Environment, Parks, Public Health

Mosquitoes: lab abuzz with disease detectives

Santa Clara County Vector Control lab: the scientists behind eradicating mosquitoes

Ideally, summer is about freedom from homework, weekends at the lake and hanging out into the night, not mosquitoes. That’s why it’s also the season when Santa Clara County is most active protecting residents from the threat of the West Nile virus-carrying insects.

The scientists and technicians at the Santa Clara County Vector Control District lab act fast when they detect a potential problem.

“Vector Control does quite a lot outside the lab in terms of mosquito monitoring, especially in the larval stages,” says Noor Tietze, the district’s manager of scientific and technical services. “The lab, on the other hand, is more involved in the testing of specimens that are brought in from the field for West Nile virus or other vector points.”

The program aims to knock out the mosquitoes before they reach the adult, biting stage. That means the field crew is out there inspecting storm sewers and other places where water may pool. If they find larvae in the water, they’ll throw in a special briquette to eliminate them.

Pesky mosquitoes

But inevitably, plenty of the pesky bugs mature, bite us, bite birds, and reproduce.

Anyplace where there’s a concentration of mosquitoes may harbor disease-carrying individuals. And the presence of dead birds is a strong sign that something might be wrong.  

When someone in the public notifies the agency that they’ve found a dead bird with no outward sign of what killed it, Vector Control rushes it into the lab for testing. A tech swabs the bird’s mouth and prepares a specimen for the lab crew. Workers then run the specimen through a machine that detects genetically the presence of West Nile virus or other diseases, some of which can be fatal.

“If there are any positives when we test them,” Tietze says, “we’ll target those (areas where the birds died) for mosquito trapping.”

A new threat: day-biting mosquitoes

Detecting trouble is an ever-changing game as species evolve and move from one area to another.

The new concern is Aedes egypti mosquitoes, which can carry several exotic diseases rarely seen in Santa Clara County.  This mosquito, which can spread the Zika and dengue fever viruses, has been found in 10 California counties, though not here. There’s nothing the Vector Control District can do to stop its arrival, and Tietze considers it “just a matter of time” before it lights here.

Luckily, the Aedes mosquito behaves in a way that makes it easy to differentiate it from the more familiar species, which start biting almost exclusively as dusk falls. “We’re sampling aggressively to find these day-biting mosquitoes,” Tietze says. Vector Control urges people to call if they get bitten in the daytime.

Identifying what kind of mosquito the lab is testing requires painstaking microscopic analysis. Lab workers carefully compare the specimens mounted on glass plates with the intricate drawings in the dozens of manuals on the bookcase. The anatomical differences can be extremely subtle. But they’re meaningful in terms of what vectors the animal might be carrying, and what to do about it, if anything. The lab also tests their lab-bred mosquitoes to see how they respond to various treatments.

Public awareness and action

In fact, the lab dedicates a whole room to breeding the pests. Sometimes they’re captured and brought to classrooms and other places for public education purposes regarding the mosquito threat.

Babak Ebrahimi, the district’s expert in vector behavior and ecology, says the public can do plenty to help. In addition to calling in dead birds, mosquito infestations, and day-biters, people can eliminate any standing water where the insects might breed.

They should also use Environmental Protection Agency-approved repellent and wear long pants and long-sleeve shirts when hiking or working outdoors.

People who have trouble controlling the mosquitoes breeding in their backyard pools, Ebrahimi says, can get help from the County. The Vector Control District has mosquito fish that eat the larvae and live for a couple of years. “It’s a free service that we provide for the public,” he says.

July 3, 2018

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July 2018
Santa Clara County