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More Dangerous Ebola Strain Unlikely, Study Shows
Researchers compared virus samples that were 9 months apart, and found normal mutating rate
By Dennis Thompson
THURSDAY, March 26, 2015 (HealthDay News) -- Ebola likely won't mutate into a strain that goes airborne or dodges current efforts to develop effective vaccines, tests and treatments for the deadly virus, a new study suggests.
That's because the Ebola virus has been mutating at its normal pace during the current West African epidemic, researchers report in the March 26 issue of the journal Science.
Samples of Ebola taken nine months apart from the West African country of Guinea revealed that the virus is mutating at about the same rate as it has in past Central African outbreaks, the study shows.
"There is no real change in the evolutionary rate, compared to what has happened before in Ebola," said study co-author Dr. Heinz Feldmann, chief of the Laboratory of Virology at the U.S. National Institute of Allergy and Infectious Diseases (NIAID).
These reassuring results should put to rest any fears that Ebola will soon evolve into an airborne form that's more easily transmitted from person to person, said NIAID Director Dr. Anthony Fauci.
In its current state, Ebola is much harder to catch than viruses such as influenza, smallpox or measles. A healthy person must come into direct contact with a sick person or their body fluids for infection to occur.
"There's this fear about, 'Suppose it becomes airborne?' This paper indicated that doesn't seem to be the case at all," Fauci said.
Ebola expert Dr. Lee Norman said the findings also should boost efforts to develop vaccines, tests and treatments for Ebola, because it means those new discoveries ought to remain effective against the virus for some time to come.
"If Ebola has less rapid of a mutation rate, we have the opportunity to stay ahead of it," said Norman, who is chief medical officer for the University of Kansas Hospital. "It bodes well for the stability of new tests and therapies, and the implications for preventing and treating the illness are positive. It would be good if it behaved nicely and did not mutate quickly."
Previous genetic studies performed during the current Ebola epidemic had raised concerns that the virus might be mutating twice as fast as it did in other outbreaks, because it has spread to so many people over an extended period of time, the authors said in background information in the study.
The Ebola outbreak that started in West Africa in 2013 has been the largest and longest outbreak ever recorded. The virus has claimed more than 10,300 lives in the countries of Guinea, Liberia and Sierra Leone, out of nearly 25,000 suspected infections, according to the U.S. Centers for Disease Control and Prevention.
To test Ebola's current mutation rate, the research team examined two separate Ebola outbreaks that occurred last October and November in Mali, a country that has remained largely untouched by the epidemic.
The outbreaks came into Mali from its neighboring country, Guinea. Researchers took samples from the outbreaks and compared the virus to Ebola samples taken from Guinea in March 2014, to see how much the virus had changed.
Viruses constantly mutate, but nearly all those mutations fail to survive as part of the evolutionary process, Feldmann explained. The goal was to see whether today's thriving Ebola strains differ drastically from those found nine months earlier.
In fact, the virus had mutated some, but not enough to affect how it interacts with humans, researchers said. The evolutionary changes occurred at a rate similar to that observed during earlier outbreaks.
"We need to stay vigilant and make sure that the virus isn't changing, but at the moment I don't think there's much of a fear this is occurring anytime soon," Feldmann said. "This is reassuring for the public health measures put into place in West Africa now."
In the same issue of Science, researchers from the University of Wisconsin-Madison reported positive results from clinical trials of a new "whole virus" Ebola vaccine.
The new vaccine protected two groups of monkeys against exposure to lethal doses of Ebola. The first group had received only one vaccination, while the second had received two.
"Whole virus" vaccines are used to treat viral illnesses like smallpox, influenza, measles and mumps. These vaccines activate people's immune systems by exposing them to complete versions of a virus that have been rendered harmless or less virulent.
In the case of this new vaccine, the researchers rendered its version of Ebola safe by deleting a key gene necessary for the virus to be able to reproduce in host cells.
Other Ebola vaccines in development rely on viral DNA fragments and other tricks to prompt an immune system response, Norman said. By exposing people to a safe version of the whole virus, this new vaccine could prove tremendously effective.
"It's the real bug, and that's one of the reasons we've had such success with other whole virus vaccines," he said. "It's coated with all kinds of things the body can recognize as abnormal, and really presents a target-rich environment."
For more information on Ebola virus, visit the U.S. Centers for Disease Control and Prevention.
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