Aug 2, 2013 - By Katie Roenigk, Staff WriterMosquitoes throughout Fremont County tested positive for West Nile virus this week, with hits recorded in Riverton, Lander, rural Hudson and Arapahoe on Wednesday.
"It's pretty much all over," said Nancy Pieropan, a biological control officer with Fremont County Weed and Pest. "People need to assume West Nile is in the area and the risk of getting it is higher than it was a month ago."
According to the U.S. Geological Survey, no human cases of West Nile virus have been reported this summer in Wyoming. But Fremont County is one of only two counties in the state with the virus in mosquitoes -- the other is Goshen County.
The Centers for Disease Control and Prevention says most people infected with West Nile virus will have no symptoms, but 20 percent of people will develop a fever, and less than 1 percent of infected people will develop a serious, sometimes fatal, neurologic illness.
Weed and Pest supervisor Lars Baker said the positive West Nile virus test results came earlier this year in Fremont County.
"It's usually mid-August before we get a hit," he said Thursday. "But last week ... we had WNV everywhere, and we haven't seen that recently. So to me that makes it look like we have more West Nile to deal with than in the past."
On July 24, the virus was found in mosquitoes in Lander, Hudson, Arapahoe and Riverton. A week before that, the virus was discovered only in Lander and rural Hudson.
Baker added that his agency traps mosquitoes in "arbitrary locations" so he can't apply statistical analysis to its results.
On Wednesday in Riverton, 1,000 mosquitoes were caught in a trap on North Smith Road, and though only 2 percent were Culex tarsalis -- the bugs that carry West Nile virus -- they did test positive.
Fifty percent of the 190 mosquitoes found on Davis Lane were Culex tarsalis, and they also tested positive for the virus.
In contrast, only 26 mosquitoes were caught in a trap on Jackson Avenue, including two Culex tarsalis bugs that did not test positive for the virus.
Baker said the results in Riverton demonstrate the effectiveness of the city's mosquito abatement program. Municipal workers currently spray malathion, an insecticide, throughout the city twice each week.
"In the heart of Riverton where the streets are uniform and close together (like Jackson Avenue)... the fogging program is 98 percent effective," Baker said. "When you get out on the outskirts of town by the golf course or on Riverview (Road), we just don't have the fogging technology."
Even in the heart of Riverton, he said people should wear long sleeves and mosquito repellant to avoid being bitten, especially in the evenings.
"Culex isn't out and about until about 7 p.m. at night when the sun's starting to go down and the temperature drops and the humidity comes up," Baker said. "During the day time there are plenty of mosquitoes chasing us all over the place, but they're not Culex."
He said the critters stay active until about 1 a.m.
On Wednesday in Lander, Weed and Pest employees caught 325 mosquitoes on Carbine Lane; 65 percent of the bugs were Culex tarsalis, and those tested positive for West Nile virus. Eighty-five mosquitoes were trapped on "East Washakie" in Lander; all of those bugs were Culex tarsalis, and the group tested positive for West Nile virus.
Another positive hit was recorded Wednesday on Tweed Lane, where 38 of 50 bugs trapped were Culex tarsalis. And on Smith Street in Lander only three bugs were caught, but two were Culex tarsalis, and those tested positive for West Nile virus.
The Wednesday hit in rural Hudson was on Snavely Lane, where 25 percent of the 400 mosquitoes trapped were Culex tarsalis. And of the 175 bugs trapped Wednesday on Mission Road near Arapahoe, 90 percent were Culex tarsalis and tested positive for the virus.
A previous version of this story misidentified malathion. The correction was made Aug. 1.
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