How Can a Viral Virus So Deadly Spread to Chickens and Other Birds?

Bird flu spreads to Southern California, infecting chickens, wild birds and other animals


Scientists are grappling with the next big question — how can a virus so deadly to chickens and other birds spread to human beings and other animals?

The answer might lie in an exotic virus known as avian influenza, which first emerged in Asia in 1997 and has spread around the world.

The virus first shows up in animals like chickens and ducks, and then spreads to other birds, said Elizabeth Mello, director of the National Center for Immunizations and Respiratory Disease at the Centers for Disease Control and Prevention.

The virus has caused more than 400 deaths in people, but its spread has been limited so far to poultry and wild birds, Mello said.

“It really has only occurred in chickens and other poultry,” Mello said.

The virus’s genetic makeup is related to the human influenza virus, but it is more pathogenic to birds, she said.

That’s why chickens are more sensitive to the virus. Most infected chickens die within 48 hours, but those that survive have been showing signs of distress, she said.

There’s little new information about how the virus spreads among birds, Mello said.

“The basic idea is that the virus jumps from bird to bird,” Mello said. “But it doesn’t just live on there, it invades other populations.”

The virus is known to exist in ducks, she said, but whether they have been spreading it to chickens and other birds is a matter of debate.

“The chicken is actually a good model of the virus’s behavior, because it seems to have a very tight genetic relationship with the bird flu virus,” she said.

There is one recent report that indicates chickens do not have a genetic link to the virus, Mello said.

Mello and other researchers are learning more about how viruses spread by sequencing the viral genes.

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