West Nile virus not slowed by dryness

Mosquitos that carry the disease find places to breed where homeowners leave water standing after irrigating their yards.

By Jason Wells
BURBANK — Vector control officials are asking the public to alter their water use as West Nile virus contraction rates continue to climb throughout the state despite an oppressive drought this year.

West Nile virus rates are up since last year amid a record-setting dry spell mostly because homeowners are over-watering their lawns and neglecting small pools of water, officials said.

The virus has not turned up in Glendale, but the city is now at the midpoint between two locations that have produced West Nile-positive mosquitoes in the county, said Truc Dever, spokeswoman for the Greater Los Angeles County Vector Control District.

The district announced last week that a mosquito sample from traps in Granada Hills on June 25 tested positive for the virus, bringing this year's tally of West Nile-positive samples in the county to three.

Positive tests registered in Rowland Heights and South El Monte earlier this year. Glendale is about 20 miles southeast of Granada Hills and 20 miles northwest of South El Monte.

But risk for contraction is equally spread throughout the county since mosquitoes can only travel between one and seven miles from where they emerge from larvae as adults, Dever said.

"The risk is basically the same across the L.A. Basin," she said.

While risk is the same from region to region, there have been more cases overall this year, according to state Department of Public Health records.

Three women in Northern California have developed West Nile-induced fevers so far this year. Two men, also in the northern part of the state, have asymptomatic infections, according to the department.

There have been 64 more dead birds and 76 more mosquito samples this year that have tested positive for the virus than in 2006, state records show.

Mosquitoes are the main transmitters for the virus, which can cause fever, headache, tremors and other neurological afflictions, according to the U.S. Centers for Disease Control and Prevention.

Researchers are studying the cause behind the strong numbers, which seem to fly in the face of conventional wisdom — that more water means more mosquitoes and vice versa, Dever said.

But for the Southland and its semi-arid climate, rain plays less of a factor in determining the size of mosquito populations, said Minoo Madon, scientific-technical services director for the count vector control district.

"There's so little rain in the L.A. Basin that it doesn't really matter if it's a rainy season," he said.

And during an especially dry year, the public tends to unknowingly create problems, he said.

The most troublesome are over-watered lawns that send run-off into storm drains — a popular breeding site for mosquitoes, he said.

The vector control district hires crews specifically assigned to mitigating that problem, Dever said, but stagnant water created on private property is the hardest to scope out.

"Those are the sources that are most difficult for us to monitor because they're in peoples' backyards," she said.
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