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New Study Reveals Ticks in Bay Area Carry Larger Diversity of Bacteria Than Expected and May Help Explain Why Lyme Disease Symptoms Vary Widely Among Bay Area Patients

Rates of tick infection with Borrelia miyamotoi are found to be higher in the Bay Area than previously documented on East Coast, and Tick-borne disease infection risk is shown to be higher in Redwood habitats than previously believed

SILICON VALLEY, Calif., August 19, 2015 — Bay Area Lyme Foundation, which is working to make Lyme disease easy to diagnose and simple to cure, highlights a new Bay Area study  conducted by researchers from Stanford and Northern Arizona Universities documenting a vast diversity of bacterial species and strains that cause tick-borne diseases in Bay Area residents and visitors.  The variety of bacterial species and strains identified may be the reason that Bay Area patients with tick-borne diseases experience a wide range of symptoms, which may or may not include flu-like complaints, joint pain, fatigue and a rash of differing shapes, thereby making exact diagnoses extremely difficult.

“The range of symptoms patients experience compounds the difficulty in diagnosing these patients and is extremely frustrating for both patients and medical professionals,” said Linda Giampa, Executive Director, Bay Area Lyme Foundation, which funded this study and is the leading private national funder of Lyme research.  “This research offers some insight into the variety of bacteria that cause Lyme, and we encourage patients and medical professionals to heed this study and be alert to the different symptoms of tick-borne infection.”

The study, published in PLOS ONE, a multidisciplinary, open access, peer-review resource, is the first to demonstrate four key findings:

  • Tick-borne disease risk is higher than previously believed in redwoods, which to-date have been widely thought to be a poor habitat for tick-borne disease. Ticks are found in redwood habitats at lower densities than oak woodland, but they are consistently present and harbor both the newly-recognized tick-borne pathogen, Borrelia miyamotoi, which causes tick-borne relapsing fever, and Borrelia burgdorferi, which causes Lyme disease.
  • Rates of Borrelia miyamotoi in nymphal ticks in the Bay Area are higher than rates documented on the East Coast
    • Borrelia miyamotoi causes tick-borne relapsing fever in humans
    • While the percentages of infected ticks are higher in the Bay Area, the number of ticks by total tick population carrying Borrelia miyamotoi remains greater on the East Coast.
    • Ticks in the Bay Area carry diverse strains of the bacteria that cause Lyme disease (Borrelia burgdorferi), which may help explain why Lyme disease symptoms vary among Bay Area patients
    • Varying risk within Bay Area parks is based on several factors which include geographic area and type of terrain (coast live oak, redwood, grassland etc.)

“We continue to be surprised by the number of ticks carrying Borrelia burgdorferi and Borrelia miyamotoi throughout the Bay Area, and believe more research into the connections between human disease and strains and species of bacteria is critical,” said Dan Salkeld, PhD, a disease ecologist working at Colorado State University and formerly with the Woods Institute for the Environment, Stanford University. “It was astonishing that we could see such variety in tick ecology, ranging from low tick infection risk on one trail to high tick infection risk on another trail in the same park.”

The host animals that most commonly carry the bacteria that causes Lyme disease in California are the western gray squirrel and dusky-footed wood rat, which are long-lived and can carry the bacteria throughout the year.  Previous studies have shown that Lyme can be contracted in California throughout the year.

To conduct this new study, researchers counted and tested western black-legged nymphal ticks (Ixodes pacificus) at various locations within parks in Napa, Santa Clara, San Mateo, Sonoma and Marin Counties.  Nymphal ticks are younger and smaller than adult ticks, but older than larvae, and are active January to October, though most abundant from March to June.

“Because nymphal ticks are even more difficult to spot than adult ticks, they are often considered more dangerous to humans, and–based on these results –we are concerned that the risk of disease  these nymphal ticks present in the Bay Area is higher than one would expect,” said Nate Nieto, PhD, Assistant Professor, Department of Biological Sciences, Northern Arizona University.  “Our findings about the risks of infection have increased our curiosity about the interactions between host animals, ecology and human cases of disease.”

The study, “Disease risk & landscape attributes of tick-borne Borrelia pathogens in the San Francisco Bay Area, California,” can be found here.

“Knowing the possible symptoms of Lyme disease and that you can have Lyme disease even if you don’t get the bull’s-eye rash is critical for residents,” added Giampa.  More prevention tips and a list of symptoms can be found at:

About Lyme Disease

One of the fastest growing vector-borne infectious diseases in the United States, Lyme disease is a potentially debilitating infection caused by bacteria transmitted through the bite of an infected tick to people and pets. If caught early, most cases of Lyme disease can be treated, but it is commonly misdiagnosed due to lack of awareness and unreliable diagnostic tests. If not treated promptly, Lyme may progress to a debilitating stage, becoming difficult, or impossible, to cure. The CDC has reported that about 300,000 people are diagnosed with the disease each year.

About Bay Area Lyme Foundation

Bay Area Lyme Foundation, a national nonprofit organization committed to making Lyme disease easy to diagnose and simple to cure is the leading sponsor of innovative Lyme disease research in the US. A national 501c3 non-profit organization, the Foundation collaborates with world-class scientists and institutions to accelerate medical breakthroughs for Lyme disease. It is also dedicated to providing reliable, fact-based information so that prevention and the importance of early treatment is common knowledge. For more information on Lyme disease or to get involved, visit or call us at 650.530.2439.


2 Comments on “New Study Reveals Ticks in Bay Area Carry Larger Diversity of Bacteria Than Expected and May Help Explain Why Lyme Disease Symptoms Vary Widely Among Bay Area Patients

  1. My sister lives in Marin County – San Anselmo CA. She thinks she has Borrelia Miyamotoi. Her doctors disagree. She started taking meds. Should she be doing anything else to cure symptoms? Thank you.

    1. Unfortunately Bay Area Lyme is not a clinical organization and cannot comment on individual cases but in all situations of tick-related infections, we would advice careful monitoring of all symptoms and persistence in following up with your care provider(s) to get the answers and treatment you need. The more informed you are, the better you can advocate. You may want to consult a physician experienced with Lyme. You can find a list of providers in the ILADS (International Lyme and Associated Diseases) directory here.

      It can be helpful to photograph as well as document any physical symptoms — you will want to note when symptoms occur, where, how long they persist, if and when they become more or less severe, etc. Symptoms you may want to pay particular attention for would include: fever, rashes, fatigue, joint pain, numbness or other neuro-sensory issues, and headaches or migraines. There is a more complete list of possible Lyme disease symptoms on our site. We wish you and your sister the best.

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