questions: Orgins of Hiv and the AIDS pandemic 1. According to the article, what
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questions: Orgins of Hiv and the AIDS pandemic
1. According to the article, what are the reasons for HIV-1’s sudden emergence, epidemic spread, and unique pathogenicity?
2. Explain the link and evidence for lentiviruses causing persistent infections in various mammalian species (bovines, horses, sheep, felines, and primates).
3. What have the serological and molecular data of SIV infections reported in over 40 primates demonstrated?
4. Why has SIVcpz been of particular interest? What are the challenges of studying this virus? How did they collect samples of this virus in natural populations?
5. What are the key differences between SIVcpz and other primate lentiviruses?
6. According to the article, is SIVcpz harmless for natural hosts? Explain.
7. Describe the origins of HIV-1. How many different lineages makes up HIV-1? Describe each of the different lineages.
8. What does the phylogenetic tree in figure 4 depict (or tell us)?
9. According to the article, what are some of the ways that the ape precursor of HIV-1 entered humans? How many times did this occur? When did they occur?
10. Describe the origins of HIV-2? Is its rate of infection increasing or decreasing? How does the infectious process differ between HIV-1 and HIV-2?
11. How many distinct lineages of HIV-2 are there?
12. Explain some of the adaptive hurdles that had to be overcome before primate lentiviruses could productively infect new species.
13. How fast does HIV-1 evolve? Why?
14. Describe the evidence that points to Leopoldville/Kinshasa as the cradle of the AIDS pandemic.
15. How many different subtypes of HIV-1 group M are there?
Explanation / Answer
HIV- 1 is very closely related to chimpanzee virus SIVcpzPtt strains, indicating that they are of chimpanzee origin. Based on the studies conducted there are evidences that these viruses were present in animals thousands of years ago and interspecies transmission has occurred due to possible association of humans with these animals for ex rapid growth of cities by deforestation . However considering the biology of these viruses the transmission must have occurred through cutaneous or mucous membrane exposure of infected ape blood or tissue ex; bush meat hunting.
The SIV virus have undergone mutation changes such as expression of some protein in order to infect the new host and evade the immune response of new host. In the beginning 20th century rapid growth of population together with increased sexually transmitted diseases, such as genital ulcer might have facilitated epidemic spread.
2.Explain the link and evidence for lentiviruses causing persistent infections in various mammalian species (bovines, horses, sheep, felines, and primates).
Lentiviruses cause chronic persistent infections in various mammalian species, including bovines, horses, sheep, felines, and primates. The great majority of lentiviruses are exogenous (horizontal transmission)but endogenous,( vertically transmission has also find out). Viral fossil examination and molecular time scale analysis is used to find out the evidence on this. Studies on SIV infected Monkeys on BOKO islands explains the infection by same subspecies in geographically isolated species and was there probably thousands of years ago. The endogenous virus in lemur also point in this direction.
So with respect to more longstanding virus/host relationship a number of naturally occurring viruses have emerged and resulted in cross specie transmission
3.What have the serological and molecular data of SIV infections reported in over 40 primates demonstrated?
The molecular and serological data obtained from 40 primates shown that great majority of primate species harbour a single type of SIV
4.Why has SIVcpz been of particular interest? What are the challenges of studying this virus? How did they collect samples of this virus in natural populations?
The , SIVcpz is have close genetic relationship to HIV-1 that is the reason it is studied with particular interest. However, studies of this virus have proven to be challenging because of the endangered status of chimpanzees. The laboratory developed noninvasive diagnostic methods that detect SIVcpz specic antibodies and nucleic acids in chimpanzee fecal and urine samples with high sensitivity and specicity.
5,What are the key differences between SIVcpz and other primate lentiviruses?
Studies have identied common chimpanzees as a natural SIVcpz reservoir. The major difference stated between SIVcpz and other primate lentivirus is its transmission pattern. In the other primates lentivirus are more widely distributed and infect their host in high prevalence rate. But SIVcpz was found in 2-4 subspecies of chimpanzees and detected in areas of Cameroon and Tanzania. There is no evidence of infection in other groups
.
6.According to the article, is SIVcpz harmless for natural hosts? Explain.
Based on the immunological and viral assay in a single naturally infected chimpanzee it was though that SIVcpz is harmless to natural host . But advance studies disproved this argument.
7,Describe the origins of HIV-1. How many different lineages makes up HIV-1? Describe each of the different lineages
HIV-1 has long been suspected to be of chimpanzee origin. But HIV-1 is not found in any of the primates. While analysing data of SIV virus ,it is established that SIVcpz is divided in to two subspecies-specic lineages, termed SIVcpzPtt and SIVcpzPts.and have lineage difference at about 30%–50% of sites in their Gag, Pol, and Env protein sequences . In addition discovery of SIVgor has identified in southern Cameroon as a potential reservoir of human infection. HIV 1 evolved due to cross species transmission.
HIV-1 comprises four distinct lineages, termed groups M, N, O, andP.
Each of this is believed to evolve from independent cross species transmission.
Group M- ; the first discovered HIV pandemic has been found that it transmitted globally. group M, likely originated in the Boumba, Ngoko, and Sangha rivers in the southeastern corner of Cameroon.
Group O- was discovered in 1990 and is much less prevalent than group M . The origin remains unknown, because there are no ape viruses that are particularly closely related to this group . Since the group O and P viruses are more closely related to SIVcpzPtt it might have originated in west central Africa.
Group N -. HIV-1 groups N is found to evolve from SIVcpzPtt strainsand found have emerged in the vicinity of the Dja Forest in south-central Cameroon,
Group P was discovered in 2009 in a Cameroonian woman living in France . Since it ie related to O group virus It association with SIVcpzPtt is proved. Only 2 reports of this lineage infection so far.
8,What does the phylogenetic tree in figure 4 depict (or tell us)?
Phylogenetic tree of representative the phylogenetic relationship between HIV-1, SIVcpz, and SIVgor strains. It shows that all four HIV-1 groups are closely associated to SIVgor from gorilla , and SIVcpzPtt from chimpanzees, identifying this subspecies as the original reservoir of both human and gorilla infections. HIV-1 groups N and M are very closely related to SIVcpzPtt strains from southern Cameroon, indicating that they are of chimpanzee origin. HIV P and O is closely relatedly to SIVgor showing its origin from gorillas . Interspecies transmission of all four HIV types is shown. And a possible transmission from Gorillas and chimpanzees is clearly shown.
9,According to the article, what are some of the ways that the ape precursor of HIV-1 entered humans? How many times did this occur? When did they occur?
It is mentioned that human-ape encounter is occurred in west central Africa at least five times and resulted in transmission of four independent cross species transmission. Molecular clock analysis revealed that group M and O epidemic began in early twenty centuries and group N and P emerged most recently.
HIV-2 origin is from SIVsmm of sooty mangabey in west Africa. SIVsmm was found to be highly prevalent in sooty mangabey and is frequently hunted as agricultural pests. Its rate of infection is coming down and is completely getting replaced by HIV 1. The reason behind this is due to law viral load of HIV-2 infection.
11,How many distinct lineages of HIV-2 are there?
Eight distinct lineages of HIV-2 are there termed from A-H. Each one is evolved from independent host transfer.
12,.Explain some of the adaptive hurdles that had to be overcome before primate lentiviruses could productively infect new species.
13. How fast does HIV-1 evolve? Why?
HIV-1 evolves around one million times faster than mammalian DNA because of mainly two reasons 1, the HIV-1 reverse transcriptase is error prone and 2, the viral generation time is short.
14.Describe the evidence that points to Leopoldville/Kinshasa as the cradle of the AIDS pandemic.
Molecular epidemiological studies have indicated the first HIV-1 group M was identified in Leopoldville .The early diversication of HIV-1 group M and evolution of subtypes likely occurred in the area around Kinshasa/Leoldville., Genetic analysis of infected blood and tissue samples collected from residents of Kinshasa in 1959 and 1960 proves this. Demographic data indicate that pandemic HIV-1 emerged at a time when urban populations in west central Africa were expanding and Leopoldville being the largest city with rivers, became a commercial hub. All current evidence points to Leopoldville/Kinshasa as the cradle of the AIDS pandemic.
15. How many different subtypes of HIV-1 group M are there?
HIV-1 group M is currently classied into nine subtypes (A–D, F–H, J, K), and also in to more than 40 different circulating recombinant forms (CRFs). The CRF forms are evolved when multiple subtypes infected the same population.
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