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More West Nile virus found in trapped mosquitoes

Aug 24, 2017 From staff reports

For the second time this summer, West Nile virus has shown up in tests of the local mosquito population.

"I was hoping to make it into September with no more indications," Fremont County Weed and Pest assistant supervisor Nancy Pieropan said in an email Wednesday. "Unfortunately culex mosquitoes trapped in Hudson last night tested positive."

Culex tarsalis is the species of mosquito that carries West Nile.

The infected bugs were found on Ohio Avenue in Hudson in a trap that contained 13 mosquitoes total, including six culex, according to Pieropan's data sheet.

Low totals

Despite the positive West Nile hit, Pieropan said the low number of total mosquitoes in the trap can be taken as "good news."

"The mosquito numbers across the county have dropped dramatically in the past week, reducing the risk of getting bit and WNV transmission," she said in her email.

At its peak July 17 the Ohio Avenue trap held 141 mosquitoes including 125 culex. The totals have generally fallen from here, to 98 mosquitoes and 83 culex Aug. 1 and 15 mosquitoes and 14 culex Aug. 8.

There was a slight uptick Aug. 15 when 37 mosquitoes and 34 culex flew into the trap, but then the numbers fell again to the totals recorded this week.

Snavely Lane outside of Hudson shows a similar pattern, peaking July 12 with 2,800 mosquitoes and 33 culex. The total plummeted o 1,300 mosquitoes and 16 culex July 18, hovering around the same numbers July 25 (1,600 mosquitoes and 45 culex) and Aug. 1 (1,500 mosquitoes and 40 culex) before dropping dramatically to 117 mosquitoes and seven culex Aug. 8.

There was another bump Aug. 15, when 1,650 mosquitoes and three culex were found in the Snavely Lane trap, but the population fell again this week, when there were only 240 mosquitoes and two culex there.

Smith Road

In a recent Weed and Pest newsletter Pieropan indicated that the number of mosquitoes trapped this year has been consistent with the totals caught in the past, with one exception.

"The trap northeast of Riverton located near the river and outside of the treatment area has had very high numbers due to flood waters," Pieropan said.

In earlier reports she noted that floodwater mosquitoes are different from the variety that carries West Nile.

Regardless, the Smith Road trap was the site of this year's other West Nile hit, which was recorded Aug. 1. The container held 300 bugs that day, including 24 culex tarsalis.

The totals at the North Smith Road location have fallen steadily since then, to 158 mosquitoes Aug. 8, down to 146 Aug. 15 and 96 this week.

The culex numbers rose before falling, though, with 42 found in the trap Aug. 8 and 41 Aug. 15, down to 19 this week.

Pieropan said the culex totals also mirror previous years.

"As in past years, the number ofculexmosquitoes increased in mid-summer as the total number of all mosquito species trapped dropped dramatically," she wrote in the newsletter.

The difference this year compared to 2016 is that West Nile was found later and in fewer areas, she noted.


Pieropan's group tests mosquitoes from several locations in Riverton, though one trap has been moved to different spots in the city throughout the summer.

The mainstay is on Davis Lane, where eight mosquitoes - all culex - were trapped this week, down from 43 mosquitoes and 17 culex Aug. 15. There were 34 mosquitoes and 24 culex Aug. 8 and 61 mosquitoes and 46 culex Aug. 2.

The traveling trap has been on the ditch above Adams Avenue for the past two weeks.

From there it collected 33 mosquitoes and six culex Aug. 15, down to four mosquitoes and one culex Wednesday.

Just south of Riverton, a trap in Arapahoe contained 62 mosquitoes and only one culex Wednesday. On Aug. 15 that trap held 39 mosquitoes and 7 culex, and on Aug. 8 it had 56 mosquitoes and five culex.


City employees place three traps in Lander, which, combined, contained 48 mosquitoes and 13 culex Wednesday. Another trap on Carbine Lane held 55 mosquitoes and four culex that day.

Earlier in the month, the city traps held 154 mosquitoes and 32 culex Aug. 15 and 60 mosquitoes with 40 culex Aug. 8. The Carbine Lane trap had 107 mosquitoes and 33 culex Aug. 15 and 156 mosquitoes and 40 culex Aug. 8.

Risk falling

As summer's end approaches and evening temperatures fall, Pieropan said the risk of West Nile goes down too, but the virus can still be transmitted until the cold weather sets in.

"People need to continue to protect themselves from being bitten by mosquitoes," she wrote in the newsletter.

She advises residents and visitors alike to wear long sleeves, stay inside at dawn and dusk, drain standing water from properties and use bug spray.

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