Extremely rare tick-borne disease resurfaces in California

The California Department of Public Health told SFGATE an individual was infected with the bacteria Rickettsia lanei this year. The development marks only the third person in the state and only the fourth person worldwide known to have tested positive for the Rickettsia lanei bacteria since it was identified in Sonoma County in 2018 in rabbit ticks.

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The bacteria, which can cause severe, life-altering symptoms such as fever, gangrene, coma and brain inflammation, is part of a family of Rickettsia bacteria associated with a group of diseases known as spotted fever rickettsioses. Rocky Mountain spotted fever, the deadliest type of these diseases, has a fatality rate that can reach 5% to 10% in the U.S.  

Anne Kjemtrup, a research scientist and veterinarian with the California Department of Public Health, explained the recently reported infection is rare but can be “fairly severe.”

“What is unusual about this is that it causes almost the same kind of disease as Rocky Mountain spotted fever,” she told SFGATE.

No details have been released about the recent case other than the individual was diagnosed in the state this year. 

While there are very few cases of people being sickened by Rickettsia lanei, thousands of people are infected with spotted fevers in the U.S. every year. Symptoms can include fever, muscle aches, headache and often a distinctive “spotted” rash on the limbs.

The antibiotic doxycycline is commonly used to treat spotted fever rickettsioses, but delaying treatment of Rocky Mountain spotted fever by just a few days can greatly increase the risk of fatality. Kjemtrup said while spotted fevers are rare in California, it’s key to seek treatment immediately if you have signs, including flu-like symptoms or a rash.

“We encourage physicians to think about this disease, if a patient has been in an area and talks about tick bites, to get them on doxycycline before they even wait for any test results,” she said. 

While researchers knew about Rickettsia lanei for years (and the species is even named for retired UC Berkeley professor Robert Lane), no one knew the microscopic organism could infect humans until 2023. In July of that year, a man showed up at a Bay Area emergency department with fever-like symptoms, including body aches, according to a 2024 report published in Emerging Infectious Diseases. 

Physicians tested the man for multiple conditions as his health worsened, and he was sent to the intensive care unit. His oxygen levels dropped, he developed seizures, and his blood acid levels rose. After three days in the hospital, his physicians considered he might have a rickettsial disease or a spotted fever and administered doxycycline.

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He became comatose, had severe kidney injury and developed gangrene in both hands, but he eventually recovered and was released from the hospital after 22 days. 

This year, CDPH experts identified Rickettsia lanei bacteria in a few Pacific Coast ticks common along the California coast. One of these ticks that tested positive was found in Contra Costa County, where that first case patient reported golfing.

“This is an important tick vector that we want people to be aware of,” Kjemtrup said of the Pacific Coast tick. 

Janet Foley, a professor of medicine and epidemiology at the UC Davis School of Veterinary Medicine, said since the disease acts similarly to Rocky Mountain spotted fever, it is very serious.

“It is the most dangerous, highly lethal vector-borne disease … in all of the Americas,” she said of Rocky Mountain spotted fever, explaining “it is more lethal” than hantavirus. 

Foley advised people to take steps to stay safe when heading out on hikes or enjoying the outdoors this summer. She recommends staying on trails, avoiding tall grasses and checking for ticks immediately after coming home. 

She cautioned since the disease is rare, experts are still learning how it affects people and how it spreads through ecosystems.

“There’s so much we don’t know,” she said.