Why Ebola Probably Won't Go Airborne

The idea that Ebola could go airborne is terrifying.

Once you are infected, few diseases are more likely to kill you - and death by hemorrhagic fever, diarrhea and vomiting often accompanied by bleeding and organ failure, sounds particularly awful. At present it's hard to get infected - healthcare workers and family members caring for victims are at highest risk - but that would change if the virus were to mutate so that it could be transmitted through the air while keeping its present lethality.

That's a nightmare scenario.

But it's more the stuff of bad dreams than of reality. There's no known precedent for a virus to change in that way.

It is theoretically possible - everything in nature changes and evolves. Some health officials highlight this as a reason to act now to contain the disease. Anthony Branbury, the UN's Ebola chief (who is not a doctor or an Ebola researcher), recently said the possibility of an airborne mutation shouldn't be ruled out.

Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, floated the possibility of airborne Ebola in a New York Times op-ed titled "What We're Afraid to Say About Ebola." He made the argument that since there are so many more Ebola cases now, more than there have ever been, the virus has more opportunities to mutate than it ever has, which makes an airborne mutation more possible.

Osterholm wrote "that virologists are loath to discuss [this possible mutation] openly but are definitely considering [it] in private."

This argument is supposed to motivate governments to act to get the virus under control before the devastation in West Africa gets worse - and that's important.

But virologists are willing to talk about the possibility of Ebola mutating to become an airborne virus, and they have great explanations for why there's almost no chance of that happening.

How Viruses Change

Vincent Racaniello, a Professor of Microbiology & Immunology at Columbia University's College of Physicians and Surgeons, recently wrote a blog post about why airborne Ebola is not something to worry about.

Here's the key line:

We have been studying viruses for over 100 years, and we've never seen a human virus change the way it is transmitted.

As Racaniello explains, HIV-1 has been around since the beginning of the 20th century. It has not ever changed its mode of transmission. Millions of people have been infected by Hepatitis C since the 1980s, and it, also, has never changed its mode of transmission. If not treated in time, rabies has an even higher mortality rate than Ebola, but it hasn't changed its mode of transmission.

It's not that viruses don't change and mutate - they do, frequently. When they copy their genome and replicate, improper copies mean that all kinds of new variants of the virus arise. Different strains of the flu go around the world all the time, which is why the flu vaccine is usually made to protect against a few different strains.

But to completely change its mode of transmission a virus would need more than a simple mutation.

Some scientists recently attempted to genetically engineer a supervirus in a lab, trying to take the H5N1 bird flu and make it airborne - this is a terrifying experiment, and one where a mistake could cause a devastating pandemic.

But even though they could genetically engineer the virus so it could be transmitted through the air, that altered other important things about the virus as well. As Racaniello explains, it lost the ability to kill.

Why The Ebola Virus Is Especially Unlikely To Go Airborne

A mutation of this sort is especially unlikely in a virus like Ebola, because - before it could go airborne - "a substantial amount of Ebola virus would need to start replicating in cells that reside in the throat, the bronchial tubes and possibly in the lungs," Scientific American explains.

But Ebola enters the human body through cuts, through the eyes, or through porous tissue in the nose or mouth. From the moment it enters the body, the virus is not designed to attack the respiratory system. It attacks blood vessels and the liver but it doesn't even cause a cough.

And even if the virus were to somehow move to the respiratory system, which would be a huge change, that still doesn't mean it would go airborne.

Viruses like avian flu that do naturally infect the throat and lungs but aren't airborne among people haven't changed to transmit through the air among humans. From Scientific American again:

The airborne method would have to be so much more efficient than the current extremely efficient means of transmission that it would overcome any genetic costs to the virus stemming from the mutation itself.

As Scientific American explains, there isn't much evolutionary pressure for Ebola to transform into this frightening but almost totally new virus. It is, unfortunately, surviving as a species already, without anything to wipe it out.

What About Pigs And Monkeys?

People who fear airborne transmission of Ebola often point to a 2012 study at the Public Health Agency of Canada, where macaque monkeys in a pen next to pigs intentionally infected with Zaire ebolavirus caught the disease. At the time, researchers thought this might mean that the pigs spread the virus to the monkeys through the air - though they noted that the monkeys themselves still seemed unable to transmit the virus that way.

The same scientists followed up on their research this summer and found that Ebola could not spread through the air between monkeys. They think that in 2012, washing the pigs' cages may have splashed virus-laden blood into monkey pens, which how they caught the disease.

In addition, when intentionally infected with the deadly strain, pigs are affected by it in a different way than humans are - the virus attacks their lungs and throat, which is exactly what it doesn't do to us. That means that those intentionally infected pigs may have even been coughing virus-containing droplets out. But then and now, monkeys have never been shown to transmit the virus through the air.

And even though pigs have been found carrying the Reston strain of Ebola, which doesn't harm humans, they don't usually catch Zaire ebolavirus, the deadliest strain, which is responsible for the ongoing epidemic. None have been found to have the virus in the current outbreak, and researchers even tested pigs in the first known Ebola investigation, but found no infected swine.

The Bottom Line

Ebola offers plenty to worry about. It's killing thousands of people in West Africa and causing economic and humanitarian disasters. Mutations could make the virus spread slightly more easily through contact or could make it even more efficient at killing the people it infects.

Most experts still say that this outbreak, like all previous Ebola outbreaks, will be contained. If it isn't, then a reservoir of the virus could remain in humans, making Ebola deaths all the more common.

But a theoretically possible and potentially physically possible - though that's not confirmed - airborne mutation is so unlikely and unprecedented that it's really not the right thing to worry about now.

There are plenty of already-existing problems to solve.