Key findings
- There has been recent interest in both the scientific and popular media concerning subtypes of the human immunodeficiency virus (HIV). Since the first published sequence of HIV-1 in 1985, it has been recognised that extensive genetic variability of HIV-1 exists, both between and within individuals. This variation is most obvious in the envelope (env) gene of HIV-1, and analysis of the sequences that make up the env gene allows HIV-1 to be classified into multiple genetic subtypes (or clades).
- There are two subtype groups of HIV-1. Within the main group (M), which has been most extensively analysed, are subtypes A-H, while the outlier (O) group includes divergent sequences from Cameroon and France, which may differ among themselves as much as they do from the M group.
- Certain subtypes of HIV-1 appear to predominate in different geographical regions. For example, it is known that two subtypes predominate in Thailand; subtype E is the most common and has been isolated in people apparently infected by heterosexual contact, and subtype B occurs mainly among injecting drug users.
- There are a number of reasons why subtyping of HIV is important. Knowledge of circulating subtypes allows one to follow the movement of HIV or indicate the origin of HIV strains in communities, assisting the targeting of appropriate interventions.
- Knowledge of subtype variation is also necessary in the design of HIV vaccines and may have relevance to therapy if different pathogenic features of individual subtypes are identified.