Two dead crows found in the Chicago suburbs have tested positive for West Nile virus, indicating that the rare but sometimes deadly pathogen has migrated to Illinois sooner than expected, state public health officials said Wednesday.
The crows were found in Arlington Heights and Lombard two weeks ago, and the virus probably is spreading through the bird population around the state by now, Illinois Department of Public Health Director John Lumpkin said.
Although severe cases of the disease are extremely rare, health officials urged residents to take special care to avoid being bitten by mosquitoes, which can carry the virus from birds to people.
Potentially deadly, the virus can cause encephalitis, an inflammation of the brain. The risk of contracting it is low; less than 1 percent of the people bitten by an infected mosquito will become severely ill, according the U.S. Centers for Disease Control. Nine deaths have been attributed to the West Nile virus in the U.S. since 1999, including one this year.
“People are not a natural target; the cycle is between mosquitoes and birds,” said Dominic Travis, a veterinary epidemiologist at the Lincoln Park Zoo. “Everyone else is an accidental host.”
Elderly and sick people are more vulnerable to West Nile than are others, but most people who are exposed to it will never display symptoms. When they appear, those symptoms range from mild fever, head and body aches and swollen lymph glands to stupor, disorientation, coma, convulsions and paralysis.
“We live in an environment that’s not sterile,” Lumpkin said. “There are organisms everywhere, there are viruses everywhere. We consider this, yes, to be a public health threat. But for the general public, the threat is fairly minimal.”
Primarily a disease that ravages the brains of wild birds, West Nile virus has been found in about 80 bird species and nine mammals since it arrived in the U.S. on the East Coast in 1999, according to the U.S. Geological Survey.
In that first summer, the virus infected more than 60 people in the New York area, killing seven of them. (A report in the British medical journal The Lancet in July concluded that as many as 8,200 New Yorkers may have contracted West Nile during 1999, though most never realized it.)
Ten people are known to have contracted the disease this year, among them a Georgia woman who died. Experts do not know why the death rate has dropped dramatically.
“It could be related to the number of birds infected, the weather, the mosquito emergence, people taking more precautions like protective clothing or other types of control measures,” said Dr. Kathy Converse, a wildlife specialist with the U.S. Geological Survey’s National Wildlife Health Center. “We really have no idea.”
What they do know is that the mosquito-borne virus has been consistently pushing west across the Great Lakes region. Through July 25 of this year, 142 infected birds were found, twice the number found in 2000, according to the CDC. All of the birds identified in the early summer of 2000 were from four states; Connecticut, Massachusetts, New Jersey, and New York. This year, new positives have occurred in Louisiana, Alabama, George, Florida, Delaware, Kentucky, Ohio, Michigan, Indiana, Wisconsin and now Illinois.
Migration plays role
Wildlife officials suspect the migration patterns of birds play a large role in the disease’s spread across the country.
“Several states funnel into wintering areas, so the birds mix and go back to their states,” Converse said.
Though dead crows were found in Rockford in May, Illinois officials had earlier expected the virus to make its way into the state sometime next year. Even though bordering states began to report infected birds in recent months–on Friday two crows found dead in Milwaukee County tested positive for West Nile–officials didn’t expect it to arrive in Illinois before the end of this year’s mosquito season.
But two weeks ago an Arlington Heights woman, Debbie Coffman, found a crow dying on the walkway in front of her home. Initially, she didn’t think much of it, but later that day a friend told her the West Nile virus had been discovered in Indiana. So Coffman alerted the local health department.
“I wasn’t sure if they’d think I was some kind of crackpot,” Coffman, 47, said.
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Four days after Coffman’s crow encounter, a Lombard resident saw a crow staggering along the side of a road. When it keeled over, she grew alarmed and called the DuPage County Health Department.
“She realized that it didn’t look very good, and something must have been wrong,” said Dennis Luehring, a public health center manager with the Health Department.
Both carcasses were sent to the U.S. Geological Survey in Madison, Wis. On Wednesday, survey scientists confirmed that they had tested positive for West Nile.
In early August, Arlington Heights public health officials sent a dead crow to the lab for a reading, but it was too decayed. Arlington Heights Health Director Tom Oas said in the last two days he sent two other bird corpses for testing.
Officials expect spread
Now wildlife experts assume the virus is quickly spreading throughout the bird population all over the state, affecting the animals susceptible to the disease.
“The fact is, it’s probably going to be statewide,” said Brent Manning, director of the state Department of Natural Resources. “We will see it in other areas. It’s carried through migratory birds and through those patterns of migrations. “
Blue jays, hawks and Canada geese are particularly susceptible to the disease.
“But it’s when the crows get it that they die,” Lumpkin said. “They’re like the canary in the mine.”
At Lincoln Park Zoo, officials stepped up surveillance this summer and created an early warning system that could detect the disease in birds and bugs. With the city’s help, the zoo tested mosquitoes trapped on zoo property and regularly drew blood from its animals.
At an afternoon press conference in Springfield, Lumpkin said people should take precautions to avoid being bitten by mosquitoes. Stay indoors at dawn, dusk and early evening, when mosquitoes are most active, he said. Wear shoes, socks, long pants, long-sleeved shirts and mosquito repellant when outside.