How Does Swine Flu Virus Spread?

One virus can make millions of new viruses inside a human cell. Watch NPR's Robert Krulwich explain how that happens.

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ROBERT KRULWICH: Hi, I'm Robert Krulwich, and to keep this story going: with more schools closed now and so many kids at home, the obvious intention here is to keep the virus from spreading further because that's what viruses do, they spread any way they can.

(Soundbite of sneeze)

KRULWICH: Yeah, that's one way. A sneeze puts lots of virus in the air where it can go up somebody's nose, down to the throat, and we thought it might be fascinating for you to see in rich, detailed, moving color what happens when a virus lands on one of your throat cells, uses a chemical key to break into your cell...

(Soundbite of door opening)

KRULWICH: ...slips down through the membrane...

(Soundbite of machine)

KRULWICH: And takes over the manufacturing apparatus at the heart of your cell to make a million new viruses. So, with help from the Zirus Research Company, we've made a video - it's very short - which lets you watch the virus attack you and then shows how your immune system...

(Soundbite of spitting)

KRULWICH: ...fights back. You got to see what that immune cell looks like. To do that, you just have to go to npr.org/health.

BLOCK: That's NPR's Robert Krulwich.

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Flu Attack! How A Virus Invades Your Body

It starts very simply. A virus, just one, latches on to one of your cells and fools that cell into making lots more. Lots, lots more, like a million new viruses. This animation shows you how viruses trick healthy cells to join the dark side.

David Bolinsky and his team at XVIVO designed this animation for a research company called Zirus (and we thank Zirus for letting us play with their pictures). Bolinsky says what you see in the video actually happens much, much faster in real life — in a fraction of a fraction of a second. So this is a very slow motion version of cellular activity.

And for those of you who were wondering, yes, the designers did add color. Proteins, DNA, organelles, and the teeny things inside a human cell are so small, and the insides of cells are so dark, that for all practical purposes, they are colorless.

So the copying molecule isn't really pink. But once you decide to colorize, pink is just as accurate as maroon or yellow.

One Last Thing

In our video we ask, if a flu virus inside your body can multiply by the millions within seconds, why don't we topple over and die quickly?

Here's a better, longer answer than the one in the video. First, some new viruses get caught in mucus and other fluids inside your body and are destroyed. Other viruses get expelled in coughs and sneezes. Second, lots of those new viruses are lemons. They don't work that well. Some don't have the right "keys" to invade healthy cells so they can't spread the infection. And third, as the animation shows, your immune system is busy attacking the viruses whenever and wherever possible.

That is why most of the time, after a struggle (when you get a fever and need to lie down), your immune system rebounds, and, in time, so do you.

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