A tick-borne bacterium that lives inside cells and causes Rocky Mountain spotted fever, where treatment delay is the main danger. Explore its illustrative 3D model, human context, and sources.
PHAC describes R. rickettsii as a small pleomorphic Gram-negative coccobacillus of 0.2 to 0.5 by 0.2 to 0.3 micrometres that is an obligate intracellular bacterium, multiplies by binary fission and has both DNA and RNA. CDC describes Rocky Mountain spotted fever as a bacterial disease spread through the bite of an infected tick, transmitted by the American dog tick, Rocky Mountain wood tick and brown dog tick, with cases occurring throughout the United States. PHAC reports 250 to 1,200 cases reported each year in the USA, making it the most common tick-borne disease there in that account, with 90 to 93% of US cases reported between April and October, and states that 20% of untreated cases are fatal compared to 5% of treated cases.
PHAC states that 20% of untreated cases are fatal compared to 5% of treated cases, with higher mortality in patients over 60. CDC states that early treatment with the antibiotic doxycycline can prevent death and severe illness. The gap between those figures is about timing rather than about the organism, which is why suspected RMSF is treated before laboratory confirmation.
Rickettsia rickettsii · A small, short, pleomorphic coccobacillus; no host-cell structures are included. This is a species-informed teaching diagram; colours, proportions, envelope spacing and internal detail are illustrative. The model uses muted illustrative colours; stains, colony pigments and microscopy colourization are not natural cell colours. Anatomy is enlarged for phone viewing. Morphology reference: Rickettsia rickettsii · pathogen safety data sheet.
Source check: 2026-09-20. Educational content; independent scientific review remains pending.