A rare and little‑understood tick‑borne pathogen has quietly emerged in California, adding a new wrinkle to the state’s already complex landscape of vector‑borne diseases.

The bacterium, Rickettsia lanei, belongs to the spotted fever group of rickettsial pathogens — a family that includes illnesses ranging from mild to life‑threatening.

Until recently, R. lanei was considered obscure, with only a handful of documented human infections worldwide.

Now, new surveillance findings from the California Department of Public Health (CDPH) indicate that the pathogen is present in California ticks and has been linked to a recent human case. The discovery underscores how much remains unknown about the diversity of rickettsial bacteria circulating in the western United States.

SF Gate recently reported on the CDPH findings, saying:

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.

No details about the recent case have been disclosed.

Rickettsia lanei is similar to Rocky Mountain spotted fever — the most dangerous illness in this group — which can be fatal in up to 10% of cases. Because symptoms overlap with other spotted fever illnesses, CDPH researchers note that R. lanei may be underrecognized.

A pathogen named for a California tick pioneer

Rickettsia lanei is named after Dr. Robert S. Lane, the longtime UC Berkeley entomologist who spent more than four decades studying ticks and tick‑borne diseases in California. His research helped define the ecology of the Pacific Coast tick and other species that shape the state’s disease landscape. Dr. Lane also served as an advisor to LymeDisease.org for many years.

Photo: Overlook at Austin Creek near Guerneville, CA by (brian) is licensed under CC BY 2.0.

TOUCHED BY LYME is written by Dorothy Kupcha Leland, President of LymeDisease.org. She is co-author of Finding Resilience: A Teen’s Journey Through Lyme Disease and of When Your Child Has Lyme Disease: A Parent’s Survival Guide. Contact her at dleland@lymedisease.org.