Weather Updates

Colder weather may slow cases of West Nile

Updated: October 10, 2012 3:21PM

After one of the worst West Nile virus seasons since the disease first began infecting humans in Illinois in 2002, the cooler weather is expected to reduce new cases to a trickle, health officials said Friday.

“We are winding down,” said Melaney Arnold, an Illinois Department of Public Health spokeswoman. “We may continue to see a few cases because there is a lag time from when a person is bitten to when they start exhibiting symptoms.”

So far this year, Public Health has logged 179 human cases of the disease, including seven deaths — Chicago Fire Department Lt. Thomas Flahive’s Thursday being the latest.

In 2011, there were 34 cases in the state, including three deaths, Arnold said. This year’s hot, dry summer is being blamed for the spike in cases, both in Illinois and nationally. A total of 3,969 cases of West Nile have been diagnosed nationally this year, with 163 deaths, according to the Centers for Disease Control. That’s the worst U.S. outbreak since 2003.

The type of mosquitos that transmit West Nile thrive in stagnant water, which was in abundance this summer as water receded into places such as ditches and catch basins.

State Public Health officials point out that not all mosquitoes carry West Nile. The floodwater variety typically appears about two weeks after a heavy rain or flooding; they usually don’t carry West Nile.

“Most of the state has been seeing quite a bit of rain,” Arnold said. “So stagnant water isn’t sitting there very much, which is helpful — and also the cooler temperatures.”

The season’s first hard frost usually signals the end of the West Nile season, Arnold said.

The disease can be difficult to recognize without a doctor’s exam, because the initial symptoms are typically flu-like — fever, nausea, muscle ache and headaches.

The disease can be fatal, particularly among the very old and young and those with compromised immune systems, Arnold said. The best protection while outdoors includes wearing shoes, socks, long pants and a long-sleeved shirt. Insect repellent containing DEET is also advised, health experts says.

West Nile claimed 67 lives and sickened 817 others in 2002 in Illinois, the first year it appeared here. Arnold attributed the large number of deaths to that year’s dry summer and the lack of education about the disease

To learn more about West Nile, log onto the state’s Public Health website,

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