NorCal Sees Rise In Exposure To Tick-Borne Bacteria

A rare tick-borne disease is on the rise among humans and man's best friend in Northern California and across the state, according to researchers.

The percentage of dogs in California that tested positive for exposure to the tick-borne disease, anaplasmosis, has tripled over the past five years, according to data from the nonprofit Companion Animal Parasite Council.

Anaplasmosis, transmitted by the blacklegged tick — which also spreads Lyme disease — can cause fever, lethargy and loss of appetite in dogs. Many show no obvious symptoms. In rare cases, dogs may develop nosebleeds or seizures.

Humans can contract the disease as well.

In California, more than half of the state has been labeled as high infection risk. After cases dipped in 2020, they have been on a steady rise since.

This is in part due to the climate-change-driven migration of blacklegged ticks into Southern California from the north in recent years.

“Anaplasmosis is not just an East Coast problem; it’s very much here in California,” said Dr. Sunjya Schweig, founder of the California Center for Functional Medicine, told the Los Angeles Times. “Unfortunately, the doctors don’t always recognize that, so it’s really hard sometimes for people to get the right care.”

Among the Northern California counties with the highest risk are San Francisco, Monterey, Santa Cruz, Sonoma, Marin, San Mateo, Alameda, Napa and San Benito. Meanwhile, counties like Santa Clara and Contra Costa have been labeled as moderate risk.

The infection is caused by the bacterium Anaplasma phagocytophilum and is typically treatable with antibiotics in both dogs and people.

California Department of Public Health data confirmed and probable anaplasmosis cases in people have climbed in recent years. While totals remain small, cases roughly doubled from 2020 to 2021 and have stayed elevated through 2023, the latest year available, the Los Angeles Times wrote, citing the state's report. In 2023, nearly all 21 cases — including eight in L.A. County — were linked to travel in Northern California or elsewhere in the U.S.

In humans, those infected may have mild or no symptoms, according to the California Department of Public Health. When symptoms do arise, they usually mimic the flu, with fever, headaches, fatigue, muscle aches and nausea.

Although the risk for serious illness is low for humans, experts warn that rising animal infections could later spell trouble for humans.

“It’s a canary in the coal mine,” said Brad Ryan, a professional services veterinarian at Antech Diagnostics, told the LA Times. “When the prevalence starts to go up in the animal population, we know that the public health risk has, by default, also gone up.”

Here's how to stay safe according to the California Department of Public Health:

• Avoid areas where ticks are common.
• Stay in the center of trails; avoid tall grass and contact with logs, tree trunks and fallen branches.
• Use an EPA-registered tick repellent; products with at least 20 percent DEET are effective. Apply to skin and clothing as directed.
• Treat clothing only with permethrin.
• Check yourself and others for ticks during and for up to three days after time in tick habitat.
• Shower as soon as possible after returning from a hike or a day in nature.
• Before washing, tumble-dry exposed clothing on high heat for 10 minutes to kill ticks.
• Keep grass along trails, buildings and campsites mowed.