Have you ever wondered why it is that everybody else in the house is sick but you? Or why your entire office feels fine but you’re having a near-death booger experience in your increasingly-unlivable apartment bedroom? Infection seems like such a capricious event in the everyday world; it’s almost as if a virus must have your name written on it.
Every day in the news we hear about another threat of Influenza, coming from birds or pigs or some other nearby threat. The virus, we understand, has mutated and become infectious to humans. A disease spreading from pigs to humans seems to have made a pretty far leap in evolutionary terms.
Now that Western Africa seems on fire with the Ebola threat – and that threat has now reached American soil in Dallas – the growing concern is that Ebola will break out in massive numbers here. We are told that Ebola spreads through direct contact with bodily fluids – from saliva or blood or stool – and that it is not possible to spread the disease through the air as is the case with Influenza.
But some worry: if the virus can mutate, perhaps it will one day become airborne. Is this really possible?
Absolutely nothing in biology is terribly simple. But when thinking about mutations, it’s worth considering that a disease’s means of transmission is different from it’s means of infection.
Infection: the jewel thief’s keys.
When it comes to the disease’s means of infection, that is a question of very specific genetic coding. It’s a lot like a jewel thief’s keys.
Imagine twenty jewel thieves in a museum, each with a different set of keys. They all have the exact same “vector” of obtaining their booty: they’re all using their keys. There is nothing fundamentally different about each thief, they just have a different set of tools to work with. But since each one does have a slightly different set, many of them are going to be out of luck: they simply won’t have the right combination of keys to get them into the doors they want.
New jewel thieves come in and out all the time. They’re all carrying a different set of tools, but the most successful jewel thieves pass their keys along. Eventually, you end up with an incredibly-effective set of keys for a huge number of museums. Now, you have a giant outbreak of Influenza, maybe even as big as the 1919 outbreak.
Ebola is a huge virus containing an incredible number of genes. It dwarves Influenza’s 120nm (nanometres), ringing in at a healthy 960nm. That’s a whole lot of genes and a whopping set of keys. The number of tools they have to work with is much larger than Influenza to start. That makes Ebola hugely infectious, with deadly results.
So far, in the current outbreak in Africa, the fatality rate has been about 50%. But keep in mind: almost none of those poor people have gotten treatment, because the places where outbreaks are occurring are very, very poor.
Transmission: fish vs. birds.
Transmission is the means by which a virus moves from one host to another. You can also think of it as part of the virus’ living environment. A disease’s means of transmission is one of the defining characteristics of the disease precisely because of this. Like any other living creature, where it is found defines the environment it needs to survive. Fish don’t walk on land, birds don’t swim.
In the case of Ebola, there has never been a documented case of airborne transmission. The reason for this seems to be because the virus does not enter the lungs. Ebola will survive for several hours outside the body, but not forever. Like a fish out of water, Ebola exposed to air is a doomed creature.
On the other hand, Influenza is very present in the lungs as most anybody with the flu can attest. And it can survive for days outside of a living host. Of course, it can: it is an airborne virus that is designed to survive the Great Outdoors in search of a new victim.
Thus on the issue of transmission, Ebola and Influenza are profoundly different types of diseases. They exist in different environments for which they are uniquely designed. Crossing the border from one environment to another is not an easy feat for any species.
The upshot: will we see airborne Ebola, soon?
Evolution is a long time coming… So anything is possible. But we may see pigs on the wing – possibly with the flu – before we see airborne Ebola. Because there is nothing about one evolutionary scenario that is any less likely than the other. All kinds of animals and plants evolve in barely-noticeable ways to adapt to their environments. Raccoons are not natural city dwellers, for example. But that is a relatively simple adjustment, relative to the paradigm-altering change some in our society envision for the Ebola virus.
While nothing is impossible, Ebola is a well-established, very old virus. It is also devastatingly successful, in the right circumstances. If the environment doesn’t threaten it’s existence, it would be hard to imagine a scenario where it would need to mutate that much. Ebola is as likely to keep it’s current form as any other creature, maybe more so.
Influenza is highly-transmissible, but with a relatively modest infection rate. That’s why you’re sick and your cube mate isn’t. Ebola is a barely transmissible disease with a huge infection rate. On top of huge genetic differences about which this article does not make a pretense of delving into, it is enough to say that they are profoundly different species that should not be lumped together as just “viruses that can mutate.”