HIV/AIDS

HIV/AIDS Human immunodeficiency virus infection / acquired immunodeficiency syndrome (HIV/AIDS) is a disease of the human immune system caused by infection with human immunodeficiency virus (HIV).[1] During the initial infection, a person may experience a brief period of influenza-like illness. This is typically followed by a prolonged period without symptoms. As the illness progresses, it interferes more and more with the immune system, making the person much more likely to get infections, including opportunistic infections and tumors that do not usually affect people who have working immune systems. HIV is transmitted primarily via unprotected sexual intercourse (including anal and even oral sex), contaminated blood transfusions, hypodermic needles, and from mother to child during pregnancy, delivery, or breastfeeding.[2] Some bodily fluids, such as saliva and tears, do not transmit HIV.[3] Prevention of HIV infection, primarily through safe sex and needle-exchange programs, is a key strategy to control the spread of the disease. There is no cure or vaccine; however, antiretroviral treatment can slow the course of the disease and may lead to a near-normal life expectancy. While antiretroviral treatment reduces the risk of death and complications from the disease, these medications are expensive and may be associated with side effects. Genetic research indicates that HIV originated in west-central Africa during the early twentieth century.[4] AIDS was first recognized by the Centers for Disease Control and Prevention (CDC) in 1981 and its cause—HIV infection—was identified in the early part of the decade.[5] Since its discovery, AIDS has caused nearly 30 million deaths (as of 2009).[6] As of 2010, approximately 34 million people are living with HIV globally.[7] AIDS is considered a pandemic—a disease outbreak which is present over a large area and is actively spreading.[8] HIV/AIDS has had a great impact on society, both as an illness and as a source of discrimination. The disease also has significant economic impacts. There are many misconceptions about HIV/AIDS such as the belief that it can be transmitted by casual non-sexual contact. The disease has also become subject to many controversies involving religion. Signs and symptoms Main article: Signs and symptoms of HIV/AIDS There are three main stages of HIV infection: acute infection, clinical latency and AIDS.[9][10] Acute infection A diagram of a human torso labelled with the most common symptoms of an acute HIV infection Main symptoms of acute HIV infection The initial period following the contraction of HIV is called acute HIV, primary HIV or acute retroviral syndrome.[9][11] Many individuals develop an influenza-like illness or a mononucleosis-like illness 2–4 weeks post exposure while others have no significant symptoms.[12][13] Symptoms occur in 40–90% of cases and most commonly include fever, large tender lymph nodes, throat inflammation, a rash, headache, and/or sores of the mouth and genitals.[11][13] The rash, which occurs in 20–50% of cases, presents itself on the trunk and is maculopapular, classically.[14] Some people also develop opportunistic infections at this stage.[11] Gastrointestinal symptoms such as nausea, vomiting or diarrhea may occur, as may neurological symptoms of peripheral neuropathy or Guillain-Barre syndrome.[13] The duration of the symptoms varies, but is usually one or two weeks.[13] Due to their nonspecific character, these symptoms are not often recognized as signs of HIV infection. Even cases that do get seen by a family doctor or a hospital are often misdiagnosed as one of the many common infectious diseases with overlapping symptoms. Thus, it is recommended that HIV be considered in patients presenting an unexplained fever who may have risk factors for the infection.[13] Clinical latency The initial symptoms are followed by a stage called clinical latency, asymptomatic HIV, or chronic HIV.[10] Without treatment, this second stage of the natural history of HIV infection can last from about three years[15] to over 20 years[16] (on average, about eight years).[17] 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.[10] 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.[9] 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 5 years.[13][18] These individuals are classified as HIV controllers or long-term nonprogressors (LTNP).[18] Another group is those who also maintain a low or undetectable viral load without anti-retroviral treatment who are known as "elite controllers" or "elite suppressors". They represent approximately 1 in 300 infected persons.[19] Acquired immunodeficiency syndrome A diagram of a human torso labelled with the most common symptoms of AIDS Main symptoms of AIDS. Acquired immunodeficiency syndrome (AIDS) is defined in terms of either a CD4+ T cell count below 200 cells per µL or the occurrence of specific diseases in association with an HIV infection.[13] In the absence of specific treatment, around half of people infected with HIV develop AIDS within ten years.[13] 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.[13] Other common signs include recurring respiratory tract infections.[13] Opportunistic infections may be caused by bacteria, viruses, fungi and parasites that are normally controlled by the immune system.[20] Which infections occur partly depends on what organisms are common in the person's environment.[13] These infections may affect nearly every organ system.[21] 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.[14] Kaposi's sarcoma is the most common cancer occurring in 10 to 20% of people with HIV.[22] 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%.[22] Both these cancers are associated with human herpesvirus 8.[22] Cervical cancer occurs more frequently in those with AIDS due to its association with human papillomavirus (HPV).[22] Additionally, people with AIDS frequently have systemic symptoms such as prolonged fevers, sweats (particularly at night), swollen lymph nodes, chills, weakness, and weight loss.[23] Diarrhea is another common symptom present in about 90% of people with AIDS.[24] They can also be affected by diverse psychiatric and neurological symptoms independent of opportunistic infections and cancers.[25] Transmission Average per act risk of getting HIV by exposure route to an infected source Exposure route Chance of infection Blood transfusion 90% [26] Childbirth (to child) 25%[27] Needle-sharing injection drug use 0.67%[26] Percutaneous needle stick 0.30%[28] Receptive anal intercourse* 0.04–3.0%[29] Insertive anal intercourse* 0.03%[30] Receptive penile-vaginal intercourse* 0.05–0.30%[29][31] Insertive penile-vaginal intercourse* 0.01–0.38% [29][31] Receptive oral intercourse*§ 0–0.04% [29] Insertive oral intercourse*§ 0–0.005%[32] * assuming no condom use § source refers to oral intercourse performed on a man HIV is transmitted by three main routes: sexual contact, exposure to infected body fluids or tissues, and from mother to child during pregnancy, delivery, or breastfeeding (known as vertical transmission).[2] 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.[28] It is possible to be co-infected by more than one strain of HIV—a condition known as HIV superinfection.[33] Sexual The most frequent mode of transmission of HIV is through sexual contact with an infected person.[2] The majority of all transmissions worldwide occur through heterosexual contacts (i.e. sexual contacts between people of the opposite sex);[2] however, the pattern of transmission varies significantly among countries. In the United States, as of 2009, most sexual transmission occurred in men who had sex with men,[2] with this population accounting for 64% of all new cases.[34] As regards 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.[35] 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.[35] The risk of transmission from anal intercourse is especially high, estimated as 1.4–1.7% per act in both heterosexual and homosexual contacts.[35][36] While the risk of transmission from oral sex is relatively low, it is still present.[37] The risk from receiving oral sex has been described as "nearly nil"[38] however a few cases have been reported.[39] The per-act risk is estimated at 0–0.04% for receptive oral intercourse.[40] In settings involving prostitution in low income countries, risk of female-to-male transmission has been estimated as 2.4% per act and male-to-female transmission as 0.05% per act.[35] Risk of transmission increases in the presence of many sexually transmitted infections[41] and genital ulcers.[35] Genital ulcers appear to increase the risk approximately fivefold.[35] Other sexually transmitted infections, such as gonorrhea, chlamydia, trichomoniasis, and bacterial vaginosis, are associated with somewhat smaller increases in risk of transmission.[40] The viral load of an infected person is an important risk factor in both sexual and mother-to-child transmission.[42] During the first 2.5 months of an HIV infection a person's infectiousness is twelve times higher due to this high viral load.[40] If the person is in the late stages of infection, rates of transmission are approximately eightfold greater.[35] Commercial sex workers (including those in pornography) have an increased rate of HIV.[43][44] Rough sex can be a factor associated with an increased risk of transmission.[45] Sexual assault is also believed to carry an increased risk of HIV transmission as condoms are rarely worn, physical trauma to the vagina or rectum is likely, and there may be a greater risk of concurrent sexually transmitted infections.