HIV (human immunodeficiency virus) is the virus that causes AIDS. This virus may be passed from one person to another when infected blood, semen or vaginal secretions come in contact with an uninfected person’s broken skin or mucous membranes. In addition, infected pregnant women can pass HIV to their baby during pregnancy or delivery, as well as through breast-feeding. People with HIV infection may develop AIDS as a result of their infection.
The earliest known case of HIV-1 in a human was from a blood sample collected in 1959 from a man in Kinshasa, Democratic Republic of Congo. Genetic analysis of this blood sample suggested that HIV-1 may have stemmed from a single virus in the late 1940s or early 1950's.
AIDS stands for Acquired Immunodeficiency Syndrome. Acquired – means that the disease is not hereditary but develops after birth from contact with a disease causing agent (in this case, HIV).
Immunodeficiency – means that the disease is characterized by a weakening of the immune system.
Syndrome – refers to a group of symptoms that collectively indicate or characterize a disease. In the case of AIDS this can include the development of certain infections and/or cancers, as well as a decrease in the number of certain cells in a person’s immune system. A diagnosis of AIDS is made by a physician using specific clinical or laboratory standards.
AIDS is caused by infection with a virus called human immunodeficiency virus (HIV). This virus is passed from one person to another through blood-to-blood and sexual contact. In addition, infected pregnant women can pass HIV to their babies during pregnancy or delivery, as well as through breast feeding.
HIV destroys a certain kind of blood cell (CD4+ T cells) which is crucial to the normal function of the human immune system. In fact, loss of these cells in people with HIV is an extremely powerful predictor of the development of AIDS. Studies have revealed that most people infected with HIV carry the virus for years before enough damage is done to the immune system for AIDS to develop. However, sensitive tests have shown a strong connection between the amount of HIV in the blood and the decline in CD4+ T cells and the development of AIDS. Reducing the amount of virus in the body with anti- retroviral therapies can dramatically slow the destruction of a person’s immune system.
Prior to 1996, scientists estimated that about half the people with HIV would develop AIDS within 10 years after becoming infected. This time varied greatly from person to person and depended on many factors, including a person's health status and their health-related behaviours.
Since 1996, the introduction of powerful anti-retroviral therapies has dramatically changed the progression time between HIV infection and the development of AIDS. Because of these advances in drug therapies and other medical treatments, estimates of how many people will develop AIDS and how soon are being recalculated, revised or are currently under study.
Although the scientific evidence is overwhelming and compelling that HIV is the cause of AIDS, the disease process is still not completely understood. This incomplete understanding has led some persons to make statements that AIDS is not caused by an infectious agent or is caused by a virus that is not HIV. This is not only misleading, but may have dangerous consequences. Before the discovery of HIV, evidence from epidemiologic studies involving tracing of patients’ sex partners and cases occurring in persons receiving transfusions of blood or blood clotting products had clearly indicated that the underlying cause of the condition was an infectious agent. Infection with HIV has been the sole common factor shared by AIDS cases throughout the world among homosexuals transfusion recipients, persons with hemophilia, sex partners of infected persons, children born to infected women and occupationally exposed health care workers.
Scientists and medical authorities agree that HIV does not survive well outside the body, making the possibility of environmental transmission remote. HIV is found in varying concentrations or amounts in blood, semen, vaginal fluid, breast milk, saliva and tears. HIV concentrations used in laboratory studies are much higher than those actually found in blood or other specimens, drying of HIV- infected human blood or other body fluids reduces the theoretical risk of environmental transmission to that which has been observed - essentially zero.
Results from laboratory studies should not be used to assess specific personal risk of infection because (1) the amount of virus studied is not found in human specimens or elsewhere in nature and (2) no one has been identified as infected with HIV due to contact with an environmental surface. Additionally, HIV is unable to reproduce outside its living host (unlike many bacteria or fungi, which may do so under suitable conditions), except under laboratory conditions; therefore, it does not spread or maintain infectiousness outside its host.
The risk to healthcare workers being exposed to HIV is extremely low, especially if they follow universal healthcare precautions. Everyday casual contact does not expose anyone, including healthcare workers, to HIV. The main risk is through accidental injuries from needles and other sharp objects that may be contaminated with HIV. It has been estimated that the risk of infection from a needlestick injury is less than 1 percent.
The risk posed by a needlestick injury may be higher if it is a deep injury; if it is made with a hollow bore needle; if the source patient has a high viral load; or if the sharp instrument is visibly contaminated with blood.
Transmission of HIV in a healthcare setting is extremely rare. All health professionals are required to follow infection control procedures when caring for any patient. These procedures are called universal precautions for infection control. They are designed to protect both patients and healthcare professionals from the transmission of blood-borne diseases such as Hepatitis B and HIV.
Research suggests that the risk of HIV infection in this way is extremely small. A very small number of people - usually in a healthcare setting - have become infected with HIV as a result of blood splashes in the eye.
Blood in the mouth carries an even lower risk. The lining of the mouth is very protective, so the only way HIV could enter the bloodstream would be if the person had a cut, open sore or area of inflammation somewhere in their mouth or throat (if the blood was swallowed). Even then, the person would have to get a fairly significant quantity of fresh blood (i.e. an amount that can been clearly seen or tasted) directly into the region of the cut or sore for there to be a risk. HIV is diluted by saliva and easily killed by stomach acid once the blood is swallowed.