EBOLA About viruses and viral disease What we are not afraid to say about Ebola virus

[China Connection]

What we are not afraid to say about Ebola virus

18 September 2014

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.

http://www.virology.ws/2014/09/18/what-we-are-not-afraid-to-say-about-ebola-virus/

 

[China Connection]

Why Ebola is very unlikely to go airborne

Updated by Brad Plumer on October 2, 2014, 10:35 a.m. ET @bradplumer brad@vox.com
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Ebola is not currently an airborne disease. You can't catch Ebola by sitting across the room from someone who has it. You can only catch Ebola from coming into direct contact with the bodily fluids of someone who has the disease and is showing symptoms.

"Fears that Ebola will mutate and spread through the air are overblown, experts say"

(One caveat: If someone with Ebola symptoms sneezes or coughs and the saliva or mucus hits your eyes, nose, or mouth, that can transmit the disease, but this is rare, and it's mainly a concern for health workers. It's also not what people mean by "airborne.")

Back in September, however, an op-ed by Michael Osterholm in The New York Times raised a disturbing possibility — what if the Ebola epidemic in West Africa goes on long enough and the virus keeps mutating? Could Ebola somehow become airborne then? And wouldn't that allow the disease to spread even faster around the world? More recently, Dr. Oz raised the specter of airborne Ebola on The Today Show.

This is a scary scenario. But fortunately for the world, most infectious disease experts remain very skeptical that Ebola will ever become airborne. "This is way down on the list of possible futures for Ebola and in all probability will never happen," explained Ian Jones, a virologist with the University of Reading, back in September.
'We've never seen a human virus change the way it is transmitted'

But why are experts so confident Ebola won't become airborne? It's worth reading this long post by Vincent Racaniello, a virologist at the College of Physicians and Surgeons at Columbia University.

He goes into detail about how viruses mutate, but here's his bottom line: "We have been studying viruses for over 100 years, and we've never seen a human virus change the way it is transmitted":

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.

This jibes with what Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases, told the Senate in mid-September: "Very, very rarely does [a virus] completely change the way it's transmitted."

Fauci noted that viruses do mutate a lot, in ways that might make the disease more virulent or a little bit more efficient at spreading. That's why researchers are currently trying to monitor the mutations. But with all the dire things to worry about with Ebola, he said, the prospect of the disease going airborne is not "something I would put at the very top of the radar screen."

Further reading: For more on the science of Ebola transmission, check out this previous post by Susannah Locke. She notes that, yes, some pigs infected with Ebola may be able to transmit the disease by coughing and sneezing large droplets. But there's a huge caveat here: Ebola affects pigs in a completely different manner than it does humans (in pigs, Ebola shows up as an infection of the lungs; in humans, it mainly targets the liver).
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How do you catch Ebola?

Ebola isn't as contagious as Hollywood would have you believe. It mostly spreads through direct contact with the bodily fluids — vomit, semen, sweat or blood — of someone who is symptomatic and shedding the virus. This means that when someone is sick, you need to get their bodily fluids into a cut on your body or your mouth, nose or eyes. That's why it's the health-care workers and family caretakers who nurse the sick that have borne the burden of Ebola.

Ebola can live on surfaces for a few hours, and in blood outside of the body, it can live for up to a few days. So there is a risk of getting Ebola by touching a contaminated surface and then putting your hands in your mouth or eyes. But this is a less common mode of transmission.

The virus isn't airborne, thankfully. Experts expect that it will never become airborne. As Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases, told the Senate recently: "Very, very rarely does [a virus] completely change the way it's transmitted."

Ebola doesn't spread quickly, either, and it hasn't mutated to become more transmissible over the years. "The good news is that Ebola has a lower reproductive rate than measles in the pre-vaccination days or the Spanish flu," wrote a mathematical epidemiologist who studies Ebola in the Washington Post. He found that each Ebola case produces between 1.3 and 1.8 secondary cases. Compare that with measles, which creates 17 secondary cases. "And the time that elapses between the first Ebola case and the generation of secondary cases is about two weeks. This should allow plenty of time to identify those who are sick and protect people who might come in contact with them."

What makes Ebola scary is the fact that there is no cure or treatment yet on the market, but those who have access to hospital care — including fluids and antivirals — have a much higher chance of beating the disease. The trouble is, Ebola usually strikes in Africa — and among populations where few have access to that kind of advanced medical care.

http://www.vox.com/2014/9/19/6543157/ebola-is-unlikely-to-go-airborne

 

[OddOne]

The only problem with this is that Ebola going airborne has happened before. Fortunately, the strain that did it was the Reston variant, which doesn't negatively impact humans. We know of five primary strains. We don't know how many more there are, and if one of them is air-transmissible it'd certainly explain the explosion of Ebola infections in this outbreak.