The pathogen that causes Lyme disease is just as common among ticks residing near the shore as it is among ticks from woodlands, known high-risk habitats, researchers reported Friday (April 23) in Applied and Environmental Microbiology. They examined the prevalence of the Lyme disease–causing bacterium Borrelia burgdorferi in two California counties and found the same proportion of western black-legged ticks (Ixodes pacificus) were infected with the pathogen in forests as they were in chaparral adjacent to beaches.

“The high rate of disease-carrying ticks in the coastal chaparral was really surprising to us,” coauthor Daniel Salkeld of Colorado State University says in a press release. 

In their paper, he and his colleagues explain that the “archetypal” habitat for Lyme disease in California is the oak woodland, home to gray squirrels, which serve as hosts to ticks. “A few years ago I would have said the ticks [near the coast] wouldn’t have been infected because there aren’t any grey squirrels, which are the source for Lyme in California,” Salkeld tells NBC News, adding that voles or rabbits could be the host in coastal habitats.

Salkeld’s group found B. burgdorferi in adult ticks sampled from Marin, Monterey, Napa, Sonoma, and Santa Cruz counties, while adult ticks from Mendocino and Santa Clara counties tested negative for the bacterium. All of the counties included sampling sites in both coastal and wooded habitats, except Napa and Santa Clara, which just included woodlands. 

According to NBC News, 4.1% of adult ticks in shrubby coastal areas of Marin and Sonoma Counties were infected with B. burgdorferi and 3.9% of adults ticks in woodlands of these same counties were infected.

“Let’s go to more beaches and other places where we think there wouldn’t be ticks, and I bet we’ll find them,” Eva Sapi, the director of the University of New Haven’s Lyme disease research program who was not involved in the study, tells The Washington Post.