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West Vile virus gaining in San Joaquin County
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The West Nile Virus is more prevalent in San Joaquin County now than it was at this time last year. 

And with the summer only halfway over, officials are urging those who spend time in the outdoors to do everything possible to avoid contact with populations of mosquitoes that transmit the deadly virus. 

So far no human cases of West Nile Virus have been reported in San Joaquin County despite a rise in the activity among active adult mosquito populations that are tested at strategic points in rural areas. According to San Joaquin Mosquito and Vector Control District Public Information Officer Aaron Devencenzi, a total of 79 mosquito group samples – where roughly 50 adult mosquitoes are tested – came back positive for the virus. 

It’s the hot, dry California climate that is creating the perfect climate for mosquito breeding, and the activity, according to Devencenzi, tends to mirror the weather cycle – populations ebb and flow with the heat of the summer and the cooling spells that have been few-and-far between.

According to the California Department of Public Health, people can protect themselves by following the basic guidelines:

• Wearing long-sleeved shirts and pants when outdoors during active mosquito biting times – typically at dawn and at dusk. 

• Making sure that doors and windows are outfitted with tight-fitting screens and replacing those that may be torn or frayed.

• Applying insect repellants with EPA-registered ingredients such as DEET, Picaridin, IR3535 and/or oil of lemon eucalyptus (PMD). 

• Removing any standing water – buckets, flower pots, old tires – that serve as reservoirs for mosquito breeding.

A bird containing West Nile Virus was first discovered this year in March on a dairy in Tracy – the earliest that it has been detected in this area since it first arrived back in 2004. Birds serve as the reservoir for the disease, and mosquitoes that bite them then transmit the disease to humans. So far 20 have been reported in San Joaquin County, as of July 14. 

As many as 80 percent of the people that become affected by West Nile Virus are asymptomatic – they show no signs or symptoms – but it can be deadly for children, the elderly and those with a weakened immune system. Last year a Stockton man was diagnosed with the disease when he was admitted to a local hospital for an unrelated condition in June, and an 83-year-old woman died in August from illness that was attributed to West Nile Virus. 

The district, Devencenzi said, has been actively spraying adult mosquito populations both on the ground and in the air for more than a month and have been were vigilant in targeting larvae-producing areas throughout the dry winter. 

People with untended swimming pools and ornamental ponds with standing water are urged to utilize mosquitofish – small, finger-length fish that target mosquito larvae – to help keep populations down. Information on where to obtain them from the district can be obtained at or by calling 209.982.4675. Anybody that discovers a dead bird is urged to contact the California Department of Public Health’s West Nile Virus hotline at 1.877.WNV.BIRD (968.2473).