Friday, 19 April 2024

Mosquito sample tests positive for West Nile virus

LAKE COUNTY, Calif. – A mosquito sample has yielded the first evidence of West Nile virus' presence in Lake County this year.

The sample, collected near Upper Lake on Aug. 10, tested positive for the disease, according to a Friday report from Lake County Vector Control District and Lake County Health Services.

The discovery comes a month later than West Nile virus was found in the county in 2009, when a necropsy on a dead crow collected in Lucerne confirmed the bird was positive for the disease, as Lake County News has reported.

Overall, West Nile virus has been detected in 28 counties so far this year, compared to 35 in 2009, according to the California West Nile Virus Web site.

In addition, the state reported that there are 16 human cases this year – there were 10 by Aug. 13, 2009 – with four horses so far affected, compared to three last year. The affected horses were in Sacramento, San Joaquin and Madera counties.

The number of dead birds is down, reported at 219 so far, with 299 reported at this time last year. There have been 51 sentinel chickens and 11 squirrels detected with the virus, compared to 56 and two, respectively, last year, the state said.

The virus usually appears in insects and animals before it affects humans, county officials reported.

Mosquitoes transmit the virus both to humans and animals, so local and state officials urged people to prevent exposure to mosquito bites. One way is to use scientifically tested repellents.

“When properly used, mosquito repellents that have been registered with the U.S. Environmental Protection Agency are safe and effective,” Lake County Health Officer Dr. Karen Tait said in a Friday statement.

Tait reported that most people who become infected with the virus show no symptoms and will recover, while 20 percent of those who contract it will develop fever, headache, and other nonspecific

symptoms that may last several weeks.

However, one in 150 people will develop severe illness known as neuroinvasive disease, Tait said. People over age 50 and diabetics appear to be at most risk for the disease's more severe forms.

There is no vaccine for humans, but horses can be vaccinated against it.

Earlier this week, California State Veterinarian Dr. Richard Breitmeyer issued a statement in which he urged horse owners across the state to have their horses vaccinated as the disease returns for the year.

All four horses diagnosed in California with the disease so far this year were either unvaccinated or hadn't been vaccinated completely, Breitmeyer reported.

Horses contract the disease from carrier mosquitoes and are not contagious to other horses or people, and Breitmeyer said not every horse exposed to the virus will die.

“Outbreaks of West Nile virus are still a risk for horses,” Breitmeyer said.

Signs of West Nile virus include stumbling, staggering, wobbling, weakness, muscle twitching and inability to stand, according to Breitmeyer.

Dr. Jamesina Scott, district manager and research director for the Lake County Vector Control District, said in a Friday statement that the district is working hard to reduce the risk of mosquito bites and West Nile virus to Lake County residents and visitors.

However, Scott said they need the public's help to find backyard habitats for mosquitoes, such as neglected swimming pools or ornamental ponds.

“Mosquitoes are easy to control in these habitats if we know where they are,” she said. “Just one neglected swimming pool can produce thousands of mosquitoes per day, and cause problems for an entire neighborhood.”

Scott said people need to drain standing water sources around their homes that may breed mosquitoes and they need to protect themselves with long sleeves or an effective repellent during dawn and dusk when mosquitoes are most active.

To report a dead bird or squirrel, call 1-877-WNV-BIRD (1-877-968-2473) or visit the California Department of Public Health’s West Nile virus Web site at

For more information about vector control services, to get mosquitofish or report neglected

swimming pools to the vector control district, call 707-263-4770 or e-mail This email address is being protected from spambots. You need JavaScript enabled to view it..

E-mail Elizabeth Larson at This email address is being protected from spambots. You need JavaScript enabled to view it. . Follow Lake County News on Twitter at and on Facebook at .

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