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Saturday, August 19th 2006

Darwin 101?

The Los Angeles Times brings us a story about how the threat of West Nile Virus is declining.

As humans and animals develop immunity to the West Nile virus, the number of confirmed human cases of the mosquito-borne disease has seen a dramatic decline in California, a trend that is expected to continue, health experts said.

The downward trend is already in its second year in Los Angeles County, which peaked at 309 human cases in 2004, with 14 deaths. That compares with 43 cases last year and no fatalities, and two cases so far this year.

“What’s occurring here now is the same thing that’s occurring in other areas: You have exposed a virus to a naive population and have had a large die-off,” said Dr. Jonathan Fielding, the county’s health officer. “Those who survived are developing antibodies to fight off the virus. It’s Darwin 2006.”

San Bernardino and Orange counties have also shown a dramatic drop in human infections largely attributed to adaptation in the bird population. San Bernardino County reported 35 human cases in 2005, down from 197 the previous year; Orange County reported 17 cases in 2005, down from 64 the prior year, and one case so far this year.

The point of the story is well taken but we’re not really talking about evolution here are we? The change in heritable traits of a population over successive generations?

The populations in high risk areas have been exposed to the virus and developed antibodies so the disease doesn’t show up in them again. But a child born today to one of them? I’d keep him away from mosquitos.