By Les Zaitz
VALE – Infected mosquitoes are on the loose in Malheur County, posing a threat to spread two viruses that can sicken people and animals.
County and state officials recently reported the first case in Oregon this year of a human infected with West Nile Virus, following testing showing several pools of mosquitoes carrying the virus. State health officials said the person didn’t require hospitalization and has recovered.
Health officials say they also have detected – for the first time ever in Oregon – mosquitoes infected with another virus known as Saint Louis encephalitis. The mosquitoes were caught in a trap west of Vale.
The viruses can produce similar symptoms in people – fever, nausea and headaches lasting several days. In more severe cases, symptoms include convulsions or disorientation.
Health officials are ramping up their efforts to go after the mosquitoes. The Malheur County Vector Control District has been sending out ground troops for several weeks now to spray suspected infested areas. The vector district has been deploying four spray trucks each week, fogging about 20 hours a week in the evenings in and around most communities in Vale, according to Gary Page, district manager.
But as more traps produced more infected mosquitoes, the county got the green light to go to the air against the little biters. Aerial spraying is planned for rural areas west of Vale to Hope School and the western part of Harper Valley.
Plans to launch, though, have been stymied by heavy smoke drifting into the area from wildfires in Washington state and Canada. The aerial application could begin later this week.
“To get the most out of this very expensive treatment, we think it best to wait for optimal conditions,” Page said.
The aerial spraying by airplane would cover all irrigated lands starting a mile west of Vale and reaching to Harper, with 35,000 acres targeted, Page said. The application is one half to three quarters of an ounce per acre of an insecticide called Naled, commonly known as Dibrom.
Page said such spraying would happen after sunset. Dibrom is toxic to bees but they should be sheltered in their hives by the time spraying starts.
“It would be good if folks could cover their hives overnight and cover or replace pet and livestock drinking water,” Page said.
Health officials urge those with virus symptoms to get medical attention.
“In particular, anybody over 50 years of age with any conditions at all could be potentially at risk,” said Dr. Emilio DeBass, public health veterinarian at the state Public Health Division.
DeBass said the number of tested mosquitoes being found positive for West Nile is a concern.
“This is more activity than we usually see,” said DeBass. “That poses a threat to the population.”
Detecting the infected mosquitoes means weekly checks of up to 42 traps set around Malheur County. The mosquitoes are sent to a laboratory for testing. The infected mosquitoes so far have been found west of Vale and around Harper.
The virus is likely carried into the area by infected birds migrating from other areas. That’s the likely source for the Saint Louis encephalitis virus found in local mosquitoes recently.
The lifecycle of a mosquito means the virus can spread rapidly. A single female can lay up to 500 eggs in as little as a teaspoon of water. The mother passes the virus on to her young, DeBass said. A mosquito can live about 200 days.
DeBass said infection rates from mosquito bites are low, but people should protect themselves and their animals during this spell. People should be particularly on guard in mornings and evenings, health officials say. They should use repellent and wear long-sleeved shirts and long pants.
Property owners should eliminate as much standing water as possible and ensure window and door screens are in good repair.