Rickettsia rickettsii subsp. californica subsp. nov., the etiologic agent of Pacific Coast tick fever.

The etiologic agent of Pacific Coast tick fever (PCTF), a moderately severe tickborne illness that resembles Rocky Mountain spotted fever (RMSF), was first isolated in 1966 from specimens of Dermacentor occidentalis (the Pacific Coast tick) obtained in California. For several decades, this bacterium was identified ambiguously as the unclassified spotted fever group Rickettsia species 364-D, Rickettsia 364, or Rickettsia philipii. However, none of these epithets satisfied criteria of formal bacterial nomenclature.