What we are not afraid to say about Ebola virus

sneezeIn a recent New York Times OpEd entitled What We’re Afraid to Say About Ebola, Michael Osterholm wonders whether Ebola virus could go airborne:

You can now get Ebola only through direct contact with bodily fluids. If certain mutations occurred, it would mean that just breathing would put one at risk of contracting Ebola. Infections could spread quickly to every part of the globe, as the H1N1 influenza virus did in 2009, after its birth in Mexico.

Is there any truth to what Osterholm is saying?

Let’s start with his discussion of Ebola virus mutation:

But viruses like Ebola are notoriously sloppy in replicating, meaning the virus entering one person may be genetically different from the virus entering the next. The current Ebola virus’s hyper-evolution is unprecedented; there has been more human-to-human transmission in the past four months than most likely occurred in the last 500 to 1,000 years.

When viruses enter a cell, they make copies of their genetic information to assemble new virus particles. Viruses such as Ebola virus, which have genetic information in the form of RNA (not DNA as in other organisms), are notoriously bad at copying their genome. The viral enzyme that copies the RNA makes many errors, perhaps as many as one or two each time the viral genome is reproduced. There is no question that RNA viruses are the masters of mutation. This fact is in part why we need a new influenza virus vaccine every few years.

The more hosts infected by a virus, the more mutations will arise. Not all of these mutations will find their way into infectious virus particles because they cause lethal defects. But Osterholm’s statement that the evolution of Ebola virus is ‘unprecedented’ is simply not correct. It is only what we know. The virus was only discovered to infect humans in 1976, but it surely infected humans long before that. Furthermore, the virus has been replicating, probably for millions of years, in an animal reservoir, possibly bats. There has been ample opportunity for the virus to undergo mutation.

More problematic is Osterholm’s assumption that mutation of Ebola virus will give rise to viruses that can transmit via the airborne route:

If certain mutations occurred, it would mean that just breathing would put one at risk of contracting Ebola. Infections could spread quickly to every part of the globe, as the H1N1 influenza virus did in 2009, after its birth in Mexico.

The key phrase here is ‘certain mutations’. We simply don’t know how many mutations, in which viral genes, would be necessary to enable airborne transmission of Ebola virus, or if such mutations would even be compatible with the ability of the virus to propagate. What allows a virus to be transmitted through the air has until recently been unknown. We can’t simply compare viruses that do transmit via aerosols (e.g. influenza virus) with viruses that do not (e.g. HIV-1) because they are too different to allow meaningful conclusions.

One approach to this conundrum would be to take a virus that does not transmit among mammals by aerosols – such as avian influenza H5N1 virus – and endow it with that property. This experiment was done by Fouchier and Kawaoka several years ago, and revealed that multiple amino acid changes are required to allow airborne transmission of H5N1 virus among ferrets. These experiments were met with a storm of protest from individuals – among them Michael Osterholm – who thought they were too dangerous. Do you want us to think about airborne transmission, and do experiments to understand it – or not?

The other important message from the Fouchier-Kawaoka ferret experiments is that the H5N1 virus that could transmit through the air had lost its ability to kill. The message is clear: gain of function (airborne transmission) is accompanied by loss of function (virulence).

When it comes to viruses, it is always difficult to predict what they can or cannot do. It is instructive, however, to see what viruses have done in the past, and use that information to guide our thinking. Therefore we can ask: has any human virus ever changed its mode of transmission?

The answer is no. We have been studying viruses for over 100 years, and we’ve never seen a human virus change the way it is transmitted.

HIV-1 has infected millions of humans since the early 1900s. It is still transmitted among humans by introduction of the virus into the body by sex, contaminated needles, or during childbirth.

Hepatitis C virus has infected millions of humans since its discovery in the 1980s. It is still transmitted among humans by introduction of the virus into the body by contaminated needles, blood, and during birth.

There is no reason to believe that Ebola virus is any different from any of the viruses that infect humans and have not changed the way that they are spread.

I am fully aware that we can never rule out what a virus might or might not do. But the likelihood that Ebola virus will go airborne is so remote that we should not use it to frighten people. We need to focus on stopping the epidemic, which in itself is a huge job.

Comments on this entry are closed.

  • Greg 15 October 2014, 12:59 am

    Ebola has gone airborne, the Reston strain. read “The Hot Zone”

  • Daniel King 15 October 2014, 1:20 am

    The law of conservation of energy is an actual law of nature which applies to all forms of energy in the universe. There’s no law of conservation of total amount of “functions” lol. It’s very common for a biological organism to gain a function and not lose any functions in the process. For example, Ebola’s preferred host is bats. At some point it gained the function to jump over into humans and gorillas too. It didn’t lose the function of residing in bats. Similarly, you can lose a function without gaining any functions e.g. if you suffer an accident and have an arm amputated. There is no universal law of conservation of functions. You won’t find it in any textbooks!

  • StanChaz 15 October 2014, 6:24 am

    How can you generalize and make a blanket statement like this?
    The other important message from the Fouchier-Kawaoka ferret experiments is that the H5N1 virus that could transmit through the air had lost its ability to kill. The message is clear: gain of function (airborne transmission) is accompanied by loss of function (virulence).

  • StacyGInTheCLE 15 October 2014, 9:28 pm

    Steve, this article says that droplet inhalation for minutes to hours after initial contamination is EXACTLY how this virus can spread, being suspended in the air and inhaled: http://www.cidrap.umn.edu/news-perspective/2014/09/commentary-health-workers-need-optimal-respiratory-protection-ebola

  • Steve 15 October 2014, 9:35 pm

    I’ve seen that article. While no one can say with absolute certainty what’s going on right now. The epidemiological evidence supports the existing scientific literature. Put most simply, the CIDRAP piece is not supported by basically any published research.

  • StacyGInTheCLE 15 October 2014, 10:18 pm

    Perhaps not, but something seems to have changed with this outbreak. Past outbreaks have been easily contained, this is doubling every two weeks: https://sites.google.com/site/ebolagraph/

  • Ronald Nicol 16 October 2014, 1:42 am
  • HavanaRick 16 October 2014, 11:34 pm

    Drivel. If someone with ebola sneezes, they are spewing bodily fluids. If you walk through the cloud or are next to them, it’s on you and in your lungs. It’s not technically “airborne” but is aerosol droplets. That’s why the CDC talks about being”very concerned” about anyone within 0-5 feet of a patient.

  • Fred Trout 18 October 2014, 3:16 am

    Please….just please stop with the bogus arguments from authority here. I can cite studies but that won’t resolve the issue or convince those who refuse to believe. I think we all can agree on a few basic points:

    1) “airborne” has a 400 year history of meaning ‘carried thru the air’ and a epidemiological specialized misuse (imo) to indicate some specific type of dry particle aerosol transmission, never mind the details at the moment, nor trying to parse a complex set of normal distributions

    2) droplet transmission of Ebola is possible with perhaps a lower or higher probability than is known AND there are indications that aerosol transmission in the restricted sense is possible perhaps only in certain conditions. We don’t know the details.

    Therefore, let’s skip the confusion in terms … “Ebola IS airborne” IS a non-zero probability true in both senses

    In my recent experience, the most common result of this hubris about ‘airborne’ is that people are simply incredulous and question motives. So lets start telling others who misinform with ‘ Ebola is NOT airborne’ categorical statements to shut their pieholes ! Use the term aerosol, explain details, or whatever but using airborne in a different way than everybody else understands it will KILL people. We have plenty of dead people and will soon enough see a horrifying number more without adding to the carnage.

  • Fred Trout 18 October 2014, 3:27 am

    Why bother ? We know Z_Ebola can infect and reproduce in primate lung tissue. And we suspect it infects that respiratory system in droplets or dry aerosols in perhaps a limited set of circumstances (like within a few minutes / in process of drying out). We don’t need any new or improved mutation either. We just need to stop trying to needlessly parse the process into arbitrary categories of no import.

  • Fred Trout 18 October 2014, 3:42 am

    I have to somewhat disagree here. Ebola has both coughing and hiccuping as common symptoms; talking, vomiting, stooling all generate droplets that can slowly or quickly evaporate into dry aerosols. Further, hospital procedures like breathing tube insertion, cleanup, etc. do the same. Ebola has more than enough chances to become airborne in both senses. It seems likely that this becomes MORE an issue if blood is present, and so later in disease progression. The latter may be why the issue needs qualification and behaves in unexpected ways.

  • Fred Trout 18 October 2014, 3:50 am

    Yeh, it is only supported by potentially misinformed people dying. Lets take a chance on being wrong and save some HCW, yes ? Require respirators or PAPR where possible. Sheesh, the default CDC Ebola protocol only recommends a face shield, no wonder nurses are getting sick. I guarantee you sick costs more than PAPRs.

  • Fred Trout 18 October 2014, 3:54 am

    Yeh, 30 – 50% bleeding seems relatively rare to me too /sarc

  • Fred Trout 18 October 2014, 4:07 am

    Funny that …I just read a piece by a nurse who watched a child bleed out. And see scenes like this:


  • Bruce Everiss 21 October 2014, 1:33 pm

    The science on Ebola is changing very quickly. The WHO and CDC are behind the curve and the MSM are even further behind.

    It is definitely airborne.

    I have tried to document this, and more science, with links through to the sources in my blog articles here: http://www.bruceonpolitics.com/2014/10/20/ebola-science-facts-even-worse-thought/

  • Chris 25 October 2014, 2:05 am

    Ebola is a virus.Coloidal silver water kills ALL known viruses.
    When will you all wake up..!!

  • Sergei Andropov 27 October 2014, 9:17 pm

    You know what else kills all known viruses? Magma.

  • Checker 29 October 2014, 7:25 am

    the difference is of course that in the case of pesticide resistance you’re applying selection pressure on the population, thus FORCING adaptation. no such mechanism is present in the case of ebola.

  • Joe Strange 3 November 2014, 10:59 am

    Rabies evolved into a ‘contact’ disease which no longer requires one to be bitten.

  • Fred Trout 3 November 2014, 7:33 pm

    And you know which set of selective pressures is actually active exactly … how ?

    The first point was that thousands of years is NOT required no matter the species and never has been — that does not change. It is simply a question of selective pressure, generation time, and the presence of suitable mutations that provide advantage. Generation time in micro-organisms is generally extremely short, while that of humans is 17-30 years.

  • Tiffany Lam 13 November 2014, 10:55 pm

    The study you mentioned by Weingartl had, indeed, shown airborne transmission. But keep in mind that the study used swine as their subjects.

    It would be more accurate to model the human-human transmission with non-human primates as done in the study linked below. Both studies had small distances between the cages (15 cm versus 30 cm). However, this study did not show airborne transmission between the NHPs.

    Why the difference in results? Perhaps, there was some unintended “mismanagement” in Weingertl’s study, as you have mentioned!

    However, I do agree further studies need to be conducted on the current strain, as that is the most relevant strain and it has evolved quite a bit in the last while.


  • LAchson 20 November 2014, 6:44 pm

    The Ebola virus may not have lost the function of infecting bats, but how can we know that it didn’t lose another function in exchange?

  • Robert 22 November 2014, 6:12 am

    Thank you for the post with lots of valuable information…

  • TheHookahMaster 31 January 2015, 2:16 am

    Never rule out the possibilities. To do so only leads to bias and narrow mindedness.