Human Immunodeficiency Virus (HIV) is a retrovirus that infects the human cells and uses the metabolites provided by those cells to evolve and this eventually causes AIDS (Acquired Immune Deficiency Syndrome), a disease that progressively damages the body's defence mechanism leaving it unable to fight infections and other illnesses that take advantage of a weakened immune system.
When an individual is infected with HIV, the virus works by first replicating itself in the infected host cell and then proceeds to spread to other cells destroying the immune cells of the host and this will consequently lead to disease. This replication is a multi stage process that requires several factors and components such as presence of specific receptors on the cell surface that interact with the protein complexes in the viral envelope to aid fusion of the membranes and thereby releasing the contents of the virus into the host cell and replication begins. Every step is important to ensure the successful replication of HIV. During replication, the viral DNA (formed from transcription) uses enzyme integrase to move into the host cell nucleus and is incorporated into the genome, which will now make viral messenger RNA that travels to the cytoplasm where it is translated to proteins for that virus. These proteins are cleaved by enzyme protease into smaller core proteins, it is this step that ensures an effective virus. Once replication is complete, the virus leaves the cell, matures and is ready to infect other cells.
Although there are a few exceptional cases that take 2-3 years or thereabouts, it normally takes 8-10 years for AIDS to develop from HIV.
There are four stages of HIV progression to AIDS. In the first stage, the virus specifically attacks the CD4+T helper cells before spreading to other cell types. It is shielded from the immune system and remains dormant for a period of time, most patients in this phase will exhibit flu-like symptoms; the immune system fights back in the second stage increasing the CD4+T cell count and in some cases bringing them back to normal. In stage 3, despite the continual replication of the virus, the individual may be asymptomatic for a long period of time. The final stage is where the immune system can no longer defend the body as the CD4+T cells (the most important part of the immune system) are almost completely destroyed. This is because the virus has spread and infected all other cells and at this stage the individual is diagnosed with AIDS which eventually leads to death. To summarise, an individual infected with HIV is diagnosed with AIDS when he or she has one or more opportunistic infections(e.g. pneumonia, tuberculosis) and has less than 200 CD4+ T cells per cubic millimetre of blood.
HIV can only be contracted by direct contact with mucous membrane or bloodstream of an infected person. This happens either via anal, vaginal or oral sex, blood transfusion, contaminated hypodermic needles, exchange between mother and baby during pregnancy, breastfeeding or other exposure to bodily fluids (blood, semen, vaginal fluid, pre-seminal fluid, and breast milk). When this happens there are different classes of antiretroviral drugs such as protease/integrase inhibitors that are used as a form of treatment to reduce the virus and its effects, since it cannot be cured.
These antivirus drugs generally work to try to imitate nucleosides found in the body. For example, AZT (azidothymidine anti-AIDS drug) works in a similar way to deoxythymidine. Byventing rev imitating the nucleosides, the viral RNA cannot be copied into DNA by preventing reverse transcriptase. This is to try to prevent the virus multiplying inside the body. 
- ↑ Organic Chemistry, Clayden et al, 2nd Edition, (2012), Oxford University Press Inc, New York
- ↑ http://www.amfar.org/abouthiv/?gclid=CKC71diH658CFUYB4wodzCquXQ
- ↑ http://pathmicro.med.sc.edu/lecture/HIV3.htm
- ↑ http://rufusrajadurai.wetpaint.com/
- ↑ http://www3.niaid.nih.gov/topics/HIVAIDS/Understanding/Biology/clinicalCourse.htm