West Nile fever

Wednesday, August 24th 2005, 10:19 am
By: News On 6

What health experts call "herd immunity" and how it applies to the West Nile Virus. The virus seemed to be everywhere three years ago and now it seems to be non-existent, but actually the opposite is true.

News on 6 reporter Emory Bryan says in blunt health jargon, Tulsa's population is considered a herd. Herd immunity means we've almost all been exposed - and become immune to West Nile Virus.

When West Nile Virus first appeared in Oklahoma, health officials didn't know what would happen with a virus carried by birds - and transmitted by mosquitoes to people. Three years later, it appears the virus has spread so far that most people have had it - but probably didn't even know it.

John Baker with the Tulsa City-County Health Department: "There's a significant portion of the population that has been infected, but their immune system fought it off like the flu and now that they've been infected and recovered, they have immunity."

The health department started a surveillance program on West Nile by collecting dead birds for testing. That stopped last year. The department has mosquito traps scattered across the county and they still check those for West Nile Virus each week.

John Ethriedge with the Tulsa City-County Health Department: "So far we've not seen anything this year on the samples we've taken." A check of 600 mosquitoes hasn't found a single one with the virus. John Baker: “as birds with West Nile Virus survive, they become immune and they don't get it anymore.”

As uninfected mosquitoes bite them, they have nothing to pass on. Even though some of the surveillance effort on West Nile has been scaled back, the Health department continues to spray for mosquitoes. They decide where to spray based on complaints. The square mile with the most complaints is where they send these trucks. The spray kills the adult mosquitoes but it just makes a dent in the population.

The department says homeowners make the biggest difference by emptying water from places where mosquitoes lay their eggs. After the recent rain, that's especially important because it only takes a week for standing water to become the perfect spot for mosquitoes to multiply.

Mosquitoes can still carry the virus and it is still possible to get it, but the health department believes most people have already been exposed, and might have already had the virus, though possibly in a form so mild they didn't even know it.