Baker City Herald

Four more groups of mosquitoes trapped in the Keating Valley area, east of Baker City, have tested positive for West Nile virus, the Oregon Health Authority announced Friday morning, Sept. 3.

So far this summer, a total of 19 “pools” of mosquitoes collected in the county have been infected with the virus.

Mosquitoes can transmit the virus to people through bites.

Most people infected with the virus have no symptoms, according to the state health officials, but about 20% will have symptoms such as a fever, headache, body aches, vomiting, diarrhea or a rash.

In rare cases the virus can be fatal.

Of the four most recent pools of infected mosquitoes — a pool usually consists of 10 to 50 insects — two were collected in a trap in Keating Valley on Aug. 25, and the other two were taken from traps near Keating Valley on Aug. 25 and 26, said Matt Hutchinson, manager of the Baker Valley Vector Control District.

Hutchinson is responsible for controlling mosquitoes in the 200,000-acre district, which includes most of Baker, Keating and Bowen valleys. The district’s budget comes from two property tax levies.

The Vector Control District maintains a network of traps across the district. Mosquitoes from those traps are mailed to a laboratory at Oregon State University, there they’re tested for West Nile virus.

Another group of traps is monitored by the U.S. Fish and Wildlife Service and Oregon Department of Fish and Wildlife, as part of a campaign to protect sage grouse, an upland bird that can also be infected with the virus through mosquito bites.

Hutchinson said mosquito populations — including the culex tarsalis species, which is most likely to carry West Nile virus — are dropping in the area due to cooler temperatures and a scarcity of standing water.

But trapping will continue, along with measures to kill adult mosquitoes and their larvae, as long as necessary, Hutchinson said.

Most of the infected mosquitoes this summer have been trapped in or near Keating Valley. The one exception is a trap about four miles north of Baker City, which also collected infected mosquitoes in early August.

So far this year there have been no cases of people being infected with West Nile virus in Oregon.

The virus has been detected in mosquitoes in five counties — Morrow (21 pools, also one bird); Baker (19 pools); Jackson (three pools); Malheur (two pools); and Umatilla (one pool). The virus also was found in one horse in Klamath County.

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