Human immunodeficiency virus (HIV) invades human body immune system (helper T cells) thus compromising its protection against infections. Deterioration of body immune system causes acquired immunodeficiency disease syndrome (AIDS) in HIV infection. There are two types of human immunodeficiency virus: HIV type 1 and HIV type 2. HIV type 1 is extremely virulent as compared to HIV type 2 and it is responsible for most of the HIV infections world wide. Human immunodeficiency virus is classified under genus lentivirus, and family retroviridae. Genus lentivirus is one of the virus groups with a long incubation period (Warren 216). Structurally, human immunodeficiency virus is enveloped, single stranded and a positive sense RNA virus. Human immunodeficiency virus has RNA which is attached to nucleocapsid protein P7. It has several enzymes which include; reverse transcriptase, intergrase, proteases and ribonuclease. Its covering envelope is made up of phospholipids which contain proteins known as Env attached to it. Env proteins are composed of glycoprotein (gp) 120 and 41 which contribute to the virus virulence (Warren 193). The glycoprotein facilitates attachment and fusion of the virus to human cell membrane. Human immunodeficiency virus RNA genome has the following genes: gag, env, pol, tat, nef, vpr, rev, vif, and vpu (Warren 193). Gag, env and pol genes are important in forming new structural proteins while rev, nef, tat, vif, vpr and vpu control virus virulence, its replication and ability to cause infection. Vif prevents activities of APOBEC3G while vpr stops cell division. CD4 T helper cells, and major histocompatibility class I and II are controlled by nef proteins. Vpu determines the release of newly assembled viruses in to blood circulation from the infected cells. The ability of LTR to switch regulates production of new viruses. Additionally, proteins of host cell or HIV genome can initiate production of new viruses in the body (Warren 221). Human immunodeficiency virus infects human body macrophages, helper T cells and microglial cells. This occurs after the glycoprotein molecules on the human immunodeficiency virus particle have interacted with the macrophages and CD4 cells through CCR5 and CXCR4 chemokine receptors (Jay141). There are various ways in which human immunodeficiency virus is transmitted. They include: transmission through blood transfusion. HIV can be passed from donor’s blood to receiver’s blood if donor is not properly screened to detect the infection. Use of blood contaminated equipments like injection needles and blood giving sets during blood transfusion transmit HIV infection. Mother to child transmission is another way in which human immunodeficiency virus is transmitted. This occurs during delivery or breastfeeding. Newborn gets infected when HIV positive mother’s blood enters into the newborn circulation during delivery. To prevent these instances infected mothers are put on antiretroviral drugs during delivery. Additionally, it is recommended that HIV infected mother should deliver through cesarean section in order to minimize chances of infecting the newborn. Breast feeding of newborn by the HIV infected mothers transmit the infection to newborn. HIV infected mothers are advised not to breast feed their babies but alter