HIV clades are distinct subgroups of HIV, broken up by geographical region. Within each clade, the virus has a number of genetic similarities and markers which can be used to learn more about the evolution of HIV. The fact that many of the clades are quite distinctive and very different from each other has some very serious implications for scientists working on HIV/AIDS vaccines. Unfortunately, it may not be possible to develop a vaccine to protect people from all HIV clades, or it may not be possible to vaccinate against certain clades.
This virus is infamous for mutating extremely rapidly, a source of great frustration to doctors and HIV researchers. Even as researchers first began studying the evolution of HIV, the virus was already mutating, developing new traits and displaying new behaviors in the body. As researchers learned more about the virus, however, they were able to start recognizing and identifying distinct HIV clades; “clade” is simply a fancy word for a taxonomic grouping.
By studying HIV clades, researchers have been able to track the evolution of the virus, in the hopes of learning more about where it came from, how it spread, and how it could potentially be treated. Learning about HIV clades was an important step in the research needed to identify the origins of the HIV epidemic, as it allowed researchers to start pinpointing the region of the virus' origin, which turned out to be Africa.
There are two basic groups of HIV clades: M or Main, and O or Outgroup. The main clades cause the bulk of HIV infections, while outgroup HIV clades are more unusual, responsible for fewer infections. Because O clades are rare, sometimes they can be used to trace a very specific pathway of infection, if researchers can track down and test a large number of people.
Among the M clades, there are eight different subtypings, lettered A through H, and each geographic region tends to have a dominant clade. Clades A and D, for example, are common in East Africa, making them among the oldest clades, while clade B appears in Europe and the Americas, with clade C cropping up in East Asia. Viruses in each clade respond differently to treatment, and they have differing levels of virulence, which explains why some people respond very well to HIV/AIDS drugs, while others struggle with a series of drug regimens.