There are two main subtypes of HIV, HIV 1 & 2. Both are similar in their basic gene arrangement, methods of transmission, intracellular replication pathway and both results in AIDS (1).
- HIV-1
- this causative agent of AIDS was originally identified as HTLV-3 in 1983. This is now termed HIV-1
- is the predominant serotype and accounts for around 95% of all infections worldwide
- can be classified into for subgroups
- M - ‘Main’, worldwide distribution
- O - ‘Other’, largely geographically limited to Central and West Africa
- N - non-M, non-O, small number of infections in West Africa
- P - several reported cases in individuals from West Africa
- HIV-2
- in 1985 a second serotype, known as HIV-2, was identified. It is more closely related to the Simian Immunodeficiency Virus (SIV) of macaques
- is found predominantly in Africa but is also seen in Asia, Southern Europe, Latin America and North America
- it is most extensive in Western African countries with Cape Verde, Côte d'Ivoire (Ivory Coast), Gambia, Mali, Mauritania, Nigeria, and Sierra Leone recording a prevalence of more than 1% in the general population (1)
- Ghana, Guinea, Liberia, Niger, São Tomé, Senegal, and Togo are few other West African countries with reported HIV – 2 infections
Compared with HIV-1, those with HIV-2
- are characterised by lower rates of sexual and perinatal transmission,
- has decreased CD4 cell killing
- has slower progression to AIDS and death
- has a relative geographical confinement (1)
- less infectious during the early stages of the infection
- infectiousness seems to increase as the disease progresses (but the duration of increased infectiousness is shorter than in HIV – 1) (1)
HIV – 2 infection is uncommon in children (2).
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