Human Immunodeficiency Virus is a bloodborne virus that is transmitted mainly via sexual intercourse. It can also be transmitted from mother to child during delivery or when the baby is breastfeeding, or by sharing of infected instruments such as needles.
Types of HIV
There are two main types of HIV that are distinct from each other;
These two viruses originated in the chimpanzee and sooty mangabey, respectively. It is likely that HIV-1 and HIV-2 infected humans as a result of these primates being hunted for food.
All these viruses belong to a family of viruses known as retroviruses of a genus Lentivitridae.
Differences between HIV-1 and HIV-2
There are clear diﬀerences between HIV-1 and HIV-2 in genomic structure and in the antibody and clinical response to infection.
HIV-1 is rapidly spreading around the world and is universally distributed, whereas HIV-2 is much less common and largely restricted to West Africa.
The two viruses are transmitted in the same way but HIV-2 seems less transmissible.
Where HIV-1 and HIV-2 coexist, HIV-1 infection is rapidly overtaking HIV-2 in prevalence.
Dual infections can occur and there is no evidence that one infection protects against the other.
Both viruses cause the same immune defects and are associated with a similar disease.
HIV-2 takes several years longer than HIV-1 to cause significant immunosuppression or death, and diseases such as Kaposi’s sarcoma do not usually occur in HIV-2 infected individuals.
The main importance of HIV-2 in areas where it is prevalent is to ensure that the kits used for blood tests can detect
Each of these two species has multiple subtypes.
Subtypes of HIV-1 tend to cause similar disease but its distribution varies worldwide.
Origin of HIV
HIV-1 is thought to have been transmitted to human beings from chimpanzees from a subspecies pan troglodytes troglodytes found in central Africa from a form known as the Simian Immunodeficiency Virus.
On the other hand, HIV-2 is thought to have been from sooty mangabey monkeys in West Africa.
According to genetic relatedness, there are 2 great lineages in HIV groups, M and N, and O and P
- Group M (Main)
- Group O (Outlier)
- Group N (Non-M/non O)
There is another subtype that has been discovered known as P.
About 90% of the infections worldwide from HIV-1 are of subtype M.
Group O subtype is endemic in Central and West Africa accounting for about 1-5% of the infections.
Group N and P are mainly confined to Cameroon.
Compared to HIV-1, HIV-2 has a slightly lower risk of transmission and tends to progress slower to AIDS.
Victims of HIV-2 usually have a lower viral load compared to HIV-1.
HIV-2 is rare in developed countries.
Subtypes of HIV-1
HIV-1 group M has been subdivided into subtypes A–L, where subtypes E and I are missing since they are circulating recombinant forms (CRF)
In HIV-1 Group M there are at least ten known subtypes.
- Subtype A is found in East and Central Africa.
- Subtype B in South America, South East Asia, West, and Central Europe, Australia, Middle East, and North Africa.
- Subtype C is found in Sub Saharan Africa, Brazil, and India.
- Subtype D is more common in the Middle East and North America.
- Subtype F in South and Southeast Asia.
- Subtype G in West and Central Africa.
- Subtype H, J, and K are found in Africa and the Middle East.
Read also about the newly discovered HIV subtype:
What are CRFs?
CRFs stands for Circulating Recombinant Forms of HIV. These forms are formed from different subtypes that combine their genetic material leading to the formation of a hybrid virus.
As retrovirus tries to enlarge its genetic repertoire it forms recombinants. When a cell gets infected by two genetically different HIV-1 viruses, the RT may use both RNA templates for the first strand synthesis. As a consequence, a recombinant virus is formed harboring parts of the genome of strain 1 and strain 2
Out of all these subtypes of HIV, subtype B is the most common in the united kingdom.
Subtypes of HIV Type 2
There are 8 known subtypes of HIV-2.
HIV-2 is divided into groups A–H, of which A and B are the most prevalent and perhaps the only pathogenic ones.