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Contact:  Deborah Bass                                                            
(925) 771-6112 - office                                                          (925) 260-4670 - mobile


- Neglected swimming pools still a threat-

CONCORD, CALIFORNIA - - The summer is not only cooler, but extended record-low temperatures are making us safer from mosquitoes, too. There are many factors that allow mosquito-borne diseases to be transmitted to animals and people, and temperature is one of them, according to the Contra Costa Mosquito and Vector Control District.

"Mother Nature is working in our favor this summer," said Steve Schutz, scientific program manager for the District. "West Nile virus is still present, but the cooler temperatures in the Bay Area are helping to keep the virus below the minimum threshold for transmission by mosquitoes." 

Mosquitoes get the virus when feeding on infected birds. There is no exact formula, but scientists believe that West Nile virus transmission occurs when outside temperatures rise and stay above 55 degrees continuously for periods of a week or more. The warmer the weather, the faster the virus is replicated in the mosquito's salivary glands. Higher temperatures also speed up the life cycle of the mosquito so that in its lifetime, there are exponentially more mosquitoes - and more mosquitoes mean more opportunities for virus transmission.

Consistent or fluctuating temperatures below 55 degrees during evening hours can drastically slow or stop the rate at which the virus  replicates itself in the mosquito. Hopefully, this means the mosquito will live out its life before it can spread the virus. For now, in essence, the virus is still present in our area, it's just not at high enough levels to be detected yet.

"We must remain diligent even in cooler weather," warns Public Affairs Manager Deborah Bass. "Neglected swimming pools still remain our number one concern. Just one can produce more than 1 million mosquitoes and affect people up to five miles away."

Neglected swimming pools may be reported to the District at (925) 771-6195. Anonymous calls are accepted. Residents are also urged to wear mosquito repellents with the ingredients DEET, Picaridin or Oil of Lemon Eucalyptus.

To understand possible mosquito water sources in yards, visit the District's website.

Most people who are bitten by a mosquito with West Nile virus will not get sick; however, up to 20 percent of the population infected with West Nile virus will get West Nile fever. West Nile fever causes people to experience mild to severe flu-like symptoms such as fever, headache, body ache and possible paralysis. Less than one percent of infected individuals will require hospitalization. The elderly and those with compromised immune systems are most susceptible to illness and death caused by West Nile virus.

Residents are urged to take the following precautions:

DEFEND yourself against mosquitoes by using a repellent with an effective active ingredient such as DEET, Picaridin or Oil of Lemon Eucalyptus. Make sure to follow label directions.

DRAIN all sources of standing water that may support mosquito-breeding habitats. Residential sources can be a big producer of mosquitoes in Contra Costa County.

DOOR and window screens should fit tight and be in good repair. This will prevent mosquitoes from entering your home.

DO vaccinate your horses. Horses are highly susceptible to West Nile virus - approximately half of the horses that get West Nile virus die or have to be euthanized.

DAWN and DUSK are times to avoid being outdoors since this is when mosquitoes are most active.

DRESS appropriately by wearing long sleeves and pants when outdoors and mosquitoes are present.

DEAD birds should be reported to 877-WNV-BIRD (877-968-2473) or online at Not all birds will be picked up and tested, but reporting dead birds provides important information for mosquito control efforts.

People wishing to be notified about adult mosquito fogging or spraying in residential areas have several options. They may visit the District's website at and opt to receive the notifications automatically by e-mail; they can view information on the District's website; or they may phone the District for a recorded message at (925) 771-6195.

Contra Costa Mosquito & Vector Control District, a public health agency, is located at 155 Mason Circle in Concord. Call the District to report mosquito problems at (925) 771-6195 or visit their office between 8:00 a.m. and 4:30 p.m. to get FREE mosquitofish for ornamental ponds or horse troughs. Fish are also available at the Antioch Corporation Yard located at 1201 W. 4th Street in Antioch.

For information concerning human West Nile virus symptoms, prevention, or testing, please call the Contra Costa Health Services department at (888) 959-9911 or visit their Web site at

For information concerning West Nile virus and horses, please call the California Department of Food and Agriculture Animal Health Branch at (916) 654-1447.


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