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 (http://www.cnn.com/2012/08/02/health/uganda-ebola-virus/index.html?hpt=hp_t2),
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!
