The world has never seen an Ebola epidemic like this one.
Instead of improving, the situation is getting worse, with infection rates growing exponentially in three West African countries. The disease is so out of control there that the World Health Organisation has said that by early December, there could be 10,000 new Ebola infections every week.
The intensity of the outbreak has prompted some researchers to ask if something is different about the virus this time. After all, the Ebola virus — like all viruses — changes over time.
Is it possible that a recent mutation transformed Ebola into something more contagious?
395 Mutations And Counting
First, to get this out of the way: though it’s theoretically possible that the virus could mutate to become airborne, we don’t even know if it’s physically possible. In the more than 100 years that we’ve studied viruses, we’ve never seen a human virus change its mode of transmission.
“That’s a genetic leap in the realm of science fiction,” Council on Foreign Relations senior fellow Laurie Garrett explains in the Washington Post.
An airborne mutation would require more than a few random changes coming together. Even when researchers have tried to genetically engineer an already deadly virus to go airborne, making those changes also made the virus unable to kill.
But other mutations are possible and with viruses, common. We’ve seen quite a few already in this outbreak.
Researchers analysed 99 Ebola virus genomes after taking samples from 78 patients in Sierra Leone in late May and early June of 2014. They added in data from three samples taken in Guinea.
Analysing the virus genome helped them track how the virus had spread in Sierra Leone. To do this genetic detective work, they looked at mutations in the virus to trace its path. When they compared their current samples to previous data, they were able to track 395 different mutations. If you take into account the number of new cases since then, there have probably been many more.
These results were published in the Sept. 12 issue of Science.
Why Viruses Change
As alarming as that number of changes may seem, viruses mutate when they replicate all the time. When viruses replicate, which is what they do inside a person they have infected, they make copies of their own genetic material.
When making these genetic copies, RNA viruses like Ebola are “notoriously bad” at doing so accurately, according to Vincent Racaniello, a Professor of Microbiology & Immunology at Columbia University’s College of Physicians and Surgeons.
“Notoriously bad” here means that they mutate a lot, which can be good for the virus if a change makes the organism better able to survive.
In the case of Ebola viruses, this may explain why different Ebola Zaire outbreaks have had different fatality rates — though many prior outbreaks have been too small to be provide accurate fatality rate data.
Even without going airborne, there are potentially frightening Ebola mutations.
Peter Jahrling, chief scientist at the National Institute of Allergy and Infectious Diseases, recently told Vox that he thinks it’s possible that this strain could be more virulent than in the past — that the virus is replicating more rapidly, meaning there are more viral particles in every drop of bodily fluid.
Ebola is already highly infectious — only a tiny amount of virus is needed to catch it, and one-fifth of a teaspoon of blood may already contain 10 billion viral particles. An increased viral load could make transmission even easier, though direct contact with body fluids would still be a necessary condition.
Another scary possibility is that the proteins in the virus recognised by our immune system could change.
At the moment, people who survive Ebola can’t be infected by the same strain again. But a change in those proteins recognised by our immune system would mean the virus might be able to infect survivors again, and would also mean that vaccines in development could be made useless.
This sort of mutation isn’t uncommon, according to Harvard geneticist Pardis Sabeti, who was part of the team that analysed the mutations in this outbreak — and Sabeti told The New York Times that they have seen some evidence that this protein changing might be happening with Ebola, occasionally at least.
But Sabeti and other researchers say that there’s no evidence that the virus is fundamentally different in any way or that it will mutate into something different.
Instead, these mutations are standard, just like with all viruses. Ebola is bad enough that no extra explanation is needed, beyond the fact that the outbreak happened in a densely populated place that wasn’t prepared for it.
“You’ve got a fairly standard Ebola virus,” Dr. Edward Holmes, a biologist at the University of Sydney in Australia, told the Times. “It’s just in the worst possible place.”
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