This article is more than 5 years old. Information may no longer be current.
Researchers explain origins of remaining groups of HIV-1
Click Here to Manage Email Alerts
The origin of the last two phylogenetic lineages of HIV-1 have been traced to western lowland gorillas in southern Cameroon, according to recent findings published in Proceedings of the National Academy of Sciences.
HIV-1 has jumped species to humans on four separate occasions, producing groups M, N, O and P. Closely related genetic relatives of group M, which is responsible for the global AIDS pandemic, as well as group N, which has only been detected in a handful of people, have been identified in chimpanzees in southern Cameroon. However, until recently, the origins of groups O and P were unknown.
“Understanding emerging disease origins is critical to gauge future human infection risks,” Martine Peeters, PhD, a virologist at the Institute of Research for Development and the University of Montpellier in France, said in a press release. “From this study and others that our team has conducted in the past, it has become clear that both chimpanzees and gorillas harbor viruses that are capable of crossing the species barrier to humans and have the potential to cause major disease outbreaks.”
Peeters and colleagues were the first to discover the origins of the M and N lineages in chimpanzees.
In their most recent study, the researchers screened fecal samples from wild gorillas — including western lowland (n = 2,611), eastern lowland (n = 103) and mountain gorillas (n = 218) — for simian immunodeficiency viruses (SIVs) throughout southern Cameroon, northern Gabon, the Democratic Republic of the Congo and Uganda.
They identified gorilla SIVs at only four sites in southern Cameroon, where the prevalence of infection ranged from 0.8% to 22%. All of the strains were identified in western lowland gorillas. Although there was considerable genetic variation, phylogenetic analysis showed that all gorilla viruses resulted from a single chimpanzee-to-gorilla virus transmission event — indicating physical encounters between the two species. Three gorilla viruses were subjected to whole-genome sequencing.
“Viral sequencing revealed a high degree of genetic diversity among the different gorilla samples,” study researcher Beatrice Hahn, MD, professor of medicine and microbiology at the University of Pennsylvania, said in the release. “Two of the gorilla virus lineages were particularly closely related to HIV-1 groups O and P. This told us that these two groups originated in western lowland gorillas.”
Beatrice Hahn
Although group P has only ever been detected in two individuals, group O is prevalent throughout west central Africa, affecting up to 100,000 people, according to Peeters and colleagues. That group O has not spread more widely may be due to a lack of “epidemiologic opportunity” rather than a failure to adapt to a human host, they said.
“It is critical to trace human zoonotic diseases to their animal source and understand exactly the barriers (or lack thereof) to transmission and onward spread,” Hahn told Infectious Disease News. “This knowledge is required to gauge the risk of future disease outbreaks.” – by John Schoen
Disclosure: The researchers report no relevant financial disclosures.
Perspective
Back to Top
David Katz, PhD
This study is dealing with HIV, but it also demonstrates an important problem that is common to many emerging zoonotic diseases. The fundamental epidemiological question of the origin of a zoonotic virus is well described for HIV, a virus that since 1981 infected 78 million people worldwide and killed about half of them. It is now well known that HIV originated from the closely related SIV monkey viruses. Of the four well-described phylogenetic HIV groups, two — groups M and N — originated from the chimpanzee SIV.
In this well-designed and well-written study, data obtained from fecal samples that were collected from gorillas dwelling in geographically defined habitats were screened for antibodies and nucleic acids.
It was discovered that the other two HIV groups (O and P) originated from gorilla SIV viruses that were most likely transmitted to the gorillas from chimpanzees.
It was estimated that group O was the cause of an epidemic affecting 100,000 people in West Africa. This case of zoonotic transmission is interesting because it demonstrates a case in which the viruses jumped and adapted to two host species — gorillas and humans — before acquiring the virulent pathogenicity for humans.
It is also interesting that both group M, which is responsible for the current HIV pandemic, and group O probably had a common ancestor. Although the two viruses spread at a similar rate until 1960, it is only then that M group managed to spread at a much higher rate and cause the pandemic. The authors believe that the difference in the viruses is not their degree of adaptability to the human host, but merely the lack of epidemiological opportunity for one group compared with the other.
The authors point out the importance of following the epidemiological traits of the chimpanzee and gorilla SIV viruses because of their capacity of crossing species and causing major outbreaks and epidemics in humans.
Click Here to Manage Email Alerts