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West Nile virus outbreak called unlikely

Jackson County residents aren't out of the woods yet but chances are no pesky mosquitoes carrying West Nile virus will be found here this year.

If so, it would mark the third consecutive year the virus has not been found in the county.

"We've been testing since May and have not found any positive for West Nile in mosquitoes, chickens, bird samples — there have been no dead bird results at all," said Eugene Papineau, manager of the Jackson County Vector Control District.

"Its been a good year so far," he added later.

Moreover, by the second week in September, the mosquitoes which can carry the virus are usually no longer flitting around looking for a blood meal, he noted.

West Nile virus can kill horses and birds and in some cases cause flu-like illness or even death in elderly people or those with weakened immune systems, according to the federal Centers for Disease Control and Prevention in Atlanta.

Mosquitoes acquire the virus after biting an infected bird. Those mosquitoes can then transmit the virus to a person, horse or to another bird. Other diseases that mosquitoes can carry include viral encephalitis and heart worms in dogs.

Originally from Egypt, West Nile was first found in the United States in 1999, when a few East Coast residents were infected. It has since spread to the West Coast and was discovered in Oregon in 2004.

West Nile was first found in Jackson County in 2004, and each summer through 2008. None was found in the county in 2009 or 2010, Papineau said.

Last year also marked the first time since 2004 that no mammals — human or otherwise — infected by the virus were found in the entire state, the Oregon Health Authority reported.

Statewide, the virus appeared to have peaked in 2006 when 73 humans were infected, according to the department. One person died in Oregon from the disease in 2006 and another the following year.

It is not unusual for mosquito-borne viruses like West Nile to spread quickly and peak, only to become less prevalent, although still maintaining its presence in an area, Papineau said.

"When a disease like that is new to an area, it can reach an epidemic stage that lasts for a couple of years," he said, adding that it then is considered endemic.

"You will still see it occasionally," he said.

Like similar operations throughout the state, Jackson County Vector Control has a mosquito surveillance program to monitor for evidence of West Nile.

In addition to testing mosquito pools for signs of the disease, the agency, working with the Oregon Department of Fish and Wildlife and its federal counterpart, tests dead birds from the corvid family for signs of the disease. Corvids include crows, ravens, jays and magpies.

Four sentinel chicken flocks are also maintained in the county as part of the local surveillance program for the virus. The chickens' blood is periodically tested for the virus.

The local vector control also checks swimming pools from the air to ensure they are not infested with mosquitoes.

Pools that are chlorinated stand out as brilliant blue in color photographs. Green pools, tinted by algae, are prime breeding areas for mosquitoes.

Despite an usually wet spring, there were fewer mosquitoes in the county this year than last year, Papineau said.

"Our mosquito numbers were down a little from last year," he said. "But we are still testing. We still have a few weeks to go."

Reach reporter Paul Fattig at 541-776-4496 or email him at pfattig@mailtribune.com.