Fourth-Ever Human Case of Rare Tick-Borne Rickettsia lanei Confirmed in Northern California
Key Insights
A Northern Californian became the fourth person ever diagnosed with Rickettsia lanei (search), a newly recognized tick-borne bacterium from the spotted fever group, with the case confirmed in April 2026.
All four documented human cases have required hospitalization, including intensive care, though no deaths have been reported; symptoms closely mimic Rocky Mountain spotted fever (search).
The California Department of Public Health urges clinicians to begin doxycycline treatment immediately upon suspicion of spotted fever group Rickettsia infection rather than waiting for lab confirmation.
A Northern Californian has been confirmed as only the fourth person ever diagnosed with Rickettsia lanei (search), a rare and newly recognized tick-borne bacterium, the California Department of Public Health (CDPH) confirmed. The case, identified in April 2026, sent the patient to the hospital with serious illness, though officials report the individual has since been discharged and is recovering.
The state agency declined to disclose the patient's home county, symptoms, or duration of hospitalization, but confirmed the infected person lived and worked in Northern California. The case was first reported by SFGATE in April.
A Pathogen Only Recently Linked to Human Disease
Rickettsia lanei (search) belongs to the spotted fever group Rickettsia, the same bacterial family that includes the potentially deadly Rocky Mountain spotted fever (search). Researchers first detected the bacterium in 2018 in rabbit ticks in Sonoma County, but its potential to harm humans remained unknown because rabbit ticks rarely bite people.
That changed with the documentation of two severe human cases nearly 20 years apart, detailed in a report published in the Centers for Disease Control and Prevention's Emerging and Infectious Diseases journal. Based on those findings, the California Department of Public Health added Rickettsia lanei (search) to the list of potentially transmittable pathogens in 2024.
"Sustained investment in public health has enabled development of the advanced molecular tools that detected these infections," CDPH said in a statement.
The Four Known Cases
Prior to the latest diagnosis, three human cases had been documented: two in California (reported in 2004 and 2023) and one in Oregon. According to the CDC report, both of the earlier California patients fell severely ill after spending time outdoors.
The first patient, who had played golf at five courses in Alameda and Contra Costa counties within 14 days of symptom onset, experienced fever, headaches, muscle pain, malaise, loss of appetite, diarrhea, and abdominal pain. His condition worsened on the third day of hospitalization, and he ultimately spent 22 days in the hospital — including 11 days in the intensive care unit — with a primary diagnosis of Rocky Mountain spotted fever (search) and a secondary diagnosis of acute kidney injury.
The second patient had visited and camped at a county park and state beach in San Mateo and Marin counties. He reported a five-day history of headaches, vomiting, light sensitivity, neck pain, and confusion. On the third day of hospitalization, he became comatose and required intubation. After 13 days, he was discharged with a primary diagnosis of severe Rickettsia.
In all documented Rickettsia lanei (search) cases, three of the four patients developed a rash. While no deaths have been reported, every known patient has required hospitalization due to the severity of illness, including time in intensive care, according to CDPH.
Transmission and Tick Vectors
The Pacific Coast tick (Dermacentor occidentalis), which bites humans more frequently than the rabbit tick, is believed to be the primary vector for human infection. "The Pacific Coast tick, which bites humans more frequently, may occasionally acquire the organism from an infected rabbit, which is the most likely route for the rare human infections that have been identified," the state health agency explained.
Infected ticks have been identified in Contra Costa County and San Mateo County, including one Pacific Coast tick and two rabbit ticks. Pacific Coast ticks are commonly found on hiking trails, in rural areas, and in grassy or shaded vegetation.
In California, three tick species — the American dog tick (Dermacentor similis), the Pacific Coast tick (Dermacentor occidentalis), and the brown dog tick (Rhipicephalus sanguineus) — can transmit the bacteria that cause Rocky Mountain spotted fever (search) in humans and dogs.
Clinical Presentation and Diagnostic Challenges
Symptoms of spotted fever group infections typically appear two to 14 days after a tick bite and can worsen quickly if left untreated. According to CDPH, symptoms may include fever, headache, muscle aches, altered mental status, hypothermia, and elevated liver enzymes. Many patients also develop a rash that often starts on the hands and feet before spreading. Fever associated with infection can last two to three weeks.
One of the biggest clinical challenges is that Rickettsia lanei (search) closely mimics other spotted fever illnesses, particularly Rocky Mountain spotted fever (search). Doctors often must rely on specialized lab testing using blood or skin samples to confirm the diagnosis, but those tests may not immediately detect the infection.
Because of that delay, health officials stress that clinicians should act quickly. "It is important that health care providers begin treatment with doxycycline as soon as a spotted fever group Rickettsia infection is suspected, and not to wait for the result of a blood test," CDPH told USA TODAY.
Underreporting and Global Context
Janet Foley, a veterinarian and disease ecologist at UC Davis, suggested that human infections may be underreported because Rickettsia lanei (search) symptoms closely resemble those of Rocky Mountain spotted fever (search). Cases could also have gone undetected because some infections were not severe, she noted.
"I think it's so new that I don't know if anybody's really gotten a grant to study it or put it under a microscope," Foley said.
The broader spotted fever group has been spreading globally since the early 2000s, most notably in Mexico and Brazil, with reported fatality rates that can exceed 50%, according to a study published by UC Davis. By comparison, Rocky Mountain spotted fever (search) affects about 1,000 people annually in the United States, primarily in the Southeast and south-central regions, with California typically reporting only a small number of cases.
Because of the extremely small number of Rickettsia lanei (search) infections, a CDPH spokesperson said that "it is difficult to make generalizations" about how the disease affects people or how best to raise awareness.
Prevention and Public Health Guidance
Health officials say the risk to the public remains low, but recommend simple precautions to reduce the chance of exposure. CDPH advises applying tick repellent before outdoor activities, wearing long sleeves and pants in brushy or grassy areas, staying on cleared trails while hiking, checking the body and clothing for ticks after spending time outdoors, and showering soon after returning indoors.
Ongoing tick surveillance across Northern California and the Pacific Coast continues to monitor for rare pathogens like Rickettsia lanei (search).