The subtypes of HIV include two major types,
HIV
The human immunodeficiency viruses (HIV) are two species of ''Lentivirus'' (a subgroup of retrovirus) that infect humans. Over time, they cause acquired immunodeficiency syndrome (AIDS), a condition in which progressive failure of the immune ...
type 1 (HIV-1) and HIV type 2 (HIV-2). HIV-1 is related to viruses found in
chimpanzee
The chimpanzee (''Pan troglodytes''), also known as simply the chimp, is a species of great ape native to the forest and savannah of tropical Africa. It has four confirmed subspecies and a fifth proposed subspecies. When its close relative th ...
s and
gorilla
Gorillas are herbivorous, predominantly ground-dwelling great apes that inhabit the tropical forests of equatorial Africa. The genus ''Gorilla'' is divided into two species: the eastern gorilla and the western gorilla, and either four or fi ...
s living in western Africa, while HIV-2 viruses are related to viruses found in the
sooty mangabey
The sooty mangabey (''Cercocebus atys'') is an Old World monkey found in forests from Senegal in a margin along the coast down to the Ivory Coast.
Habitat and ecology
The sooty mangabey is native to tropical West Africa, being found in Guinea, G ...
, a vulnerable West African primate.
HIV-1 viruses can be further divided into groups M, N, O and P. 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
Virulence is a pathogen's or microorganism's ability to cause damage to a host.
In most, especially in animal systems, virulence refers to the degree of damage caused by a microbe to its host. The pathogenicity of an organism—its ability to ca ...
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 also known to cause AIDS.
One of the obstacles to treatment of the
human immunodeficiency virus
The human immunodeficiency viruses (HIV) are two species of ''Lentivirus'' (a subgroup of retrovirus) that infect humans. Over time, they cause AIDS, acquired immunodeficiency syndrome (AIDS), a condition in which progressive failure of the ...
(HIV) is its high genetic variability.
Major types
HIV-1
HIV-1 is the most common and pathogenic strain of the virus. Over 2 million such infections occur annually. Scientists divide HIV-1 into a major group (Group M) and two or more minor groups, namely Group N, O and possibly a group P. Each group is believed to represent an independent transmission of
SIV into humans (but subtypes within a group are not).
A total of 39
ORFs
ORFS stands for ''Output RF Spectrum'', where 'RF' stands for Radio Frequency.
The acronym ORFS is used in the context of mobile communication systems, e.g., GSM. It stands for the relationship between (a) the frequency offset from the carrier a ...
are found in all six possible
reading frame
In molecular biology, a reading frame is a way of dividing the nucleic acid sequence, sequence of nucleotides in a nucleic acid (DNA or RNA) molecule into a set of consecutive, non-overlapping triplets. Where these triplets equate to amino acids or ...
s (RFs) of HIV-1 complete genome sequence, but only a few of them are functional.
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. This major HIV virus which was the source of pre-1960 pandemic viruses originated in the 1920s in
Léopoldville
Kinshasa (; ; ln, Kinsásá), formerly Léopoldville ( nl, Leopoldstad), is the capital and largest city of the Democratic Republic of the Congo. Once a site of fishing and trading villages situated along the Congo River, Kinshasa is now one o ...
, the
Belgian Congo
The Belgian Congo (french: Congo belge, ; nl, Belgisch-Congo) was a Belgian colony in Central Africa from 1908 until independence in 1960. The former colony adopted its present name, the Democratic Republic of the Congo (DRC), in 1964.
Colo ...
, today known as Kinshasa, which is now the capital of the
Democratic Republic of Congo
The Democratic Republic of the Congo (french: République démocratique du Congo (RDC), colloquially "La RDC" ), informally Congo-Kinshasa, DR Congo, the DRC, the DROC, or the Congo, and formerly and also colloquially Zaire, is a country in ...
(DRC).
Its zoonotic origin is SIVcpz, which infects chimpanzees. 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 eastern Africa.
* Subtype B is the dominant form in Europe, the Americas, Japan, and Australia.
In addition, subtype B is the most common form in the Middle East and North Africa. It may have been exported from Africa when Haitian professionals visited Kinshasa in the 1960s and brought it to Haiti in 1964.
* Subtype C is the dominant form in Southern Africa, Eastern Africa, India, Nepal, and parts of China.
* Subtype D is generally only seen in Eastern and central Africa.
* Subtype E was originally used to describe a strain that is now accounted for as the combined strain CRF01_AE.
This means the original, singular, E strain has disappeared, but we know it existed, as it is visible in this combined strain form.
* 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 (DRC) and Cameroon.
* Subtype L is limited to the Democratic Republic of Congo (DRC).
The spatial movement of these subtypes moved along the railways and waterways of the Democratic Republic of Congo (DRC) from Kinshasa to these other areas. These subtypes are sometimes further split into sub-subtypes such as A1 and A2 or F1 and F2. In 2015, the strain
CRF19
The subtypes of HIV include two major types, HIV type 1 (HIV-1) and HIV type 2 (HIV-2). HIV-1 is related to viruses found in chimpanzees and gorillas living in western Africa, while HIV-2 viruses are related to viruses found in the sooty mangabey ...
, a recombinant of subtype A, subtype D and subtype G, with a subtype D
protease
A protease (also called a peptidase, proteinase, or proteolytic enzyme) is an enzyme that catalyzes (increases reaction rate or "speeds up") proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurring the ...
, was found to be strongly associated with rapid progression to AIDS in
Cuba
Cuba ( , ), officially the Republic of Cuba ( es, República de Cuba, links=no ), is an island country comprising the island of Cuba, as well as Isla de la Juventud and several minor archipelagos. Cuba is located where the northern Caribbea ...
. 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 by a Franco-Cameroonian team in 1998, when they identified and isolated the HIV-1 variant strain, YBF380, from a Cameroonian woman who died of AIDS in 1995. When tested, the YBF380 variant reacted with an envelope antigen from SIVcpz rather than with those of Group M or Group O, indicating it was indeed a novel strain of HIV-1. As of 2015, fewer than 20 Group N infections have been recorded.
Group O
The O ("Outlier") group has infected about 100,000 individuals located in West-Central Africa and is not usually seen outside of that area.
It is reportedly most common in Cameroon, where a 1997 survey found that about 2% of HIV-positive samples were from Group O.
Its zoonotic origin is SIVgor, which infects gorillas (rather than the more common source, SIVcpz).
The group caused some concern because it could not be detected by early versions of the HIV-1 test kits. More advanced
HIV tests
HIV tests are used to detect the presence of the human immunodeficiency virus (HIV), the virus that causes acquired immunodeficiency syndrome (AIDS), in serum, saliva, or urine. Such tests may detect antibodies, antigens, or RNA.
AIDS diagn ...
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
gorilla
Gorillas are herbivorous, predominantly ground-dwelling great apes that inhabit the tropical forests of equatorial Africa. The genus ''Gorilla'' is divided into two species: the eastern gorilla and the western gorilla, and either four or fi ...
s (SIVgor) than to SIVs from
chimpanzee
The chimpanzee (''Pan troglodytes''), also known as simply the chimp, is a species of great ape native to the forest and savannah of tropical Africa. It has four confirmed subspecies and a fifth proposed subspecies. When its close relative th ...
s (SIVcpz). The virus had been isolated from a
Cameroon
Cameroon (; french: Cameroun, ff, Kamerun), officially the Republic of Cameroon (french: République du Cameroun, links=no), is a country in west-central Africa. It is bordered by Nigeria to the west and north; Chad to the northeast; the C ...
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 recognized outside of Africa. The first identification of HIV-2 occurred in 1985 in Senegal by microbiologist
Souleymane Mboup
Souleymane Mboup (born 1951) is a Senegalese microbiologist, medical researcher, and colonel in the Armed Forces of Senegal. In 1985, he was a member of the first team to identify HIV-2, a form of HIV that is typically found in West Africa and ...
and his collaborators. The first case in the United States was in 1987. The first confirmed case of HIV-2 was a Portuguese man who was treated at the
London Hospital for Tropical Diseases
The Hospital for Tropical Diseases (HTD) is a specialist tropical disease hospital located in London, United Kingdom. It is part of the University College London Hospitals NHS Foundation Trust and is closely associated with University College Lon ...
and later died in 1987. He was believed to have been exposed to the disease in
Guinea-Bissau
Guinea-Bissau ( ; pt, Guiné-Bissau; ff, italic=no, 𞤘𞤭𞤲𞤫 𞤄𞤭𞤧𞤢𞥄𞤱𞤮, Gine-Bisaawo, script=Adlm; Mandinka: ''Gine-Bisawo''), officially the Republic of Guinea-Bissau ( pt, República da Guiné-Bissau, links=no ) ...
where he lived between 1956 and 1966. His pathological diagnosis at the time was cryptosporidium and enterovirus infection, but an analysis of his stored serum in 1987 found that he was infected with HIV-2.
Many test kits for HIV-1 will also detect HIV-2.
As of 2010, there are eight known HIV-2 groups (A to H). Of these, only groups A and B are pandemic. Group A is found mainly in West Africa, but has also spread globally to
Angola
, national_anthem = " Angola Avante"()
, image_map =
, map_caption =
, capital = Luanda
, religion =
, religion_year = 2020
, religion_ref =
, coordina ...
,
Mozambique
Mozambique (), officially the Republic of Mozambique ( pt, Moçambique or , ; ny, Mozambiki; sw, Msumbiji; ts, Muzambhiki), is a country located in southeastern Africa bordered by the Indian Ocean to the east, Tanzania to the north, Malawi ...
, Brazil, India, Europe, and the US. Despite the presence of HIV-2 globally, Group B is mainly confined to West Africa.
Despite its relative confinement, HIV-2 should be considered in all patients exhibiting symptoms of HIV that not only come from West Africa, but also anyone who has had any body fluid transfer with a person from West Africa (i.e. needle sharing, sexual contact, etc.).
HIV-2 is closely related to
simian immunodeficiency virus
''Simian immunodeficiency virus'' (''SIV'') is a species of retrovirus that cause persistent infections in at least 45 species of non-human primates. Based on analysis of strains found in four species of monkeys from Bioko Island, which was isola ...
endemic in
sooty mangabey
The sooty mangabey (''Cercocebus atys'') is an Old World monkey found in forests from Senegal in a margin along the coast down to the Ivory Coast.
Habitat and ecology
The sooty mangabey is native to tropical West Africa, being found in Guinea, G ...
s (''Cercocebus atys atys'') (SIVsmm), a monkey species inhabiting the forests of Littoral West Africa. Phylogenetic analyses show that the virus most closely related to the two strains of HIV-2 which spread considerably in humans (HIV-2 groups A and B) is the SIVsmm found in the sooty mangabeys of the Tai forest, in western
Ivory Coast
Ivory Coast, also known as Côte d'Ivoire, officially the Republic of Côte d'Ivoire, is a country on the southern coast of West Africa. Its capital is Yamoussoukro, in the centre of the country, while its largest city and economic centre is ...
.
[
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 mangabeys to humans. Groups C and D have been found in two people from ]Liberia
Liberia (), officially the Republic of Liberia, is a country on the West African coast. It is bordered by Sierra Leone to Liberia–Sierra Leone border, its northwest, Guinea to its north, Ivory Coast to its east, and the Atlantic Ocean ...
, groups E and F have been discovered in two people from Sierra Leone
Sierra Leone,)]. officially the Republic of Sierra Leone, is a country on the southwest coast of West Africa. It is bordered by Liberia to the southeast and Guinea surrounds the northern half of the nation. Covering a total area of , Sierra ...
, and groups G and H have been detected in two people from the Ivory Coast. Each of these HIV-2 strains, for which humans are probably Host (biology), dead-end hosts, is most closely related to SIVsmm strains from sooty mangabeys living in the same country where the human infection was found.[
]
Diagnosis
HIV-2 diagnosis can be made when a patient has no symptoms but positive blood work indicating the individual has HIV. The Multispot HIV-1/HIV-2 Rapid Test is currently the only FDA approved method for such differentiation between the two viruses. Recommendations for the screening and diagnosis of HIV has always been to use enzyme immunoassays that detect HIV-1, HIV-1 group O, and HIV-2. When screening the combination, if the test is positive followed by an indeterminate HIV-1 western blot
The western blot (sometimes called the protein immunoblot), or western blotting, is a widely used analytical technique in molecular biology and immunogenetics to detect specific proteins in a sample of tissue homogenate or extract. Besides detect ...
, a follow up test, such as amino acid
Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...
testing, must be performed to distinguish which infection is present.[Human Immunodeficiency Virus Type 2 (HIV-2) by New York State Department of Health AIDS Institute: http://www.hivguidelines.org] According to the NIH, a differential diagnosis of HIV-2 should be considered when a person is of West African descent or has had sexual contact or shared needles with such a person. West Africa is at the highest risk as it is the origin of the virus.
Treatments
HIV-2 has been found to be less pathogenic than HIV-1. The mechanism of HIV-2 is not clearly defined, nor the difference from HIV-1, however the transmission rate is much lower in HIV-2 than HIV-1. Both viruses can lead to AIDS in infected individuals and both can mutate to develop drug resistance. Disease monitoring in patients with HIV-2 includes clinical evaluation and CD4 cell counts, while treatment includes anti-retroviral therapy
The management of HIV/AIDS normally includes the use of multiple antiretroviral drugs as a strategy to control HIV infection. There are several classes of antiretroviral agents that act on different stages of the HIV life-cycle. The use of multiple ...
(ART), nucleoside reverse transcriptase inhibitors
Reverse-transcriptase inhibitors (RTIs) are a class of antiretroviral drugs used to treat HIV infection or AIDS, and in some cases hepatitis B. RTIs inhibit activity of reverse transcriptase, a viral DNA polymerase that is required for replicatio ...
(NRTIs), protease inhibitors
Protease inhibitors (PIs) are medications that act by interfering with enzymes that cleave proteins. Some of the most well known are antiviral drugs widely used to treat HIV/AIDS and hepatitis C. These protease inhibitors prevent viral replicat ...
(PI), and non-nucleoside reverse transcriptase inhibitors
Reverse-transcriptase inhibitors (RTIs) are a class of antiretroviral drugs used to treat HIV infection or AIDS, and in some cases hepatitis B. RTIs inhibit activity of reverse transcriptase, a viral DNA polymerase that is required for replicatio ...
(NNRTIs) with the addition of CCR5 co-receptor antagonists and fusion inhibitors.[R Kannangai, S David, G Sridharan. "Human immunodeficiency virus type 2-A milder, kinder virus: An update". ''Indian Journal of Medical Micobiology'', (2012) 30(1): 6–15.]
Choice of initial and/or second-line therapy for HIV-2 has not yet been defined. HIV-2 appears to be resistant to NNRTIs intrinsically, but may be sensitive to NRTIs, though the mechanism is poorly understood. Protease inhibitors have shown variable effect, while integrase inhibitors are also being evaluated. Combination regimens of the above listed therapies are being looked into as well, also showing variable effect depending on the types of therapies combined. While the mechanisms are not clearly understood for HIV-1 and HIV-2, it is known that they use different pathways and patterns, making the algorithms used to evaluate HIV-1 resistance-associated mutations irrelevant to HIV-2.
Each virus can be contracted individually, or they can be contracted together in what is referred to as co-infection. HIV-2 seems to have lower mortality rates, less severe symptoms and slower progression to AIDS than HIV-1 alone or the co-infection. In co-infection, however, this is largely dependent on which virus was contracted first. HIV-1 tends to out compete HIV-2 for disease progression. Co-infection seems to be a growing problem globally as time progresses, with most cases being identified in West African countries, as well as some cases in the USA. A study found that individuals who acquire HIV-2 before HIV-1 have a slower rate of disease progression, indicating that the proliferation of HIV-1 is limited by the immune response to HIV-2.
Pregnancy
If a pregnant mother is exposed, screening is performed as normal. If HIV-2 is present, a number of perinatal ART drugs may be given as a prophylactic to lower the risk of mother-to-child transmission. After the child is born, a standard six-week regimen of these prophylactics should be initiated. Breast milk may also contain particles of HIV-2; therefore, breastfeeding is strictly advised against.
Evolution
The rapid evolution of HIV can be attributed to its high mutation rate. During the early stages of mutation, evolution appears to be neutral due to the absence of an evolutionary response. However, when examining the virus in several different individuals, convergent mutations can be found appearing in these viral populations independently.
HIV evolution within a host influences factors including the virus' set-point viral load
Viral load, also known as viral burden, is a numerical expression of the quantity of virus in a given volume of fluid, including biological and environmental specimens. It is not to be confused with viral titre or viral titer, which depends on the ...
. If the virus has a low set-point viral load, the host will live longer, and there is a greater probability that the virus will be transmitted to another individual. If the virus has a high set-point viral load, the host will live for a shorter amount of time and there is a lower probability that the virus will be transmitted to another individual. HIV has evolved to maximize the number of infections to other hosts, and this tendency for selection to favor intermediate strains shows that HIV undergoes stabilizing selection.
The virus has also evolved to become more infectious between hosts. There are three different mechanisms that allow HIV to evolve at a population level. One includes the continuous battle to evolve and overcome the immune system which slows down the evolution of HIV and shifts the virus’ focus towards a population level. Another includes the slow evolution of viral load due to viral load mutations being neutral within the host. The last mechanism focuses on the virus' preference to transmit founding viral strains stored during the early stages of infection. This preference of the virus to transmit its stored genome copies explains why HIV evolves more quickly within the host than between hosts.
HIV is evolving to a milder form but is ''"an awfully long way"'' from no longer being deadly and new severe variants are still appearing.
Drug resistance mutations
Isolates of HIV-1 and HIV-2 with resistance to antiretroviral drugs arise through natural selection
Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations. Charle ...
and 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 Database.
See also
* HIV superinfection
HIV superinfection (also called HIV reinfection or SuperAIDS) is a condition in which a person with an established human immunodeficiency virus infection acquires a second strain of HIV, often of a different subtype. These can form a recombinant ...
* HIV/AIDS research
HIV/AIDS research includes all medical research that attempts to prevent, treat, or cure HIV/AIDS, as well as fundamental research about the nature of HIV as an infectious agent and AIDS as the disease caused by HIV.
Transmission
A body of sc ...
* Discovery and development of CCR5 receptor antagonists
CCR5 receptor antagonists are a class of small molecules that antagonize the CCR5 receptor. The C-C motif chemokine receptor CCR5 is involved in the process by which HIV, the virus that causes AIDS, enters cells. Hence antagonists of this rec ...
* History of HIV/AIDS
AIDS is caused by a human immunodeficiency virus (HIV), which originated in non-human primates
in Central and West Africa. While various sub-groups of the virus acquired human infectivity at different times, the present pandemic had its origins ...
References
External links
*
HIV Types
at Avert.org
* ttps://www.hiv.lanl.gov/components/sequence/HIV/geo/geo.html Geographic distribution of subtyped sequences in the GenBank HIV Database
{{DEFAULTSORT:Subtypes Of Hiv
HIV/AIDS
Sexually transmitted diseases and infections
Infraspecific virus taxa
hi:एचआइवी#प्रमुख प्रकार