AIDS

Acquired Immune Deficiency Syndrome (usually referred to as AIDS) is a collection of diseases and symptoms caused by long-term infection with the Human Immunodeficiency Virus (HIV).

Definition

According to the CDC's 1993 guidelines, as follows: HIV infection plus any of the following:

• CD4 count less than 200 or
• CD4 percentage less than 14% of total lymphocytes or
• Any of the following illnesses: pulmonary TB, recurrent pneumonia, invasive cervical cancer.
• Expanded definition including 23 clinical conditions published elsewhere

The World Health Organization uses a different staging method for HIV disease.

History

The illness was first recognized in the early 1980s as gay men presented to their doctors with a rare lung disease called Pneumocystis carinii pneumonia (PCP). Early on, as researchers struggled to determine the cause of the disease, several names were used by researchers and the press, including "gay-related immunodeficiency" (GRID) and "gay cancer", referring to the classic symptom of Kaposi's sarcoma. The Centers for Disease Control noticed an increase in the requests for the drugs needed to treat this illness and launched an epidemiologic investigation. Although the first cases of the disease probably go back to the 1950s, the epidemic was not recognized until the early 1980s. The early epidemic occurred in two main branches; in the US and other developed countries, and in sub-Saharan Africa. In the US, the early epidemic was primarily spread by homosexual intercourse, intravenous drug use, and blood transfusions. In Africa, transmission was almost exclusively by heterosexual intercourse. Currently, most new infections worldwide are spread by heterosexual intercourse.

Natural history

After infection with HIV, the virus quickly replicates in lymphatic tissue and travels through the blood to infect most areas of the body. The largest consequence of this is the "hijacking" of certain immune cells, especially so-called T-Helper, or CD-4, cells. Early in the infection, the immune system holds the infection at bay, often causing "Acute Retroviral Syndrome", a flu-like illness. Patients often have swollen lymph nodes. After approximately 8-10 years of infection, the immune system begins to lose its battle. This is primarily seen in the loss of numbers of CD4 cells, however the changes are somewhat more complex. When the CD4 cell level drops low enough, AIDS becomes apparent. The first symptoms of the illness are generally night sweats, weight loss, and oral thrush.

Opportunistic infections (OIs)

The hallmark of AIDS is the appearance of opportunistic infections, meaning infections with organisms that do not usually cause human disease, unless given the right "opportunity". This opportunity is the reduction in cell-mediated immunity, first seen in patients with certain cancers or on anti-rejection drugs for organ transplantation. These infections include:

• Pneumocystis jiroveci, previously Pneumocystis carinii
• Candida albicans (the cause of thrush and vaginal yeast infections)
• Staphylococcus aureus (primarily causes skin infections)
• Toxoplasma gondii
• Cytomegalovirus
• Streptococcus pneumoniae (the primary cause of pneumonia in AIDS patients)
• Mycobacterium tuberculosis (TB)
• Mycobacterium avium complex (atypical mycobacterium)
• Cryptococcus neoformans (a cause of meningitis)
• Epstein Barr virus (leads to a type of lymphoma)
• Human herpesvirus-8 (causes Kaposi's sarcoma)

Origin

Scientists have identified a type of chimpanzee in West Africa as the source of HIV infection in humans. The virus most likely jumped to humans when humans hunted these chimpanzees for meat and came into contact with their infected blood. Over several years, the virus slowly spread across Africa and later into other parts of the world.

Transmission

HIV is a fragile virus. It cannot live for very long outside the human body. As a result, the virus is not transmitted through day-to-day activities such as shaking hands, hugging, or a casual kiss. Transmission can not occur from contact with toilet seats, drinking fountains, doorknobs, dishes, drinking glasses, food, pets, or insect bites.

HIV is primarily found in the blood, semen, or vaginal fluid of an infected person, and is transmitted in 3 main ways:

• Having unprotected sex (anal, vaginal, or oral) with someone infected with HIV
• Sharing needles and syringes with someone infected with HIV
• Being exposed (fetus or infant) to HIV before or during birth or through breast feeding

HIV also can be transmitted through blood infected with HIV. However, in developed countries, the risk for HIV infection through the transfusion of blood or blood products is extremely low, as supplies and/or donors are screened for infection. Currently, HIV/AIDS kills approximately 2-3 million people per year, primarily in developing countries. Currently in the U.S., there are approximately 500,000 people infected with HIV.

HIV is primarily spread by sexual contact and intravenous drug use. Most early infections in the US were via homosexual sex, and to a lesser extent via intravenous drug use and blood transfusions; most current infections in the world are via heterosexual contact and vertical transmission from mother to child. Mothers infected with HIV transmit the virus to their baby in utero, during childbirth. Mother-to-child transmission can be significantly reduced by the proper use of antiretroviral agents.

Less commonly, contact with infected blood causes HIV transmission. This can occur in health care providers (HCPs) or others exposed to infectious bodily fluids. Transmission is facilitated by breaks in the skin or direct contact with mucosal tissues, such as those found in the eyes, mouth, anus, or vagina. Early in the epidemic, blood transfusions were a significant source of HIV transmission.

Other less likely means of transmission exist, though are rare. There are no confirmed cases from contact with the saliva, sweat or tears of an infected person.

Early on in the epidemic, there was much confusion about the transmission of HIV. After decades of study, this has been clarified. HIV can be found in various body fluids, however its highest concentrations are found in semen, blood, and vaginal secretions. It can also be found in breast milk, but recent research shows that exclusive breastfeeding tends to protect against HIV transmission.

As summarized by the Centers for Disease Prevention and Control:

An exposure that might place HCP at risk for HIV infection is defined as a percutaneous injury (e.g., a needlestick or cut with a sharp object) or contact of mucous membrane or nonintact skin (e.g., exposed skin that is chapped, abraded, or afflicted with dermatitis) with blood, tissue, or other body fluids that are potentially infectious. In addition to blood and visibly bloody body fluids, semen and vaginal secretions also are considered potentially infectious. Although semen and vaginal secretions have been implicated in the sexual transmission of HIV, they have not been implicated in occupational transmission from patients to HCP.

Potentially infectious fluids

The risk for transmission of HIV infection from these fluids is unknown; the potential risk to HCP from occupational exposures has not been assessed by epidemiologic studies in health-care settings.

• cerebrospinal fluid
• synovial fluid
• pleural fluid
• peritoneal fluid
• pericardial fluid
• amniotic fluid.

Non-infectious fluids

The following fluids are not considered potentially infectious unless they are visibly bloody; the risk for transmission of HIV infection from these fluids and materials is low.

• feces
• nasal secretions
• saliva
• sputum
• sweat
• tears
• urine
• vomitus

Any direct contact (i.e., contact without barrier protection) to concentrated virus in a research laboratory or production facility requires clinical evaluation. For human bites, clinical evaluation must include the possibility that both the person bitten and the person who inflicted the bite were exposed to bloodborne pathogens. Transmission of HIV infection by this route has been reported rarely.

Data

Per-contact risk of HIV transmission:

URA with a known seropositive partner: 0.82 percent

URA with a partner of unknown serostatus, 0.27 percent (95% CI: 0.06, 0.49 percent)

Unprotected insertive anal sex: 0.06 percent.

Receptive oral sex: 0.04 percent.

(URA=unprotected anal-receptive sex) AIDSWEEKLY Plus; Monday, August 9, 1999

"The overall, unadjusted probability of HIV-1 transmission per coital act is 0·0011 in this Ugandan population, and greater infectivity of predominant HIV-1 viral subtypes is unlikely to account for the explosive HIV-1 epidemic in sub-Saharan Africa. Transmission probability per act varies greatly with the HIV-1 viral load of the HIV-1-infected partner, which suggests that interventions to reduce viral load could reduce transmission.15,28 Younger age and genital ulceration also increased the probability of transmission per act." THE LANCET, Volume 357: Pages 1149-1153, 14 April 2001.

Symptoms

Many people who are infected with HIV do not have symptoms for many years. Someone can look and feel healthy but can still be infected. In fact, one quarter of the HIV-infected persons in the United States do not know that they are infected.

The following may be warning signs of advanced HIV infection:

• rapid weight loss
• dry cough
• recurring fever or profuse night sweats
• profound and unexplained fatigue
• swollen lymph glands in the armpits, groin, or neck
• diarrhea that lasts for more than a week
• white spots or unusual blemishes on the tongue, in the mouth, or in the throat
• pneumonia
• red, brown, pink, or purplish blotches on or under the skin or inside the mouth, nose, or eyelids
• memory loss, depression, and other neurological disorders

However, each of these symptoms can be related to other illnesses. The only way to determine whether a person's infection status is by testing for HIV infection.

HIV testing

Once HIV enters the body, the body starts to produce antibodies — substances the immune system creates after infection. Most HIV tests look for these antibodies rather than the virus itself. There are many different kinds of HIV tests, including rapid tests and home test kits.

Source

http://www.cdc.gov/hiv/topics/basic/index.htm#aids

See also Demography, mortality