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Spike in West Nile virus alarms vector control folks

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POSTED September 5, 2013 1:06 a.m.

Mosquitoes are all the buzz these days, turning up in record numbers throughout the country.

Southeast of Manteca, mosquito experts have reported 2-year-old eggs hatching amid dry conditions, creating an endless wave of blood-suckers.

Here, San Joaquin County officials aren’t seeing the same infestation. In fact, population counts are down from last year.

What alarms county officials, though, are the one-week spikes in samples infected with the West Nile virus.

The San Joaquin County Mosquito and Vector Control District reported its highest-ever count of infected mosquitoes – 1.62 in every 100 mosquitoes tested positive for West Nile virus — during the week of Aug. 11-17. By comparison, the highest infection rate in 2012 was 1.43 for every 100 mosquitoes.

“We had more mosquitoes last year,” said Aaron Devencenzi, public information officer for the San Joaquin County Mosquito and Vector Control District. “But we’ve had some peaks that were the highest infected rates we’ve ever had.”

And so the man-versus-wild struggle continues, especially in the south county where efforts to control mosquito populations continued this week.

Ground spraying was scheduled for Wednesday evening in south Manteca near the San Joaquin and Stanislaus rivers, as well as rural Ripon and the Ripon sewer area.

The area in Manteca treated: North to East Perrin Road/Melton Road; west to Airport Way/Division and Two Rivers Road; south to  the San Joaquin and Stanislaus rivers; and east to Austin Road.

Treatment in southwest rural Ripon included: North to one mile north of West Ripon Road; west to Austin Road; south to Moncure Road; east to South Highland Avenue and Mohler Road.

The Ripon sewer area included: North to Doak Road; west to Robert Avenue; south to the Stanislaus County line; and east to Stockton Avenue.

Devencenzi said those areas in the south county stand a very high chance of continued treatment.

“The area we’re continuing to treat is based on the fact that we’re finding many mosquitoes in those areas … finding significant West Nile virus in those areas,” he said. “It can be coming from a number of different sources.”

The afternoon drizzle on Monday, which produced tropical conditions the remainder of the day, should not have an effect on the bug count, Devencenzi said.

“If we had it day after day,” Devencenzi said of Monday’s weather, suggesting that prolonged humidity could drive up mosquito and West Nile virus counts.

Right now, the county’s biggest frustration is the heat and the looming possibility of an Indian Summer.

The forecast calls for temperatures in the high-80s through Friday, according to Accuweather. Mother Nature will turn up the thermostat on the weekend with temperatures soaring back into the high-90s.

Saturday calls for a high of 97 degrees, while Sunday is supposed to reach 98.

“When you have warm weather, the virus in the mosquito tends to replicate faster. You also have the population of mosquitoes; the life cycle go quicker,” Devencenzi said. “So you have faster life cycles and faster replication of the virus, which sets up for high mosquito counts and a higher risk for the public.”

It’s not enough to pray for cooler weather, Devencenzi said. Residents should take every precaution to protect themselves and their homes from mosquitoes.

“The virus behaves slightly different each year. This is the time when you see the population push,” Devencenzi said. “It would be nice to see things cool down, but in my 20 years, we’ve had spraying into November. It’s a day-by-day surveillance.”

The orders this late in the season are no different.

County officials will pay close attention to the adult populations throughout the county, weather patterns and feedback from the communities they serve.

“We’re right at the peak of West Nile virus,” he said. “This is when everything tends to hit its peak.”

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