While the mosquito-borne Zika virus has made headlines, local residents can take comfort that the two mosquito species that carry Zika, have not been found in the county since mosquito season started in March, according to Santa Clara County Vector Control District.
Indeed, the agency says the last time one of the two relevant species—Aedes aegypti, also known as the yellow fever mosquito, and Aedes albopictus, or the Asian tiger mosquito—was spotted in the county was in Gilroy in 2001 and Mountain View in 2003, when on both occasions, an Asian tiger mosquito was found.
“If these invasive mosquitoes are here in the county we want to ensure we get rid of them before they are established,” said Denise Bonilla, manager at vector control. “In those cases we found them really quickly.”
In this region, West Nile Virus is of primary concern to county officials tasked with surveilling, trapping and testing mosquitoes for diseases that affect humans. While the virus causes mild symptoms, like fever or body aches in the majority of sufferers, people over age 60 or with existing medical conditions like cancer, can develop other serious conditions including encephalitis or meningitis.
As part of their monitoring efforts, field technicians lay out mosquito traps whenever they are notified of dead birds, a major sign that the disease could be present in the area.
“We rely on the public to report dead birds and once they give us a call, we’ll pick them up to test,” said Bonilla. “Crows, ravens, magpies and jays will most likely die from West Nile Virus, so we tell the public, ‘if you saw it acting weird before it died, or it’s been dead for less than a few days, let us know, as those are optimal conditions for testing.’”
If the dead birds come back positive for West Nile Virus, the agency tests the mosquitoes in the area for the virus. Field technicians lay out 40 traps overnight within a mile radius of the dead bird site and return to pick them up the next morning. The trap sites are registered with the state so officials are able to track and monitor the types of mosquito species present in California.
Each trap is equipped with a small motor and fan attached to a fine mesh net. At the top of the net is a piece of dry ice, which slowly melts overnight, the fan sending out a waft of carbon dioxide, which draw the mosquitos to the trap.
If the mosquitos come back positive, the agency knows there is a risk to humans.
“Then we fog,” said Bonilla.
Deemed a “last resort,” fogging entails small amounts of pesticide released into the targeted area in the middle of the night, when people are not out and about. In the beginning of July, a recent fogging happened in a part of San Jose. The agency notifies affected neighbors in advance.
“We tell everyone in the fogging zone that we are going out to apply pesticides to kill adult mosquitos.”
After a fogging, the mosquitos in the area are tested again to ensure the virus has been eradicated.
The agency rarely fogs in Gilroy, partly because it does not get very many notifications of dead birds.
“We almost never fog in Gilroy, but we think West Nile Virus is down there,” Bonilla said. “Someone in Morgan Hill last year actually transmitted the virus, so we know the virus is present.”
In addition to trapping mosquitoes around dead bird sites, the agency has two flocks of chickens, one at the Gilroy High School FFA farm, the other at the South County Office Building in San Martin, which they use as part of their surveillance program.
Every two weeks during the seven-month mosquito season, agency technicians draw blood from the chickens, which are hosts for arboviruses—a group of viruses that includes encephalitis and yellow fever that are transmitted by mosquitoes, ticks or other arthropods. The specimens are then tested and tracking information goes to the state.
Everyone can help mitigate the risk of mosquito-borne diseases. “I love to talk to media outlets in South County because it’s important that residents call us, to report dead birds and neglected pools of water that breed mosquitoes, or any other stagnant water sources, so we can treat them before they turn into a bad mosquito breeding area,” said Bonilla. “We have ways to treat water sources and kill larvae that is way better for the environment.
“Ninety-eight point five percent of all mosquito control we do is immature mosquito control,” she added.
Who you gonna call?
The Santa Clara County Vector Control District has some handy tips for residents who want to remain itch-free this summer:
1. Dump and drain stagnant water sources around your home.
2. Wear repellent and/or long-sleeves and pants if you are out during dusk and dawn, when mosquitos are most active.
3. Wear repellent that is tested and approved by the Food and Drug Administration. Read the label.
4. While repellents containing the chemical DEET remain the market leader, and are most effective, natural repellents which have oil of lemon eucalyptus have been proven effective.
5. Check that the screens on your windows are not damaged or have holes in them. Keep doors closed; mosquitos will come in and bite at night.
Rats, wildlife
Vector control is not just about mosquitos. Call them at (408) 918-4770 if you have questions about any type of encroaching wildlife, including snakes, raccoons, bats, opossums, mice and rats. While they are not pest control, they can shed light on the situation and help you determine your next steps. For example, roof rats are a common problem. A vector control technician can show you how to rodent-proof your home, finding holes in the roof or ventilation system where the rodents can get in.
“Most people don’t realize they got a hole in their screen, or into their attic,” said Bonilla. “We help point out these things and explain how to eradicate these points of entry. We will try to see what is going on out there and educate people on how to change their behavior so the animals behavior can change. We are encroaching more on their habitat, they have nowhere to go.”
