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1、AcquiredAcquired immuneimmune deficiencydeficiency syndromesyndrome or acquiredacquired immunodeficiencyimmunodeficiency syndromesyndrome (AIDSAIDS) is a disease of the human immune system caused by the human immunodeficiency virus (HIV).123 This condition progressively reduces the effectiveness of
2、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.45 This transmissi
3、on can involve anal, vaginal or oral sex, blood transfusion, contaminated hypodermic needles, exchange between mother and baby during pregnancy, childbirth, breastfeeding or other exposure to one of the above bodily fluids.AIDS is now a pandemic.6 In 2007, it was estimated that 33.2 million people l
4、ived with the disease worldwide, and that AIDS killed an estimated 2.1 million people, including 330,000 children.7 Over three-quarters of these deaths occurred in sub-Saharan Africa.7Genetic research indicates that HIV originated in west-central Africa during the late nineteenth or early twentieth
5、century.89 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.10Although treatments for AIDS and HIV can slow the course of the disease, there is currently no known cure or vaccine. Antiretroviral treatment reduc
6、es 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.11 Due to the difficulty in treating HIV infection, preventing infection is a key aim in controlling the AIDS pandemic, with healt
7、h organizations promoting safe sex and needle-exchange programmes in attempts to slow the spread of the virus.SymptomsThe symptoms of AIDS are primarily the result of conditions that do not normally develop in individuals with healthy immune systems. Most of these conditions are infections caused by
8、 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.12 These infections affect nearly every organ system.People with AIDS also have an increased risk of developing various c
9、ancers 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.1314 The specific opportunistic
10、 infections that AIDS patients develop depend in part on the prevalence of these infections in the geographic area in which the patient lives.PulmonaryPulmonary infectionsinfectionsPneumocystis pneumonia (originally known as Pneumocystis carinii pneumonia, and still abbreviated as PCP, which now sta
11、nds for P Pneumoc cystis p pneumonia) is relatively rare in healthy, immunocompetent people, but common among HIV-infected individuals. It is caused by Pneumocystis jirovecii.Before the advent of effective diagnosis, treatment and routine prophylaxis in Western countries, it was a common immediate c
12、ause of death. In developing countries, it is still one of the first indications of AIDS in untested individuals, although it does not generally occur unless the CD4 count is less than 200 cells per L of blood.15Tuberculosis (TB) is unique among infections associated with HIV because it is transmiss
13、ible to immunocompetent people via the respiratory route, is not easily treatable once identified,16 Multidrug resistance is a serious problem. Tuberculosis with HIV co- infection (TB/HIV) is a major world health problem according to the World Health Organization: in 2007, 456,000 deaths among incid
14、ent TB cases were HIV-positive, a third of all TB deaths and nearly a quarter of the estimated 2 million HIV deaths in that year.17Even 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 develop
15、ing countries where HIV is most prevalent. In early-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
16、are not localized to one particular site, often affecting bone marrow, bone, urinary and gastrointestinal tracts, liver, regional lymph nodes, and the central nervous system.18GastrointestinalGastrointestinal infectionsinfectionsEsophagitis is an inflammation of the lining of the lower end of the esophagus (gullet or swallowing tube leading to the stomach). In HIV infected individuals
