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Rickettsia rickettsii subsp californica subsp nov, the Etiologic Agent of Pacific Coast Tick Fever

Christopher D Paddock1, Sandor E Karpathy1, Asa Henry2

  • 1Rickettsial Zoonoses Branch, Centers for Disease Control and Prevention, Atlanta, Georgia, USA.

The Journal of Infectious Diseases
|October 21, 2024
PubMed

Insights

Pacific Coast tick fever is caused by a bacterium previously misidentified. Researchers propose a new subspecies name, Rickettsia rickettsii subsp californica, for this distinct pathogen.

Area of Science:

  • Microbiology
  • Bacteriology
  • Tick-borne diseases

Background:

  • Pacific Coast tick fever is a tick-borne illness similar to Rocky Mountain spotted fever (RMSF).
  • The causative agent, isolated in 1966, was ambiguously identified as Rickettsia species 364-D, Rickettsia 364, or Rickettsia philipii.
  • Previous studies indicated it was related to, but distinct from, Rickettsia rickettsii, the RMSF agent.

Purpose of the Study:

  • To formally identify and name the etiologic agent of Pacific Coast tick fever.
  • To differentiate this bacterium from Rickettsia rickettsii using modern genomic and phenotypic data.

Main Methods:

  • An integrative taxonomic approach was employed.
  • Whole-genome sequencing of 11 contemporary isolates.
  • Phenotypic, ecological, and clinical data were combined.

Main Results:

  • The bacterium was identified as a distinct subspecies of Rickettsia rickettsii.
  • The proposed name is Rickettsia rickettsii subsp californica subsp nov.
  • This resolves decades of ambiguous nomenclature.

Conclusions:

  • Rickettsia rickettsii subsp californica is formally proposed as a new subspecies.
  • This classification clarifies the identity of the Pacific Coast tick fever agent.
  • Accurate identification is crucial for understanding and managing tick-borne diseases.
Keywords:
Rickettsia 364DRickettsia philipiiRickettsia rickettsiiPacific Coast tick fever

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