Scientists identified a type of chimpanzee in West Africa as the source of HIV infection in humans. They believe that the chimpanzee version of the immunodeficiency virus (called simian immunodeficiency virus, or SIV) most likely was transmitted to humans and mutated into HIV when humans hunted these chimpanzees for meat and came into contact with their infected blood. Studies show that HIV may have jumped from apes to humans as far back as the late 1800s. Over decades, the virus slowly spread across Africa and later into other parts of the world. We know that the virus has existed in the United States since at least the mid- to late 1970s.

HIV disease has a well-documented progression. Untreated, HIV is almost universally fatal because it eventually overwhelms the immune system—resulting in acquired immunodeficiency syndrome (AIDS). HIV treatment helps people at all stages of the disease, and treatment can slow or prevent progression from one stage to the next.

A person can transmit HIV to others during any of these stages:

Acute infection: Within 2 to 4 weeks after infection with HIV, you may feel sick with flu-like symptoms. This is called acute retroviral syndrome (ARS) or primary HIV infection, and it’s the body’s natural response to the HIV infection. (Not everyone develops ARS, however—and some people may have no symptoms.)

During this period of infection, large amounts of HIV are being produced in your body. The virus uses important immune system cells called CD4 cells to make copies of itself and destroys these cells in the process. Because of this, the CD4 count can fall quickly.

Your ability to spread HIV is highest during this stage because the amount of virus in the blood is very high.

Eventually, your immune response will begin to bring the amount of virus in your body back down to a stable level. At this point, your CD4 count will then begin to increase, but it may not return to pre-infection levels.

Clinical latency (inactivity or dormancy): This period is sometimes called asymptomatic HIV infection or chronic HIV infection. During this phase, HIV is still active, but reproduces at very low levels. You may not have any symptoms or get sick during this time. People who are on antiretroviral therapy (ART) may live with clinical latency for several decades. For people who are not on ART, this period can last up to a decade, but some may progress through this phase faster. It is important to remember that you are still able to transmit HIV to others during this phase even if you are treated with ART, although ART greatly reduces the risk. Toward the middle and end of this period, your viral load begins to rise and your CD4 cell count begins to drop. As this happens, you may begin to have symptoms of HIV infection as your immune system becomes too weak to protect you.

AIDS (acquired immunodeficiency syndrome): This is the stage of infection that occurs when your immune system is badly damaged and you become vulnerable to infections and infection-related cancers called opportunistic illnesses. When the number of your CD4 cells falls below 200 cells per cubic millimeter of blood (200 cells/mm3), you are considered to have progressed to AIDS. (Normal CD4 counts are between 500 and 1,600 cells/mm3.) You can also be diagnosed with AIDS if you develop one or more opportunistic illnesses, regardless of your CD4 count. Without treatment, people who are diagnosed with AIDS typically survive about 3 years. Once someone has a dangerous opportunistic illness, life expectancy without treatment falls to about 1 year. People with AIDS need medical treatment to prevent death.

The only way to know if you are infected with HIV is to be tested. You cannot rely on symptoms to know whether you have HIV. Many people who are infected with HIV do not have any symptoms at all for 10 years or more. Some people who are infected with HIV report having flu-like symptoms (often described as “the worst flu ever”) 2 to 4 weeks after exposure. Symptoms can include:

Fever

Enlarged lymph nodes

Sore throat

Rash

These symptoms can last anywhere from a few days to several weeks. During this time, HIV infection may not show up on an HIV test, but people who have it are highly infectious and can spread the infection to others.

However, you should not assume you have HIV if you have any of these symptoms. Each of these symptoms can be caused by other illnesses. Again, the only way to determine whether you are infected is to be tested for HIV infection.

For most people, the answer is no. Most reports of a cure involve HIV-infected people who needed treatment for a cancer that would have killed them otherwise. But these treatments are very risky, even life-threatening, and are used only when the HIV-infected people would have died without them. Antiretroviral therapy (ART), however, can dramatically prolong the lives of many people infected with HIV and lower their chance of infecting others. It is important that people get tested for HIV and know that they are infected early so that medical care and treatment have the greatest effect.

Sharing your HIV status with certain family members and friends has both emotional and practical benefits. Emotionally, having trusted people to talk to can help you deal with the early stages of dealing with an HIV diagnosis. They can also support you with the longer-term issues of treatment adherence and disclosing to others. Practically, trusting people with this knowledge will allow them to speak for you in case of an emergency and to help you navigate the medical system. Don’t overlook the expertise of individuals you know. Many people have had these difficult conversations and they can help you work through what you will say. For example:

Friends or family members living with HIV can share with you how they told other people in their lives.

Your health care provider, social worker, or case manager can help you practice telling people and can share their experiences helping other patients share this information.

Join an HIV support group in your area and hear how others told people in their lives.

Some conversation starters to help you begin talking about your status with others include:

Revealing your HIV-positive status:

There’s something I want to tell you, I’ve been living with HIV since [xx year]. Have you ever known someone with HIV?

About a year ago, I found out that I’m HIV-positive. Since then, I’ve been taking HIV medication consistently and correctly. The virus is controlled and at undetectable levels, and I feel good.

I really like you, and like where this is going, but before we go any further, there’s something I want to tell you. I’m HIV-positive.

Get tested for HIV when you are planning a pregnancy or as soon as possible after you find out you are pregnant.

If you are HIV-negative but your partner has HIV, ask your health care provider about pre-exposure prophylaxis (PrEP), a daily pill that can prevent HIV during conception and pregnancy. Encourage your partner to get and stay on treatment with antiretroviral therapy, which greatly reduces the chance that he will pass HIV to you.

If you are HIV-positive, the right prevention steps can lower your risk of giving HIV to your baby from 20% (no prevention steps) to 2% (if you receive antiretroviral drugs during pregnancy, labor, and delivery; have your baby by cesarean, or C-section; and avoid breastfeeding). Newborn babies born to HIV-infected mothers are also given medicine to protect them.

You should be tested again in your third trimester if you engage in behaviors that put you at risk for HIV.

Of course, some women do not find out they are HIV-positive until they are already in labor. But if they receive antiretroviral drugs during labor and delivery and avoid breastfeeding, the chance of passing the infection to the baby can still be significantly decreased.

Avoid having your partner ejaculate in your mouth, and use barriers such as condoms, natural rubber latex sheets, dental dams, or cut-open non-lubricated condoms between your mouth and your partners’ genitals.

Oral sex involves giving or receiving oral stimulation to the penis (fellatio), the vagina (cunnilingus), or the anus (anilingus or rimming). Most types of oral sex carry little to no risk of HIV. Your highest oral sex risk is performing oral sex (fellatio) with ejaculation in your mouth. However, the risk is still low, and much lower than anal or vaginal sex. Factors that may increase the risk of transmitting HIV through oral sex are oral ulcers, bleeding gums, genital sores, and the presence of other sexually transmitted diseases (STDs) (which may or may not be visible).

The risk is lower if the partner with HIV is taking antiretroviral therapy (ART) consistently and correctly, and if the partner who is HIV-negative is taking pre-exposure prophylaxis (PrEP) consistently and correctly. Condoms and HIV medicines can greatly lower the risk of transmitting HIV.

Keep in mind that barrier methods are the only way to protect you from some STDs, including gonorrhea of the throat. And although the chance of getting or transmitting HIV from anilingus (rimming) is small, there is a big chance of transmitting hepatitis A and B, parasites, and other bacteria to the partner who is doing the rimming. There are effective vaccines that protect against hepatitis A and B and human papillomavirus infections. Talk to your health care provider to see if these are right for you, if you have not already been vaccinated.

Male circumcision reduces the risk that a man will get HIV from an infected female partner, and also lowers the risk of other sexually transmitted infections (STIs), penile cancer, and infant urinary tract infection. Studies have not consistently shown that it prevents HIV among men who have sex with men. Circumcision is only partly effective and should be used with other prevention measures. Men who are considering circumcision should weigh its risks and costs against its potential benefits.

No. There is currently no vaccine that will prevent HIV infection or treat those who have it.

No. Microbicides are gels, films, or suppositories that can kill or neutralize viruses and bacteria. Researchers are studying both vaginal and rectal microbicides to see if they can prevent sexual transmission of HIV, but none are currently available for use.

Yes. Post-exposure prophylaxis (PEP) is medicine that can prevent HIV after a possible exposure if started within 3 days.

An example of a possible exposure is if you have anal or vaginal sex without a condom with someone who is HIV-positive or whose HIV status you don’t know. You take PEP for 4 weeks if you may have been recently exposed to HIV and are not on PrEP. PEP keeps HIV from making copies of itself and turning into infection. To be effective, PEP must begin as soon as possible, but always within 72 hours (3 days) of a possible exposure. Keep in mind that PEP should only be used in situations right after a potential exposure. PEP is not intended for long-term use. It is not a substitute for other proven HIV prevention methods, such as correct and consistent condom use.

You should continue to use condoms with sex partners while taking PEP. If you have repeated exposures to HIV, you should consider PrEP.