Human Immunodeficiency Virus is a retrovirus that causes AIDS. It comes under a subgroup lentivirus. HIV infests helper T cells, macrophages, and dendritic cells and ultimately decreses the CD4+ T cell count. As the infection of HIV proceeds, it compromises, more and more, the immune system. HIV can be transmitted in many ways, such as vaginal, oral sex, anal sex, blood transfusion, and contaminated hypodermic needles.