《优选整合》人教版高中英语选修6 UNIT 3 A HEALTHY LIFE PERIOD 3 素材（4） .doc

1、AIDSAcquired immunodeficiency syndrome (AIDS)Classification and external resourcesThe Red ribbon is a symbol for solidarity with HIV-positive people and those living with AIDS.ICD-10B24.ICD-9042DiseasesDB5938MedlinePlus000594eMedicineemerg/253MeSHD000163List of abbreviations used in this articleAIDS

2、: Acquired immune deficiency syndromeHIV: Human immunodeficiency virusCD4+: CD4+ T helper cellsCCR5: Chemokine (C-C motif) receptor 5CDC: Centers for Disease Control and PreventionWHO: World Health OrganizationPCP: Pneumocystis pneumoniaTB: TuberculosisMTCT: Mother-to-child transmissionHAART: Highly

3、 active antiretroviral therapySTI/STD: Sexually transmitted infection/diseaseAcquired immune deficiency syndrome or acquired immunodeficiency syndrome (AIDS) is a disease of the human immune system caused by the human immunodeficiency virus (HIV).123This condition progressively reduces the effective

4、ness of the immune system and leaves individuals susceptible to opportunistic infections and tumors. HIV is transmitted through direct contact of a mucous membrane or the bloodstream with a bodily fluid containing HIV, such as blood, semen, vaginal fluid, preseminal fluid, and breast milk.45This tra

5、nsmission can involve anal, vaginal or oral sex, blood transfusion, contaminated hypodermic needles, exchange between mother and baby during pregnancy, childbirth, or breastfeeding, or other exposure to one of the above bodily fluids.AIDS is now a pandemic.6 In 2007, it was estimated that 33.2millio

6、n people lived with the disease worldwide, and that AIDS had killed an estimated 2.1million people, including 330,000 children.7 Over three-quarters of these deaths occurred in sub-Saharan Africa,7 retarding economic growth and destroying human capital.8Genetic research indicates that HIV originated

7、 in west-central Africa during the late nineteenth or early twentieth century.910 AIDS was first recognized by the U.S. Centers for Disease Control and Prevention in 1981 and its cause, HIV, identified in the early 1980s.11Although treatments for AIDS and HIV can slow the course of the disease, ther

8、e is currently no vaccine or cure. Antiretroviral treatment reduces both the mortality and the morbidity of HIV infection, but these drugs are expensive and routine access to antiretroviral medication is not available in all countries.12 Due to the difficulty in treating HIV infection, preventing in

9、fection is a key aim in controlling the AIDS epidemic, with health organizations promoting safe sex and needle-exchange programmes in attempts to slow the spread of the virus.SymptomsA generalized graph of the relationship between HIV copies (viral load) and CD4 counts over the average course of unt

10、reated HIV infection; any particular individuals disease course may vary considerably. CD4+ T Lymphocyte count (cells/mm) HIV RNA copies per mL of plasmaThe symptoms of AIDS are primarily the result of conditions that do not normally develop in individuals with healthy immune systems. Most of these

11、conditions are infections caused by bacteria, viruses, fungi and parasites that are normally controlled by the elements of the immune system that HIV damages.Opportunistic infections are common in people with AIDS.13 HIV affects nearly every organ system.People with AIDS also have an increased risk

12、of developing various cancers such as Kaposis sarcoma, cervical cancer and cancers of the immune system known as lymphomas. Additionally, people with AIDS often have systemic symptoms of infection like fevers, sweats (particularly at night), swollen glands, chills, weakness, and weight loss.1415 The

13、 specific opportunistic infections that AIDS patients develop depend in part on the prevalence of these infections in the geographic area in which the patient lives.Main symptoms of AIDS.Pulmonary infectionsX-ray of Pneumocystis pneumonia (PCP). There is increased white (opacity) in the lower lungs

14、on both sides, characteristic of PCPPneumocystis pneumonia (originally known as Pneumocystis carinii pneumonia, and still abbreviated as PCP, which now stands for Pneumocystis pneumonia) is relatively rare in healthy, immunocompetent people, but common among HIV-infected individuals. It is caused by

15、 Pneumocystis jirovecii.Before the advent of effective diagnosis, treatment and routine prophylaxis in Western countries, it was a common immediate cause of death. In developing countries, it is still one of the first indications of AIDS in untested individuals, although it does not generally occur

16、unless the CD4 count is less than 200 cells per L of blood.16Tuberculosis (TB) is unique among infections associated with HIV because it is transmissible to immunocompetent people via the respiratory route, is easily treatable once identified, may occur in early-stage HIV disease, and is preventable

17、 with drug therapy. However, multidrug resistance is a potentially serious problem.Even though its incidence has declined because of the use of directly observed therapy and other improved practices in Western countries, this is not the case in developing countries where HIV is most prevalent. In ea

18、rly-stage HIV infection (CD4 count 300 cells per L), TB typically presents as a pulmonary disease. In advanced HIV infection, TB often presents atypically with extrapulmonary (systemic) disease a common feature. Symptoms are usually constitutional and are not localized to one particular site, often

19、affecting bone marrow, bone, urinary and gastrointestinal tracts, liver, regional lymph nodes, and the central nervous system.17Gastrointestinal infectionsEsophagitis is an inflammation of the lining of the lower end of the esophagus (gullet or swallowing tube leading to the stomach). In HIV infecte

20、d individuals, this is normally due to fungal (candidiasis) or viral (herpes simplex-1 or cytomegalovirus) infections. In rare cases, it could be due to mycobacteria.18Unexplained chronic diarrhea in HIV infection is due to many possible causes, including common bacterial (Salmonella, Shigella, List

21、eria or Campylobacter) and parasitic infections; and uncommon opportunistic infections such as cryptosporidiosis, microsporidiosis, Mycobacterium avium complex (MAC) and viruses,19 astrovirus, adenovirus, rotavirus and cytomegalovirus, (the latter as a course of colitis).In some cases, diarrhea may

22、be a side effect of several drugs used to treat HIV, or it may simply accompany HIV infection, particularly during primary HIV infection. It may also be a side effect of antibiotics used to treat bacterial causes of diarrhea (common for Clostridium difficile). In the later stages of HIV infection, d

23、iarrhea is thought to be a reflection of changes in the way the intestinal tract absorbs nutrients, and may be an important component of HIV-related wasting.20Neurological and psychiatric involvementHIV infection may lead to a variety of neuropsychiatric sequelae, either by infection of the now susc

24、eptible nervous system by organisms, or as a direct consequence of the illness itself.Toxoplasmosis is a disease caused by the single-celled parasite called Toxoplasma gondii; it usually infects the brain, causing toxoplasma encephalitis, but it can also infect and cause disease in the eyes and lung

25、s.21 Cryptococcal meningitis is an infection of the meninx (the membrane covering the brain and spinal cord) by the fungus Cryptococcus neoformans. It can cause fevers, headache, fatigue, nausea, and vomiting. Patients may also develop seizures and confusion; left untreated, it can be lethal.Progres

26、sive multifocal leukoencephalopathy (PML) is a demyelinating disease, in which the gradual destruction of the myelin sheath covering the axons of nerve cells impairs the transmission of nerve impulses. It is caused by a virus called JC virus which occurs in 70% of the population in latent form, caus

27、ing disease only when the immune system has been severely weakened, as is the case for AIDS patients. It progresses rapidly, usually causing death within months of diagnosis.22AIDS dementia complex (ADC) is a metabolic encephalopathy induced by HIV infection and fueled by immune activation of HIV in

28、fected brain macrophages and microglia. These cells are productively infected by HIV and secrete neurotoxins of both host and viral origin.23 Specific neurological impairments are manifested by cognitive, behavioral, and motor abnormalities that occur after years of HIV infection and are associated

29、with low CD4+ T cell levels and high plasma viral loads.Prevalence is 1020% in Western countries24 but only 12% of HIV infections in India.2526 This difference is possibly due to the HIV subtype in India. AIDS related mania is sometimes seen in patients with advanced HIV illness; it presents with mo

30、re irritability and cognitive impairment and less euphoria than a manic episode associated with true bipolar disorder. Unlike the latter condition, it may have a more chronic course. This syndrome is less often seen with the advent of multi-drug therapy.Tumors and malignanciesKaposis sarcomaPatients

31、 with HIV infection have substantially increased incidence of several cancers. This is primarily due to co-infection with an oncogenic DNA virus, especially Epstein-Barr virus (EBV), Kaposis sarcoma-associated herpesvirus (KSHV), and human papillomavirus (HPV).2728Kaposis sarcoma (KS) is the most co

32、mmon tumor in HIV-infected patients. The appearance of this tumor in young homosexual men in 1981 was one of the first signals of the AIDS epidemic. Caused by a gammaherpes virus called Kaposis sarcoma-associated herpes virus (KSHV), it often appears as purplish nodules on the skin, but can affect o

33、ther organs, especially the mouth, gastrointestinal tract, and lungs.High-grade B cell lymphomas such as Burkitts lymphoma, Burkitts-like lymphoma, diffuse large B-cell lymphoma (DLBCL), and primary central nervous system lymphoma present more often in HIV-infected patients. These particular cancers

34、 often foreshadow a poor prognosis. In some cases these lymphomas are AIDS-defining. Epstein-Barr virus (EBV) or KSHV cause many of these lymphomas.Cervical cancer in HIV-infected women is considered AIDS-defining. It is caused by human papillomavirus (HPV).29In addition to the AIDS-defining tumors

35、listed above, HIV-infected patients are at increased risk of certain other tumors, such as Hodgkins disease and anal and rectal carcinomas. However, the incidence of many common tumors, such as breast cancer or colon cancer, does not increase in HIV-infected patients. In areas where HAART is extensi

36、vely used to treat AIDS, the incidence of many AIDS-related malignancies has decreased, but at the same time malignant cancers overall have become the most common cause of death of HIV-infected patients.30Other opportunistic infectionsAIDS patients often develop opportunistic infections that present

37、 with non-specific symptoms, especially low-grade fevers and weight loss. These include infection with Mycobacterium avium-intracellulare and cytomegalovirus (CMV). CMV can cause colitis, as described above, and CMV retinitis can cause blindness.Penicilliosis due to Penicillium marneffei is now the

38、third most common opportunistic infection (after extrapulmonary tuberculosis and cryptococcosis) in HIV-positive individuals within the endemic area of Southeast Asia.31CauseFor more details on this topic, see HIV.Scanning electron micrograph of HIV-1, colored green, budding from a cultured lymphocy

39、te.AIDS is the most severe acceleration of infection with HIV. HIV is a retrovirus that primarily infects vital organs of the human immune system such as CD4+ T cells (a subset of T cells), macrophages and dendritic cells. It directly and indirectly destroys CD4+ T cells.32Once HIV has killed so man

40、y CD4+ T cells that there are fewer than 200 of these cells per microliter (L) of blood, cellular immunity is lost. Acute HIV infection progresses over time to clinical latent HIV infection and then to early symptomatic HIV infection and later to AIDS, which is identified either on the basis of the

41、amount of CD4+ T cells remaining in the blood, and/or the presence of certain infections, as noted above.33In the absence of antiretroviral therapy, the median time of progression from HIV infection to AIDS is nine to ten years, and the median survival time after developing AIDS is only 9.2 months.3

42、4 However, the rate of clinical disease progression varies widely between individuals, from two weeks up to 20years.Many factors affect the rate of progression. These include factors that influence the bodys ability to defend against HIV such as the infected persons general immune function.3536 Olde

43、r people have weaker immune systems, and therefore have a greater risk of rapid disease progression than younger people.Poor access to health care and the existence of coexisting infections such as tuberculosis also may predispose people to faster disease progression.343738 The infected persons gene

44、tic inheritance plays an important role and some people are resistant to certain strains of HIV. An example of this is people with the homozygous CCR5-32 variation are resistant to infection with certain strains of HIV.39 HIV is genetically variable and exists as different strains, which cause diffe

45、rent rates of clinical disease progression.404142Sexual transmissionSexual transmission occurs with the contact between sexual secretions of one person with the rectal, genital or oral mucous membranes of another. Unprotected receptive sexual acts are riskier than unprotected insertive sexual acts,

46、and the risk for transmitting HIV through unprotected anal intercourse is greater than the risk from vaginal intercourse or oral sex.However, oral sex is not entirely safe, as HIV can be transmitted through both insertive and receptive oral sex.4344 Sexual assault greatly increases the risk of HIV t

47、ransmission as condoms are rarely employed and physical trauma to the vagina occurs frequently, facilitating the transmission of HIV.45Other sexually transmitted infections (STI) increase the risk of HIV transmission and infection, because they cause the disruption of the normal epithelial barrier b

48、y genital ulceration and/or microulceration; and by accumulation of pools of HIV-susceptible or HIV-infected cells (lymphocytes and macrophages) in semen and vaginal secretions. Epidemiological studies from sub-Saharan Africa, Europe and North America suggest that genital ulcers, such as those cause

49、d by syphilis and/or chancroid, increase the risk of becoming infected with HIV by about fourfold. There is also a significant although lesser increase in risk from STIs such as gonorrhea, chlamydia and trichomoniasis, which all cause local accumulations of lymphocytes and macrophages.46Transmission

50、 of HIV depends on the infectiousness of the index case and the susceptibility of the uninfected partner. Infectivity seems to vary during the course of illness and is not constant between individuals. An undetectable plasma viral load does not necessarily indicate a low viral load in the seminal li

51、quid or genital secretions.However, each 10-fold increase in the level of HIV in the blood is associated with an 81% increased rate of HIV transmission.4647 Women are more susceptible to HIV-1 infection due to hormonal changes, vaginal microbial ecology and physiology, and a higher prevalence of sex

52、ually transmitted diseases.4849People who have been infected with one strain of HIV can still be infected later on in their lives by other, more virulent strains.Infection is unlikely in a single encounter. High rates of infection have been linked to a pattern of overlapping long-term sexual relatio

53、nships. This allows the virus to quickly spread to multiple partners who in turn infect their partners. A pattern of serial monogamy or occasional casual encounters is associated with lower rates of infection.50HIV spreads readily through heterosexual sex in Africa, but less so elsewhere. One possib

54、ility being researched is that schistosomiasis, which affects up to 50 per cent of women in parts of Africa, damages the lining of the vagina.5152Exposure to blood-borne pathogensCDC poster from 1989 highlighting the threat of AIDS associated with drug useThis transmission route is particularly rele

55、vant to intravenous drug users, hemophiliacs and recipients of blood transfusions and blood products. Sharing and reusing syringes contaminated with HIV-infected blood represents a major risk for infection with HIV.Needle sharing is the cause of one third of all new HIV-infections in North America,

56、China, and Eastern Europe. The risk of being infected with HIV from a single prick with a needle that has been used on an HIV-infected person is thought to be about 1 in 150 (see table above). Post-exposure prophylaxis with anti-HIV drugs can further reduce this risk.53This route can also affect peo

57、ple who give and receive tattoos and piercings. Universal precautions are frequently not followed in both sub-Saharan Africa and much of Asia because of both a shortage of supplies and inadequate training.The WHO estimates that approximately 2.5% of all HIV infections in sub-Saharan Africa are trans

58、mitted through unsafe healthcare injections.54 Because of this, the United Nations General Assembly has urged the nations of the world to implement precautions to prevent HIV transmission by health workers.55The risk of transmitting HIV to blood transfusion recipients is extremely low in developed c

59、ountries where improved donor selection and HIV screening is performed. However, according to the WHO, the overwhelming majority of the worlds population does not have access to safe blood and between 5% and 10% of the worlds HIV infections come from transfusion of infected blood and blood products.

60、56Perinatal transmissionThe transmission of the virus from the mother to the child can occur in utero during the last weeks of pregnancy and at childbirth. In the absence of treatment, the transmission rate between a mother and her child during pregnancy, labor and delivery is 25%.However, when the

61、mother takes antiretroviral therapy and gives birth by caesarean section, the rate of transmission is just 1%.57 The risk of infection is influenced by the viral load of the mother at birth, with the higher the viral load, the higher the risk. Breastfeeding also increases the risk of transmission by

62、 about 4%.58MisconceptionsMain article: HIV and AIDS misconceptionsA number of misconceptions have arisen surrounding HIV/AIDS. Three of the most common are that AIDS can spread through casual contact, that sexual intercourse with a virgin will cure AIDS, and that HIV can infect only homosexual men

63、and drug users. Other misconceptions are that any act of anal intercourse between gay men can lead to AIDS infection, and that open discussion of homosexuality and HIV in schools will lead to increased rates of homosexuality and AIDS.59PathophysiologyThis section may require cleanup to meet Wikipedi

64、as quality standards. Please improve this section if you can. (April 2008)The pathophysiology of AIDS is complex, as is the case with all syndromes.60 Ultimately, HIV causes AIDS by depleting CD4+ T helper lymphocytes. This weakens the immune system and allows opportunistic infections. T lymphocytes

65、 are essential to the immune response and without them, the body cannot fight infections or kill cancerous cells. The mechanism of CD4+ T cell depletion differs in the acute and chronic phases.61During the acute phase, HIV-induced cell lysis and killing of infected cells by cytotoxic T cells account

66、s for CD4+ T cell depletion, although apoptosis may also be a factor. During the chronic phase, the consequences of generalized immune activation coupled with the gradual loss of the ability of the immune system to generate new T cells appear to account for the slow decline in CD4+ T cell numbers.Al

67、though the symptoms of immune deficiency characteristic of AIDS do not appear for years after a person is infected, the bulk of CD4+ T cell loss occurs during the first weeks of infection, especially in the intestinal mucosa, which harbors the majority of the lymphocytes found in the body.62 The rea

68、son for the preferential loss of mucosal CD4+ T cells is that a majority of mucosal CD4+ T cells express the CCR5 coreceptor, whereas a small fraction of CD4+ T cells in the bloodstream do so.63HIV seeks out and destroys CCR5 expressing CD4+ cells during acute infection. A vigorous immune response e

69、ventually controls the infection and initiates the clinically latent phase. However, CD4+ T cells in mucosal tissues remain depleted throughout the infection, although enough remain to initially ward off life-threatening infections.Continuous HIV replication results in a state of generalized immune

70、activation persisting throughout the chronic phase.64 Immune activation, which is reflected by the increased activation state of immune cells and release of proinflammatory cytokines, results from the activity of several HIV gene products and the immune response to ongoing HIV replication. Another c

71、ause is the breakdown of the immune surveillance system of the mucosal barrier caused by the depletion of mucosal CD4+ T cells during the acute phase of disease.65This results in the systemic exposure of the immune system to microbial components of the guts normal flora, which in a healthy person is

72、 kept in check by the mucosal immune system. The activation and proliferation of T cells that results from immune activation provides fresh targets for HIV infection. However, direct killing by HIV alone cannot account for the observed depletion of CD4+ T cells since only 0.01-0.10% of CD4+ T cells

73、in the blood are infected.A major cause of CD4+ T cell loss appears to result from their heightened susceptibility to apoptosis when the immune system remains activated. Although new T cells are continuously produced by the thymus to replace the ones lost, the regenerative capacity of the thymus is

74、slowly destroyed by direct infection of its thymocytes by HIV. Eventually, the minimal number of CD4+ T cells necessary to maintain a sufficient immune response is lost, leading to AIDSCells affectedThe virus, entering through which ever route, acts primarily on the following cells:66 Lymphoreticula

75、r system: o CD4+ T-Helper cells o Macrophages o Monocytes o B-lymphocytes Certain endothelial cells Central nervous system: o Microglia of the nervous system o Astrocytes o Oligodendrocytes o Neurones - indirectly by the action of cytokines and the gp-120 The effectThe virus has cytopathic effects b

76、ut how it does it is still not quite clear. It can remain inactive in these cells for long periods, though. This effect is hypothesized to be due to the CD4-gp120 interaction.66 The most prominent effect of the HIV virus is its T-helper cell suppression and lysis. The cell is simply killed off or de

77、ranged to the point of being function-less (they do not respond to foreign antigens). The infected B-cells can not produce enough antibodies either. Thus the immune system collapses leading to the familiar AIDS complications, like infections and neoplasms (vide supra). Infection of the cells of the

78、CNS cause acute aseptic meningitis, subacute encephalitis, vacuolar myelopathy and peripheral neuropathy. Later it leads to even AIDS dementia complex. The CD4-gp120 interaction (see above) is also permissive to other viruses like Cytomegalovirus, Hepatitis virus, Herpes simplex virus, etc. These vi

79、ruses lead to further cell damage i.e. cytopathy. Molecular basisFor details, see: Structure and genome of HIV HIV replication cycle HIV tropism DiagnosisThe diagnosis of AIDS in a person infected with HIV is based on the presence of certain signs or symptoms. Since June 5, 1981, many definitions ha

80、ve been developed for epidemiological surveillance such as the Bangui definition and the 1994 expanded World Health Organization AIDS case definition. However, clinical staging of patients was not an intended use for these systems as they are neither sensitive, nor specific. In developing countries,

81、 the World Health Organization staging system for HIV infection and disease, using clinical and laboratory data, is used and in developed countries, the Centers for Disease Control (CDC) Classification System is used.WHO disease staging systemMain article: WHO Disease Staging System for HIV Infectio

82、n and DiseaseIn 1990, the World Health Organization (WHO) grouped these infections and conditions together by introducing a staging system for patients infected with HIV-1.67 An update took place in September 2005. Most of these conditions are opportunistic infections that are easily treatable in he

83、althy people. Stage I: HIV infection is asymptomatic and not categorized as AIDS Stage II: includes minor mucocutaneous manifestations and recurrent upper respiratory tract infections Stage III: includes unexplained chronic diarrhea for longer than a month, severe bacterial infections and pulmonary

84、tuberculosis Stage IV: includes toxoplasmosis of the brain, candidiasis of the esophagus, trachea, bronchi or lungs and Kaposis sarcoma; these diseases are indicators of AIDS. CDC classification systemMain article: CDC Classification System for HIV InfectionThere are two main definitions for AIDS, b

85、oth produced by the Centers for Disease Control and Prevention (CDC). The older definition is to referring to AIDS using the diseases that were associated with it, for example, lymphadenopathy, the disease after which the discoverers of HIV originally named the virus.6869 In 1993, the CDC expanded t

86、heir definition of AIDS to include all HIV positive people with a CD4+ T cell count below 200 per L of blood or 14% of all lymphocytes.70 The majority of new AIDS cases in developed countries use either this definition or the pre-1993 CDC definition. The AIDS diagnosis still stands even if, after tr

87、eatment, the CD4+ T cell count rises to above 200 per L of blood or other AIDS-defining illnesses are cured.HIV testMain article: HIV testMany people are unaware that they are infected with HIV.71 Less than 1% of the sexually active urban population in Africa has been tested, and this proportion is

88、even lower in rural populations. Furthermore, only 0.5% of pregnant women attending urban health facilities are counseled, tested or receive their test results. Again, this proportion is even lower in rural health facilities.71 Therefore, donor blood and blood products used in medicine and medical r

89、esearch are screened for HIV.HIV tests are usually performed on venous blood. Many laboratories use fourth generation screening tests which detect anti-HIV antibody (IgG and IgM) and the HIV p24 antigen. The detection of HIV antibody or antigen in a patient previously known to be negative is evidenc

90、e of HIV infection. Individuals whose first specimen indicates evidence of HIV infection will have a repeat test on a second blood sample to confirm the results.The window period (the time between initial infection and the development of detectable antibodies against the infection) can vary since it

91、 can take 36months to seroconvert and to test positive. Detection of the virus using polymerase chain reaction (PCR) during the window period is possible, and evidence suggests that an infection may often be detected earlier than when using a fourth generation EIA screening test.Positive results obt

92、ained by PCR are confirmed by antibody tests.72 Routinely used HIV tests for infection in neonates, born to HIV-positive mothers, have no value because of the presence of maternal antibody to HIV in the childs blood. HIV infection can only be diagnosed by PCR, testing for HIV pro-viral DNA in the ch

93、ildrens lymphocytes.73PreventionEstimated per act risk for acquisitionof HIV by exposure route74Exposure RouteEstimated infectionsper 10,000 exposuresto an infected sourceBlood Transfusion9,00075Childbirth2,50057Needle-sharing injection drug use6776Percutaneous needle stick3077Receptive anal interco

94、urse*507879Insertive anal intercourse*6.57879Receptive penile-vaginal intercourse*10787980Insertive penile-vaginal intercourse*57879Receptive oral intercourse*179Insertive oral intercourse*0.579* assuming no condom use source refers to oral intercourseperformed on a manThe three main transmission ro

95、utes of HIV are sexual contact, exposure to infected body fluids or tissues, and from mother to fetus or child during perinatal period. It is possible to find HIV in the saliva, tears, and urine of infected individuals, but there are no recorded cases of infection by these secretions, and the risk o

96、f infection is negligible.81Sexual contactThe majority of HIV infections are acquired through unprotected sexual relations between partners, one of whom has HIV. The primary mode of HIV infection worldwide is through sexual contact between members of the opposite sex.828384During a sexual act, only

97、male or female condoms can reduce the chances of infection with HIV and other STDs and the chances of becoming pregnant. The best evidence to date indicates that typical condom use reduces the risk of heterosexual HIV transmission by approximately 80% over the long-term, though the benefit is likely

98、 to be higher if condoms are used correctly on every occasion.85The male latex condom, if used correctly without oil-based lubricants, is the single most effective available technology to reduce the sexual transmission of HIV and other sexually transmitted infections. Manufacturers recommend that oi

99、l-based lubricants such as petroleum jelly, butter, and lard not be used with latex condoms, because they dissolve the latex, making the condoms porous. If necessary, manufacturers recommend using water-based lubricants.Oil-based lubricants can however be used with polyurethane condoms.86The female

100、condom is an alternative to the male condom and is made from polyurethane, which allows it to be used in the presence of oil-based lubricants. They are larger than male condoms and have a stiffened ring-shaped opening, and are designed to be inserted into the vagina.The female condom contains an inn

101、er ring, which keeps the condom in place inside the vagina inserting the female condom requires squeezing this ring. However, at present availability of female condoms is very low and the price remains prohibitive for many women.Preliminary studies suggest that, where female condoms are available, o

102、verall protected sexual acts increase relative to unprotected sexual acts, making them an important HIV prevention strategy.87Studies on couples where one partner is infected show that with consistent condom use, HIV infection rates for the uninfected partner are below 1% per year.88 Prevention stra

103、tegies are well-known in developed countries, but epidemiological and behavioral studies in Europe and North America suggest that a substantial minority of young people continue to engage in high-risk practices despite HIV/AIDS knowledge, underestimating their own risk of becoming infected with HIV.

104、8990Randomized controlled trials have shown that male circumcision lowers the risk of HIV infection among heterosexual men by up to 60%.91 It is expected that this procedure will be actively promoted in many of the countries affected by HIV, although doing so will involve confronting a number of pra

105、ctical, cultural and attitudinal issues.Some experts fear that a lower perception of vulnerability among circumcised men may result in more sexual risk-taking behavior, thus negating its preventive effects.92 However, one randomized controlled trial indicated that adult male circumcision was not ass

106、ociated with increased HIV risk behavior.93Exposure to infected body fluidsHealth care workers can reduce exposure to HIV by employing precautions to reduce the risk of exposure to contaminated blood. These precautions include barriers such as gloves, masks, protective eyeware or shields, and gowns

107、or aprons which prevent exposure of the skin or mucous membranes to blood borne pathogens. Frequent and thorough washing of the skin immediately after being contaminated with blood or other bodily fluids can reduce the chance of infection. Finally, sharp objects like needles, scalpels and glass, are

108、 carefully disposed of to prevent needlestick injuries with contaminated items.94 Since intravenous drug use is an important factor in HIV transmission in developed countries, harm reduction strategies such as needle-exchange programmes are used in attempts to reduce the infections caused by drug ab

109、use.9596Mother-to-child transmission (MTCT)Current recommendations state that when replacement feeding is acceptable, feasible, affordable, sustainable and safe, HIV-infected mothers should avoid breast-feeding their infant. However, if this is not the case, exclusive breast-feeding is recommended d

110、uring the first months of life and discontinued as soon as possible.97 It should be noted that women may breastfeed other children who are not their own; see wetnurse.TreatmentSee also HIV Treatment and Antiretroviral drug. Abacavir a nucleoside analog reverse transcriptase inhibitor (NARTI or NRTI)

111、The chemical structure of AbacavirThere is currently no vaccine or cure for HIV or AIDS. The only known methods of prevention are based on avoiding exposure to the virus or, failing that, an antiretroviral treatment directly after a highly significant exposure, called post-exposure prophylaxis (PEP)

112、.98 PEP has a very demanding four week schedule of dosage. It also has very unpleasant side effects including diarrhea, malaise, nausea and fatigue.99Antiviral therapyCurrent treatment for HIV infection consists of highly active antiretroviral therapy, or HAART.100 This has been highly beneficial to

113、 many HIV-infected individuals since its introduction in 1996 when the protease inhibitor-based HAART initially became available.12 Current optimal HAART options consist of combinations (or cocktails) consisting of at least three drugs belonging to at least two types, or classes, of antiretroviral a

114、gents. Typical regimens consist of two nucleoside analogue reverse transcriptase inhibitors (NARTIs or NRTIs) plus either a protease inhibitor or a non-nucleoside reverse transcriptase inhibitor (NNRTI). Because HIV disease progression in children is more rapid than in adults, and laboratory paramet

115、ers are less predictive of risk for disease progression, particularly for young infants, treatment recommendations are more aggressive for children than for adults.101 In developed countries where HAART is available, doctors assess the viral load, rapidity in CD4 decline, and patient readiness while

116、 deciding when to recommend initiating treatment.102Standard goals of HAART include improvement in the patients quality of life, reduction in complications, and reduction of HIV viremia below the limit of detection, but it does not cure the patient of HIV nor does it prevent the return, once treatme

117、nt is stopped, of high blood levels of HIV, often HAART resistant.103104 Moreover, it would take more than the lifetime of an individual to be cleared of HIV infection using HAART.105 Despite this, many HIV-infected individuals have experienced remarkable improvements in their general health and qua

118、lity of life, which has led to the plummeting of HIV-associated morbidity and mortality.106107108 In the absence of HAART, progression from HIV infection to AIDS occurs at a median of between nine to ten years and the median survival time after developing AIDS is only 9.2months.34 HAART is thought t

119、o increase survival time by between 4 and 12years.109110For some patients, which can be more than fifty percent of patients, HAART achieves far less than optimal results, due to medication intolerance/side effects, prior ineffective antiretroviral therapy and infection with a drug-resistant strain o

120、f HIV. Non-adherence and non-persistence with therapy are the major reasons why some people do not benefit from HAART.111 The reasons for non-adherence and non-persistence are varied. Major psychosocial issues include poor access to medical care, inadequate social supports, psychiatric disease and d

121、rug abuse. HAART regimens can also be complex and thus hard to follow, with large numbers of pills taken frequently.112113114 Side effects can also deter people from persisting with HAART, these include lipodystrophy, dyslipidaemia, diarrhoea, insulin resistance, an increase in cardiovascular risks

122、and birth defects.115 Anti-retroviral drugs are expensive, and the majority of the worlds infected individuals do not have access to medications and treatments for HIV and AIDS.Experimental and proposed treatmentsIt has been postulated that only a vaccine can halt the pandemic because a vaccine woul

123、d possibly cost less, thus being affordable for developing countries, and would not require daily treatments. However, even after almost 30years of research, HIV-1 remains a difficult target for a vaccine.116Research to improve current treatments includes decreasing side effects of current drugs, fu

124、rther simplifying drug regimens to improve adherence, and determining the best sequence of regimens to manage drug resistance. A number of studies have shown that measures to prevent opportunistic infections can be beneficial when treating patients with HIV infection or AIDS. Vaccination against hep

125、atitis A and B is advised for patients who are not infected with these viruses and are at risk of becoming infected.117 Patients with substantial immunosuppression are also advised to receive prophylactic therapy for Pneumocystis jiroveci pneumonia (PCP), and many patients may benefit from prophylac

126、tic therapy for toxoplasmosis and Cryptococcus meningitis as well.99Researchers have discovered an abzyme that can destroy the protein gp120 CD4 binding site. This protein is common to all HIV variants as it is the attachment point for B lymphocytes and subsequent compromising of the immune system.1

127、18In Berlin, Germany, a 42-year-old leukemia patient infected with HIV for more than a decade was given an experimental transplant of bone marrow with cells that contained an unusual natural variant of the CCR5 cell-surface receptor. This CCR5-32 variant has been shown to make some cells from people

128、 who are born with it resistant to infection with some strains of HIV. Almost two years after the transplant, and even after the patient reportedly stopped taking antiretroviral medications, HIV has not been detected in the patients blood. 119Alternative medicineVarious forms of alternative medicine

129、 have been used to treat symptoms or alter the course of the disease.120 Current studies indicate that alternative medicine therapies have little effect on the mortality or morbidity of the disease, but may improve the quality of life of individuals with AIDS. The psychological benefits of these the

130、rapies are the most important use.120 Acupuncture has been used to alleviate some symptoms with no success and cannot cure the HIV infection.121 Several randomized clinical trials testing the effect of herbal medicines have shown that there is no evidence that these herbs have any effect on the prog

131、ression of the disease, but may instead produce serious side-effects.122Morbidity and mortality among HIV-infected adults with adequate dietary nutritional intake is unaffected by multivitamin supplementation. A large Tanzanian trial in immunologically- and nutritionally-compromised pregnant and lac

132、tating women showed a number of benefits to daily multivitamin supplementation for both mothers and children.123 Dietary intake of micronutrients at RDA levels by HIV-infected adults is recommended by the World Health Organization.124 There is some evidence that vitamin A supplementation in children

133、 reduces mortality and improves growth.123 Daily doses of selenium can suppress HIV viral burden with an associated improvement of the CD4 count. Selenium can be used as an adjunct therapy to standard antiviral treatments, but cannot itself reduce mortality and morbidity.125PrognosisWithout treatmen

134、t, the net median survival time after infection with HIV is estimated to be 9 to 11 years, depending on the HIV subtype,7 and the median survival rate after diagnosis of AIDS in resource-limited settings where treatment is not available ranges between 6 and 19 months, depending on the study.126 In a

135、reas where it is widely available, the development of HAART as effective therapy for HIV infection and AIDS reduced the death rate from this disease by 80%, and raised the life expectancy for a newly diagnosed HIV-infected person to about 20 years.127As new treatments continue to be developed and be

136、cause HIV continues to evolve resistance to treatments, estimates of survival time are likely to continue to change. Without antiretroviral therapy, death normally occurs within a year.34 Most patients die from opportunistic infections or malignancies associated with the progressive failure of the i

137、mmune system.128 The rate of clinical disease progression varies widely between individuals and has been shown to be affected by many factors such as host susceptibility and immune function353639 health care and co-infections,34128 as well as which particular strain of the virus is involved.41129130

138、EpidemiologyMain article: AIDS pandemicThis article may need to be updated. Please update this article to reflect recent events or newly available information, and remove this template when finished. Please see the talk page for more information.Estimated prevalence of HIV among young adults (15-49)

139、 per country at the end of 2005The AIDS pandemic can also be seen as several epidemics of separate subtypes; the major factors in its spread are sexual transmission and vertical transmission from mother to child at birth and through breast milk.6 Despite recent, improved access to antiretroviral tre

140、atment and care in many regions of the world, the AIDS pandemic claimed an estimated 2.1million (range 1.92.4million) lives in 2007 of which an estimated 330,000 were children under 15years.7 Globally, an estimated 33.2million people lived with HIV in 2007, including 2.5million children. An estimate

141、d 2.5 million (range 1.84.1million) people were newly infected in 2007, including 420,000 children.7Sub-Saharan Africa remains by far the worst affected region. In 2007 it contained an estimated 68% of all people living with AIDS and 76% of all AIDS deaths, with 1.7million new infections bringing th

142、e number of people living with HIV to 22.5million, and with 11.4million AIDS orphans living in the region. Unlike other regions, most people living with HIV in sub-Saharan Africa in 2007 (61%) were women. Adult prevalence in 2007 was an estimated 5.0%, and AIDS continued to be the single largest cau

143、se of mortality in this region.7 South Africa has the largest population of HIV patients in the world, followed by Nigeria and India.131 South & South East Asia are second worst affected; in 2007 this region contained an estimated 18% of all people living with AIDS, and an estimated 300,000 deaths f

144、rom AIDS.7 India has an estimated 2.5million infections and an estimated adult prevalence of 0.36%.7 Life expectancy has fallen dramatically in the worst-affected countries; for example, in 2006 it was estimated that it had dropped from 65 to 35 years in Botswana.6HistoryMain article: Origin of AIDS

145、AIDS was first reported June 5, 1981, when the U.S. Centers for Disease Control (CDC) recorded a cluster of Pneumocystis carinii pneumonia (now still classified as PCP but known to be caused by Pneumocystis jirovecii) in five homosexual men in Los Angeles.132 In the beginning, the CDC did not have a

146、n official name for the disease, often referring to it by way of the diseases that were associated with it, for example, lymphadenopathy, the disease after which the discoverers of HIV originally named the virus.6869 They also used Kaposis Sarcoma and Opportunistic Infections, the name by which a ta

147、sk force had been set up in 1981.133 In the general press, the term GRID, which stood for Gay-related immune deficiency, had been coined.134 The CDC, in search of a name, and looking at the infected communities coined “the 4H disease,” as it seemed to single out Haitians, homosexuals, hemophiliacs,

148、and heroin users.135 However, after determining that AIDS was not isolated to the homosexual community,133 the term GRID became misleading and AIDS was introduced at a meeting in July 1982.136 By September 1982 the CDC started using the name AIDS, and properly defined the illness.137A more controver

149、sial theory known as the OPV AIDS hypothesis suggests that the AIDS epidemic was inadvertently started in the late 1950s in the Belgian Congo by Hilary Koprowskis research into a poliomyelitis vaccine.138139 According to scientific consensus, this scenario is not supported by the available evidence.

150、140141142A recent study states that HIV probably moved from Africa to Haiti and then entered the United States around 1969.143Society and cultureStigmaRyan White became a poster child for HIV after being expelled from school because of his infection.AIDS stigma exists around the world in a variety o

151、f ways, including ostracism, rejection, discrimination and avoidance of HIV infected people; compulsory HIV testing without prior consent or protection of confidentiality; violence against HIV infected individuals or people who are perceived to be infected with HIV; and the quarantine of HIV infecte

152、d individuals.144 Stigma-related violence or the fear of violence prevents many people from seeking HIV testing, returning for their results, or securing treatment, possibly turning what could be a manageable chronic illness into a death sentence and perpetuating the spread of HIV.145AIDS stigma has

153、 been further divided into the following three categories: Instrumental AIDS stigmaa reflection of the fear and apprehension that are likely to be associated with any deadly and transmissible illness.146 Symbolic AIDS stigmathe use of HIV/AIDS to express attitudes toward the social groups or lifesty

154、les perceived to be associated with the disease.146 Courtesy AIDS stigmastigmatization of people connected to the issue of HIV/AIDS or HIV- positive people.147 Often, AIDS stigma is expressed in conjunction with one or more other stigmas, particularly those associated with homosexuality, bisexuality

155、, promiscuity, prostitution, and intravenous drug use.In many developed countries, there is an association between AIDS and homosexuality or bisexuality, and this association is correlated with higher levels of sexual prejudice such as anti-homosexual attitudes.148 There is also a perceived associat

156、ion between AIDS and all male-male sexual behavior, including sex between uninfected men.146Economic impactMain article: Economic impact of AIDSChanges in life expectancy in some hard-hit African countries. Botswana Zimbabwe Kenya South Africa UgandaHIV and AIDS affects economic growth by reducing t

157、he availability of human capital.8 Without proper nutrition, health care and medicine that is available in developed countries, large numbers of people suffer and die from AIDS-related complications. They will not only be unable to work, but will also require significant medical care. The forecast i

158、s that this will probably cause a collapse of economies and societies in countries with a significant AIDS population. In some heavily infected areas, the epidemic has left behind many orphans cared for by elderly grandparents.149The increased mortality in this region will result in a smaller skille

159、d population and labor force. This smaller labor force will be predominantly young people, with reduced knowledge and work experience leading to reduced productivity. An increase in workers time off to look after sick family members or for sick leave will also lower productivity. Increased mortality

160、 will also weaken the mechanisms that generate human capital and investment in people, through loss of income and the death of parents. By killing off mainly young adults, AIDS seriously weakens the taxable population, reducing the resources available for public expenditures such as education and he

161、alth services not related to AIDS resulting in increasing pressure for the states finances and slower growth of the economy. This results in a slower growth of the tax base, an effect that will be reinforced if there are growing expenditures on treating the sick, training (to replace sick workers),

162、sick pay and caring for AIDS orphans. This is especially true if the sharp increase in adult mortality shifts the responsibility and blame from the family to the government in caring for these orphans.149On the level of the household, AIDS results in both the loss of income and increased spending on

163、 healthcare by the household. The income effects of this lead to spending reduction as well as a substitution effect away from education and towards healthcare and funeral spending. A study in Cte dIvoire showed that households with an HIV/AIDS patient spent twice as much on medical expenses as othe

164、r households.150Religion and AIDSThe topic of religion and AIDS has become highly controversial in the past twenty years, primarily because many prominent religious leaders have publicly declared their opposition to the use of contraception, which scientists feel is currently the only means to stop

165、the epidemic. Other issues involve religious participation in global health care services and collaboration with secular organizations such as UNAIDS and the World Health Organization.AIDS denialismMain article: AIDS denialismA small number of activists question the connection between HIV and AIDS,1

166、51 the existence of HIV,152 or the validity of current treatment methods (even going so far as to claim that the drug therapy itself was the cause of AIDS deaths). Though these claims have been examined and thoroughly rejected by the scientific community,153 they continue to be promulgated through t

167、he Internet154 and have had a significant political impact. In South Africa, former President Thabo Mbekis embrace of AIDS denialism resulted in an ineffective governmental response to the AIDS epidemic that has been blamed for hundreds of thousands of AIDS-related deaths.155156Active pursuit of HIV

168、 infectionMain article: Bugchasing and giftgivingA subculture of homosexual men desire and actively pursue HIV infection by seeking partners who are HIV-positive and voluntarily having unprotected intercourse with them. In slang terms, those who seek infection are called bugchasers and those who inf

169、ect them are called giftgivers.157 This phenomenon should be distinguished from barebacking, which is the preference for unprotected intercourse without the active desire for HIV infection.The exact extent of practice remains largely unknown. Not all those who self-identify as part of this subcultur

170、e are actually intent on spreading HIV.158 Some bugchasers try to connect with giftgivers via the Internet.159 Other bugchasers organize and participate in bug parties or conversion parties, sex parties where HIV positive and negative men engage in unprotected sex, in hopes of acquiring HIV (getting the gift).