Mosquitoes caught in east Petaluma near the Ellis Creek Water Recycling Facility have tested positive for West Nile virus, vector control officials said Thursday.

The mosquitoes are the first in Sonoma County this year to test positive for the virus, the Marin/Sonoma Mosquito & Vector Control District said.

Test results and other surveillance data suggest a high risk of transmission of the virus in the area near the wastewater treatment facility, said Erik Hawk, assistant manager of the district. He warned local residents to take precautions.

“It is extremely important that residents protect themselves from mosquito bites by employing personal protection measures such as wearing long sleeves and long pants, and applying an effective insect repellent to exposed skin,” Hawk said in a statement.

Nizza Sequeira, a spokeswoman for the vector control district, said the rains followed by warm weather may increase the amount of mosquitoes in areas with stagnant water. The mosquitoes that tested positive were likely already infected before the recent rains, she said.

“We ask that residents check their properties for items holding water and dump them out,” Sequeira said in an email.

You can reach Staff Writer Martin Espinoza at 707-521-5213 or On Twitter @renofish.