The height of the West Nile virus season has arrived and the county is responding in part with a faster, cheaper test it perfected last year to detect the disease in birds.

The new test, in which tissue taken from a dead bird's eye is analyzed for evidence of the virus, was developed as a record number of birds were being diagnosed with West Nile in San Diego County.

"Necessity is the mother of invention," said county Veterinarian Dr. Nikos Gurfield, who oversaw development of the test in the county's Animal Disease and Diagnostic laboratory.

In 2008, Gurfield and his staff diagnosed 563 dead wild birds with West Nile virus.

By contrast, only 217 birds had been diagnosed in 2007, according to county statistics.

West Nile virus is generally a bird disease, but it can be transmitted to people and other animals through bites from mosquitoes that have fed on infected birds.

It produces flulike symptoms in people and, in rare instances, death.

The old test for avian West Nile involved performing a necropsy on each bird and harvesting several internal organs to see where the virus might be hiding in each specimen.

A necropsy for West Nile takes between 10 and 20 minutes per bird, not including the time it might take an outside lab to analyze the tissue, Gurfield said.

Battling a barrage of birds to be analyzed in 2008, Gurfield and his staff reviewed scientific literature on the virus and learned that it could be detected in a bird's eye tissue.

That's when they got to work developing a "rapid test" and studying its effectiveness in detecting West Nile in crows, which are especially susceptible to the virus, Gurfield said.

Sampling eye tissue takes just two minutes and the sample can be analyzed at the county lab, he said.

"This really allowed us to ramp up and process over a thousand birds with limited staff," Gurfield said.

The new method also is cheaper, he said.

"We figured that if we had run all the samples the old way versus the new way, the cost savings -- in labor hours, and equipment and supplies -- was about $25,000 for the high season," Gurfield said.

Gurfield's lab study of this new technique was published this month in the Journal of Veterinary Diagnostic Intervention, and the technique has caught the attention of other public agencies tracking West Nile.

Robert Cummings, director of scientific services for Orange County Vector Control, said Orange County has started using the test but has run into a snag trying to evaluate it.

"It turns out this year we have so little West Nile virus activity in our birds compared to last year," Cummings said. "We only have five West Nile virus-positive dead birds. By this time last year, we had almost 300.

"It's hard to get any valid statistics from a sample of five," he said.

San Diego County also has seen a drop in avian West Nile cases compared with 2008, said Chris Conlan, the county's supervising vector ecologist.

Conlan said 2008 was an exceptional year for the virus, but the reason isn't clear.

"Overall, the weather was a little warmer," Conlan said. "Could it have been that the overall immunity in birds was lower? That green pools on foreclosure properties were contributing? We just don't know enough about this to say."

No human cases of West Nile have been reported in the county so far this year.

Earlier this week, San Diego County environmental health officials announced that just 16 wild birds had tested positive for the virus since January.

In addition, two "sentinel chickens" have tested positive, officials said.

Vector Control maintains four sentinel chicken flocks around the county and periodically tests them for the virus.

When a chicken tests positive, officials know that mosquitos carrying the virus are breeding nearby.

Stagnant water provides a breeding ground for mosquitoes and should be eliminated or reported, county officials said.

To report dead birds or mosquito-breeding sites, call the county's West Nile virus information line at (888) 551-INFO or visit www.sdfightthebite.com.

Call staff writer Colleen Mensching at 760-739-6675.

Steps to protect yourself from West Nile virus:

West Nile virus, which typically affects birds, can be transmitted to humans by mosquitoes that have fed on an infected bird.

- Mosquitoes breed in standing water. Eliminate standing water in yards, gardens, children's pools, flower pots and other receptacles.

- When outdoors, wear long sleeves and pants, and cover exposed skin with insect repellent containing DEET, Picaridin or oil of lemon eucalyptus.

- Stock ornamental ponds and birdbaths with free mosquito-eating fish from the county.

- Avoid outdoor activity, especially near water, at dawn and dusk.

- Make sure window and door screens are tight and free of holes.

- Report mosquito breeding sites and dead birds to the county at www.sdfightthebite.com or (888) 551-INFO.

-- Source: County of San Diego