Rocky Mountain spotted fever is a tick-borne bacterial infection caused by the obligate intracellular pathogen Rickettsia rickettsii, classified within the spotted fever rickettsiosis group [1]. The organism infects vascular endothelial cells throughout the body, producing a systemic vasculitis that underlies both the acute illness and its potential complications [1][2].
Disease overview
BacterialRocky Mountain spotted fever
落基山斑点热
Evidence-backed informationEN 5/7 applicable sections · ZH 5/7 applicable sectionsUpdated Sep 3, 2026
Rocky Mountain spotted fever (RMSF) is a bacterial disease spread by ticks. It typically begins with a fever and headache, which is followed a few days later with the development of a rash. The rash is generally made up of small spots of bleeding and starts on the wrists and ankles. Other symptoms may include muscle pains and vomiting. Long-term complications following recovery may include hearing loss or loss of part of an arm or leg. The disease is caused by Rickettsia rickettsii, a type of bacterium that is primarily spread to humans by American dog ticks, Rocky Mountain wood ticks, and brown dog ticks. [1]
Read the full clinical and epidemiological profile6
The illness typically begins with fever and headache, and within a few days many patients develop a rash that begins as small, flat, pink, non-itchy spots on the wrists, forearms, and ankles and may evolve into a characteristic petechial rash involving the palms and soles in up to 80% of those affected [1]. Additional acute features include muscle pains and vomiting, while severe disease can involve the respiratory, central nervous, gastrointestinal, and renal systems [1]. Long-term complications among survivors of severe illness may include partial paralysis of the lower extremities, gangrene requiring amputation, hearing loss, and loss of bowel or bladder control [1].
Fewer than 5,000 cases of Rocky Mountain spotted fever are reported annually in the United States, with most cases occurring during the summer months of June and July [1]. The disease has been diagnosed throughout the contiguous United States, Western Canada, and parts of Central and South America, reflecting the geographic range of its tick vectors [1]. The overall case-fatality ratio is approximately 0.5%, although mortality exceeded 10% before the introduction of tetracycline antibiotics in the 1940s [1].
Rocky Mountain spotted fever is primarily transmitted to humans through the bite of infected ticks, with American dog ticks, Rocky Mountain wood ticks, and brown dog ticks identified as the principal vectors [1]. Transmission by blood transfusion has rarely been documented [1]. The disease is grouped with other spotted fever rickettsioses transmitted by similar tick-borne mechanisms [1].
Antibiotic prophylaxis is not recommended for prevention of Rocky Mountain spotted fever [1].
- 1Wikipedia contributors. Rocky Mountain spotted fever - Wikipedia [Internet]. Wikipedia. cited 3 Sept 2026.Available from: https://en.wikipedia.org/wiki/Rocky_Mountain_spotted_fever
- 2Redford AH et al. HLA-B27 spondyloarthritis and spotted fever rickettsiosis: case-based review. Rheumatol Int. 2019 Sep. PMID: 31134290. doi: 10.1007/s00296-019-04330-8.PubMed: https://pubmed.ncbi.nlm.nih.gov/31134290/
- 3Choi E et al. Tick-Borne Illnesses. Curr Sports Med Rep. 2016 Mar-Apr. PMID: 26963018. doi: 10.1249/JSR.0000000000000238.PubMed: https://pubmed.ncbi.nlm.nih.gov/26963018/
- A77.0
- 1C30.1
Coverage
Reporting countries and regions
Trends by reporting country
Monthly patterns over time
Data access
Page dataset index with source links and update metadata.
Official sourcesAuthority, cadence, notes1
JP NIID Weekly
Japan
Japan weekly infectious disease surveillance via NIID/JIHS.