The human immunodeficiency virus (HIV)[9][10][11] is a retrovirus[12] that attacks the immune system. It can be managed with treatment. Without treatment it can lead to a spectrum of conditions including acquired immunodeficiency syndrome (AIDS).[5] Effective treatment for HIV-positive people (people living with HIV) involves a life-long regimen of medicine to suppress the virus, making the viral load undetectable. There is no vaccine or cure for HIV. An HIV-positive person on treatment can expect to live a normal life, and die with the virus, not of it.[5][6]
Treatment is recommended as soon as the diagnosis is made.[13] An HIV-positive person who has an undetectable viral load as a result of long-term treatment has effectively no risk of transmitting HIV sexually.[14][15] Campaigns by UNAIDS and organizations around the world have communicated this as Undetectable = Untransmittable.[16] Without treatment the infection can interfere with the immune system, and eventually progress to AIDS, sometimes taking many years. Following initial infection an individual may not notice any symptoms, or may experience a brief period of influenza-like illness.[4] During this period the person may not know that they are HIV-positive, yet they will be able to pass on the virus. Typically, this period is followed by a prolonged incubation period with no symptoms.[5] Eventually the HIV infection increases the risk of developing other infections such as tuberculosis, as well as other opportunistic infections, and tumors which are rare in people who have normal immune function.[4] The late stage is often also associated with unintended weight loss.[5] Without treatment a person living with HIV can expect to live for 11 years.[7] Early testing can show if treatment is needed to stop this progression and to prevent infecting others.
HIV is spread primarily by unprotected sex (including anal and vaginal sex), contaminated hypodermic needles or blood transfusions, and from mother to child during pregnancy, delivery, or breastfeeding.[17] Some bodily fluids, such as saliva, sweat, and tears, do not transmit the virus.[18] Oral sex has little risk of transmitting the virus.[19] Ways to avoid catching HIV and preventing the spread include safe sex, treatment to prevent infection ("PrEP"), treatment to stop infection in someone who has been recently exposed ("PEP"),[4] treating those who are infected, and needle exchange programs. Disease in a baby can often be prevented by giving both the mother and child antiretroviral medication.[4]
Recognized worldwide in the early 1980s,[20] HIV/AIDS has had a large impact on society, both as an illness and as a source of discrimination.[21] The disease also has large economic impacts.[21] There are many misconceptions about HIV/AIDS, such as the belief that it can be transmitted by casual non-sexual contact.[22] The disease has become subject to many controversies involving religion, including the Catholic Church's position not to support condom use as prevention.[23] It has attracted international medical and political attention as well as large-scale funding since it was identified in the 1980s.[24]
HIV made the jump from other primates to humans in west-central Africa in the early-to-mid-20th century.[25] AIDS was first recognized by the U.S. Centers for Disease Control and Prevention (CDC) in 1981 and its cause—HIV infection—was identified in the early part of the decade.[20] Between the first time AIDS was readily identified through 2021, the disease is estimated to have caused at least 40 million deaths worldwide.[26] In 2021, there were 650,000 deaths and about 38 million people worldwide living with HIV.[8] An estimated 20.6 million of these people live in eastern and southern Africa.[27] HIV/AIDS is considered a pandemic—a disease outbreak which is present over a large area and is actively spreading.[28] The United States' National Institutes of Health (NIH) and the Gates Foundation have pledged $200 million focused on developing a global cure for AIDS.[29] While there is no cure or vaccine, antiretroviral treatment can slow the course of the disease and may lead to a near-normal life expectancy.[5][6]
There are three main stages of HIV infection: acute infection, clinical latency, and AIDS.[1][30]
The initial period following infection with HIV is called acute HIV, primary HIV or acute retroviral syndrome.[30][31] Many individuals develop an illness like influenza, mononucleosis or glandular fever 2–4 weeks after exposure while others have no significant symptoms.[32][33] Symptoms occur in 40–90% of cases and most commonly include fever, large tender lymph nodes, throat inflammation, a rash, headache, tiredness, and/or sores of the mouth and genitals.[31][33] The rash, which occurs in 20–50% of cases, presents itself on the trunk and is maculopapular, classically.[34] Some people also develop opportunistic infections at this stage.[31] Gastrointestinal symptoms, such as vomiting or diarrhea may occur.[33] Neurological symptoms of peripheral neuropathy or Guillain–Barré syndrome also occur.[33] The duration of the symptoms varies, but is usually one or two weeks.[33]
These symptoms are not often recognized as signs of HIV infection. Family doctors or hospitals can misdiagnose cases as one of the many common infectious diseases with similar symptoms. Someone with an unexplained fever who may have been recently exposed to HIV should consider testing to find out if they have been infected.[33]
The initial symptoms are followed by a stage called clinical latency, asymptomatic HIV, or chronic HIV.[1] Without treatment, this second stage of the natural history of HIV infection can last from about three years[35] to over 20 years[36] (on average, about eight years).[37] While typically there are few or no symptoms at first, near the end of this stage many people experience fever, weight loss, gastrointestinal problems and muscle pains.[1] Between 50% and 70% of people also develop persistent generalized lymphadenopathy, characterized by unexplained, non-painful enlargement of more than one group of lymph nodes (other than in the groin) for over three to six months.[30]
Although most HIV-1 infected individuals have a detectable viral load and in the absence of treatment will eventually progress to AIDS, a small proportion (about 5%) retain high levels of CD4+ T cells (T helper cells) without antiretroviral therapy for more than five years.[33][38] These individuals are classified as "HIV controllers" or long-term nonprogressors (LTNP).[38] Another group consists of those who maintain a low or undetectable viral load without anti-retroviral treatment, known as "elite controllers" or "elite suppressors". They represent approximately 1 in 300 infected persons.[39]
Acquired immunodeficiency syndrome (AIDS) is defined as an HIV infection with either a CD4+ T cell count below 200 cells per μL or the occurrence of specific diseases associated with HIV infection.[33] In the absence of specific treatment, around half of people infected with HIV develop AIDS within ten years.[33] The most common initial conditions that alert to the presence of AIDS are pneumocystis pneumonia (40%), cachexia in the form of HIV wasting syndrome (20%), and esophageal candidiasis.[33] Other common signs include recurrent respiratory tract infections.[33]
Opportunistic infections may be caused by bacteria, viruses, fungi, and parasites that are normally controlled by the immune system.[40] Which infections occur depends partly on what organisms are common in the person's environment.[33] These infections may affect nearly every organ system.[41]
People with AIDS have an increased risk of developing various viral-induced cancers, including Kaposi's sarcoma, Burkitt's lymphoma, primary central nervous system lymphoma, and cervical cancer.[34] Kaposi's sarcoma is the most common cancer, occurring in 10% to 20% of people with HIV.[42] The second-most common cancer is lymphoma, which is the cause of death of nearly 16% of people with AIDS and is the initial sign of AIDS in 3% to 4%.[42] Both these cancers are associated with human herpesvirus 8 (HHV-8).[42] Cervical cancer occurs more frequently in those with AIDS because of its association with human papillomavirus (HPV).[42] Conjunctival cancer (of the layer that lines the inner part of eyelids and the white part of the eye) is also more common in those with HIV.[43]
Additionally, people with AIDS frequently have systemic symptoms such as prolonged fevers, sweats (particularly at night), swollen lymph nodes, chills, weakness, and unintended weight loss.[44] Diarrhea is another common symptom, present in about 90% of people with AIDS.[45] They can also be affected by diverse psychiatric and neurological symptoms independent of opportunistic infections and cancers.[46]
HIV is spread by three main routes: sexual contact, significant exposure to infected body fluids or tissues, and from mother to child during pregnancy, delivery, or breastfeeding (known as vertical transmission).[17] There is no risk of acquiring HIV if exposed to feces, nasal secretions, saliva, sputum, sweat, tears, urine, or vomit unless these are contaminated with blood.[55] It is also possible to be co-infected by more than one strain of HIV—a condition known as HIV superinfection.[56]
The most frequent mode of transmission of HIV is through sexual contact with an infected person.[17] However, an HIV-positive person who has an undetectable viral load as a result of long-term treatment has effectively no risk of transmitting HIV sexually, known as Undetectable = Untransmittable.[14][15] The existence of functionally noncontagious HIV-positive people on antiretroviral therapy was controversially publicized in the 2008 Swiss Statement, and has since become accepted as medically sound.[57]
Globally, the most common mode of HIV transmission is via sexual contacts between people of the opposite sex;[17] however, the pattern of transmission varies among countries. As of 2017[update], most HIV transmission in the United States occurred among men who had sex with men (82% of new HIV diagnoses among males aged 13 and older and 70% of total new diagnoses).[58][59] In the US, gay and bisexual men aged 13 to 24 accounted for an estimated 92% of new HIV diagnoses among all men in their age group and 27% of new diagnoses among all gay and bisexual men.[60]
With regard to unprotected heterosexual contacts, estimates of the risk of HIV transmission per sexual act appear to be four to ten times higher in low-income countries than in high-income countries.[61] In low-income countries, the risk of female-to-male transmission is estimated as 0.38% per act, and of male-to-female transmission as 0.30% per act; the equivalent estimates for high-income countries are 0.04% per act for female-to-male transmission, and 0.08% per act for male-to-female transmission.[61] The risk of transmission from anal intercourse is especially high, estimated as 1.4–1.7% per act in both heterosexual and homosexual contacts.[61][62] While the risk of transmission from oral sex is relatively low, it is still present.[63] The risk from receiving oral sex has been described as "nearly nil";[64] however, a few cases have been reported.[65] The per-act risk is estimated at 0–0.04% for receptive oral intercourse.[66] In settings involving prostitution in low-income countries, risk of female-to-male transmission has been estimated as 2.4% per act, and of male-to-female transmission as 0.05% per act.[61]
Risk of transmission increases in the presence of many sexually transmitted infections[67] and genital ulcers.[61] Genital ulcers increase the risk approximately fivefold.[61] Other sexually transmitted infections, such as gonorrhea, chlamydia, trichomoniasis, and bacterial vaginosis, are associated with somewhat smaller increases in risk of transmission.[66]
The viral load of an infected person is an important risk factor in both sexual and mother-to-child transmission.[68] During the first 2.5 months of an HIV infection, a person's infectiousness is twelve times higher due to the high viral load associated with acute HIV.[66] If the person is in the late stages of infection, rates of transmission are approximately eightfold