Friday, March 27, 2015

NIH: Ebola Virus More Stable Than Previous Study Suggested



# 9873


Last August, while Ebola was still accelerating in West Africa, we saw a study warning that the Ebola Virus Is Rapidly Evolving.  Specifically, that 99 Ebola viruses taken from 78 people from Sierra Leone during the month of June, and found that the virus is showing a marked propensity to accumulate `interhost and intrahost genetic variation’ as it passages through the population.

This led to media reports such as Ebola virus mutating rapidly as it spreads from Nature News, and  Ebola Is Rapidly Mutating As It Spreads Across West Africa via NPR’s Goats & Soda Blog.

As I noted at the time,  while scientists have the ability to sequence and compare these variant viruses, they don’t necessarily know what these individual mutations (or their aggregate) means to the virus, or how it might change its behavior.


Still, this study raised the level of concern over how this virus was evolving, and what changes in its behavior that might eventually bring.


Yesterday the NIH announced a far more reassuring survey of the Ebola virus’s evolution, which found a far less aggressive rate of change in the virus than previously announced.  First the NIH announcement, followed by a link to the study, then I’ll be back with a bit more.


NIH study finds no evidence of accelerated Ebola virus evolution in West Africa


The Ebola virus circulating in humans in West Africa is undergoing relatively few mutations, none of which suggest that it is becoming more severe or transmissible, according to a National Institutes of Health study in Science. The study compares virus sequencing data from samples taken from patients in Guinea (March 2014), Sierra Leone (June 2014) and Mali (November 2014).


“The Ebola virus in the ongoing West African outbreak appears to be stable—that is, it does not appear to be mutating more rapidly than viruses in previous Ebola outbreaks, and that is reassuring,” said Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases (NIAID), part of NIH. “We look forward to additional information to validate this finding, because understanding and tracking Ebola virus evolution are critical to ensuring that our scientific and public health response keeps pace.”

Obtaining virus samples for analysis was challenging for researchers during the outbreak. The NIAID study published today relies on data from the Guinea and Sierra Leone cases as well as samples from two case clusters in Mali obtained from the International Center for Excellence in Research (ICER) located in Bamako. NIAID and the Malian government have been partners in the ICER since 2002. The Mali case clusters originated from people who became infected in Guinea and traveled to Mali, where they were diagnosed.

Today’s study, from NIAID’s Rocky Mountain Laboratories, finds that there appear to be no genetic changes that would increase the virulence or change the transmissibility of the circulating Ebola virus, and that despite extensive human-to-human transmission during the outbreak, the virus is not mutating at a rate beyond what is expected. Further, they say, based on their data it is unlikely that the types of genetic changes thus far observed would impair diagnostic measures, or affect the efficacy of candidate vaccines or potential virus-specific treatments.

As of March 11, the World Health Organization listed more than 24,000 confirmed, suspected or probable cases of Ebola virus disease in West Africa, with about 10,000 deaths.


Mutation rate and genotype variation of Ebola virus from Mali case sequences

T. Hoenen1,*, D. Safronetz1,*, A. Groseth1,*,  K. R. Wollenberg2,*, O. A. Koita3,  B. Diarra3, I. S. Fall4, F. C. Haidara5, F. Diallo5, M. Sanogo3, Y. S. Sarro3, A. Kone3, A. C. G. Togo3, A. Traore5, M. Kodio5, A. Dosseh6, K. Rosenke1, E. de Wit1, F. Feldmann7, H. Ebihara1, V. J. Munster1, K. C. Zoon8, H. Feldmann1,†,‡, S. Sow5,†,‡


The occurrence of Ebola virus (EBOV) in West Africa during 2013–2015 is unprecedented. Early reports suggested that in this outbreak EBOV is mutating twice as fast as previously observed, which indicates the potential for changes in transmissibility and virulence and could render current molecular diagnostics and countermeasures ineffective. We have determined additional full-length sequences from two clusters of imported EBOV infections into Mali, and we show that the nucleotide substitution rate (9.6 × 10–4 substitutions per site per year) is consistent with rates observed in Central African outbreaks. In addition, overall variation among all genotypes observed remains low. Thus, our data indicate that EBOV is not undergoing rapid evolution in humans during the current outbreak. This finding has important implications for outbreak response and public health decisions and should alleviate several previously raised concerns.



Last night Lisa Schnirring of CIDRAP News reviewed these findings, and looked at reports of two new Ebola cases in Liberia, an update on the American being treated at the NIH, and news on one of the candidate vaccines in:


Gene study finds no worrisome changes in Ebola virus

Lisa Schnirring | Staff Writer | CIDRAP News

A genetic analysis published today of Ebola virus samples over the course of the outbreak found few changes and noted that the virus is apparently more stable than a study back in August had suggested.

(Continue . .. )

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