Transmission and Epidemiology

Rocky Mountain spotted fever (RMSF) is a tickborne disease caused by the intracellular bacterium Rickettsia rickettsii.

Transmission

Tick Bites

Primarily, through tick bites.

• American dog ticks (Dermacentor variabilis) widely distributed east of the Rocky Mountains and in portions of the Pacific Coast.
• Rocky Mountain wood tick (Dermacentor andersoni) in the Rocky Mountain region.
• Brown dog ticks (Rhipicephalus sanguineus) can be found worldwide and serves as the primary vector of RMSF in parts of the southwestern United States and Mexico.

Blood transfusion or organ transplant

• Transmission of R. rickettsii through blood transfusion is extremely rare.
• Organ transplant acquired RMSF has not been documented, but is physiologically possible.

Epidemiology

• Geographic range: RMSF is one of several diseases reported under the category “Spotted fever rickettsiosis (SFR).” SFR are reported in each of the lower 48 states, but more than 60% of the cases are reported out of five states (North Carolina, Oklahoma, Arkansas, Tennessee, and Missouri).
  • For more information, see geography
• Peak transmission: Although cases are reported in every month of the year, most cases occur during May–August.
  • For more information, see seasonality
• Different epidemiology for Arizona and Northern Mexico: Transmission of R. rickettsii by the brown dog tick (Rhipicephalus sanguineus) in these areas results in distinct differences in epidemiology.

  • Figure 2: Estimated geographic distribution of brown dog ticks

    

    This tick species is found throughout the world and spends the majority of its life on domestic dogs or in areas where dogs may be found (including kennels, yards, and even inside homes).

  • RMSF cases in these areas occur year-round and tick exposure occurs in and around the home.
  • Unlike other areas of the United States, cases in areas Arizona and Northern Mexico are characterized by unusually high incidence and case fatality rates, particularly among children.