( ains isolated from 1979-83 in the north...)Drug resistant avian influenza viruses more common in Southeast Asia than North America

ains isolated from 1979-83 in the northeastern United States and Southeast Asia. However, 31 percent of H5 and 11 percent of H9 influenza viruses from Southeast Asia isolated in 2000�{04 carried M2 mutations. Isolates of H5 and H9 subtypes from North America during that time remained sensitive to amantadine, while 16 percent of H7 isolates were resistant to this drug.

"These data are clear and convincing," said Elena A. Govorkova, Ph.D., of the St. Jude Infectious Diseases department, a co-author of the paper. "The specific amantadine-resistance mutations in M2 that we identified can occur randomly throughout the world. But we now have solid proof that in Southeast Asia, and especially in China, these mutations are undergoing strong selective pressure."

Selective pressure refers to the extent to which an organism has acquired either a beneficial genetic trait that gives it a survival advantage in a particular environment and therefore makes the organism more likely to survive and multiply; or a trait that makes it vulnerable to something in the environment, and therefore more likely to become extinct.

The increasing incidence of amantadine-resistant H5N1 viruses in China indicates that these variants appear to have survival advantages over the wild, drug-sensitive strains. In addition, the infected birds die so rapidly there is no time for the virus to acquire a large number of mutations, among which could be changes in the M2 protein. Therefore, the high rate of M2 mutations in China probably arises from some human activity that encourages selection of such changes, the researchers said. For example, treating chickens with amantadine to prevent infection with H5N1 would put selective pressure on the M2 gene to acquire mutations that made it resistant to this antiviral drug.

"H5N1 is now endemic-a permanent- resident- in Southeast Asia, including China," Webster said. "Therefore, any selective pressure on this virus ensures plenty of
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Source:St. Jude Children's Research Hospital

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