(Reuters) - The
Ebola virus raging through West Africa is mutating rapidly as it tears a
deadly path through cities, towns and villages, but the genetic changes
are for now not giving it the ability to spread more easily.
Concern that the virus
could gain capability to transmit through the air - creating a
nightmare scenario of the disease being able to spread like a flu
pandemic, killing millions - was fueled by a top infectious disease
expert in the United States.
Michael
Osterholm, director of the Center for Infectious Disease Research and
Policy at the University of Minnesota, said in an opinion article he
believed the risk of airborne Ebola is real, and warned: "Until we
consider it, the world will not be prepared to do what is necessary to
end the epidemic."
Yet
many other virus and infectious disease specialists say that while the
prospect of an airborne Ebola virus is not impossible, it is extremely
remote.
"This is way down on the list of possible
futures for Ebola and in all probability will never happen," said Ian Jones, a virologist at Britain's University of Reading.
Ebola
is contagious, but spreads via direct contact with the bodily fluids of
an infected person, such as their blood, faeces or vomit. The virus has
infected 5,357 people in West Africa this year, killing 2,630 of them,
in the worst Ebola epidemic the world has seen. [ID:nL6N0RJ3N0]
Ben
Neuman, a Reading virologist who has been monitoring the Ebola epidemic
since it began in Guinea, noted that under carefully controlled
laboratory conditions, scientists have shown it is feasible to make
Ebola transmit through air, but added: "So far there is no solid
evidence that it actually happens out there in the real world."
"One
clue is how slow the virus is spreading," he told Reuters. "Compared to
this Ebola outbreak, the H1N1 swine flu had already spread to an
estimated 10,000 times as many people in its first 10 months."
That's not to say the Ebola virus isn't mutating. It is, rapidly, all the time.
In
a study published in the journal Science late last month, a team of
researchers sequenced 99 Ebola virus genomes isolated from blood samples
of 78 patients in Sierra Leone -- one of the four countries at the
heart of the epidemic.
They
found what they described as "a rapid accumulation of interhost and
intrahost genetic variation" -- in other words, a large number of
frequent changes in the virus -- even in the initial few weeks of the
outbreak.
"SLOPPY" RNA VIRUS
Unlike
some other nasty viruses such us smallpox and hepatitis B, Ebola, like
HIV and flu, is an RNA virus -- one whose genetic material is contained
in ribonucleic acid (RNA) rather than deoxyribonucleic acid (DNA).
RNA
viruses are renowned for their rapidly changing nature and are often
described by virologists as "sloppy" viruses because when they
replicate, they make copies of themselves that are full of errors.
But
most of these mistakes, or changes, are just "irrelevant mutations",
explained Anthony Fauci of the United States National Institute of
Allergy and Infectious Diseases.
Fauci
told a U.S. senate hearing this week that the changes so far observed
in Ebola in this outbreak, while prolific, were generally "not
associated with a biological change or a biological function" of the
virus, meaning they were highly unlikely to give it an entirely new
skill, such as the ability to transmit in droplets in the air.
"It
is an unusual situation where a mutation would completely change the
way a virus is transmitted," Fauci said. "It's not impossible, but it
would be unlikely."
Jones
added that the so-called tropism of the Ebola virus -- the tissue it
prefers to infect -- is the vasculature, not the airway surfaces.
"As
a result it is not in the right place to make the leap to a new
transmission route," he told Reuters. "In fact very few viruses do this.
Most stay in the niche they have established over evolutionary time."
Experts
stress, however, that keeping close tabs on the mutations in the Ebola
virus is vitally important, particularly for those working on developing
potential drugs to treat the infection, or vaccines to prevent it.
The
researchers who sequenced the Ebola genomes and published their
findings in Science said many of the mutations they found had altered
protein sequences or other biologically meaningful targets within the
virus.
"They should be monitored for impact on diagnostics, vaccines, and therapies critical to outbreak response," they wrote
