New Spotted Fever Group Pathogen Recognized in Northern California

Photo of rabbit in sand dunesEmerging Infectious Diseases (Probert, W.S., et al.) 5.30.2024 published the early release article, “Newly Recognized Spotted Fever Group Rickettsia as Cause of Severe Rocky Mountain Spotted Fever–Like Illness, Northern California, USA.” In this study, authors report case studies on a newly recognized Rickettsia pathogen, Rickettsia sp. CA6269, Candidatus Rickettsia lanei. This novel pathogen has been found to cause severe Rocky Mountain spotted fever (RMSF)–like illness in 2 residents of northern California. Researchers that discovered this new pathogen have proposed the naming in honor of internationally recognized tick and tick-borne disease researcher, Robert S. Lane, PhD, Professor Emeritus of Medical Entomology, at the University of California, Berkeley.

Rickettsia sp. CA6269, was first reported in rabbit ticks (Haemaphysalis leporispalustris) collected in Northern California in 2018 (Science Direct, Eremeeva M.E., et al.) Researchers have now developed a Rickettsia sp. CA6269–specific real-time PCR to identify this novel pathogen. A plasma specimen from the initial case patient as well as 8 archival clinical specimens (serum or plasma) collected over the past 20 years from confirmed Spotted Fever Group (SFG) rickettsiosis patients were used for molecular characterization of the novel pathogen. The new tests differentiate this novel pathogen from other SFG Rickettsia sp. 

Researchers describe the spectrum of severe RMSF-like clinical disease observed in 2 patient cases, and the ecologic epidemiology of this new SFG species in California. Both case patients presented to the emergency room (ER) and were admitted to the hospital for symptoms of high fever, severe headache, fatigue, nausea, vomiting, diarrhea, abdominal pain, and muscle and joint pains. Both were hospitalized for extended stays (22 and 13 days). Only one of the two cases developed the characteristic Rocky Mountain Spotted Fever (RMSF) rash. One patient developed “cutaneous necrosis” (injury to skin cells) on several fingers of both hands which had to be amputated. Each patient required time in the intensive care unit (ICU) within days of hospitalization due to the progression of severe illness including coma, seizures, and respiratory failure. 

Initial treatment for each patient was a combination of antibiotics that did not include the the first line antibiotic for SFG infections,  doxycycline. When infectious disease was consulted and RMSF was suspected, each patient was then started on doxycycline.

These cases demonstrate that Rickettsia CA6269 may result in severe and life-threatening illness. Both cases developed in patients from the San Francisco Bay area, with no known travel history outside of this area in the weeks preceding onset of illness. Though the rabbit tick is not a commonly documented human-biter, it is suspected to have been the potential vector in these two cases. 

The application of this new test that differentiates Rickettsia CA6269 from other SFG infections could identify additional cases in the future as well as from past samples, which may provide a better understanding of the illness impacts caused by Rickettsia sp. CA6269. It may further elucidate the potential impact of the increasing incidence of SFG rickettsioses in the US. 

For More Information: 

Read the Emerging Infectious Diseases Article

Read the 2018 Science Direct Article

Read More LDA Articles on Rickettsiosis