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June 18, 2010 > West Nile Virus activity increases

West Nile Virus activity increases

Submitted By Santa Clara County Public Affairs

The Santa Clara County Vector Control District (SCCVCD) conducted its second aerial survey of the season over the urban areas in southwest San Jose, Saratoga, Cupertino, Campbell, Los Gatos, Monte Sereno and southern Santa Clara on Saturday, June 12. The operation covered approximately 80 square miles to detect neglected swimming pools and other possible sources that could harbor mosquitoes.

"All indications are that we're headed into a very busy West Nile Virus season", said Russ Parman, Acting District Manager. "Given all of the extra water this spring, and the continued abundance of neglected pools, mosquitoes and the virus are showing increased activity this year. To date, we have confirmed 13 positive dead birds in the County. The counts of both reported and confirmed positive dead birds are well above average".

In addition, risk models provided by the State of California show the southwest San Jose, Campbell and Cupertino areas may be particularly active and may indicate an elevated risk of human cases later in the season. In response, SCCVCD will enhance its surveillance and control efforts in this region.

On June 12, a survey plane flew at an altitude of 5,000 feet taking aerial photos. The District will review the photos and determine which pools need immediate attention. District Technicians will then contact the pool owners to arrange for the pools to be checked and treated if they are developing mosquitoes.

A prior 90 square mile survey conducted in early May over southeast San Jose identified over 800 green or half-empty swimming pools. Since that survey, District staff has conducted over 600 inspections, about 25 percent of which required immediate treatment to eliminate active mosquito breeding.

Since 2007, the District's aerial survey has cataloged over 3,000 neglected pool locations and District Technicians have performed over 6,000 inspections and 1,600 treatments. Almost half of the mosquito control treatments have consisted of free delivery and planting of mosquito fish, which eat immature mosquitoes.

Response to the aerial survey program has been encouraging. District Technicians who contact and explain to property owners the health risk posed by poorly maintained swimming pools note that most owners take immediate steps to resolve the problem. Formal legal abatement is seldom necessary.

A single, poorly-maintained pool in the backyard can produce millions of mosquitoes. Transmitted by mosquito bites, West Nile Virus (WNV) causes mild to severe flu-like symptoms such as fever, headache, body ache and, in severe cases, significant neurological damage or even death. The elderly and those with compromised immune systems are most susceptible.

It is important for all residents to take the following measures against mosquito bites:

At home:
* DRAIN or DUMP standing water weekly since this is where mosquitoes lay eggs. Check items such as flowerpots and planter bases, toys, cans, leaky water faucets and sprinklers, rain gutters, buckets, pools, ponds, and old tires.
* Make sure your DOORS and windows have tight-fitting screens.

* Limit activities during DUSK & DAWN to prevent mosquito bites. Those are the times when the mosquitoes that transmit WNV are most active.

If you need to go outside at dusk or dawn, or when in an area where mosquitoes are active:
* Apply insect repellent containing D.E.E.T., Picaridin, or Oil of Lemon Eucalyptus (p-menthane diol), following label instructions.
* DRESS in long sleeve shirts and long pants, preferably of light colors.

Anyone bothered by mosquitoes or aware of a potential mosquito-breeding source should contact the Vector Control District at (408) 918-4770. Report dead birds to the State of California WNV hotline at 877-WNV-BIRD or at

Dead birds may indicate the presence of West Nile Virus. The Vector Control District asks Santa Clara County residents to call if they find crows, jays, sparrows, finches, or birds of prey that have been dead for less than 48 hours and do not appear to have died because of an injury.

In 2009, California reported 129 WNV infections, with 112 symptomatic cases and four fatalities.

For assistance on mosquito control, residents can contact the Santa Clara County Vector Control District office by calling (408) 918-4770 / (800) 675-1155 or online at To hear updates and general advice about WNV in Santa Clara County, residents can call (888) SCC-WNV1.

In Alameda County, contact the Public Health Department, Division of Communicable Disease Control & Prevention (510) 267-3200 or Alameda County Mosquito Abatement District (510) 783-7744. A fact sheet is available in several languages at:

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