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Vector Control District Surveys Ground Squirrel Burrows for Disease-Carrying Fleas

MILPITAS – Taylor Kelly knelt at the entrance to a ground squirrel burrow near Sandy Wool Lake in the Diablo Range foothills.

The vector ecologist attached a piece of cloth to a metal plumber’s snake and threaded it into the hole, one of several near the trunk of a small coast live oak. 

After a few moments, she pulled out the swab and examined it. No sign of fleas. She moved on to the next opening. 

A vector ecologist examines a ground squirrel burrow.
Taylor Kelly, a vector ecologist, checks squirrel burrows for fleas.

Kelly was among half a dozen employees with the County of Santa Clara Vector Control District who visited Ed R. Levin County Park on an overcast morning in March as part of a new study. Donning protective white suits, they probed ground squirrel burrows near a picnic area surrounding the lake, searching for fleas. The goal of the study is to determine what species of flea reside in Sant Clara County and what types of bacteria and other infectious agents they may carry.

Fleas are among the most common vectors, or transmitters, of disease, including the bubonic plague, which killed as many as 50 million people in Europe during the Black Death in the 1300s. 

The County has records for the plague being detected in California ground squirrels going back to 1909, not long after an outbreak of plague among residents of San Francisco in 1900. 

Nowadays the plague, caused by a bacteria known as Yesteria pestis, isn’t much of a problem. There are just seven human cases reported in the United States per year on average, according to the Centers for Disease Control and Prevention.

Instead, the Vector Control District’s study is focusing on bacteria such as Bartonella, which can cause meningitis, among other diseases, and Rickettsia, which can lead to a disease called murine typhus. If the study shows that fleas carrying these bacteria are present in the county, the district may develop plans to prevent and control potential human infection. 

A vector control manager looks at a map.
Noor Tietze consults a map at Ed R. Levin County Park.

“Fleas are a potential vector for a variety of diseases and, given the wide distribution of ground squirrels throughout the county, the district is looking into potential diseases that could affect the public,” said Noor Tietze, scientific-technical services manager for the district. “We want to know what’s out there, what the infection rates are, and then we can get some kind of risk estimate for the public. There’s not a whole lot of risk identified right now, but we want to determine that and advise the public accordingly.”

So far, the district has collected flea samples from four County parks, including Ed R. Levin. It expects to begin getting results of tests on the fleas by this summer.

Though ground squirrels don’t pose a significant danger to the public, the district advises people to steer clear of their burrows. When visiting parks, make sure not to let your children play around the entrances to their underground dwellings.

Fleas are just one of the vectors the district monitors. District staff regularly conduct “tick-flagging” in County parks, dragging large pieces of cloth through the brush to pick up ticks and test them for Lyme disease and other maladies.

And, of course, there are mosquitoes. The district has a robust program to control mosquito populations and monitor for West Nile virus, the most common and serious vector-borne disease in California, according to the state Department of Public Health. When the district detects West Nile virus in mosquitoes, it conducts adult mosquito control treatments to reduce the threat.

In 2022, the district detected an invasive mosquito known as aedes aegypti for the first time and mounted a successful campaign to prevent the insect from establishing itself in Santa Clara County.

To learn more about the Vector Control District and how it protects public health, visit its website at