Overview of HIV/AIDS


For an explanation of terms used, please reference our Glossary of Terms.

HIV (human immunodeficiency virus) is a retrovirus that carries its genetic code in the form of RNA (ribonucleic acid). Retroviruses use RNA and the reverse transcriptase enzyme to create DNA (deoxyribonucleic acid) from the RNA template. The HIV virus invades a human cell and produces its viral DNA which is subsequently inserted into the genetic material (chromosomes) of the cell. This infection converts helper T cells (a type of white blood cell) from immunity producing cells into cells that produce and release HIV virus particles into the blood stream destroying the immune defense system of the individual.

Several AIDS-causing HIV-1 virus subtypes, or "clades", exist in different regions throughout the world. These subtypes are identified as subtype A, subtype B on through C, D, E, F, etc. The predominant subtype found in the European Union, North America, South America, Japan and Australia is B; whereas the predominant subtypes in Africa are A and C. In India, the subtype is C. Each subtype is at least 20% different in its genetic sequence from other subtypes. This difference may cause a vaccine, known to be effective against one subtype, unsuccessful against other subtypes.

HIV-1, even within subtypes, has a high rate of variation or mutation. In drug treatment programs, virus mutation can result in virus escape rendering drug therapy ineffective. Hence, multi-drug therapy is very important. If several drugs are active against virus replication, the virus must undergo multiple simultaneous mutations to escape… an action which is very unlikely. The same is true for immune responses. HIV-1 can escape simple immune responses. However, if an immune response is directed against multiple targets (epitopes), virus escape is much less frequent. Vaccination against more that one of the proteins found in HIV-1 virus maximizes the number of targets for the immune response and increases the chance HIV will not escape the vaccine-stimulated immune response, thus resulting in protection against clinical AIDS.


For an explanation of terms used, please reference our Glossary of Terms.

AIDS is the final, life threatening stage of infection with the virus known as HIV-1.

Infection with HIV-1 severely damages the immune system, the body's defense against disease. HIV-1 infects and gradually destroys T cells and macrophages, both white blood cells that play key roles in protecting humans against infectious disease caused by viruses, bacteria, fungi and other micro-organisms.

Opportunistic infections by organisms normally posing no problem for control by a healthy immune system, can ravage persons with immune systems damaged by HIV-1 infections. Destruction of the immune system occurs over years; the average onset of clinical disease recognized as AIDS occurs after 3-10 years of HIV-1 infection but can be earlier or later.

AIDS in humans was first identified in the U.S. in 1981, but researchers believe it was present in Central Africa as early as 1959. AIDS is most often transmitted sexually from one person to another but is also transmitted by blood via shared needles (drug users) and through pregnancy and childbirth. Heterosexual activity is the most frequent route of transmission worldwide. According to UNAIDS, over 33 million people are believed to be HIV-infected globally with 2.7 new infections annually.

Viral load is the best indicator of the speed with which an individual will progress to AIDS, as well as the frequency with which an individual will spread infection. An estimated 1% or fewer of those infected have low enough levels of the virus to preclude progression to disease and to not transmit the infection. These individuals are classified as long-term non-progressors.