Quentin Tarantino vs. Ebola: It Still Isn't Airborne

There are a number of articles making the rounds that claim that there is now an airborne version of the Ebola virus.  I want to set the record straight on this because misinformation tends to spread a lot faster than the actual facts.  The good news is that those articles are all, for lack of a better term, full of shit.  Let me state it in one simple, easy to read sentence with relatively small words:

Ebola is NOT passed on through the air. 

Viruses just don't seem to ever change their primary mode of infection like that.  There has never been a case of this happening and, as I mentioned in a previous post, it is unlikely that this will ever happen.  Ebola is not an airborne virus. 

What is likely happening here is that someone reads a sentence that says, at least in part, "...a germ like Ebola gets passed on via larger, wet droplets..." and they freak right out, completely ignoring the rest of the article which states, in no uncertain terms, that Ebola is not airborne.  They then do some quick "logical" thinking along the lines of:

1.  Ebola virus can be passed through droplets of fluid
2.  Fluid droplets are in the air after someone vomits or coughs
3.  Droplets in the air = airborne virus
4.  Panic

Now, to be fair, it is possible that the people who are writing those articles are simply misunderstanding basic facts. To be even more fair it is possible that they are trying to share their new found knowledge with people in the hopes of making the world a better place.  Both of these things are possible, but, unfortunately, it doesn't really matter.  This is the kind of thing that incites panic rather than makes things better.

For a virus to be airborne it has to be able to form protective little clusters that allow it to survive in the air while it floats around.  Viruses like this totally suck and can be serious problems because simply being in a room with someone who is sick can be enough to infect you.  By contrast, to get infected with Ebola you have to get those fluid droplets into your body which means you have to be within a few feet of an infected person.  Blood and other body fluids don't fly in the air forever.  Just watch the fight scene where The Bride fights all those bad guys in Kill Bill vol 1 (NSFW).  Even when blood is at its most Quentin Tarantino-y, flying through the air in mass quantities, it is still a fluid and thus will obey gravity.  It eventually falls, typically within 3 or 4 feet of the patient, and thus becomes floor-borne.  

Everyone repeat after me:  To get Ebola, you must get body fluids into your body.  Unless you are a health care worker who is actively treating patients with Ebola, your chances of getting the disease hover right around zero.  You would be more likely to be struck by lightening while winning the lottery.

     

Could Ebola Become Airborne?

Yesterday a student came to class freaked out about Ebola.  Again.  He was freaked out this time because he had read an article which quoted Dr. Michael Osterholm, the director of the Center for Infectious Disease Research and Policy at the University of Minnesota.  In the article, Dr. Osterholm is quoted as saying about an airborne Ebola virus, "It is the single greatest concern I've ever had in my 40-year public health career.  I can't imagine anything in my career - and this includes HIV - that would be more devastating to the world than a respiratory transmissible Ebola virus."

It is important to note that he was not talking about an already existing airborne version of Ebola.  He was talking hypothetically about a possible future airborne Ebola virus.  In fact there has not ever been a case where any virus has shifted its main mode of infection this dramatically.  However this idea - that Ebola could mutate and become airborne - is pants wettingly scary and could result in mass casualties worldwide were it to become a reality.  But how likely is it that this would happen?

The simple answer to this question is "very unlikely, bordering on impossible".  Let's start with an analogy.  You are a quarterback for a football team, and a darned good one.  Last season you were the top passer in the league where you threw over 230 touchdown passes and broke 600 yards of total passing in every game.  It is offensive how good you are.  On top of that you have a natural scent that perfume companies around the world are attempting to copy for their fall scent line.  Lets face it, you are amazing and everyone wants to be you.

You are such an amazing quarterback and all around heckuva guy that your coach decides to throw you in as a defensive lineman for a few plays.  This goes wrong in an almost every possible way.  You are thrown down repeatedly by the larger, more highly trained offensive linemen and manage to get pushed around almost immediately.  You soldier on, however, and on the next play manage to hurt not only yourself but also several of your teammates when your ill advised diving tackle manages to not only miss the running back but takes out 3 of your own players as well.  The overall consensus is that you are amazing on offense with your quick reflexes and the ball in your hand but terrible on defense when size and strength matter more.

Now imagine that you are asked not just to play on a different aspect of a football team, but to play in the French Open tennis tournament.  Sure, it is still a physically demanding activity and you are used to that sort of thing, but it is demanding in an entirely new way that your body is most certainly not trained to handle.  You are used to throwing a ball on a grass field while 11 large men try to kill you.  Tennis requires finesse and years of practice with a racket, not to mention the fact that you are now playing on a slippery clay surface which is difficult even for most pros. With years of time and dedication our star athlete quarterback might be able to make it to the Open, but why would he want to give up his completely successful career to do so?

Ebola is a lot like this quarterback.  It is amazing at what it does which is infecting people and living in their blood.  For it to become airborne it would be the equivalent of our quarterback playing in the French Open.  Sure, with lots of mutations and some significant changes to its structure it could happen, but why would it do so?  It would have to give up its already excellent infection and transmission pathway in favor of one that is almost completely different.  It would have to abandon the blood stream as its primary hiding/replicating place in favor of the lungs or throat.  Then it would have to mutate to become able to survive in the air or on surfaces which, at present, it doesn't seem to be able to do very well (Piercy, et al 2010).

Let's talk a little science here for a bit.  Not too much, but enough to get through some basics.  Viruses don't just magically attach to cells and infect them.  They have to be able to grab on to the cells and, after they have successfully done that, invade the cell so it can reproduce.  Without getting into a cell a virus is unable to make more copies of itself and without being able to attach to a cell it can't begin to do that.  Ebola is an interesting virus in that, like HIV, it grabs onto little handles (glycoproteins and other receptors) in the cell membrane and tricks the cell into allowing it access.  Studies show that its preferred mode of infection is to grab onto cells involved in the creation of connections between tissue layers (like the connections that hold your skin to your muscles) and some immune system cells.  It basically does the same thing that HIV does only way more aggressively.

The types of cells it prefers to attack are relatively specific cell types and, despite the fact that all of the cells in your body have the same DNA they are not, in fact, all identical.  Many have different glycoproteins (handles) and therefore different attachment points.  There is a reason Ebola doesn't infect your sinuses or your throat and that is because it appears to have difficulty binding to the cells in those areas.

So in order for Ebola to become airborne it would require a whole series of mutations which would allow it to:

1. survive in the air and on surfaces at room temperature for long periods of time.
2. stop attaching to its preferred host cells in the blood and connective tissue
3. begin attaching to a new type of host cell in the lungs and throat
4. stop killing patients so darn quickly

Each of these steps would most likely require several mutations which is the equivalent of our football player picking up a tennis racket and learning to serve the ball like Pete Sampras.  Possible?  Sure. Likely?  Not really.

Last, and probably most importantly, is the evolutionary reason for why this isn't going to happen:  there is no selection pressure.  Selection pressure occurs when an organism finds itself in a difficult situation, environment-wise.  If the environment changes significantly then species have to either adapt or go extinct.  Ebola is not facing any sort of selection pressure at this point.  It is wildly good at what it does and is incredibly successful as a blood/fluid born virus.  Would our hypothetical quarterback switch to playing tennis in the middle of his amazing career if the NFL still exists and is willing to pay him millions of dollars?  Neither would Ebola.

I have purposely simplified the explanations in this post to make it easier to read.  If there are any bits that you feel need some expansion or clarification, let me know!



Piercy, T.J., Smither, S.J., Steward, J.A., Eastaugh, L., Lever, M.S. (2010) The survival of filoviruses in liquids, on solid substrates and in a dynamic aerosol. J Appl Microbiol. 109(5): 1531-9.

Ebola: Should I Start Wetting Myself Now or Wait Until Later?

The thing in the picture above is an Ebola virus, and it has many of my students pooping their pants right now. Well, probably not right this second, but there has been some general loosening of a particular sphincter muscle over the idea that Ebola will come and claim their young lives in a rather horrible way.  In this post I hope to pass on a bit of knowledge that will hopefully help you and others to understand what Ebola is and what it can do.  I'll let you decide when and if you need to begin wetting yourself.

First off, Ebola is a filovirus which simply means that it is shaped like a thread.  It has a characteristic "shepherds crook" at one end which gives it a rather unique look - a rather long, skinny structure with a loopy thing at the end.  It causes a hemorrhagic fever which is a fancy way of saying that it has a relatively disturbing habit of causing a massive amount of bleeding which eventually leads to death.  How it works is sort of fascinating, but I think I'll skip that bit for now and instead talk about other things.

At the top of the list of questions people want answered is "How can I get it?"  or, to put it a different way, "How can I avoid getting it?"  It is actually rather easy to avoid getting it because Ebola is transmitted in a very specific way.  Since this virus tends to hang out in the bloodstream, you generally have to get Ebola laden blood into your bloodstream.  This is often referred to as "blood to blood contact".  It has been shown that Ebola can also be found in the sweat, tears, saliva, breast milk, and semen of infected people and it is therefore possible for it to be passed along through those fluids.  Those fluids still need to get into your body, however, so unless you are touching, cleaning, or otherwise handling a person with Ebola or the body of a person who died from Ebola, you are not going to get it.  And if you are planning on touching, cleaning, or otherwise handling a person with Ebola or the body of a person who died from Ebola, wear protective clothing to avoid getting it.  A good rule to follow in Ebola outbreaks is if it is wet and not yours then don't touch it.  Come to think of it, this is a pretty good rule to follow even when there is not an Ebola outbreak. 

Additionally, Ebola cannot be transmitted through the air.  Sure, if someone is violently coughing or vomiting they may spread droplets of fluid into their immediate surroundings - normally no more than 3-4 feet from their body - but the virus still needs to be in a fluid to be transmitted.  So the idea of a single carrier of Ebola on the subway in New York infecting an entire subway car is not going to happen.  Oh, and one more thing, a person is only contagious when they are showing symptoms of the disease, and since Ebola is rather debilitating, it is highly unlikely that someone who is sick with it will be walking around after they start showing symptoms.  So, to sum up, Ebola is rather difficult to catch.

Unless, of course, you aren't aware of what it is or how it is spread.  The main reason it is a problem in Africa is that people are generally unaware of how to avoid getting sick, and when they do get sick the medical facilities are often poor or nonexistent.  Without proper protective clothing the people who are dealing with the sick or dead often become infected themselves.  So when a person who is wearing little or no protective gear transports or handles an Ebola victim they are likely to get the disease themselves.  This is what contributes to the outbreaks in Africa.  People who are unaware of the disease or how to avoid getting it are coming in direct contact with those who have died from it.  They don't know what precautions to take and the virus spreads.  

But what happens when an infected person leaves their country in Africa and travels to the United States?  Aren't we all at risk?

The answer is typically "no".  As mentioned before, if the person is able to walk around he or she is not infectious.  When they do show symptoms they can easily be quarantined in a hospital and treated only by those wearing protective gear.  Anyone that they came in contact with can be monitored to see if symptoms show up and then quarantined should they become sick. It is incredibly unlikely that an outbreak of Ebola would ever cause massive problems here because we are aware of how to avoid getting it and we know what to do with people who have it.  Basically, don't touch a person who is showing symptoms of Ebola and you will be fine.  The only way Ebola could become a problem in the United States is if it became airborne, which, as we will examine in another post, is incredibly unlikely.

So to answer the question in the title of this post, I'd wait a while before you start wetting yourself.