West Nile down, not out

( ())

E-mail this story

Print this story

Share

WOODSTOCK – The West Nile virus has been eclipsed this year in the news media by reports on the H1N1 swine flu virus.

But it’s for good reason. No cases were found in McHenry County so far in 2009 in humans, birds or mosquitoes.

The number of confirmed cases of West Nile virus this year is at a record low both locally and throughout the state, continuing a trend of waning prevalence.

Debra Quackenbush, community information coordinator for the McHenry County Department of Health, said this summer’s weather probably played a big part in keeping the virus at bay.

“It has been a very mild year,” she said. “We didn’t have hot, dry temperatures that help spread West Nile virus.”

This year’s totals are down from the one confirmed case in a dead bird last year and five reported human cases in 2007.

Statewide, this year only four human cases have been reported.

Last year, 20 human cases were reported, and in 2007, 101 human cases were reported. Those years showed a marked decline from 2006 and 2005, when more than 200 human cases were reported.

But the weather, and not some kind of resistance to the virus, was the cause of the drop, said Linn Haramis, a state entomologist who studies West Nile virus.

“The risk may be lower to people, but that doesn’t mean it has disappeared,” he said. “It’s largely driven by weather, specifically low temperatures.”

Temperatures this summer and last were below average, but in 2005 and 2004 they were above average. Haramis said those temperatures were reflected in the number of West Nile virus cases.

And while the number of cases has fallen, the virus was found in more counties this year than last year, Haramis said. The number of horses infected also increased this year.

Those increases were due, in part, Haramis said, to a type of mosquito that can spread the virus, but typically does not bite humans. Nonetheless, they spread the virus that then can be picked up later by mosquitoes with a taste for human blood.

By the numbers

McHenry County:

2009: 0

2008: 1 bird

2007: 5 human cases, 1 bird

2006: 6 human cases, 19 birds, 10 mosquito pools

2005: 3 human cases, 38 birds, 11 mosquito pools

Statewide:

2009: 4 human cases, 25 birds, 389 mosquito pools

2008: 20 human cases, 31 birds, 658 mosquito pools

2007: 101 human cases, 39 birds, 1,552 mosquito pools

2006: 215 human cases, 161 birds, 2,980 mosquito pools

2005: 252 human cases, 227 birds, 2,465 mosquito pools

Source: Illinois Dept. of Public Health