Human Immunodeficiency Syndrome (HIV) is a retrovirus that infects and destroys helper T cells of the immune system, causing the marked reduction in their numbers. Once the level of helper T cells drops low enough, the disease progresses from HIV to AIDS (acquired immunodeficiency syndrome). This stage is marked by:
HIV and AIDS are spread through:
Definition from MedlinePlus Meriam Webster: http://www.merriam-webster.com/medlineplus/HIV
Photo taken by Jon Rawlinson Source: http://www.flickr.com/photos/london/75148497/