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West Nile treatment ‘a success’: San Mateo abatement reduces mosquito numbers by 99 percent
August 05, 2014, 05:00 AM By Samantha Weigel Daily Journal

After more than a month of battling San Mateo County’s first reports of mosquitoes infected with West Nile virus, the San Mateo County Mosquito and Vector Control District was pleased to announce Monday its fogging abatement treatments were successful.

However, as the warm summer weather continues and more reports of deceased birds and squirrels are made, the district said it would continue to closely monitor for further outbreaks.

The district first identified the virus in San Mateo in mid-July and has fogged four times with the largest concluding Thursday morning. Traps set before and after the treatment turned up no infected mosquitoes and showed the population was reduced by 99 percent, Vector Ecologist Theresa Shelton said. The district fogged more than a square mile with an epicenter of the Sunnybrae neighborhood, according to the district. Previous foggings on June 19, July 19 and July 28 evenings focused in the North Central neighborhood.

“It definitely reduced the threat not just because they tested negative, but mostly because the trap numbers were much lower. So the population was reduced a lot. So that will help, but we could have a lot more warm weather,” Shelton said. “So I wouldn’t say it’s gone from San Mateo for the summer. We don’t know that, but the immediate threat was lessened.”

Since its successful treatments, the district picked up a few dead squirrels on Friday and three dead birds on Monday, Shelton said. The birds were found in Menlo Park, Ladera and Redwood City. The district has in-house equipment to test the birds and expects results Tuesday, but the squirrels will be sent off-site and the cause of their death will take more time to determine, Shelton said.

San Mateo has been notorious for having high numbers of culex mosquitoes — the genus that caries West Nile virus, the district’s Assistant Manager Brian Weber said.

Although San Mateo has been the focus of the recent foggings, Weber said, it also conducted an abatement treatment in Ladera, near Portola Valley.

The district hadn’t conducted a fogging abatement treatment since 2006 and Weber said it covered roughly 3.5 square miles in the last month and a half alone.

“Considering that we have West Nile, it’s the busiest season that I can remember,” Weber said. “Obviously, it feels good for all of us. Everyone’s waiting on those results and when we get them back, obviously everyone here gets excited that our efforts were successful.”

The district has made some changes since it first started fogging, including using a new chemical and providing residents with more notice. During its last two abatement treatments it used the adulticide Zenivex, which the Environmental Protection Agency has determined to be less harmful and safe for urban use.

It has also closely collaborated with the San Mateo city officials and police to provide more notice to residents before fogging.

Prior to last Wednesday’s treatment, notice was sent out 36 hours in advance via Nixel,, the San Mateo County Alert system, through social media and press releases, police Sgt. Rick Decker wrote in an email. It also used a rapid notify reverse phone system and called 2,990 residents in the affected area, Decker wrote.

Residents complained after the first two foggings that they were only given a few hours notice and Weber said the city manager’s office and police have been an invaluable help in getting the word out.

Weber said West Nile reports have also increased statewide but a cause has yet to be determined. According to the state’s West Nile website, Santa Clara County has had 496 reports of West Nile infected dead birds this year, nearly half of the entire amount found statewide. Weber said the district is continuing to communicate with Santa Clara County officials and share information.

“We’re going to continue to monitor and make sure it isn’t in San Mateo County,” Weber said. “But unfortunately that’s all you can do, is continue to monitor and when we find something, react as quickly as possible.”

To report a dead bird or squirrel call (877) 968-2473. For more information about the district visit or call (650) 344-8592. For more information about West Nile visit To sign up for alerts visit or or

(650) 344-5200 ext. 106



Tags: district, mateo, weber, birds, county, abatement,

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San Mateo County Community College District seeks $388M bond: Funds would go toward modernizing buildings and updating labs, computers
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