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Cheshire mosquitoes test positive for West Nile virus

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LIFE HEALTH-MOSQUITO-BITES SJ

If you haven't already, grab your long sleeves and insect repellent: a second group of Flagstaff mosquitoes has tested positive for West Nile virus.

Mosquitoes from the Cheshire area in northwest Flagstaff tested positive for the virus during routine weekly testing of county traps, Coconino County Health and Human Services confirmed Thursday.

It is the second group to test positive in the county this year, following mosquitoes collected south of Lake Mary Road last week.

No human cases of the virus have been reported in the county yet this year.

Positive tests from insects collected at least 10 miles apart -- in two of the about 40 county traps -- suggest there could be even more virus-laden blood suckers in town.

“In Coconino County, West Nile virus is endemic to the area. It can live here. So whenever we find a positive, though we are only taking samples from very specific spots, that doesn’t mean the virus is not in the community at large,” said County Environmental Health Division Manager Eve Wolters.

Residents are encouraged to avoid going outside during dawn and dusk, when these carrier mosquitoes are most active, or wear clothing that covers the skin and use insect repellent containing DEET, Picaridin, Oil of Lemon Eucalyptus or PMD and IR3535. They should also dump and clean any outdoor containers that can hold water to prevent mosquitoes from breeding nearby.

Although the virus affects only about 20% of people -- the last human cases in Coconino County occurred nearly a decade ago -- it can cause fever-like minor symptoms and more severe effects like tremors, numbness, coma or paralysis in rare cases. There is no specific treatment or vaccine for the virus in humans.

If individuals begin to have fever symptoms, body aches or rashes or swollen lymph nodes, county officials have advised them to contact their health provider.

“The best medicine is prevention,” Wolters said.

She warned County Fair attendees and participants to take extra care this holiday weekend to prevent bites.

County prevention and testing

County staff use a powdered, non-toxic larvicide on water pools near in areas throughout the county where mosquitoes are present. This process occurs monthly throughout each mosquito season.

Though there are other (often more expensive) options to reduce mosquito populations, Wolters said this method is effective for northern Arizona, where the mosquito season is shorter than average, especially this year because of the late monsoon season.

Wolters said mosquitoes typically arrive as early as the late spring -- and “would have been booming” by July -- but the county traps did not begin collecting any mosquitoes until this month.

Though effective for the area, she added that use of this larvicide, which is harmful only to mosquito and midge larva, is not noticeable immediately because it targets the insects before they develop wings. Mosquitoes already flying will continue their multi-week life cycle.

Testing of trapped mosquitoes is conducted locally by separating carrier mosquitoes from non-carriers and putting the carriers into a machine that crushes them up and spins them until mosquito body parts and blood are separated from the virus-affected parts.

When analyzed, if the concentration of the virus reaches more than 200 parts per million, it is confirmed positive.

In the most recent positive batch, four carrier mosquitoes from the Cheshire trap were put into the machine for testing. For the Lake Mary Road batch, it was 15.

Both groups resulted in a parts-per-million concentration of West Nile in the 600s.

According to the Arizona Department of Health Services, last year Coconino County tested nearly more than 200 mosquitoes for West Nile virus. As of Monday, it has tested 89 this year.

Maricopa County, where the virus is most prevalent in Arizona, has more than 100 confirmed and probable human cases this year and 37,000 mosquitoes tested.

Coconino County staff will continue to trap and test mosquitoes throughout the region until colder weather arrives, signaling the end of the mosquito season.

Locals should get used to being covered in long garments or bug spray until then, too, unless they can resist the end-of-summer weather and stay inside during prime mosquito time.

Kaitlin Olson can be reached at the office at kolson@azdailysun.com or by phone at (928) 556-2253. 

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