Subtypes of HIV
| Human immunodeficiency virus | |
|---|---|
 |
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| Phylogenetic Tree of the SIV and HIV viruses. | |
| Virus classification | |
| Group: | Group VI (ssRNA-RT) |
| Family: | Retroviridae |
| Genus: | Lentivirus |
| Species | |
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| International Statistical Classification of Diseases and Related Health Problems Codes | |
|---|---|
| Classification and external resources | |
| Specialty | infectious disease |
| ICD-10 | B20-B24 |
| ICD-9-CM | 042-044 |
One of the obstacles to treatment of the human immunodeficiency virus is its high genetic variability. HIV can be divided into two major types, HIV type 1 (HIV-1) and HIV type 2 (HIV-2). HIV-1 is related to viruses found in chimpanzees and gorillas living in western Africa, while HIV-2 viruses are related to viruses found in the endangered west African primate sooty mangabey. HIV-1 viruses may be further divided into groups. The HIV-1 group M viruses predominate and are responsible for the AIDS pandemic. Group M can be further subdivided into subtypes based on genetic sequence data. Some of the subtypes are known to be more virulent or are resistant to different medications. Likewise, HIV-2 viruses are thought to be less virulent and transmissible than HIV-1 M group viruses, although HIV-2 is known to cause AIDS.
HIV-1 is the most common and pathogenic strain of the virus. Scientists divide HIV-1 into a major group (Group M) and two or more minor groups, namely Group N, O and possibly a group P. Each group is believed to represent an independent transmission of SIV into humans (but subtypes within a group are not). A total of 39 ORFs are found in all six possible reading frames (RFs) of HIV-1 complete genome sequence, but only a few of them are functional.
With 'M' for "major", this is by far the most common type of HIV, with more than 90% of HIV/AIDS cases deriving from infection with HIV-1 group M. The M group is subdivided further into clades, called subtypes, that are also given a letter. There are also "circulating recombinant forms" or CRFs derived from recombination between viruses of different subtypes which are each given a number. CRF12_BF, for example, is a recombination between subtypes B and F.
These subtypes are sometimes further split into sub-subtypes such as A1 and A2 or F1 and F2. In 2015, the strain CRF19, a recombinant of subtype A, subtype D and subtype G, with a subtype D protease, was found to be strongly associated with rapid progression to AIDS in Cuba. This is not thought to be a complete or final list, and further types are likely to be found.
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