Rocky Mountain Spotted Fever
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Rocky Mountain spotted fever (RMSF) is one of the spotted fever rickettsioses (SFR) and is associated with the highest rates of severe and fatal outcomes of all reportable rickettsial diseases in the United States.
- RMSF is a potentially fatal tick-borne systemic small vessel vasculitis caused by the bacterium Rickettsia rickettsii.
- Symptoms include fever, headache, and myalgia followed by a macular rash; begins at wrists and ankles, spreading toward palms, soles, and the trunk
- System(s) affected: cardiovascular, musculoskeletal, skin, CNS, renal, hepatic, and pulmonary
In the United States, ticks are both vectors and main reservoirs; the American dog tick, Dermacentor variabilis in the eastern two-thirds of the states; the Rocky Mountain wood tick, Dermacentor andersoni in the western states; and the Brown dog tick, Rhipicephalus sanguineus is distributed throughout all states (1,2)[A].
- In the United States, incidence of SFR was 8.9 cases per million from 2008 to 2012. Cases have been reported in all states except Hawaii and Alaska. RMSF also seen in Canada, Mexico, and throughout Central and South America (1,2)[A],(3)[B].
- North Carolina, Arkansas, Missouri, Oklahoma, and Tennessee account for over 60% of cases (1,2)[A].
- Cases occur year round. Most are reported during April to September during the peak of outdoor activity (1,2)[A],(3)[B].
- All ages are susceptible; highest incidence occurs in age 60 to 69 years. Highest case-fatality rate is in children <10 years (1)[A].
In the United States, 4,470 cases were reported in 2012. <0.1% of ticks carry virulent rickettsial species.
Etiology and Pathophysiology
- An adult tick releases R. rickettsii, an obligate intracellular gram-negative coccobacilli, from its salivary glands after 6 to 10 hours of feeding.
- Pathogens infect vascular endothelial cells, causing small-vessel injury, microhemorrhages, and local consumption of platelets resulting in characteristic petechial rash.
- Damage leads to progressively increased vascular permeability, pulmonary and cerebral edema, hypovolemia, and hyponatremia in late-stage disease.
- Subsequent end-organ injury may also result in meningoencephalitis, ARF, ARDS, shock, arrhythmia, and seizure (1)[A].
- Symptoms appear 3 to 12 days after bite or between 4 to 8 days after discovery of an attached tick. Incubation period is typically 5 days or less.
- Transplacental transmission has not been reported.
- RMSF can rarely be caused by direct inoculation of tick blood into open wounds or conjunctivae.
R. rickettsii has one of the smallest bacterial genomes (1.1 to 1.6 Mb), making the organism highly adapted to the intracellular environment.
- Known tick bite, engorged tick, or presence of tick for >20 hours; likelihood of infection increases with duration of tick attachment.
- Tick crushed during removal
- Accumulated outdoor exposure or residence in wooded areas
- Contact with outdoor pets or wild animals
- Limit tick exposure when possible in endemic areas, highest tick exposure with time spent in tall grasses, open areas of low bushy vegetation or wooded areas.
- Wear light-colored clothing, long sleeves, pants, socks, and closed-toed shoes.
- Use DEET-containing insect repellents.
- Permethrin spray on clothing
- Regular tick checks
- Prompt tick removal.
- Wash hands and site of bite with soap and water after tick removal to avoid potential mucosal inoculation.
- Nail polish, petrolatum jelly, and heat do not aid in tick removal. Do not use bare hands to remove ticks.
- Protect pets with ectoparasite control (1,2)[A].
- Prophylactic antibiotic treatment is not recommended.