The area covers neighborhoods in Palo Alto, Milpitas, Sunnyvale and San Jose.
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The fear from experts of a more active mosquito season after an extremely wet winter is beginning to play out.
"This year because of the rain, there are a lot of mosquito sources and we have a much higher number of mosquitoes," SCC Vector Control District manager Nayer Zahiri said. "Our surveillance teams have set up the traps almost everywhere, every day."
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These traps have found positive mosquitoes in Santa Clara County in three separate areas.
In Palo Alto and Stanford, in the 94301, 94304, 94305, and 94306 zip codes, which were treated by SCC Vector Control last week.
Also in North San Jose and Milpitas, zip codes 95035 and 95134 will be treated Wednesday, Aug. 2.
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And to start August, a positive within the area of Santa Clara and Sunnyvale. Zip codes 94085, 94086, 94087 and 95051 will be treated Thursday, Aug. 3.
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"It's normal to see the activity of West Nile virus right now," Zahiri said.
That's why vector control says work to treat and kill mosquito larva is so important.
Methods very from normal spraying to using a new drone to spray areas not easily accessible by crews.
"Our staff is checking all mosquito sources to make sure to monitor and treat mosquito larva to make sure they are not in the developing to the biting stage, which is adult mosquitos," Zahiri said.
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At this stage, UCSF Infectious Diseases expert Dr. Peter Chin-Hong says mosquitoes bite birds that carry West Nile Virus, like crows, and then the mosquitoes transmit the virus to humans.
Dr. Chin-Hong says symptoms can vary from mild to chronic, but they can be hard to recognize.
"Many people won't even know they have them and only about one in five people have symptoms," Dr. Chin-Hong said. "So, the bottom line is, it's probably easier to prevent than to actually be aware."
Vector control says the best way to do this is to spray with EPA-approved bug sprays, remove standing water in your yard where larva can grow, avoid being outside in the afternoon and evening if mosquitoes are around and reach out to the county if removal help is needed.