Subtypes of HIV
Encyclopedia
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 chimpanzee
s and gorilla
s living in western Africa, while HIV-2 viruses are related to viruses found in sooty mangabey
s. 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.
Group M
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. This is not thought to be a complete or final list, and further types are likely to be found.
Group N
The 'N' stands for "non-M, non-O". This group was discovered in 1998 and has only been seen in Cameroon
. As of 2006, only 10 Group N infections had been identified.
Group O
The O ("Outlier") group is not usually seen outside of West-central Africa. It is reportedly most common in Cameroon, where a 1997 survey found that about 2% of HIV-positive samples were from Group O. The group caused some concern because it could not be detected by early versions of the HIV-1 test kits. More advanced HIV tests have now been developed to detect both Group O and Group N.
Group P
In 2009, a newly-analyzed HIV sequence was reported to have greater similarity to a simian immunodeficiency virus recently discovered in wild gorillas (SIVgor) than to SIVs from chimpanzees (SIVcpz). The virus had been isolated from a Cameroon
ian woman residing in France who was diagnosed with HIV-1 infection in 2004. The scientists reporting this sequence placed it in a proposed Group P "pending the identification of further human cases".
was in 1987. Many test kits for HIV-1 will also detect HIV-2.
As of 2010, there are 8 known HIV-2 groups (A to H). Of these, only groups A and B are epidemic. Group A spread mainly in West Africa, but also to Angola
, Mozambique
, Brazil
, India
, and very limitedly to Europe or the US. Group B is mainly confined to West Africa.
HIV-2 is mostly related to simian immunodeficiency virus
endemic in sooty mangabey
s (Cercocebus atys atys) (SIVsmm), a monkey species inhabiting the forests of littoral West Africa. Phylogenetic analyses show that the viruses most closely related to the two strains of HIV-2 which spread considerably in humans (HIV-2 groups A and B) are the SIVsmm found in the sooty mangabeys of the Tai forest, in western Ivory Coast.
There are six additional known HIV-2 groups, each having been found in just one person. They all seem to derive from independent transmissions from sooty mangabey
s to humans. Groups C and D have been found in two people from Liberia
, groups E and F have been discovered in two people from Sierra Leone
, and groups G and H have been detected in two people from the Ivory Coast. These HIV-2 strains are probably dead end infections, and each of them is most closely related to SIVsmm strains from sooty mangabey
s living in the same country where the human infection was found.
.
Chimpanzee
Chimpanzee, sometimes colloquially chimp, is the common name for the two extant species of ape in the genus Pan. The Congo River forms the boundary between the native habitat of the two species:...
s and gorilla
Gorilla
Gorillas are the largest extant species of primates. They are ground-dwelling, predominantly herbivorous apes that inhabit the forests of central Africa. Gorillas are divided into two species and either four or five subspecies...
s living in western Africa, while HIV-2 viruses are related to viruses found in sooty mangabey
Sooty Mangabey
The sooty mangabey is an Old World monkey found in forests from Senegal east to Ghana. It is famous for being believed to be the monkey that HIV-2 might have originated in before jumping species...
s. 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
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. Each group is believed to represent an independent transmission of SIV into humans (but subtypes within a group are not).Group M
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.
- Subtype A is common in West Africa.
- Subtype B is the dominant form in Europe, the Americas, Japan, Thailand, and Australia.
- Subtype C is the dominant form in Southern Africa, India, and Nepal.
- Subtype D is generally only seen in Eastern and central Africa.
- (Subtype E) has never been identified as a nonrecombinant, only recombined with subtype A as CRF01_AE.
- Subtype F has been found in central Africa, South America and Eastern Europe.
- Subtype G (and the CRF02_AG) have been found in Africa and central Europe.
- Subtype H is limited to central Africa.
- (Subtype I) was originally used to describe a strain that is now accounted for as CRF04_cpx, with the cpx for a "complex" recombination of several subtypes.
- Subtype J is primarily found in North, Central and West Africa, and the Caribbean
- Subtype K is limited to the Democratic Republic of Congo and Cameroon.
These subtypes are sometimes further split into sub-subtypes such as A1 and A2 or F1 and F2. This is not thought to be a complete or final list, and further types are likely to be found.
The 'N' stands for "non-M, non-O". This group was discovered in 1998 and has only been seen in Cameroon
Cameroon
Cameroon, officially the Republic of Cameroon , is a country in west Central Africa. It is bordered by Nigeria to the west; Chad to the northeast; the Central African Republic to the east; and Equatorial Guinea, Gabon, and the Republic of the Congo to the south. Cameroon's coastline lies on the...
. As of 2006, only 10 Group N infections had been identified.
Group O
The O ("Outlier") group is not usually seen outside of West-central Africa. It is reportedly most common in Cameroon, where a 1997 survey found that about 2% of HIV-positive samples were from Group O. The group caused some concern because it could not be detected by early versions of the HIV-1 test kits. More advanced HIV tests have now been developed to detect both Group O and Group N.
Group P
In 2009, a newly-analyzed HIV sequence was reported to have greater similarity to a simian immunodeficiency virus recently discovered in wild gorillas (SIVgor) than to SIVs from chimpanzees (SIVcpz). The virus had been isolated from a Cameroon
Cameroon
Cameroon, officially the Republic of Cameroon , is a country in west Central Africa. It is bordered by Nigeria to the west; Chad to the northeast; the Central African Republic to the east; and Equatorial Guinea, Gabon, and the Republic of the Congo to the south. Cameroon's coastline lies on the...
ian woman residing in France who was diagnosed with HIV-1 infection in 2004. The scientists reporting this sequence placed it in a proposed Group P "pending the identification of further human cases".
HIV-2
HIV-2 has not been widely seen outside of Africa. The first case in the United StatesUnited States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
was in 1987. Many test kits for HIV-1 will also detect HIV-2.
As of 2010, there are 8 known HIV-2 groups (A to H). Of these, only groups A and B are epidemic. Group A spread mainly in West Africa, but also to Angola
Angola
Angola, officially the Republic of Angola , is a country in south-central Africa bordered by Namibia on the south, the Democratic Republic of the Congo on the north, and Zambia on the east; its west coast is on the Atlantic Ocean with Luanda as its capital city...
, Mozambique
Mozambique
Mozambique, officially the Republic of Mozambique , is a country in southeastern Africa bordered by the Indian Ocean to the east, Tanzania to the north, Malawi and Zambia to the northwest, Zimbabwe to the west and Swaziland and South Africa to the southwest...
, Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
, India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
, and very limitedly to Europe or the US. Group B is mainly confined to West Africa.
HIV-2 is mostly related to simian immunodeficiency virus
Simian immunodeficiency virus
Simian immunodeficiency virus , also known as African Green Monkey virus and also as Monkey AIDS is a retrovirus able to infect at least 33 species of African primates...
endemic in sooty mangabey
Sooty Mangabey
The sooty mangabey is an Old World monkey found in forests from Senegal east to Ghana. It is famous for being believed to be the monkey that HIV-2 might have originated in before jumping species...
s (Cercocebus atys atys) (SIVsmm), a monkey species inhabiting the forests of littoral West Africa. Phylogenetic analyses show that the viruses most closely related to the two strains of HIV-2 which spread considerably in humans (HIV-2 groups A and B) are the SIVsmm found in the sooty mangabeys of the Tai forest, in western Ivory Coast.
There are six additional known HIV-2 groups, each having been found in just one person. They all seem to derive from independent transmissions from sooty mangabey
Sooty Mangabey
The sooty mangabey is an Old World monkey found in forests from Senegal east to Ghana. It is famous for being believed to be the monkey that HIV-2 might have originated in before jumping species...
s to humans. Groups C and D have been found in two people from Liberia
Liberia
Liberia , officially the Republic of Liberia, is a country in West Africa. It is bordered by Sierra Leone on the west, Guinea on the north and Côte d'Ivoire on the east. Liberia's coastline is composed of mostly mangrove forests while the more sparsely populated inland consists of forests that open...
, groups E and F have been discovered in two people from Sierra Leone
Sierra Leone
Sierra Leone , officially the Republic of Sierra Leone, is a country in West Africa. It is bordered by Guinea to the north and east, Liberia to the southeast, and the Atlantic Ocean to the west and southwest. Sierra Leone covers a total area of and has an estimated population between 5.4 and 6.4...
, and groups G and H have been detected in two people from the Ivory Coast. These HIV-2 strains are probably dead end infections, and each of them is most closely related to SIVsmm strains from sooty mangabey
Sooty Mangabey
The sooty mangabey is an Old World monkey found in forests from Senegal east to Ghana. It is famous for being believed to be the monkey that HIV-2 might have originated in before jumping species...
s living in the same country where the human infection was found.
Drug resistance mutations
Isolates of HIV-1 and HIV-2 with resistance to antiretroviral drugs arise through genetic mutations, which have been tracked and analyzed. The Stanford HIV Drug Resistance Database and the International AIDS Society publish lists of the most important of these; first year listing 80 common mutations, and the latest year 93 common mutations, and made available through the Stanford HIV RT and Protease Sequence DatabaseHIV Drug Resistance Database
HIV Drug Resistance Database, also known as Stanford HIV RT and Protease Sequence Database is a database at Stanford University that tracks 93 common mutations of HIV. It has been recompiled in 2008 listing 93 common mutations, after its initial mutation compilation in 2007 of 80 mutations...
.
See also
- HIV superinfectionHIV SuperinfectionHIV superinfection is a condition in which a person with established human immunodeficiency virus infection acquires a second strain of the virus...
- Discovery and development of CCR5 receptor antagonistsDiscovery and development of CCR5 receptor antagonistsCCR5 receptor antagonists are a class of small molecules that antagonize the CCR5 receptor. The C-C motif chemokine receptor CCR5 is involved in the HIV entry process...
- The Origin of HIV and AIDS
External links
- HIV Types at Avert.org