Thursday, August 2, 2012

Ebola: Pandemic Virus Fail

I can’t help it; I find Ebola fascinating.  It pops out of nowhere.  It makes its victims bleed out of mucus membranes (is there really anything scarier than bleeding out of your mouth and eyeballs?).  It kills between 50-90% of those infected, depending on the strain.  But you know what?  If someone offered to let me go to the front lines to help collect samples during an Ebola outbreak, I’d jump at that opportunity.  Yeah, call me crazy, but to this virologist, seeing the effects of one of the scariest viruses is pretty much irresistible.  Okay, so no one is going to call me up and make such an offer, but I imagine even non-scientists have an interest (or at least a healthy fear) of Ebola, which is why I am taking the recent Ugandan Ebola outbreak as an opportunity to write another blog post.  After reading some of the comments on the cnn article (, I thought it might be worthwhile to clear up some misconceptions about the actual threat of Ebola to the average person.
There are several strains of ebolavirus, and each strain has its own mortality rate.  For instance, Zaire ebolavirus kills 80-90% of those infected, while Reston ebolavirus is not pathogenic in humans (though it kills some non-human primate species).  The current Ugandan outbreak is Sudan ebolavirus, which typically kills 50-60% of those infected. Ebola is pretty cool in that most people think of virus shape as some type of geometric shape, but Ebola’s shape is essentially like a long, flexible rope.  It can be straight or twisted into various shapes as seen in this photo:
© Centre for Disease Control/AP
The thing that makes this particular outbreak interesting is that infected people don’t have the normal symptoms (like hemorrhaging) that Ebola victims typically exhibit.  As I write this, there are about 30 suspected cases, with 16 deaths, but I am pretty sure that number is going to increase based on the odd symptoms (people may think they have something less severe and not seek treatment), the fact that potentially-infected people fled the hospital (and may infect others), that infected people may not seek treatment out of fear (and thus infect those around them), and they are now reporting 5 prisoners are suspected of having the virus (close quarters, poor hygienic conditions increase the chances of transmission). Comments on popular news articles seem to suggest that many people are worried that Ebola could spread worldwide, but I am going to tell you why that is highly unlikely.
Although Ebola seems pretty scary, it is actually not a very “successful” virus in humans.  If you take into consideration that the whole point for a virus is to keep replicating (virus version of reproducing) and infecting new hosts, then the most deadly ebolaviruses pretty much fail.  Sure, they cause scary disease/death in a few humans before health officials realize that Ebola is afoot, but most ebolavirus outbreaks never make it past the immediate area they began.  Why? 
First, because ebolaviruses cause disease severe enough in a short amount of time that people recognize the need to contain the infection (separate sick from non-sick, identify people who might be infected). 
Second, transmission of ebolavirus is not as efficient as many other viruses.  This is because it is passed when infected bodily fluids like blood, vomit, and diarrhea contact mucus membranes or open wounds.  (This may just be me, but I try to make it a habit of NOT coming into contact with other peoples’ blood, vomit, and fecal matter—okay, the last is kind of lie since I study norovirus—but it holds true for pretty much everyone else) Note that Ebola is NOT passed via aerosols like many highly-contagious respiratory viruses.  By the time an infected person is highly contagious, it is usually obvious that they are sick (because they are either bleeding, vomiting, or having diarrhea), so oftentimes the only people infected are those caring for the patient without proper protective clothing (gloves, eye protection, mask, etc…).
Third, it cannot survive for long outside the body (unlike my beloved norovirus), so people don’t need to worry about touching an infected doorknob or something and picking it up.  (Well, unless you are caring for someone with Ebola who just used the threw up all over the floor and you decide to clean it up.)
Fourth, oftentimes, people die too quickly to infect others. 
Fifth, outbreaks start in remote areas. While we do not yet know for sure the reservoir animal (the animal that carries the virus around in between human infections), it is likely that it is either bats or non-human primates.  People in more remote areas come into contact with these animals, while those in populated areas tend not to.
Finally, most of these remote areas do not have adequate medical care, so many of the first people to handle Ebola patients do not use proper precautions when treating them and end up infected themselves.  Once trained medical staff arrive, outbreaks are usually contained relatively quickly.
Now how does this all relate to the relative non-risk of a worldwide Ebola pandemic?  Think about pandemic viruses:  influenza, HIV, norovirus, etc…All of these viruses have characteristics that allow them to quickly spread in a human population or evade immediate detection.  Influenza is air-borne, so it is very easy to transmit. HIV has a very long incubation period before symptoms start.  This means that you can infect someone (or many people) before you even know you’re sick.  Norovirus is extremely hardy and takes less than 10 virions to make you sick.  Ebola has none of these features.  It has a short incubation period, so you know you’re sick quickly, you know you’re sick by the time you really risk getting others sick, and the virus doesn’t stick around on surfaces waiting to be picked up by an unsuspecting victim.
 But let’s just run through a scenario:  One of the patients that ran away from the Ugandan hospital had Ebola—we’ll call them “Person A”.  For argument’s sake, let’s say that Person A actually made it onto a plane going to France (they must have been well enough to make it to a populated place from their remote village and rich enough to buy a plane ticket to a foreign country).  Let’s say they threw up on the person sitting next to them on the plane (that’s a better scenario than the other possible bodily fluids I’ve been talking about)—we’ll call this person “Person B”.  You can bet this will attract attention since everyone already knows there’s an Ebola outbreak in the country Person A is leaving, and they are displaying symptoms.  You can bet that there will be government health agencies at the airport by the time the plane lands.  But let’s say no one notices (well, except one pissed off Person B).  Person B lands in France, newly infected with Ebola.  Person A also lands in France, but ends up in the hospital within days.  They figure out Person A has Ebola.  They then try to figure out every person that Person A has been in contact with over the past several days.  You can bet they will be contacting every person on the plane.  They will quickly identify Person B as highly likely to be infected.  Those in contact with person B will also be examined, of course, and from here, it will probably be relatively easy to stop the virus from going too far.  Really, though, even the chance that Person A could make it onto a plane and then infect someone on the plane is very low. 
You might make the point that someone who does not know they are infected could leave the country before symptoms start and before anyone knows about the Ebola outbreak.  This is true, but unlikely.  If this did happen, chances are that the people on the plane would not be infected since this person is still well enough to go about their normal business.  This person may infect a few people around them in the country they go to, but the disease would quickly be identified as Ebola, and it would be contained.  The bottom line is that this is a virus that has burned itself out within a matter of weeks every time it has emerged.  It is too deadly too quickly in humans to keep up the transmission cycle long-term.  Make no mistake:  Ebola is no Herpes...or HIV…or influenza…or norovirus.  In my option, Ebola is a pandemic virus FAIL, but a REALLY cool one!