Tuesday, December 2, 2014

Ebola In The Air: What Science Says About How The Virus Spreads

Here's an Ebola puzzle for you: If the virus isn't airborne, why do doctors and nurses need to wear full protective suits, with face masks, while treating patients?

After we dug through studies and talked to scientists, the answer slowly emerged.

Ebola does spread through the air. But not through the airborne route.
h goodness! No wonder there's been such a kerfuffle about how the virus is transmitted.

The story began quite innocently at Harvard University way back in the 1930s. William Wells was a hotshot engineer there at the time. He was figuring out a slew of important ideas about infectious disease, like the fact that UV light kills bacteria.

One day in 1933, Wells discovered that pathogens (he was studying bacteria) get trapped in tiny droplets of fluid — maybe some mucus when you sneeze or some saliva when you cough. The pathogens stay alive in the fluid and can move through the air inside these droplets.

Clearly this is one way infections spread. But Wells didn't stop there.

He knew that liquid drops don't last for long in the air. They take one of two courses:
1. Large droplets fall to the ground because of gravity. (Just like rain.)

2. Small drops start evaporating as they fall. Eventually, they become so light that they float in the air. (Just like fog.)

"It appears, therefore, that transmission of infection through air may take one of two forms depending upon the size of the infected droplet," Wells wrote in the American Journal of Epidemiology in 1934. He gave these two routes names:

1. Droplet route: The pathogen falls to the ground in large droplets. The pathogen doesn't make it very far away from the source of the fluid, but if you intercept the drop's path, you could get infected.

2. Airborne route: The pathogen is lifted up into the air inside tiny droplets. The pathogen floats and can move long distances with air currents. If you inhale this mist, you could get infected.

Over the years, the first term didn't really stick with the media or general public. But the second one sure has. And what we've ended up with is one term that often gets used to describe both routes of transmission.

But oh, how they are different! npr

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