Cold, Flu, & Cough Health Center

Fears of Global Bird Flu Outbreak Increase

Bird Flu Virus Evolving continued...

All three times, a bird flu evolved a way to spread among humans. For decades, experts have predicted another outbreak. In 1976, for example, it looked as though swine flu would do the trick. But to the embarrassment of health officials of the time, it fizzled out almost before it began.

This time, the fears are based on more solid science. Modern genetic techniques have traced major flu outbreaks to birds. Birds can carry 15 known types of type A influenza, the most serious kind of flu virus. Humans -- so far -- get infected with only three of them.

There are two ways a flu virus can jump from birds to humans. One is evolution; the virus simply mutates into a form that infects humans.

The evidence so far isn't reassuring. Someone sold chickens that died of bird flu to a Bangkok zoo. Keepers fed the chickens to captive tigers. The virus not only infected the big cats, but also spread easily among them. So far, 147 of the zoo's 441 tigers have died.

The other way flu viruses figure out how to infect humans is reassortment. When two flu viruses infect the same person or animal, they swap DNA. So far, that hasn't happened. But pigs get infected with human flu viruses. And Chinese health officials report that the bird flu has been infecting pigs for more than a year.

Early hopes of eradicating the bird flu virus have evaporated. Now the virus is firmly entrenched in domestic and wild birds in Southeast Asia. Could it spread? Recently, officials in Belgium stopped a man getting off a plane from Thailand. They found that he was illegally carrying two hawk eagles. Both birds were infected with H5N1 bird flu. And the veterinarian who examined them came down with a suspicious eye infection, although swab tests were negative for bird flu.

Public Health Response Slow

The WHO last month convened an informal meeting of all 11 companies that make flu vaccines, regulatory authorities, and the health ministers of several nations. The bottom line: If and when bird flu breaks out in humans, there won't be a vaccine for at least several months.

"The most basic thing we are recommending is increased surveillance. It is important we have a global surveillance system in place," the WHO's Cheng says. "We are working with national authorities to accelerate the process of making a vaccine."

Surveillance means identifying human-to-human bird flu transmission in its earliest stages. That's not an easy task, given that bird flu is spreading in some of the most remote and rural areas of Asia. And people whose livelihood depends on small flocks of chickens are loath to report bird deaths when it means that public health officials will exterminate their only source of income.