HIV/AIDS

Epidemiology

HIV-1 has spread worldwide, infecting more than 36 million people by 2001. HIV-2, which seems to be less clinically severe and possibly less transmissible from person to person, has mainly been a public health problem for West African nations. Originally epidemic in African and urban settings, HIV and AIDS are now among the most common serious infections globally, including in the Americas and Eurasia and in rural settings. All ages, racial and ethnic groups, and persons of all sexual orientations have been infected.
Virology
HIVs are all members of the family known as retroviruses, so named because of their unique method of reproduction which uses the enzyme (protein catalyst) reverse transcriptase (RT) to incorporate its genetic material (RNA) into the DNA of the infected host's cells. HIV infects specific white blood cells of the host's immune system, known as T-helper lymphocytes (often referred to as CD4+ cells), and destroys them. Even though the immune system produces millions of new CD4+ cells every day, HIV destroys them just as rapidly. The genetic material of HIV has been sequenced, providing a database useful for research on vaccine and antiviral drug development. Many subtypes of HIV-1 have been characterized, but all are transmitted via the same routes and result in the same immunodeficiency.
Symptoms, Diagnosis, and Treatment
Persons initially infected with HIV may develop an "acute retroviral syndrome" characterized by fever, lymph node enlargement, and flu-like symptoms. If symptoms are present, they clear spontaneously, but all infected persons, both with and without symptoms, remain infected and infectious to others indefinitely. The incubation period is highly variable, averaging about a decade, but ranging from a few months or years to possibly longer than two decades. When sufficient damage to the immune system has been sustained, measured either by laboratory cell counts of the Thelper cells or by onset of opportunistic infections, the patient is said to have AIDS. Common manifestations of HIV infection include tiredness, lymph node enlargement, fever, weight loss, and yeast infections of the mouth and vagina.
HIV infection is diagnosed by laboratory detection of evidence of infection, usually identification of HIV-specific antibodies in a blood, oral fluid, or urine specimen. AIDS can be diagnosed in HIV-infected persons in several ways, based on either laboratory evidence of immunodeficiency (lowered levels of CD4+ cells), or clinically by onset of any one or more of a specific list of opportunistic diseases. Opportunistic diseases are those that occur only, or most severely, in patients whose immune systems are impaired. The most common opportunistic diseases in AIDS patients are Pneumocystis carinii pneumonia, Kaposi's sarcoma, toxoplasmosis of the brain, tuberculosis and other mycobacterial infections, and severe herpes, cytomegalo virus, and yeast infections.
As of 2001, all of the more than seventeen antiviral drugs used to treat HIV infection act by interfering with one of the enzymes that HIV needs to complete its life cycle. No treatments result in a cure for HIV infection. The antiviral drugs prevent HIV from growing and further damaging the host's immune system. Thus, the goal of treatment is to preserve the patient's health. Patients must take several antiviral drugs daily. Research on more and better antiviral drugs, and on methods to reconstitute the impaired immune system, is ongoing. A key part of treatment is the prevention of opportunistic infections with specific vaccines and antibiotics.
Prevention
Prevention of HIV infections is deceptively simple: Refrain from having sexual contact and from sharing drug-injecting paraphernalia with anyone who is infected. However, the rapid and continuing global spread of HIV, despite its well-known and severe clinical consequences, points out how difficult it is to change risky sexual and drug-taking behaviors. Many successful educational and social interventions have been demonstrated, but sustaining them in large populations for long periods requires extensive resources and a strong public health commitment. For example, latex condoms effectively prevent sexual transmission of HIV, but making them available and educating infected persons or their sex partners to use them correctly and consistently has been accomplished only with extraordinary efforts in a few nations or settings. Some prevention efforts are considered controversial or are opposed by religious or other groups who interpret prevention efforts to reflect an acceptance of behaviors they do not condone on moral grounds.
The research effort to develop a vaccine to prevent HIV infection has been intense, but the biologic obstacles to success are immense and unprecedented. Because HIV permanently infects cells of the immune system, infection of a single cell results in lifelong infection for the host. Thus, a completely effective vaccine would need to prevent even a single cell from becoming infected. No such vaccine exists for any infection, so HIV will require a new vaccine paradigm. Possible lines of research include stimulating the immune system to detect and eliminate HIV-infected cells, or genetically transforming the HIV in an infected person so as to render it nonvirulent.
Further information on HIV and AIDS is widely available in many user-friendly and scholarly formats. The Internet is a rich source of information, with sites sponsored by public health agencies, such as the Joint United Nations Programme on HIV/AIDS and the Centers for Disease Control and Prevention particularly recommended. Several texts, popular books, and scholarly journals have been devoted exclusively to AIDS public health issues and scientific research. The first of December has been designated World AIDS Day, and many governments, schools, and organizations sponsor community and educational events to coincide with that date each year.


Acquired immune deficiency syndrome or acquired immunodeficiency syndrome (AIDS or Aids) is a collection of symptoms and infections resulting from the specific damage to the immune system caused by the human immunodeficiency virus (HIV) in humans,[1] and similar viruses in other species (SIV, FIV, etc.). The late stage of the condition leaves individuals susceptible to opportunistic infections and tumors. Although treatments for AIDS and HIV exist to decelerate the virus' progression, there is currently no known cure. HIV, et al., are 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.[2][3] This transmission can come in the form of 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.

Most researchers believe that HIV originated in sub-Saharan Africa during the twentieth century;[4] it is now a pandemic, with an estimated 33.2 million people now living with the disease worldwide.[5] As of January 2006, the Joint United Nations Programme on HIV/AIDS (UNAIDS) and the World Health Organization (WHO) estimate that AIDS has killed more than 25 million people since it was first recognized on June 5, 1981, making it one of the most destructive epidemics in recorded history. In 2005 alone, AIDS claimed an estimated 2.4–3.3 million lives, of which more than 570,000 were children.[6] A third of these deaths are occurring in sub-Saharan Africa, retarding economic growth and destroying human capital. Antiretroviral treatment reduces both the mortality and the morbidity of HIV infection, but routine access to antiretroviral medication is not available in all countries.[7] HIV/AIDS stigma is more severe than that associated with other life-threatening conditions and extends beyond the disease itself to providers and even volunteers involved with the care of people living with HIV.
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.[8] CD4+ T cells are required for the proper functioning of the immune system. When HIV kills CD4+ T cells so that there are fewer than 200 CD4+ T cells per microliter (µL) of blood, cellular immunity is lost. In some countries, such as the United States, this leads to a diagnosis of AIDS. In other jurisdictions, such as in Canada, AIDS is only diagnosed when a person infected with HIV is diagnosed with one or more of several AIDS-related opportunistic infections or cancers[9][10][11]. 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 amount of CD4+ T cells in the blood, and/or the presence of certain infections, as noted above.

In 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.[12] However, the rate of clinical disease progression varies widely between individuals, from two weeks up to 20 years. Many factors affect the rate of progression. These include factors that influence the body's ability to defend against HIV such as the infected person's general immune function.[13][14] Older 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.[12][15][16] The infected person's genetic inheritance plays an important role and some people are resistant to certain strains of HIV. An example of this is people with the CCR5-Δ32 mutation are resistant to infection with certain strains of HIV.[17] HIV is genetically variable and exists as different strains, which cause different rates of clinical disease progression.[18][19][20] The use of highly active antiretroviral therapy prolongs both the median time of progression to AIDS and the median survival time.

The 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 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.[30] HIV affects nearly every organ system. People with AIDS also have an increased risk of developing various cancers such as Kaposi's 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.[31][32] After the diagnosis of AIDS is made, the current average survival time with antiretroviral therapy (as of 2005) is estimated to be more than 5 years,[33] but because new treatments continue to be developed and because 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.[12] Most patients die from opportunistic infections or malignancies associated with the progressive failure of the immune system.[34]

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 function[13][14][17] health care and co-infections,[12][34] as well as factors relating to the viral strain.[19][35][36] The 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.