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Lyme Disease in California: Seeking Answers in People and Pets

November 29, 2012

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Class of 2015 student Hannah Wachtell, and doctoral candidate Nicole Stephenson, left, simulate taking a blood sample from a dog while a Canadian film company shoots footage for a documentary involving Lyme disease and Stephenson's research. The crew set up a simulated clinic to sample dogs for Lyme disease and other tick-borne pathogens; the actual clinics take place in Humboldt County. Photo by Don Preisler/UC Davis (c) 2012 UC Regents

November 19, 2012

How important is Lyme disease in California? Twenty-five years ago it was believed that the infection was not even present in the state. Since the 1990s, however, public health officials have reported that California cases have turned up in many counties, including coastal areas such as Humboldt County.

Finding Connections

Nicole Stephenson, DVM, MPVM, pursuing a doctorate in epidemiology, has begun a One Health research project to assess the risks of tick-borne disease in people and animals in Humboldt County and to explore the health disparities of a rural population that may reduce access to diagnostics and treatment. 

Lyme disease, which is the most common vector-borne disease in North America, occurs when a tick infected with the Lyme disease bacterium attaches and feeds on a person or animal. It was discovered in the 1970s near Lyme, Connecticut, and has since spread to many states, including California.
A Canadian documentary film company visited the School of Veterinary Medicine November 27-28 to interview Stephenson, her adviser Janet Foley, and Lyme disease researcher Stephen Barthold. The film crew, making an episode of a science program called “The Nature of Things” focused on the recent arrival of ticks into Canada, asked about ticks, the Lyme disease pathogen, how it affects dogs, and what makes Lyme disease such a challenge to prevent, diagnose and treat. The filmmakers came to the School of Veterinary Medicine to learn how veterinarians are discovering new knowledge and insights about Lyme disease—knowledge that will ultimately benefit humans and animals. (Broadcast dates are still to be determined.) 

Screening and Assessment

Stephenson’s work focuses on Humboldt County. Working with public health officials, she has invited members of local communities to take part in a series of clinics to screen for Lyme and other tick-borne diseases. Participants allow blood samples to be taken for testing and fill out questionnaires that assess exposure and risk factors. While a registered nurse attends to the people, veterinarians and veterinary students examine dogs, take blood samples and collect ticks from the animals. Stephenson will test for several tick-borne diseases in Foley’s laboratory, using DNA and serologic methods that may detect different strains of bacteria as well as other pathogens. Participants are notified about their test results.

How Does Veterinary Medicine Contribute?

The project incorporates the One Health approach whereby human medicine and veterinary medicine play equal parts in addressing one problem. Stephenson told the interviewers that veterinarians are trained to evaluate disease in many species, giving them a broad perspective on diagnosis. Because their patients do not talk, veterinarians must also “think outside the box” and observe multiple factors before they draw conclusions about their patients. Veterinarians are also well aware of the many diseases that can be transmitted from animals to humans. By including domestic animals as well as humans in the study, researchers will be able use information from several species to gain insights into the disease as a whole. For example, veterinarians know that dogs get Lyme disease six times more often than people in endemic areas. One objective of the study is to learn whether dog ownership raises the risk of the disease in their owners.

Is There a Greater Risk of Lyme Disease in Poor Populations?

In the second part of the study, Stephenson has developed a questionnaire to assess exposure, demographic and socioeconomic factors that may delay the diagnosis and treatment of Lyme disease and other tick-borne diseases in people. An estimated 17 percent of Humboldt County residents are living below the poverty level; among American Indians, the figure is closer to 27 percent. Access to health care is limited, while living and working in rural areas increases exposure to ticks and tick-borne disease. Stephenson aims to identify the most significant risks so that they can be addressed.


Stephenson’s third and final goal is to educate people about the tick-borne diseases present in their community, how to prevent tick bites, remove ticks safely and recognize symptoms of tick-borne diseases. Her team is also providing information about flea and tick preventative in pets and when to take them to the veterinarian for evaluation.

Lyme disease is still less prevalent in California than it is on the East Coast. Little data is available about its presence and which factors are most important in its prevention, although Lyme disease testing in dogs is common in veterinary practice. Stephenson, who expects that her project will take about two years to complete, will tally information from almost 500 dogs and roughly 300 people, giving researchers solid figures to work with as they address the problem of tick-borne diseases.  

See a slide show featuring images from the filming November 28 on the School of Veterinary Medicine's Facebook page,

More about Lyme disease from the California Department of Public Health