Read This to Get a Better Understanding of How Ebola Spreads

Celine Gounder, Reuters, October 13, 2014

{snip} Many, including CDC Director Tom Frieden, are questioning how the nurse became infected despite wearing the appropriate personal protective equipment, which should have shielded her from direct contact with Duncan and his bodily fluids.

Once again, the specter of airborne Ebola is being raised.

No virus that causes disease in humans has ever been known to mutate to change its mode of transmission. This means it is highly unlikely that Ebola has mutated to become airborne. It is, however, droplet-borne–and the distinction between the two is crucial.

Doctors mean something different from the public when they talk about a disease being airborne. To them, it means that the disease-causing germs are so small they can live dry, floating in the air for extended periods, thus capable of traveling from person to person at a distance. When inhaled, airborne germs make their way deep into the lungs.

Chickenpox, measles and tuberculosis are airborne diseases. Droplets of mucus and other secretions from the nose, mouth and respiratory tract transmit other diseases, including influenza and smallpox.

When someone coughs, sneezes or, in the case of Ebola, vomits, he releases a spray of secretions into the air. This makes the infection droplet-borne.  Some hospital procedures, like placing a breathing tube down a patient’s air passage to help him breathe, may do the same thing.

Droplet-borne germs can travel in these secretions to infect someone a few feet away, often through the eyes, nose or mouth. This may not seem like an important difference, but it has a big impact on how easily a germ spreads. Airborne diseases are far more transmittable than droplet-borne ones.


In 1995, more than 300 people became sick with Ebola in Kikwit, Democratic Republic of the Congo. Disease detectives were unable to determine how 12 of the patients were exposed–again raising questions about the possibility of airborne transmission. But if Ebola could be transmitted through the air, at least some family members of Ebola patients should have gotten sick even without direct contact. That didn’t happen.

Ebola struck again in 2000, this time affecting more than 400 people in Gulu, Uganda. Not all had direct contact with another Ebola patient. Bedding and mattresses seemed to be one source of infection. So did sharing a meal with an Ebola patient–which often meant using fingers to eat from the same plate. Each had in common likely exposure to infected bodily fluids.


For Ebola Zaire [the strand of Ebola affecting West Africa] to become airborne in humans, it would need to cause lung disease significant enough to release lots of virus into respiratory secretions. The virus would then need to survive outside the body, dried and in sunlight for a prolonged time. And it would need to be able to infect another person more than a couple feet away.

There’s no evidence from previous epidemics or laboratory experiments that Ebola Zaire behaves in this way. Although the virus is mutating as the Ebola epidemic continues to grow in West Africa, it has multiple hurdles to overcome in order to become airborne.


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