Explore the recorded discovery and history of Rickettsia rickettsii, with source links and stated limits.
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.
LPSN records the basonym “Dermacentroxenus rickettsii” Wolbach 1919. The epithet honours Howard Taylor Ricketts for his classic studies of the etiology of Rocky Mountain spotted fever, so the name records who investigated the disease rather than where it came from.
LPSN records Rickettsia rickettsii corrig. (Wolbach 1919) Brumpt 1922, retained on the 1980 Approved Lists of Bacterial Names. Type strains include ATCC VR-149, Iowa and Sheila Smith.
These references do not identify a first person ever infected. The disease was investigated in the Rocky Mountain region before the organism was described, and the sources bundled here do not establish a first human case or the geographic origin of the species.
Source check: 2026-09-20. Educational content; independent scientific review remains pending.