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209 region ground zero for West Nile virus
There have been 313 samples of mosquitos carrying the West Nile virus confirmed so far this year in San Joaquin County. - photo by Photo Contributed

It’s a bird. It’s a plane. It’s the San Joaquin County Mosquito and Vector Control District trying to make sure that you don’t catch West Nile Virus. 

Last week residents took to social media to post theories about a low-flying, fast-moving plane that was spotted over the Woodward Park subdivision – spurring a flurry of phone calls to the Manteca Police Department and eventually prompting the city to post something to its Facebook page about the incident. 

According Mosquito and Vector Control Spokesman Aaron Devencenzi, the plane that was identified was spraying in an area south of Manteca and west of Ripon but had to utilize an offset approach because of winds in the area – calculating where the pesticides used would fall once wind patterns were considered. Because of the unique spraying conditions, Devencenzi said that people likely saw the plane flying over areas that aren’t traditionally sprayed, but none of the pesticides that were used last week near Manteca fell over the housing tracts that reported the unexpected air traffic. 

And while the summer is winding down, it has been a busy season for the agency tasked with keeping San Joaquin County residents safe and preventing other mosquitos that spread deadly communicable diseases from taking root. 

The virus has been on the radar of public health experts ever since it arrived in California 15 years ago, but it is being watched especially closely in San Joaquin County this year as the area has emerged as part of the region with the largest concentration of affected adult mosquitoes in the entire state. 

That means that the Northern San Joaquin Valley and the Southern Sacramento Valley has been a hotbed of spraying to prevent the disease from being transferred to humans. 

So far this year four people in San Joaquin County have contracted the virus, while five confirmed cases have also been reported in Stanislaus County.

Sacramento County, which Devencenzi said has been active in working to keep populations down, leads the State of California in the number of dead birds that have been reported – a marker of West Nile Virus activity – with 211 of the 363 total birds found to be containing the virus. 

San Joaquin County leads the entire state with the number of cases in mosquito samples with 313 – roughly 25 percent of all of the positive mosquito samples in the state. When coupled with the 257 positive samples from Sacramento County and the 67 from Stanislaus County, the area contains almost half of the adult mosquitoes found to be carrying the disease. 

While spraying is used to help keep populations down and prevent infections, residents are urged to take necessary precautions when outdoors, especially in the early morning or late evening dusk hours. 

Those include:

uChecking your property for standing water and eliminating it as needed. Abandoned swimming pools were a major breeding ground for mosquitos during the economic downturn, but something as small as an old tire or a bucket that has collected rain or sprinkler water can provide the environment necessary for mosquitos to breed. 

uApplying mosquito repellant that contains the ingredients DEET or Picaridin when outdoors in accordance with usage instructions. 

uAvoiding being outside when mosquitoes are the most active, which is typically at dawn and at dusk, and especially for the first two hours after sunset. 

uWearing long pants, long-sleeved shirts, and other protective clothing when forced to be outdoors – especially during peak activity times. 

uMaking sure that windows and doors have tight-fitting screens to keep active mosquitoes outside of the home. 

Devencenzi said that the district remains diligent about posting the locations of areas that will be sprayed – both with ground trucks that spray from a boom for smaller areas and airplane spraying for larger areas – at least 24 hours in advance. The exact location of spraying, he said, is dependent on the results of tests performed on mosquitoes that are picked up in dozens of traps located across the country. 

Both types of spraying, Devencenzi said, deploy less than ounce of pesticide per acre that is being treated. Any remnants of the spraying typically breaks down in the sunlight the following day. Both trucks and planes are outfitted with special nozzles to control the amount of pesticides that are deployed, the exact types of which are listed on the district’s spray schedule on its website. 

The virus is typically carried by birds and transmitted by mosquitos who feed on their carcasses and then bite humans. The State of California has a website to report dead birds for removal and subsequent study that can be found at 

To report unusually strong mosquito infestations or daytime biting, to request email updates on spraying locations, or for additional information about efforts to control West Nile Virus in San Joaquin County, contact the San Joaquin Mosquito and Vector Control District at 209.982.4675 or visit them on the web at 

To contact reporter Jason Campbell email or call 209.249.3544.