Mosquitoes Carrying West Nile Virus Detected in San Gabriel Valley

Published : Wednesday, September 5, 2018 | 4:44 AM

A mosquito sample collected this past week in the city of Arcadia has tested positive for West Nile virus (WNV), the San Gabriel Valley Mosquito and Vector Control District (SGVMVCD) announced Tuesday.

The SGVMVCD has been routinely monitoring populations of adult mosquitoes using traps and tests groups of adult female mosquitoes for the presence of the virus and other mosquito-borne diseases. It also tests wild birds, such as crows, which can provide insight into the spread of the virus.

Recently, the District adopted the City of Pasadena under its vector control jurisdiction, adding strength to the Pasadena Public Health Department’s efforts to eradicate disease-carrying mosquitoes.

Year-to-date, SGMVCD has confirmed the presence of West Nile virus in one dead bird and one mosquito sample in its jurisdiction.

“Autumn may be around the corner, but don’t let that fool you into thinking mosquitoes are gone,” Levy Sun, SGVMVCD’s public information officer, said. “Mosquitoes are opportunistic and, as long as the weather is warm, they will bite anyone who is not wearing repellent.”

Sun said their staff will continue to monitor mosquito sources in Pasadena and surrounding areas, and expand outreach activities to alert residents to the detection of the virus.

He said the SGVMVCD and all other vector control districts in Los Angeles County are working with the Los Angeles County Department of Public Health to promote the 2018 Champion for WNV Prevention Challenge, encouraging cities and communities to take specific measures against mosquito-transmitted disease.

WNV, a Flavivirus spread by certain species of mosquitoes, is the most predominant mosquito borne disease in California, and is endemic in the state – which means it’s always present in the environment as it cycles between mosquitoes and a wide variety of bird species. Humans and other animals, including horses, are susceptible to the disease but do not contribute to the cycle.

Only certain species of mosquitoes can transmit the virus. Unfortunately, the most efficient WNV vectors, including the southern house mosquito, or Culex quinquefasciatus, are common in Los Angeles County.

Anyone living in an area where West Nile-infected mosquitoes exist is at risk of infection. Those most susceptible to symptoms and severe illness include the very young, elderly, chronically ill, and those with a suppressed immune system, the SGVMVCD said.

“The debilitating effects of West Nile virus can take months to overcome for some patients,” said Sun. “One bite from a mosquito infected with West Nile virus is all it takes to get sick.”

To stay healthy and bite-free, the SGVMVCD urges everyone to stay healthy and bite-free by removing standing water around the home and eliminating containers that might catch and hold water, making sure all window and doors screens are in good repair, and by wearing insect repellent containing ingredients recommended by the U.S. Centers for Disease Control; these ingredients include Picaridin, DEET, oil of lemon eucalyptus, or IR3535.

If mosquito problems persist after eliminating stagnant water, contact San Gabriel Valley Mosquito and Vector Control District at or (626) 814-9466.

To learn more about how to help eliminate disease-carrying mosquitoes, visit


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