CELLOU BINANI\/AFP\/Getty <\/p>\n
A woman gets vaccinated on 10 March 2015 at a health centre in Conakry, Guinea, during the first clinical trials of the VSV-EBOV vaccine against the Ebola virus. <\/p>\n
The Ebola virus is evolving more slowly than previously thought, contends a controversial study of viral genomes from the current West African epidemic. The findings, published in Science on 26 March1, allay concerns that the pathogen could become more difficult to control and thwart therapies and vaccines in development. <\/p>\n
But other experts say that the papers focus on the pace at which Ebola virus is changing is misplaced; the more important issue is whether the virus has gained mutations that make it more transmissible or dangerous to humans. <\/p>\n
The ongoing epidemic, which has killed more than 10,000 people, mostly in Liberia, Sierra Leone and Guinea, is now waning. But researchers say that it is important to chart the evolution of the virus so that they can track its spread more accurately and watch for strains that are acquiring worrisome mutations. <\/p>\n
Researchers first described viral genome sequences from the current epidemic in April 2014, from patients in Guinea2. Then in late August, Pardis Sabeti, a computational geneticist at the Broad Institute in Cambridge, Massachusetts, and her collaborators reported 99 Ebola genome sequences from 78 patients in Sierra Leone3. <\/p>\n
The paper identified the chain of transmissions that had exported the virus from Guinea to Sierra Leone. It also noted that the Ebola viruses from West Africa contained hundreds of mutations not seen in previous outbreaks all of which occurred farther east including many that had altered the virus's proteins. The team estimated that the viruses were evolving at twice the rate during the outbreak, compared to Ebolas long-term rate of change in its animal host. They speculated that mutations hindering the virus had yet to be purged from its genome through natural selection, leading to a faster rate of evolution, at least in the short term. The team cautioned that the virus could develop mutations that would make it more harmful as the epidemic wears on but found no evidence that this had occurred. <\/p>\n
We have always been clear that our study only provided data for what everyone already knows that viruses mutate, says Sabeti. Anthony Fauci, director of the US National Institute of Allergy and Infectious Diseases (NIAID) in Bethesda, Maryland, says that many people misconstrued this observation as meaning that the virus was gaining new properties and potentially even the ability to spread through the air, like the common cold, rather than just through direct contact with bodily fluids. The data never said that, but it was the way people interpreted the data, he says. People were getting concerned. <\/p>\n
A paper posted to the bioRxiv.org preprint site in November, meanwhile, questioned the significance of the doubled rate of evolution4. The conclusions ultimately left readers, and indeed the scientific community at large, with the impression that Ebola virus is fast-evolving and possibly adapting to humans, the authors wrote, adding that more sequence data were needed to determine how Ebola was changing. <\/p>\n
In the new Science paper, Heinz Feldmann, head of the NIAID's Laboratory of Virology in Hamilton, Montana, and his collaborators report genome sequences from two small clusters of cases, after the virus spread to Mali last October and again in November. The team used the data to recalculate Ebolas rate of evolution. The result is a figure about half that of Sabetis team's, and more in line with the virus's long-term rate of evolution. <\/p>\n
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See the article here: CELLOU BINANI\/AFP\/Getty A woman gets vaccinated on 10 March 2015 at a health centre in Conakry, Guinea, during the first clinical trials of the VSV-EBOV vaccine against the Ebola virus. Continue reading
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