Simian immunodeficiency virus | |
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SIV virion model obtained with cryo-electron microscopy scanning | |
Virus classification | |
(unranked): | Virus |
Realm: | Riboviria |
Kingdom: | Pararnavirae |
Phylum: | Artverviricota |
Class: | Revtraviricetes |
Order: | Ortervirales |
Family: | Retroviridae |
Genus: | Lentivirus |
Species: | 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. [1] [2] Based on analysis of strains found in four species of monkeys from Bioko Island, which was isolated from the mainland by rising sea levels about 11,000 years ago, it has been concluded that SIV has been present in monkeys and apes for at least 32,000 years, and probably much longer. [3] [4]
Virus strains from three of these primate species, SIVsmm in sooty mangabeys, SIVgor in gorillas and SIVcpz in chimpanzees, are believed to have crossed the species barrier into humans, resulting in HIV-2 and HIV-1 respectively, the two HIV viruses. The most likely route of transmission of HIV-1 to humans involves contact with the blood of chimps and gorillas that are often hunted for bushmeat in Africa. Four subtypes of HIV-1 (M, N, O, and P) likely arose through four separate transmissions of SIV to humans, and the resulting HIV-1 group M strain most commonly infects people worldwide. [5] [6] Therefore, it is theorized that SIV may have previously crossed the species barrier into human hosts multiple times throughout history, but it was not until recently, after the advent of modern transportation and global commuterism, that it finally took hold, spreading beyond localized decimations of a few individuals or single small tribal populations.
Unlike HIV-1 and HIV-2 infections in humans, SIV infections in their natural simian non-human hosts appear in many cases to be non-pathogenic due to evolutionary adaptation of the hosts to the virus. Extensive studies in sooty mangabeys have established that SIVsmm infection does not cause any disease in these primates, despite high levels of circulating virus. Regulation of the activity of the CCR5 coreceptor is one of the natural strategies to avoid disease in some natural host species of SIV. [7]
Unlike SIVsmm infection in sooty mangabeys, a recent[ when? ] study of SIVcpz in wild living chimpanzees suggests that infected chimpanzees experience an AIDS-like illness similar to HIV-1 infected humans. The later stages of SIV infection develop into sAIDS, much like how HIV infection develops into AIDS.
The simian (monkey-hosted) immunodeficiency viruses are a species of retrovirus in the Primate group of genus Lentivirus along with the human viruses HIV-1 and HIV-2 that cause AIDS, and a few other viruses that infect other primates. Related viruses in other groups in the genus infect other mammals like sheep and goats, horses, cattle, cats, and a few others. The genus is one of six genera in subfamily orthoretrovirinae, which together with genus Spumavirus form family retroviridae of all RNA retroviruses (RNA viruses which use a DNA intermediate). [8]
The ICTVdB code of SIV is 61.0.6.5.003. [9] Although HIV-1 and HIV-2 cladistically fall into SIV, [10] ICTV considers them distinct species from ordinary, non-human-infecting SIV.
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Phylogenetic relations between simian immunodeficiency viruses (SIVs) [10] [11] [12] [13] [14] |
While human immunodeficiency virus has a limited number of subtypes, SIV is now known to infect a few dozen species of non-human primates, and distinct strains are often associated with each species, or with a set of closely related species. The thus far categorized ~40 strains are divided into five distinct groups and one subgroup: [10]
In addition to the subgroups defined for extent SIVs, two endogenous SIVs are found in prosimian lemurs. These paleo-SIVs form a basal branch relative to extant SIVs. [15]
Immunodeficiency resembling human AIDS was reported in captive monkeys in the United States beginning in 1983. [16] [17] [18] SIV was isolated in 1985 from some of these animals, captive rhesus macaques suffering from simian AIDS (SAIDS). [17] The discovery of SIV was made shortly after HIV-1 had been isolated as the cause of AIDS and led to the discovery of HIV-2 strains in West Africa. HIV-2 was more similar to the then-known SIV strains than to HIV-1, suggesting for the first time the simian origin of HIV. Further studies indicated that HIV-2 is derived from the SIVsmm strain found in sooty mangabeys, whereas HIV-1, the predominant virus found in humans, is derived from SIV strains infecting chimpanzees (SIVcpz).[ citation needed ]
It is not believed that chimpanzees are the original hosts of an independent lineage of SIV, but rather that SIVcpz is a relatively recent acquisition resulting from a recombination of SIVgsn (greater spot-nosed monkeys) and SIVrcm (red-capped mangabeys) within the host chimpanzee. It is known that chimpanzees hunt and consume these monkeys for food. [19] In 2010, researchers reported that SIV had infected monkeys in Bioko for at least 32,000 years. Based on molecular clock analyses of sequences, it was previously thought by many that SIV infection in monkeys had happened over the past few hundred years. [3] Scientists estimated that it would take a similar amount of time before humans would adapt naturally to HIV infection in the way monkeys in Africa have adapted to SIV and not suffer any harm from the infection. [20]
In 2008, discovery of an endogenous lentivirus in a prosimian (proto-monkey) primate, the gray mouse lemur native to Madagascar, pushed the origin of SIV-like lentivirus infections in primates back to at least 14 Ma, the last time there was intermingling of mammals between the island of Madagascar and the African mainland, if the infection is attributed to horizontal transmission between homologous hosts. If the virus was coevolved with the host, rather than acquired, that potentially pushes the date of the endogenous event back to approx. 85 Ma, the split between the lemur-like and monkey-like primate lineages. That date barely antedates the emergence of the primates 87.7 Ma. [21]
The SIV virion is a spherical to pleomorphic glycoprotein envelope 110-120 nm across enclosing a 110x50nm truncated cone or wedge-shaped (occasionally rod) capsid containing a dimeric pair of positive-sense single-stranded RNA genomes.[ citation needed ]
Differences in species specificity of SIV and related retroviruses may be partly explained by variants of the protein TRIM5α in humans and non-human primate species. This intracellular protein recognizes the capsid of various retroviruses and blocks their reproduction. Other proteins, such as APOBEC3G/3F, which exerts antiretroviral immune activity, may also be important in restricting cross-species transmission. [22]
+ssRNA → -ssDNA → dsDNA → +ssRNA (viral genome) → +ssmRNA → viral protein
The speed and transcription inaccuracies of RNA viruses give rise to antigenically distinct varieties in a single host animal. These quasispecies do not necessarily give rise to population-wide new organisms. The rate of proliferation of quasispecies has significant implication for host immune control, and therefore virulence of the organism.[ citation needed ]
SIV pathogenesis encompasses both pathogenic and non-pathogenic SIV infections. SIV infection of non-human primates (NHPs) invariably results in persistent infection, but rarely acute disease. Pathogenic infection is typified by Rhesus macaques infected with SIV strains derived from sooty mangabeys. Disease progression to AIDS occurs within a period of months to years, depending upon the SIV strain used. Non-pathogenic infection is typified by African NHPs naturally infected with SIV. These animals rarely progress to AIDS despite maintaining viral loads that are equivalent to SIV viral loads in pathogenic infections. It is postulated that AIDS-like disease in African NHPs represents horizontal transmission of the virus from one or more homologous species in the recent evolutionary past, before equilibrium of co-adaptation has occurred.[ citation needed ]
The similarities of the two types of virus infections: [23]
The differences (what happens in nonhuman primates):
strain | lineage | host | binomial | disease |
---|---|---|---|---|
HIV-1 | SIVcpz | humans | H. sapiens | AIDS |
HIV-2 | SIVsmm | humans | H. sapiens | AIDS |
SIVcpz | SIVrcm/SIVgsn | Chimpanzee | P. Troglodytes | SAIDS |
SIVgor | SIVcpz | Gorilla | G. gorilla | ( - ) |
SIVsmm | Sooty mangabey | ( - ) |
Beatrice Hahn of the University of Pennsylvania and a team of researchers in 2009 found that chimpanzees do die from simian AIDS in the wild and that the AIDS outbreak in Africa has contributed to the decline of chimpanzee populations. Testing wild chimpanzees, researchers detected organ and tissue damage similar to late-stage human AIDS. The infected chimpanzees had a 10 to 16 times greater risk of dying than uninfected ones; infected females were less likely to give birth, could pass the virus to their infants, and had a higher infant mortality rate than uninfected females. [24] [25] Bonobos appear to avoid simian immunodeficiency virus (SIV) and its effects, though it is not known why. [19]
African green monkeys (also called vervets, genus Chlorocebus) in African populations are heavily infected with SIVagm, [26] [27] while the virus is absent in the founder isolate vervet populations in the Caribbean. [28] The prevalence of SIV infection in African populations ranges 78-90% in adult females and 36-57% in adult males, while SIV infection is rare in immature individuals. [27] [26] SIV infected vervets in the wild do not develop chronic immune activation or microbial translocation (assessed by sCD14 as a surrogate biomarker). During natural SIV infection, the gut microbiome showed a significant increase in microbial diversity, a decrease in Proteobacteria/Succinivibrio and an increase of Veillonella, a decrease in genes involved in pathways of microbial invasion, and partial reversibility of acute infection-related shifts in microbial abundance. [29] The pattern of natural selection in the monkey genome in genes involved in HIV responses and those regulated in response to experimental SIV infection in monkeys, but not macaques, suggests a natural adaptation to SIV in Chlorocebus monkeys in Africa. [30]
In 2012, researchers reported that initial infection of rhesus monkeys by neutralization-resistant SIV strains [31] could be partially prevented through use of an anti-SIVSME543 vaccine obligately including Env protein antigens. [32]
In 2013, a study by a group of authors reported on successful testing of a vaccine containing SIV protein-expressing rhesus cytomegalovirus vector. Approximately 50% of vaccinated rhesus macaques manifested durable, aviraemic control of infection with the highly pathogenic strain SIVmac239. [33]
The human immunodeficiency viruses (HIV) are two species of Lentivirus that infect humans. Over time, they cause acquired immunodeficiency syndrome (AIDS), a condition in which progressive failure of the immune system allows life-threatening opportunistic infections and cancers to thrive. Without treatment, the average survival time after infection with HIV is estimated to be 9 to 11 years, depending on the HIV subtype.
Bushmeat is meat from wildlife species that are hunted for human consumption. Bushmeat represents a primary source of animal protein and a cash-earning commodity in poor and rural communities of humid tropical forest regions of the world.
The oral polio vaccine (OPV) AIDS hypothesis is a now-discredited hypothesis that the AIDS pandemic originated from live polio vaccines prepared in chimpanzee tissue cultures, accidentally contaminated with simian immunodeficiency virus and then administered to up to one million Africans between 1957 and 1960 in experimental mass vaccination campaigns.
Chlorocebus is a genus of medium-sized primates from the family of Old World monkeys. Six species are currently recognized, although some people classify them all as a single species with numerous subspecies. Either way, they make up the entirety of the genus Chlorocebus.
The sooty mangabey is an Old World monkey found in forests from Senegal in a margin along the coast down to the Ivory Coast.
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 in the emergence of one specific strain – HIV-1 subgroup M – in Léopoldville in the Belgian Congo in the 1920s.
The California National Primate Research Center (CNPRC) is a federally funded biomedical research facility, dedicated to improving human and animal health, and located on the University of California, Davis, campus. The CNPRC is part of a network of seven National Primate Research Centers developed to breed, house, care for and study primates for medical and behavioral research. Opened in 1962, researchers at this secure facility have investigated many diseases, ranging from asthma and Alzheimer's disease to AIDS and other infectious diseases, and has also produced discoveries about autism. CNPRC currently houses about 4,700 monkeys, the majority of which are rhesus macaques, with a small population of South American titi monkeys. The center, located on 300 acres (1.2 km2) 2.5 miles west of the UC Davis campus, is sponsored by the National Institutes of Health (NIH).
Simian foamy virus (SFV) is a species of the genus Spumavirus that belongs to the family of Retroviridae. It has been identified in a wide variety of primates, including prosimians, New World and Old World monkeys, as well as apes, and each species has been shown to harbor a unique (species-specific) strain of SFV, including African green monkeys, baboons, macaques, and chimpanzees. As it is related to the more well-known retrovirus human immunodeficiency virus (HIV), its discovery in primates has led to some speculation that HIV may have been spread to the human species in Africa through contact with blood from apes, monkeys, and other primates, most likely through bushmeat-hunting practices.
HIV/AIDS was recognised as a novel illness in the early 1980s. An AIDS case is classified as "early" if the death occurred before 5 June 1981, when the AIDS epidemic was formally recognized by medical professionals in the United States.
HIV superinfection 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 strain that co-exists with the strain from the initial infection, as well from reinfection with a new virus strain, and may cause more rapid disease progression or carry multiple resistances to certain HIV medications.
C-X-C chemokine receptor type 6 is a protein that in humans is encoded by the CXCR6 gene. CXCR6 has also recently been designated CD186.
The subtypes of HIV include two main subtypes, known as HIV type 1 (HIV-1) and HIV type 2 (HIV-2). These subtypes have distinct genetic differences and are associated with different epidemiological patterns and clinical characteristics.
The agile mangabey is an Old World monkey of the white-eyelid mangabey group found in swampy forests of Central Africa in Equatorial Guinea, Cameroon, Gabon, Central African Republic, Republic of Congo, and DR Congo. Until 1978, it was considered a subspecies of the Tana River mangabey. More recently, the golden-bellied mangabey has been considered a separate species instead of a subspecies of the agile mangabey.
The central chimpanzee or the tschego is a subspecies of chimpanzee. It can be found in Central Africa, mostly in Gabon, Cameroon, Republic of Congo and the Democratic Republic of Congo.
Nef is a small 27-35 kDa myristoylated protein encoded by primate lentiviruses. These include Human Immunodeficiency Viruses and Simian Immunodeficiency Virus (SIV). Nef localizes primarily to the cytoplasm but also partially to the Plasma membrane (PM) and is one of many pathogen-expressed proteins, known as virulence factors, which function to manipulate the host's cellular machinery and thus allow infection, survival or replication of the pathogen. Nef stands for "Negative Factor" and although it is often considered indispensable for HIV-1 replication, in infected hosts the viral protein markedly elevates viral titers.
Janice Ellen Clements is vice dean for faculty at the Johns Hopkins School of Medicine and the Mary Wallace Stanton Professor of Faculty Affairs. She is a professor in the departments of Molecular and Comparative Pathobiology, Neurology, and Pathology, and has a joint appointment in molecular biology and genetics. Her molecular biology and virology research examines lentiviruses and how they cause neurological diseases.
Mason-Pfizer monkey virus (M-PMV), formerly Simian retrovirus (SRV), is a species of retroviruses that usually infect and cause a fatal immune deficiency in Asian macaques. The ssRNA virus appears sporadically in mammary carcinoma of captive macaques at breeding facilities which expected as the natural host, but the prevalence of this virus in feral macaques remains unknown. M-PMV was transmitted naturally by virus-containing body fluids, via biting, scratching, grooming, and fighting. Cross contaminated instruments or equipment (fomite) can also spread this virus among animals.
Beatrice H. Hahn is an American virologist and biomedical researcher best known for work which established that HIV, the virus causing AIDS, began as a virus passed from apes to humans. She is a professor of Medicine and Microbiology in the Perelman School of Medicine at the University of Pennsylvania. In November 2002, Discover magazine listed Hahn as one of the 50 most important women scientists.
In parasitology and epidemiology, a host switch is an evolutionary change of the host specificity of a parasite or pathogen. For example, the human immunodeficiency virus used to infect and circulate in non-human primates in West-central Africa, but switched to humans in the early 20th century.
Theodora Hatziioannou is a Greek-American virologist. She known for her work discovering restriction factors that counteract HIV-AIDS and other primate lentiviruses, thus restricting them to specific species, and making it hard to study HIV-1 in animals. Her findings allowed her to develop the first HIV-1-based virus which is capable of recapitulating AIDS-like symptoms in a non-hominid. She is a Research Associate Professor in the Laboratory of Retrovirology at The Rockefeller University in New York. She is a co-author of a textbook on virology, Principles of Virology.