Human immunodeficiency virus (HIV) is a viral infection that weakens an infected person's immune system.
HIV is transmitted by contact or transfer of blood, semen, pre-ejaculate, and vaginal fluids, and can also be transmitted from an infected mother to her infant during pregnancy, childbirth, or through breast milk.
HIV infects immune system cells, such as macrophages, dendritic cells and helper T cells (specifically CD4+ cells). In the absence of effective treatment, the number of CD4+ cells decline, eventually leading to a loss of cell-mediated immunity, and the development of acquired immunodeficiency syndrome (AIDS).
There are two types of HIV. HIV-1 is the virus that was initially discovered. It is more virulent and infective than HIV-2 and is associated with most of the HIV infections around the world. HIV-2 is not transmitted as easily and is predominantly confined to infections in West Africa.
There is currently no cure for HIV, but daily medications can effectively control HIV, preventing the progression of the disease and the transmission to sexual partners.
Early symptoms of HIV can include flu-like symptoms (e.g. fever, chills, fatigue, sore throat) that can last a few days or several weeks. However, some people do not get sick in the early stages, so the only way to accurately diagnose HIV is with HIV testing.
The stages of HIV are stage 1: acute infection, stage 2: chronic infection, and stage 3: AIDS. During stage 1, people have lots of HIV in their blood and are very contagious (but many people are unaware that they are infected). Stage 2 tends to not be associated with any symptoms, but the virus is still present. At the end of stage 2, the amount of HIV in the blood increases a lot, more immune system cells are destroyed, and the infection moves into stage 3. Stage 2 is the most severe phase of HIV infection. By this point, the virus has badly damaged the immune system, increasing the likelihood of other severe illnesses, and without treatment, most people in stage 3 will usually only survive about three years.