County tackles West Nile County tackles West Nile (September 16, 2005)

By Katie Vaughn

Reported cases of West Nile virus in both animals and humans have been increasing throughout the state and Santa Clara County. And while no cases have been found this year in Mountain View, residents have reason to stay on alert, according to some officials.

"We do know West Nile virus is in this county," said Kriss Costa of the Santa Clara County Vector Control District. In order to combat the disease, she said, "We've spent 20 percent more on products this year than ever before."

West Nile virus is spread to humans and animals through the bite of an infected mosquito. When infected, most people show no symptoms, though some experience a fever, headache or body aches.

"The majority of people will never know they're infected," Costa said.

However, she said, of the roughly 20 percent of people infected with West Nile who do have warning signs, more than one-third may experience neurologically invasive symptoms such as muscle weakness, paralysis or even coma.

In other words, around 7 percent of those infected -- and it is not known exactly how many people that is -- show serious symptoms. Particularly among the elderly and people with lowered immune systems, the virus can be deadly.

After reaching New York in 1999, the virus has since been found in 42 states. So far this year, 370 people from 27 counties in California are known to have been infected with West Nile, and eight virus-related fatalities have been reported. Santa Clara County confirmed its first 2005 case in July, although the 34-year-old woman who contracted the virus is believed to have been bitten in Sacramento. She has since recovered.

The county's most common strategy against the virus is regularly spraying a protein mixture called BTI to areas of standing water where mosquitoes live and breed. The chemical stays in the water for a few days, and is lethal only to the mosquitoes and two kinds of flies closely related to them, said Vector Control ecologist Dan Strickland.

"If you spray these chemicals, you won't affect dragonflies, you won't affect aquatic beetles, and you certainly won't affect salamanders, ducks, children and things like that," he said.

Vector Control also uses a number of methods to monitor the status of West Nile virus in the county. Strickland said it relies a good deal on residents, asking people to call if they find a dead bird or notice swarms of mosquitoes. After a call comes in, technicians pick up the bird for testing or scour mosquito-heavy areas for breeding sites. They also trap mosquitoes and test them for the virus, and keep four "sentinel flocks" -- coops of a dozen or so chickens whose blood is tested on a weekly basis -- around the county.

Crows in particular, Strickland said, serve as good indicators of where the virus moves, as the birds contract a high level of West Nile and therefore die from it more often than other animals. The birds have provided "a really good idea of the distribution of the virus in the Valley," Strickland said.

Recently, that distribution seemed to be getting worse and worse, he said. "If you just make a graph of the [dead] crows, it makes a sort of ski-slope shape that indicates an epidemic." (Strickland then clarified that the word "epidemic" indicates disease among humans. The correct word is "epizootic," indicating disease among animals.)

Strickland emphasized that the "epizootic" is only being seen in the San Jose area, and theorized that warmer temperatures and a higher population density are to blame. Recently, Vector Control found more than 60 dead West Nile-positive birds and a large number of infected adult mosquitoes in a pair of two-square-mile neighborhoods in southern San Jose, prompting the first residential ground fogging in the county to kill adult mosquitoes. Technicians fogged both neighborhoods twice, completing the second fogging Sept. 9.

For those treatments, officials administered Pyrenone 25-5, a chemical containing pyrethrins, which are made from the extract of chrysanthemum flowers and are a common ingredient in household insect sprays, head lice medications and pet shampoos. The chemical is non-carcinogenic and low enough in toxicity to be safe for humans and pets, officials said.

Despite the fogging in San Jose, Strickland said that there are "absolutely no positive birds within the last three months in Palo Alto, Mountain View or Sunnyvale."

According to Costa, Vector Control did find one infected bird in Mountain View last year. But whereas a single bird may have flown into the city and died, the large number in San Jose suggests the birds -- and the virus -- were based there.

But, Costa warned, a lack of infected birds does not necessarily mean Mountain View doesn't harbor the virus.

"People need to realize that even though we haven't found infected birds in Mountain View, that doesn't mean it's not there," Costa said.

Costa said there are three important steps residents can take to protect themselves against West Nile virus: Remove standing water on property to eliminate mosquito breeding grounds, contact the Vector Control District if they spot a dead bird or notice excessive mosquitoes or bites, and wear an insect repellant if they are going to be outdoors at dawn or dusk -- times when mosquitoes are particularly active.

"The odds of being bitten by an infected mosquito are low, but it only takes one bite," Costa said.

E-mail Katie Vaughn at kvaughn@mv-voice.com

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