City Council Member and Fremont County Weed and Pest Supervisor John “Lars” Baker displayed a mosquito trap used by his agency to monitor the number of mosquitos and to collect mosquitos to test for West Nile Virus. (Ernie Over photo) 

(Fremont County, Wyo.) – It’s summertime, hot weather has returned and mosquitos are biting. Fremont County Weed and Pest issued an advisory Wednesday to county residents and visitors who are enjoying the outdoors here to take precautions to avoid being infected with West Nile Virus. The advisory is especially important for people living outside of communities where there is no mosquito fogging.

The department’s Biological Control specialist, Nancy Pieropan, reported Wednesday that a pool of mosquitos on Snavely Lane between Lander and Hudson tested positive for the virus, which mosquitos acquire when they have a blood meal from birds that are infected with the disease.

“It usually takes 21 days for the virus to incubate in the mosquito,” said Riverton City Council member John “Lars” Baker who is also the county’s weed and pest control supervisor. In a presentation to the Riverton council Tuesday night, Baker said when the weather gets hot, that incubation period drops to only five days.  “And people are running around in tee shirts and shorts and there is a lot of skin exposed. We need to be vigilant, especially now, mid-July through mid-August,” he said. “People need to use repellant to protect yourselves, otherwise you are inviting infection from that disease.”

Pieropan said a WNV tester, known as RAMP, measures from 0.0 to >650. She said the samples from Snavely Lane measured at the maximum >650 level.

“It’s been really hot in Fremont County, so I am not surprised that I had a pool of mosquitoes tested positive for West Nile Virus,” she said in an email notification message to municipal officials across the county.

One mosquito species in particular is the one to watch out for. “Culex Tarsalis comes out at sunset and is most active until 1 or 2 a.m.,” said Baker. “They are the sneaky mosquitos, not like the aggressive ones you mostly see during the day. Culex Tarsalis will fly about looking for an opportunity to land and bite, they just don’t go in an attack.”

In his report to the Riverton council, Baker said Fremont County is right in the epicenter having the most incidence of West Nile Virus in the country, according to the Centers for Disease and Control in Atlanta, which tracks the disease. “From Fremont County north to the Big Horn Basin, into Montana and North and South Dakota, it’s really a problem that the CDC considers to be a significant health issue,” he said.

According to report from the CDC that was published on June 14th, West Nile Virus in the United States: Guidelines for surveillance, Prevention and Control, recurring high levels of WNV transmission and risk to humans, “High average annual incidence of  WNV disease occurs in the West Central and Mountain regions (CDC 2010), with the highest cumulative  incidence of infection occurring in the central plains states (i.e., South Dakota, Wyoming and North Dakota),” the report stated. A map that accompanied the report showed Fremont County, and points north, along with the Midwest, as the locations where most incidence of the disease is found.

Lars said his department sets mosquito traps around town to monitor the number of mosquitos and test them for WNV. “Where we trap in town, we get between 5-10 mosquitos every night and rarely find one with WNV. However, on Smith Road where the city does not fog, we get hundreds and sometimes thousands of mosquitos. Fogging is 99 percent effective inside the city. It falls apart on the edge of the community where there is flood irrigation and roads are few and far between.” Baker said a fogger needs to treat a 300-foot swath to be most effective.

“Lander and Riverton have the most environmentally sound West Nile Virus management program that you can have,” he said. “It’s very effective.” Baker said the more adult mosquitos that can be removed lowers the possibility of the WNV transmission.

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