HIV
Human Immunodeficiency Virus is a lentivirus that causes acquired immunodeficiency syndrome. It was first identified in the United States in 1983, and no effective way to cure it has yet been found. It is estimated that in 2004 there were over 35.9 million to 44.3 million HIV-infected persons, and the number is increasing. The most seriously infected area is still Sub-Saharan Africa, followed by South Asia and Southeast Asia.