Thanks in large part to Matt Drudge’s incessant ambulance chasing and other worry-warts mostly on the right, everybody seems to be scared shitless of Ebola. I’m here as a microbiologist to tell you why that’s stupid. Let’s break it down point by point, with comparisons to other bugs.

REASON ONE: EBOLA DOESN’T SPREAD VERY EFFICIENTLY.

Even though Ebola kills 60% of the people who get it, there’s little reason to worry because it’s so hard to catch it. The news keeps telling you that you can only catch Ebola from wild animals or from direct contact with the bloody secretions of a terminal Ebola patient. But think numbers: if 3300 people in Africa have died and Ebola is 60% lethal that means only around 5000 people have gotten the disease. But think about where this is happening. There’s LOTS of people there.

Population density of Sierra Leone, ground zero of the current Ebola outbreak

Sierra Leone is roughly as densely populated as Michigan. It ain’t China, but a sick person is going to run into a few people before he drops dead. If this was the flu there would’ve been millions of people catching it. Of course, the flu has a much smaller mortality rate (something like 0.1%), but nevertheless, over 100,000 Africans were killed by flu in 2009. Good old malaria, spread by mosquitoes, kills 17% of Sierra Leonians, in contrast to the 0.05% killed so far by Ebola. If you want to feel sorry about the plight of Africans, worry about these much more efficiently disseminated diseases.

REASON TWO: EBOLA ALMOST CERTAINLY CAN’T BECOME “AIRBORNE”.

Let’s do some math. Evolutionary biologists love math.

The ebolavirus genome is about 19,000 base pairs long. One virus weighs in the vicinity of 0.01 femtograms. Ebola kills its victims essentially by converting them into a horrible stew of ebolavirus, so let’s make the quick assumption that by the time a person has been killed by ebola 0.1% of their biomass has been converted into virus. Thus, a 75 kg human being would yield about 7.5 quintillion ebolavirus particles. If we further assume that the mutation rate for the virus is at the low-end reported for other RNA viruses (0.00001 per bp per genome replication, as reported by Domingo and Holland), we can figure that there are roughly 1.4 quintillion mutations that have been sampled in the process of that corpse’s infection. That’s 75 trillion times the size of the ebola genome, which means that every possible 2-bp mutation of the genome exists somewhere in that corpse. Expand that out to 3000 corpses and we’ve sampled every possible 3-bp mutation, which covers every possible single amino acid substitution of every protein in the genome.

These numbers are staggering. The potential for these infectious particles to find the right mutation that will give them a fitness advantage is astronomical. Therefore, I think it’s safe to conclude that if there was a simple mutation that could make Ebola airborne IT WOULD ALREADY EXIST!

Remember this disease has been around for quite a while. Humans have been getting it since 1976, but it’s been killing other apes even longer. Also remember that there are other hemorrhagic fevers out there, none of which have ever become transmissible by casual contact with aerosols. It’s possible — likely even — that it can’t be airborne and still be ebola-like.

I’m old enough to remember when AIDS first became a thing. There was this mystery gay plague starting to spread to the rest of the country and the rest of the world, killing thousands, with millions more infected. It was 100% lethal, and what was worse, it had a long gestation period during which you were asymptomatic but could still transmit the virus. It was all very scary, and many people conjectured about what would happen if AIDS became airborne. Basically it would mean the end of the human race. But it never happened, of course. Why not? Probably because it can’t, for whatever reason. If Ebola already liquefies you, and it still spreads so poorly, it seems highly unlikely it’s going to get any catchier.

Yeah, sure, something super crazy could happen. Ebola and the flu could have a kid together and turn into Captain Trips. Somebody could weaponize the goddamn thing. But I’m pretty confident evolution isn’t favoring airborne transmission of this illness.

REASON THREE: IF YOU’RE READING THIS, YOU’RE NOT GOING TO GET EBOLA.

Let’s think about another illness for a minute — cholera. Most cholera cases in the modern US come from contaminated shellfish, but in the past people got it from contaminated drinking water. You see, when you get cholera, you shit a lot, and what you shit out is basically water full of cholera bacteria. In places with bad sewage treatment (like everywhere before about 100 years ago), those bacteria get into the water supply and infect whoever drinks the water. In the past, cholera could spread through whole cities like this, killing thousands. Cholera infections of this sort disappeared from the developed world when we discovered sewage treatment, antibiotics, and so forth. Basically, modernity killed cholera.

But cholera is still a problem in places like Africa. Because modernity hasn’t really gotten there yet, and many of these illnesses that are either trivially treated or easily prevented in the West still run rampant in the third world. In the same way, modernity will prevent the spread of Ebola if it gets into the US. Many people wonder why so many health professionals are catching Ebola in Africa. It’s because they’re working in such difficult conditions, without access to the supplies and infrastructure they would have in the US. In the West, we actually have problems because things are too clean, too sterile. A disease that requires piles of unsterilized human waste to lay about in order to spread just isn’t going to get very far.

IN CONCLUSION, if Ebola was like the flu, all of western Africa would already be infected, its hapless residents being turned into vomitous bags of bloody, deliquescent organs. The part of me that grew up loving death metal wouldn’t mind seeing that, but alas, I think we’re just seeing another outbreak of a nasty disease ravaging an unfortunate part of the world. Ebola is like the Great White Shark of the microbial world: in the final tally it doesn’t kill many people, but when it does it’s so spectacularly gruesome that it of course makes the news. And just like shark attacks, we would do better to worry about more common, less gaudy ways to die.

If you just want to worry about something, of course, and why would you want to do that?

Update 10/6: None of this should indicate I don’t think Ebola is a problem, nor that we shouldn’t be combating it. The outbreak in Africa is terrible, and scientists should keep working until this virus is eradicated. My point is that there’s no reason to WORRY about it, especially if you’re a Westerner. Or at least, there’s no reason to worry about it any more than a dozen other diseases out there.

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