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Last Updated: Mar 1, 2019


The human immunodeficiency virus (HIV) is a virus that infects humans and can lead to an advanced disease state called acquired immunodeficiency syndrome (AIDS). There are two types of the HIV virus: HIV-1 and HIV-2. HIV-1 is more virulent and the dominant strain seen globally.

HIV is transmitted through bodily fluids (e.g. semen, blood and breast milk) via activities like sexual intercourse, needle injection and breastfeeding. What makes this virus unique is its ability to evade the body’s natural defense system by hiding in immune cells called CD4+ T cells. In fact, HIV effectively hijacks these immune cells and uses them to replicate before destroying them.

AIDS occurs in the final stage of HIV infection, when so many immune cells are destroyed that the immune system can no longer fight disease. Although HIV and AIDS are often used interchangeably, it is important to know they refer to the virus and the late-stage disease, respectively.

The earliest case of HIV in the United States dates back to mid- to late 1970s. According the Centers for Disease Control (CDC), over 1.2 million people in the United States are currently living with HIV, with 50,000 new infections expected each year. In the United States, men who have sex with men have the highest risk of contracting HIV.

Globally, the World Health Organization (WHO) estimates that roughly 35 million people are living with HIV/AIDS; of them, approximately 3.2 million are children under the age of 15. HIV/AIDS continues to be a global health problem with low-income countries in Sub-Saharan Africa being the most affected.

Without treatment, the life expectancy of an HIV-infected individual is 9-11 years. Following an AIDS diagnosis, that life expectancy is reduced to less than 2 years. The cause of death is generally due to complications from certain cancers (e.g. Kaposi’s sarcoma and lymphomas) and opportunistic infections (e.g. cytomegalovirus, tuberculosis, toxoplasmosis and cryptosporidiosis) that arise because of the body’s failing immune system.

There is no cure for HIV, but with proper treatment called “antiretroviral therapy” (ART), it is possible to maintain a low viral count and live a nearly normal life expectancy of up to 50 years. The best way to prevent HIV/AIDS is by avoiding high-risk activities associated with disease transmission, such as unsafe sexual intercourse and needle sharing.

HIV-1 virus budding

Causes and Risk Factors

HIV originated from a variant strain that infected non-human primates in Africa.  It is believed that contact with blood from an infected monkey transmitted the virus to humans, where it mutated to HIV. HIV is a retrovirus; its genomic content is stored in the form of RNA that is reverse transcribed into DNA once in the host cell. The primary targets of HIV are human immune cells, such as CD4+ T cells, macrophages and dendritic cells.

HIV is transmitted between individuals via bodily fluids, and primarily through sexual contact. The virus can transmit when infected bodily fluids (blood, semen, seminal fluid, rectal fluids and vaginal fluids) from one person make contact with broken tissue or the mucus membrane on another person. HIV-infected pregnant women can pass on the virus to their infant during childbirth, or through breast milk. HIV is not spread by air/water, tear/saliva/sweat, hand-shaking or cohabitation with an infected individual. Activities that allow contact with another person’s bodily fluids and increase the chances of contracting HIV include:

  • Sexual activity.  Unprotected anal, vaginal and oral sex with an infected partner allows HIV to pass from the blood, vaginal/rectal fluids or semen through sores or open skin. This risk is higher for those who have unprotected sex with multiple partners.
  • Needle sharing. Sharing needles and other devices used for intravenous drug delivery carries a high risk for transmitting HIV. Traces of blood in the syringe or device from one user can pass to other users.
  • Occupational hazards. Nurses, doctors and scientists who have frequent contact with human bodily fluids are considered high-risk. For example, an accidental needle prick while treating an infected patient can transmit HIV to the caregiver.
  • Mother-to-infant contact. Expectant mothers with HIV can infect their child during childbirth or afterwards through breast milk. Routine prenatal screening and timely therapy can significantly lower this risk.
  • Blood transfusions. Although blood banks screen donated blood for HIV and other diseases, there is a small risk of acquiring HIV during a blood transfusion.
  • Other STIs. Sexually transmitted infections (STIs) often leave open sores in or around the mouth or genital areas. Anyone with an STI is more likely to have open sores, making them more susceptible to other infections like HIV.
  • Race. In the United States, African Americans are most affected by HIV/AIDS and considered a high-risk group. This increased burden is due to insufficient awareness, socioeconomic factors, and stigma about HIV testing.
  • Age/gender. Gay, bisexual and other men who have sex with men - especially within the younger African American community - have the greatest risk of contracting HIV in the United States.

AIDS is caused by the gradual destruction of the immune system (CD4+ T cells) by HIV. The rate at which AIDS develops varies per person, but can happen faster without antiretroviral treatment. Without protection from the immune system, the body becomes a target for secondary infections, some cancers and other complications including kidney disease, neurological disorders and wasting syndrome.

Symptoms and Stages of Infection

Sometimes infection with HIV does not produce symptoms until the disease has progressed to AIDS; this could take 10 years for some people. Symptoms vary highly from one person to the next and depend on the stage of infection.

Early stage infection typically produces flu-like symptoms that appear within 2-4 weeks of infection. The body’s viral load (number of virus particles) is especially high at this stage, and therefore HIV testing for at-risk individuals is strongly recommended. Buying an STD home test even allows you to test from the convenience of home without waiting for anything but the speedy, discreet delivery of the kit.

Symptoms for early stage infection include:

  • Fever
  • Headaches
  • Muscle pain and fatigue
  • Sore throat
  • Swollen glands
  • Rash.

During the clinical latency stage the virus “hides” in the immune cells and is minimally active. Although symptoms tend to disappear and viral load is low during latency, it is still possible to transmit HIV. The latency stage may last up to ten years without treatment, or for many decades with treatment.

Once the infection progresses to AIDS, symptoms for secondary infections or other complications appear. These include:

  • Significant weight loss
  • Fever and night sweats
  • Extreme fatigue
  • Chronic diarrhea
  • Sores in the mouth or genital areas
  • Swelling of the lymph glands
  • Pneumonia
  • Red/brown/purple blotches on the skin
  • Neurological disorders (e.g. depression and memory loss).

Diagnosis and Treatment

HIV is routinely diagnosed by testing for HIV antibodies in blood or saliva. It may take 3-6 months for HIV antibodies to accumulate to detectable amounts, which is why it is critical to use protection during sex. Following a positive diagnosis, tests for CD4+ T cell count, viral load and drug resistance are performed to determine the optimal treatment regimen. Additional tests may be required to address secondary infections or complications, such as tuberculosis, hepatitis, other STIs and kidney damage.

There is no cure for HIV, so the goals of therapy are to prevent viral replication, keep the immune system functioning, and minimize adverse reactions. The timing and method of treatment is decided based on the patient’s test results (CD4 count, viral load and drug resistance) and other existing conditions. It is generally recommended to begin treatment as early as possible in order to maintain a low viral count and prevent progression to AIDS. A typical treatment consists of a drug cocktail with at least three pills (representing different classes of antiviral drugs) taken daily, for life. With antiretroviral treatment, viral numbers drop to undetectable levels, but the body still carries and can transmit the virus.

HIV drugs include:

  • Reverse transcriptase inhibitors. HIV uses its own reverse transcriptase enzyme to synthesize DNA from RNA. The function of this enzyme is required for viral replication in the host cell. Non-nucleoside reverse transcriptase inhibitors (NNRTIs) directly inhibit the activity of this enzyme. Nucleoside reverse transcriptase inhibitors (NRTIs) are faulty mimics of the building blocks used by the enzyme to synthesize DNA.
  • Protease inhibitors. HIV protease is another enzyme that is essential to the viral life cycle. Protease inhibitors are molecules that block the activity of this enzyme.
  • Integrase inhibitors. The integrase enzyme allows HIV to insert its genetic material into its host cells. Molecules that inhibit HIV integrase block this essential step.
  • Entry/fusion inhibitors. These drugs prevent the virus from attaching to and entering CD4+ T cells.
diagram of hiv virus


The most effective way to prevent HIV infection/transmission is by avoiding activities that allow exchange of bodily fluids with others. Anyone suspecting an infection should be tested for HIV. Following a positive HIV diagnosis, it is vital to contact existing and previous sexual partners who might have become infected.

  • Safe sex. Using a new, un-compromised condom during sex prevents the transmission of virus through open sores or open skin.
  • Occupational safety. Medical care providers and scientists who frequently treat patients or handle patient samples must use personal protection equipment and follow safety guidelines set by their respective institutions.
  • Needle exchange programs.  These programs provide sterile needles to those who inject drugs.
  • Prophylactics. This preventative option is available to at-risk groups who are not already infected with HIV. The combination drug Truvada was approved by the Food and Drug Administration in 2012 for preventing HIV infection; Truvada is also used to treat HIV.
  • Prenatal care. Pregnant women who have HIV must receive timely treatment in order to prevent infecting their baby.
  • Circumcision. There is some evidence suggesting that male circumcision lowers the risk of acquiring HIV in men.


  • “HIV 101”. Centers for Disease Control and Prevention (CDC). Retrieved Dec 16, 2014.
  • “HIV/AIDS”. Mayo Clinic Foundation. Retrieved Dec 16, 2014.
  • “HIV/AIDS 101”., U.S. Department of Health & Human Services. Retrieved Dec 16, 2014.

Additional Resources

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Tina Shahian, PhD

Tina is a writer for Innerbody Research, where she has written a large body of informative guides about health conditions.


A communication specialist in life science and biotech subjects, Tina’s successful career is rooted in her ability to convey complex scientific topics to diverse audiences. Tina earned her PhD in Biochemistry from the University of California, San Francisco and her BS degree in Cell Biology from U.C. Davis. Tina Shahian’s Linkedin profile.


In her spare time, Tina enjoys drawing science-related cartoons.