In the spring, a young man’s fancy turns to thoughts of love; a young tick’s to thoughts of lunch. (Which, should he happen to be an outdoorsy type, could well be that young man.) Prodigious in wooded and grassy areas and in sandy soil near rivers, ticks carry several pathogens that can be transmitted to humans via their bite. The best-known isBorrelia burgdorferi, the microorganism that causes Lyme disease, which initially presents as flu-like symptoms and, left untreated, can cause persistent joint pain, cognitive deficits and, in rare cases, cardiac arrhythmia. But there are others. In 2010, the National Academy of Sciences Institute of Medicine called ticks “the Swiss Army knife of disease vectors.”

In a study published in March in the journal Emerging Infectious Disease, Dan Salkeld, a disease ecology research associate at the Woods Institute for the Environment, encountered a newly identified human pathogen, Borrelia miyamotoi, along with B. burgdorferi, in nearly all the Bay Area recreation areas he and his collaborators examined. B. miyamotoi had previously been known to infect ticks, but it was only in 2013 that the first human cases in the United States were reported, and those were in New England. Given that little is known about the transmissibility of B. miyamotoi from ticks to humans and its health consequences, it’s possible that other cases may have gone undiagnosed.

Stanford students taking the Conservation Medicine in Practice course taught by Salkeld and Woods senior fellow Eric Lambin in the spring of 2012 aided the research effort by collecting tick samples from the Jasper Ridge Biological Preserve and neighboring communities. Salkeld then expanded the study to include a total of 12 locations in Santa Cruz, Santa Clara, San Mateo, Marin, Mendocino and Contra Costa counties. Across all sites, 3.6 percent of the ticks were infected with Borrelia species, a relatively low prevalence compared with Northeastern states. Still, the Lyme-causing variant, B. burgdorferi, was detected at four sites, while B. miyamotoi was found at seven sites.

The surprising findings are “an important step toward dispelling the perception that you cannot acquire Lyme disease in California,” says Ana Thompson, executive director of the Bay Area Lyme Foundation, which funded the research.See also:

Human Borrelia miyamotoi Infection in the United States

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To the Editor:

Borrelia miyamotoi, a spirochete that is genetically related to the species of borrelia that cause relapsing fever, has been detected in all tick species that are vectors of Lyme disease.1,2 It was detected in Ixodes scapularis ticks from Connecticut in 2001 and subsequently has been detected in all areas of the United States where Lyme disease is endemic. The first human cases of B. miyamotoi infection were reported in Russia in 2011.3 We now provide evidence of B. miyamotoiinfection and the prevalence of this infection among people in the United States.