Friday, January 09, 2009

Mutation, Natural Selection and Exaptation in Action.

Health officials are concerned that the dominant flu strain cropping up this year seems to be Tamiflu resistant. The story in the Herald Tribune notes:

Last winter, about 11 percent of the throat swabs from patients with the most common type of flu that were sent to the Centers for Disease Control and Prevention for genetic typing showed a Tamiflu-resistant strain. This season, 99 percent do.

"It's quite shocking," said Dr. Kent Sepkowitz, director of infection control at Memorial Sloan-Kettering Cancer Center in New York. "We've never lost an antimicrobial this fast. It blew me away."

The single mutation that creates Tamiflu resistance appears to be spontaneous, and not a reaction to overuse of the drug. It may have occurred in Asia, and it was widespread in Europe last year.

It has undergone selection and will become the dominant strain until we find something to combat it. Now the kicker:

The mutation conferring resistance to Tamiflu, known in the shorthand of genetics as H274Y on the N gene, was actually, he said "just a passenger, totally unrelated to Tamiflu usage, but hitchhiking on another change."

The other mutation, he said, known as A193T on the H gene, made the virus better at infecting people.

This is a classic example of a genetic mutation that codes for a protein that does something else being co-opted by the virus' defense mechanism to ward off Tamiflu. Evolution in action!

Hat tip to Glenn Reynolds. Stay Healthy!!

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