Human Immunodeficiency Virus (HIV)
HIV, or human immunodeficiency virus, is the virus that causes AIDS. It attacks the immune system by destroying CD4 positive (CD4+) T cells that are vital to fighting off infection. HIV belongs to a class of viruses known as retroviruses. Within that class, HIV is in the lentivirus subgroup, the members of which are known for having a long time period between initial infection and the beginning of serious symptoms. This is why there are many people who are unaware of their HIV infection and can unknowingly spread the virus to others.
Early detection of HIV infection is critical in helping to minimize further transmission of the disease. The four main routes of infection are unsafe sex, contaminated needles, breast milk from an infected mother, and birth to an infected mother. Transmission through blood and blood products has largely been eliminated as a result of screening of blood donations.
According to the WHO, there were 33.4 million people that were HIV positive in 2008. In that year, 2 million people died and an additional 2.7 million became infected.