HIV-1 HIV-1 is the most common and most pathogenic strain of the virus. , approximately 1.3 million such infections occur annually. Scientists divide HIV-1 into a major group (group M) and two or more minor groups, namely groups N, O and possibly a group P. Each group is believed to represent an independent transmission of
simian immunodeficiency virus (SIV) into humans, excluding subtypes within a specific group.
Group M With 'M' for "major", this is by far the most common type of HIV, with more than 90% of HIV/AIDS cases caused by infection with HIV-1 group M viruses. This major HIV, which was the source of pre-1960 pandemic viruses, originated in the 1920s in
Léopoldville, the
Belgian Congo, today known as Kinshasa, which is now the capital of the
Democratic Republic of Congo (DRC). Its
zoonotic origin is the
SIVcpz strain, 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
genetic recombination between viruses of different subtypes which are in addition each given a number. CRF12_BF, for example, is a recombination between subtypes B and F. • 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. This means the original, singular, E strain has disappeared, but we know it existed, as it is visible in this combined strain form. • Subtype G (and the CRF02_AG) have been found in Africa and central Europe. • Subtype K is limited to the DRC and Cameroon. The spatial movement of these subtypes moved along the railways and waterways of the 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. 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 a
viral envelope antigen from SIVcpz rather than with those of Group M or Group O, indicating it was indeed a novel strain of HIV-1. , 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. 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 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 SIVgor, than SIVcpz. The virus had been isolated from a Cameroonian 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 is mostly found in Africa, and therefore less recognized elsewhere in the world.
History HIV-2 was first identified by microbiologist
Souleymane Mboup and his collaborators in 1985. At the time of the discovery, little data existed about HIV in Africa.
Mboup began to test for the virus in
Senegal. Some of his samples tested positive, but they did not produce a
GP41 band on
Western Blot analysis. So, Mboup sent the samples to colleagues in France and at
Harvard Medical School to confirm the result. The first confirmed case of HIV-2 was a Portuguese man who was treated at the
London Hospital for Tropical Diseases and later died in 1987. He was believed to have been exposed to the disease in
Guinea-Bissau, where he lived between 1956 and 1966. His pathological diagnosis at the time was
cryptosporidiosis and
enterovirus infection, but an analysis of his stored
serum in 1987 found that he was infected with HIV-2. HIV-2 is closely related to SIV endemic in
sooty mangabeys (
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.
Subgroups There are eight known HIV-2 groups, designated A to H. Of these, only groups A and B are
pandemic. Group A is found mainly in West Africa, but has also spread to Angola, Mozambique, Brazil, India, Europe, and the US. Despite the presence of HIV-2 globally, Group B is mainly confined to West Africa. 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, 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. Each of these HIV-2 strains, for which humans are probably
dead-end hosts, is most closely related to SIVsmm strains from sooty mangabeys living in the same country where the human infection was found. 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, a follow-up test, such as
amino acid testing, must be performed to distinguish which infection is present. 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.
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. 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.
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 viral particles of HIV-2; therefore, breastfeeding is strictly advised against. ==Evolution==