Why West Nile could spring this summer Just because the virus was silent for two years doesn’t mean it won’t roar in ‘05
Monday, June 27, 2005
by Rob Olmstead
You may not realize it, but a disaster was narrowly avoided last year when it came to West Nile.
The number of tested birds in Illinois that were infected at this time was actually greater than in 2002, the worst year here for human infections, when 66 people died.
And then the weather turned cold.
“That was almost like someone flipped off a switch and shut down the cycle for a few weeks,” said Linn Haramis, entomologist for the Illinois Department of Public Health. “We really dodged a bullet last year.”
But that luck, Haramis and other experts fear, has led Illinoisans to believe West Nile is no longer a problem. Not true.
“If you have a very wet spring and then a very hot, dry summer … as we did in 2002, that’s really ripe for mosquito breeding,” said Kitty Loewy, spokeswoman for the Cook County Bureau of Health Services.
Our spring has been relatively dry — and scorchingly hot in recent days, but there’s no telling if things will get stay hot this summer, because no meteorologist can accurately predict more than a week in advance, Loewy said.
But if it’s going to get bad, we might know by mid-August, Haramis said.
Until then, county health departments are anxiously monitoring mosquito traps and testing them for the virus.
In DuPage County, that monitoring has never been better, said Dave Hass, public information officer for county health department.
“We believe that we have the best surveillance system in Illinois,” Hass said. “Our total number of traps was increased from last year (48) to 68 this year.”
So far this year, West Nile has been found in mosquito samples in DuPage, Cook, Kane and Will Counties, but not Lake and McHenry.
What health officials are so carefully looking for is a steep upturn in the percentage of infected mosquitoes that signals a potential oncoming human epidemic.
“What we watch for is evidence of what we call amplification,” said Haramis.
In 2002, shortly before the large number of humans became infected, mosquito samples (which are sampled in batches of 50 mosquitoes) went from 30 percent positive to 80 percent positive in a relatively short period of time, “which was, frankly, unprecedented for mosquito-borne diseases,” Haramis said.
Even if amplification is found, however, it won’t give people warning “till really the last minute,” Haramis said.
West Nile is so named because it was first isolated from a woman in the West Nile district in Uganda in 1937, according to the Centers for Disease Control and Prevention. Mosquitoes typically get it from infected birds and can pass it to humans.
In humans, people over 50 are most susceptible to the disease. Of those infected with the virus, about 8 percent show no symptoms. A little less than 20 percent will get West Nile Fever, consisting of fever, headache, and body aches, nausea, vomiting, and sometimes swollen lymph glands or a rash. The sickness can be short, but sometimes even healthy people get sick for several weeks, according to the CDC. Finally, about one in every 150 infected people experience extremely serious symptoms such as high fever, headache, neck stiffness, disorientation, coma and even death.
As health experts wait to see how bad it will be this year, they’re not standing still. Health departments are out putting larvacide in standing water pools — a much more effective, if less noticeable, measure of reducing mosquito population than spraying, experts say.
And though they sound like a broken record, health officials keep harping on two basics that will lessen the chance of infection.
“Everyone is sort of preaching the same sermon,” said Hass.
Use insect repellant and get rid of any standing water near your home. If you can’t get rid of the water, call the county health department to see if they’ll put larvacide in it.
What’s worrying health officials right now is the perception that West Nile is no longer a problem.
“We hear (people say) these things: ‘well, it’s gone away,’” Haramis said.
That is just not true.
“West Nile virus is a episodic disease and in a given area you can have a huge outbreak one year followed by moderate or even no activity the following year, and one or more years may go by with relatively low activity and then there's another outbreak,” Dr. Lyle Petersen noted this spring. Petersen is director of the CDC’s division of vector-borne infectious diseases.
It’s chiefly because 2003 and 2004 were record cool summers that outbreaks weren’t bad, said Haramis, so people should still be vigilant with the bug spray, particularly at dusk and dawn.
“We don’t like counting up the cases afterward. We prefer preventing them,” he said.
For more information
Cook County 2003 diseases report
Map of infected mosquito samples in DuPage
Kane County West Nile statistics
Lake County 2004 West Nile report
McHenry County West Nile statistics
Illinois Department of Public Health
CDC info, including national map