The bloodsuckers are back: Local officials warn of mosquito, tick activity

James Gathany/CDC
A female Aedes aegypti (yellow fever) mosquito acquires a blood meal from her host. Aedes aegypti mosquitoes, which are capable of transmitting Zika, the birth-defect-causing virus, are not currently active in the Bay Area but have been found locally in recent years.

Recent temperature fluctuations notwithstanding, warm weather has returned to the Bay Area, and with it comes the annual onslaught of disease carriers like mosquitoes and ticks, county officials warned last week.

Locally, May and June are considered the start of the active West Nile virus season, and Lyme disease peaks in ticks in July, according to Russell Parman, Santa Clara County Vector Control District assistant manager.

“As things heat up, most of the processes that go on inside the bug also run faster,” Parman said.

Flying foes

Culex tarsalis (Western encephalitis mosquito) and Culex pipiens (Northern house mosquito) are the two local mosquito species that transmit West Nile, a viral infection that can lead to flu-like symptoms and even death.

Vector Control has yet to trap any mosquitoes infected with the virus so far this season. Last year’s season marked the first time the agency did not detect West Nile-positive mosquitoes since 2004, when the virus appeared in Santa Clara County.

“We’re hoping for the same this year, but it’s not likely,” Parman said.

Officials also hope to keep Zika, the birth-defect-causing virus, at bay. Aedes aegypti (yellow fever mosquito) and Aedes albopictus (Asian tiger mosquito), the species capable of transmitting Zika, are not native to California and are not currently active in the Bay Area, but they have been in the past. Aedes aegypti was discovered in Menlo Park in 2013 and Aedes albopictus made an appearance in Mountain View in 2003, according to Vector Control.

The most recent California Department of Public Health infestation detection report, published May 4, indicates either Aedes aegypti or Aedes albopictus are now present in 12 counties, including as far north as Merced County. There is still no record of mosquito-borne transmission of Zika in the state, however.

Vector Control urges county residents to report aggressive daytime biting, which is characteristic of Aedes mosquitoes.

“The Aedes aegypti, they call them ankle biters because they tend to go for the lower legs, and compared to our Culex mosquitoes, they’re pretty quick,” Parman said. “So it’s kind of hard to swat them, and they bite you in an area that’s the hardest to reach.”

Discourage mosquito activity by applying DEET-fortified insect repellent, donning long sleeves and pants and routinely dumping standing water, including pet dishes, buckets, plant saucers and bird baths; a container left for a week with as little as a quarter-inch of water provides mosquitoes with a place to breed, according to Vector Control.

Abandoned and neglected swimming pools without chlorine and circulating water are especially attractive to mosquitoes, and county officials conduct routine aerial surveillance to identify green and half-empty pools visible from the sky. The most recent survey, completed in the Sunnyvale-Santa Clara area in April, uncovered 117 new offenders that joined an inventory of approximately 3,200. Property owners with violations are notified and potentially fined.

Bloodsucking hitchhikers

The Western blacklegged tick (Ixodes pacificus) is the local species capable of spreading the Lyme disease bacterium, Borrelia burgdorferi, which can cause rashes, debilitating pain, fatigue, fever and, when left untreated, infection to the joints, heart and nervous system, according to the Centers for Disease Control and Prevention.

Western blacklegged ticks are active in California year-round, but spring and mid-summer are especially busy times for the arachnids, according to Vector Control. Now in their immature nymphal life stage, the ticks are smaller and harder to spot compared to their adult counterparts, and they are more likely to carry disease pathogens.

Local tick surveillance conducted in the winter, when ticks are larger and easier to sample, typically reveals less than 1 percent are infected with Lyme disease, Parman said. But outdoorsy types exposed to foothill and mountainous terrain – tick habitat – should nevertheless take precautions to protect themselves, including applying repellent sprays, wearing long sleeves and pants and avoiding leaf litter, a common source of tick activity.

“If you want to increase your chances of getting infested with ticks, go ahead and sit on logs and rocks – under oak trees,” Parman said.

When post-excursion body checks reveal bloodsucking hitchhikers, the offending parasites should be removed with fine-point tweezers applied close to the skin, Parman advised.

Subsequent bull’s-eye-shaped rashes, present in approximately six out of 10 Lyme disease cases, or the onset of flu-like symptoms, should trigger a doctor visit.

To report daytime-biting mosquitoes, dead birds and abandoned pools to Santa Clara County Vector Control, call (408) 918-4770 or visit

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