Disease-carrying ticks are regularly finding their way onto beachfront property, new research suggests. The study found similar levels of tick infestation in the woodlands and near beaches around Northern California, indicating that they can live in more varied environments than assumed — even without the presence of obvious natural hosts. What’s worse, these ticks often carried bacteria responsible for illnesses like Lyme disease.
The study was published last week in the journal Applied and Environmental Microbiology. It involved researchers from Colorado State University and Northern Arizona University and was funded by the Bay Area Lyme Foundation, a public charity focused on supporting Lyme disease research.
Between 2015 to 2018, every winter and spring, the researchers swept various areas in Northern California for Western black-legged ticks, including woodlands, grasslands, and coastal chaparral, the low-lying scrubland and brush found close to beaches. Across all habitats, including the chaparral, the team found similar levels of tick presence. The researchers also tested these ticks for up to five species of bacteria known to cause illness, such as Borrelia burgdorferi, which causes Lyme disease in the U.S. They found similar levels of B. burgdorferi in both woodland- and chaparral-living ticks.
“The high rate of disease-carrying ticks in the coastal chaparral was really surprising to us. And when looking at all the tickborne pathogens simultaneously, it makes you rethink the local disease risk,” said lead author Daniel Salkeld, a biologist from Colorado State University, in a statement from the Bay Area Lyme Foundation. “Previously, we, along with other researchers, may have missed the big picture when we focused our attention on investigating the risk of one pathogen at a time. Now, we have a new imperative to look at the collective risk of all tickborne pathogens in an area.”
Other research has found that problematic tick species have been spreading to areas of the country where they haven’t been found before, aided in part by the warming climate. As they’ve spread, so too have annual cases of tickborne illnesses like Lyme (the most common illness spread by insects or arachnids in the U.S.). But the new findings are worrying because the beaches and coastal chaparral of Northern California contain fence lizards, considered a potential Lyme deterrent.
Fence lizards are a common tick host but carry blood that is thought to kill Lyme bacteria, leading to theories that they’ve played a key role in reducing the incidence of Lyme in the area. But if these findings are valid, then these native lizard populations may not be enough to protect beachgoers from Lyme and similar diseases, especially if the tick population continues to grow over time. (In the woodlands of the eastern U.S., where ticks are plentiful and Lyme disease has long been endemic, research has found that related lizards do little to curb transmission.)
Another unanswered question right now is exactly how these germs are managing to stay alive in beach-adjacent ticks. In the woods of California, there are known hosts like grey squirrels, but there aren’t any obvious candidates that would allow these bacteria to keep circulating in the area. Lizards, as mentioned before, would often be a dead end for Lyme bacteria. More research will be needed to understand the ecology of these ticks and their bacteria.
In the meantime, the authors argue that the people going to these beaches need to know about the potential danger of coming across ticks so they can prepare accordingly.
“I’m not trying to ruin anyone’s vacation or outdoor time,” Salkeld told the Washington Post, but he added that people should “always be aware that ticks are around in most of the habitats in California.”
The U.S. Centres for Disease Control and Prevention recommends that if people expect to visit places where ticks are found, they should wear insect repellent, treat their clothing with 0.5% permethrin, and generally avoid wooded and brushy areas with high grass and leaf litter. Afterwards, they should check themselves, their pets, and their clothing for ticks and remove them safely if needed. Taking a shower within two hours of returning from an excursion is also thought to reduce the risk of tickborne illness, by washing off unattached ticks and allowing for a clearer body inspection.