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Inter-species illness: What's special about swine flu?

April 27, 2009 |  6:34 pm


Swine flu is everywhere, or at least in the media, at the moment. All of the buzz has us wondering -- how are viruses passed from animals to people? It turns out that pigs play a unique role in the whole exchange.

The avian flu has been worrisome for those who fear a pandemic, particularly since 2004, when the World Health Organization began confirming cases of it in people. But unlike its avian counterpart, swine flu appears to be spreading easily from human to human.

This could be because human anatomy is more similar to pig anatomy than to bird anatomy. Science classes often dissect fetal pigs in order to understand the human body. Pigs are large mammals, and thus it's possible for them to spread the illness to other large mammals, including humans.

But why have pigs passed the virus to people, and not to other mammals (like dogs and cats)? And why don't we catch the flu from our pets? They are, after all, the mammals we deal with on a daily basis. But there is no evidence that dog flu has ever spread to other species, according to Wikipedia.

The answer goes back to the bird flu. This strain is especially deadly in humans. When it is transmitted to pigs, it can mutate to form a virus that adapts more easily to people. In other words, the pigs act as incubators for new forms of the virus that can infect people.

The origin of the current outbreak is not known, but it's possible that migratory birds infected Mexican factory farm pigs, who then infected farm workers. Or the pigs could have become infected through manure and flies carrying the virus. A crowded farm or slaughterhouse probably doesn't have much in common with your backyard doghouse.

-- Clare Abreu

More on swine flu from the CDC.

Photo credit: Paul Ellis / AFP/Getty Images

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