Gram-negative γ-proteobacteria, small (0.3-0.5 X 0.8-1.0 μm).

Spotted fever group rickettsiae including R. rickettsii (Rocky Mountain spotted fever, RMSF) and R. conorii (Mediterranean spotted fever, MSF) are pathogenic organisms transmitted to humans through tick salivary contents during the blood meal.
The TG rickettsiae include R. prowazekii, the etiologic agent of epidemic typhus, and R. typhi, the causative agent of murine typhus.

Bacteria; Proteobacteria; Alphaproteobacteria; Rickettsiales; Rickettsiaceae; Rickettsia