Northern California resident becomes fourth person ever diagnosed with rare Rickettsia lanei tick-borne illness

Jun 16, 2026

A Northern California resident has been diagnosed with Rickettsia lanei, an extremely rare tick-borne illness, marking the fourth known human case worldwide. The patient was hospitalized in April 2026 but has recovered. This is the third case in California of the newly recognized bacterium, which causes symptoms similar to Rocky Mountain spotted fever. Previous cases involved severe illness, and officials urge tick bite prevention.

Fourth Rickettsia lanei case diagnosis

▪The April 2026 diagnosis marks the fourth confirmed human case of Rickettsia lanei infection worldwide.
▪The patient diagnosed in April 2026 was seriously ill and hospitalized but has since been discharged and is recovering.
▪A resident of Northern California was diagnosed with a Rickettsia lanei bacterial infection in April 2026.
▪The recent case is the third infection of Rickettsia lanei to be reported in California, with others occurring in 2004 and 2023.

Rickettsia lanei bacterial identification

▪The bacterium was first detected in rabbit ticks in Sonoma County in 2018, but its risk to humans was initially unclear.
▪Human infections may be underreported because Rickettsia lanei symptoms are very similar to those of Rocky Mountain spotted fever.
▪The California Department of Public Health added Rickettsia lanei to its list of potentially transmittable pathogens in 2024.
▪Rickettsia lanei is a newly recognized bacterium in the spotted fever group, causing symptoms similar to Rocky Mountain spotted fever.

Pacific Coast tick transmission

▪In California, the American dog tick, Pacific Coast tick, and brown dog tick can transmit the bacteria that cause Rocky Mountain spotted fever.
▪Rickettsia lanei is transmitted to humans through the bite of an infected tick.
▪The Pacific Coast tick is considered a likely route for human infection, possibly acquiring the bacteria from infected rabbits.

Severe hospitalization outcomes

▪One of the two previously identified California patients was hospitalized for 22 days, including 11 days in intensive care.
▪Symptoms of related tick-borne illnesses can include fever, headache, muscle aches, and rash.
▪The other previously identified patient was hospitalized for 13 days, during which they became comatose and required intubation.

Tick bite prevention measures

▪Recommended prevention measures include wearing long sleeves and pants and staying on cleared paths away from grass.
▪Health officials recommend using tick repellent and checking people and pets for ticks after being outdoors.
▪If a tick is found attached, it should be removed using fine-tipped tweezers, pulling upward with steady pressure close to the skin.