Mosquito trap

A technician with the West Valley Mosquito and Vector Control District sets a mosquito trap where samples are collected for testing. Residents with concerns may request a trap in their neighborhood by contacting the district.

The West Valley Mosquito and Vector Control District detected the presence of St. Louis Encephalitis (SLE) virus in two mosquito samplings collected Oct. 21 to 25 in Chino Hills at Butterfield Ranch Road and Ridgegate Drive, and in Chino at Comet Avenue and Chino-Corona Road.

SLE-positive samples were found in the same Chino location in September.

Previously, SLE had not been detected in the area since the formation of the district in 1983, according to district manager Michelle Brown.

The mosquitoes carrying SLE are not the black and white Aedes mosquitoes that have been aggressively biting residents during the day and night, but the native “Culex” mosquitoes, Dr. Brown said.

SLE is a mosquito-transmitted virus in the “flavivirus family,” which is the same as the West Nile Virus, Dr. Brown said.

Symptoms include headache, fever, dizziness and nausea, similar to the symptoms of West Nile Virus, she said.

Although some residents have expressed concern that they will get sick from mosquito bites, it is important to know that the mosquito has to have come in contact with the disease in the first place, Dr. Brown said.

“The reservoir host in this case are wild birds such as house sparrows and pigeons,” she said. “Mosquitoes have to bite birds carrying the virus first before being able to transmit to humans.”

The elderly run a greater risk of severe effects than others, Dr. Brown said.

She said while humans can acquire SLE infections, they are not able to replicate the virus in sufficient numbers to serve as an amplifying host for the virus.

She said less than one percent of SLE infections are clinically apparent, according to the Centers for Disease Control and Prevention.

The best way to prevent mosquito-borne illnesses is to wear mosquito repellent and reduce breeding sites, she said.

She recommended wearing repellant containing DEET, Picaridin, Oil of Lemon Eucalyptus, or IR3535.

Dumping standing water around the home and even inside the house is recommended, she said. Making sure door and window screens have no holes or tears is also suggested.

Residents should contact the district if they have standing water they cannot remove, are getting bitten by mosquitoes or have further concerns.

Information: 635-0307 or

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