such as hepatitis.
• During pregnancy or delivery or through breast-feeding. Infected mothers can pass the virus on to their babies. HIV-positive mothers who get treatment for the infection during pregnancy can significantly lower the risk to their babies.

How HIV doesn't spread

You can't become infected with HIV through ordinary contact. That means you can't catch HIV or AIDS by hugging, kissing, dancing or shaking hands with someone who has the infection.

HIV isn't spread through the air, water or insect bites.

When HIV/AIDS first appeared in the United States, it mainly affected men who had sex with men. However, now it's clear that HIV also spreads through heterosexual sex.

Anyone of any age, race, sex or sexual orientation can be infected. However, you're at greatest risk of HIV/AIDS if you:

• Have unprotected sex. Use a new latex or polyurethane condom every time you have sex. Anal sex is more risky than is vaginal sex. Your risk of HIV increases if you have multiple sexual partners.
• Have an STI. Many STIs produce open sores on your genitals. These sores act as doorways for HIV to enter your body.
• Use intravenous drugs. People who use intravenous drugs often share needles and syringes. This exposes them to droplets of other people's blood.
• Are an uncircumcised man. Studies suggest that lack of circumcision increases the risk of heterosexual transmission of HIV.

HIV infection weakens your immune system, making you much more likely to develop numerous infections and certain types of cancers.

Infections common to HIV/AIDS

• Tuberculosis (TB). In resource-limited nations, TB is the most common opportunistic infection associated with HIV. It's a leading cause of death among people with AIDS.
• Cytomegalovirus. This common herpes virus is transmitted in body fluids such as saliva, blood, urine, semen and breast milk. A healthy immune system inactivates the virus, and it remains dormant in your body. If your immune system weakens, the virus resurfaces — causing damage to your eyes, digestive tract, lungs or other organs.
• Candidiasis. Candidiasis is a common HIV-related infection. It causes inflammation and a thick, white coating on the mucous membranes of your mouth, tongue, esophagus or vagina.
• Cryptococcal meningitis. Meningitis is an inflammation of the membranes and fluid surrounding your brain and spinal cord (meninges). Cryptococcal meningitis is a common central nervous system infection associated with HIV, caused by a fungus found in soil.
• Toxoplasmosis. This potentially deadly infection is caused by Toxoplasma gondii, a parasite spread primarily by cats. Infected cats pass the parasites in their stools, which may then spread to other animals and humans. Seizures occur when it spreads to the brain.
• Cryptosporidiosis. This infection is caused by an intestinal parasite that's commonly found in animals. You get it when you eat or drink contaminated food or water. The parasite grows in your intestines and bile ducts, leading to severe, chronic diarrhea in people with AIDS.

Cancers common to HIV/AIDS

• Kaposi's sarcoma. A tumor of the blood vessel walls, this cancer is rare in people not infected with HIV, but common in HIV-positive people. It usually appears as pink, red or purple lesions on the skin and mouth. In people with darker skin, the lesions may look dark brown or black. Kaposi's sarcoma can also affect the internal organs, including the digestive tract and lungs.
• Lymphoma. This cancer starts in the white blood cells. The most common early sign is painless swelling of the lymph nodes in your neck, armpit or groin.

Other complications

• Wasting syndrome. Aggressive treatment approaches have reduced the number of cases of wasting syndrome, but it still affects many people with AIDS. It's defined as a loss of at least 10 percent of body weight, often accompanied by diarrhea, chronic weakness and fever.
• Neurological complications. Although AIDS doesn't appear to infect the nerve cells, it can cause neurological symptoms such as confusion, forgetfulness, depression, anxiety and difficulty walking. One of the most common neurological complications is AIDS dementia complex, which leads to behavioral changes and reduced mental functioning.
• Kidney disease. HIV-associated nephropathy (HIVAN) is an inflammation of the tiny filters in your kidneys that remove excess fluid and wastes from your blood and pass them to your urine. It most often affects blacks or Hispanics. Anyone with this complication should be started on antiretroviral therapy.