Spotted fever group rickettsioses (spotted fevers) are a group of diseases caused by closely related bacteria. These bacteria are spread to people through the bite of infected mites and ticks. The most serious and commonly reported spotted fever group rickettsiosis in the United States is Rocky Mountain spotted fever.

It is spread by several species of ticks in the United States, including the American dog tick (Dermacentor variabilis), Rocky Mountain wood tick (Dermacentor andersoni), and, in parts of the southwestern United States and Mexico, the brown dog tick (Rhipicephalus sanguineus). RMSF cases occur throughout the United States, but are most commonly reported from North Carolina, Tennessee, Missouri, Arkansas, and Oklahoma.

Causes of spotted fever group rickettsioses (spotted fevers) in the United States include:

  • Rocky Mountain spotted fever (RMSF), caused by Rickettsia rickettsii
  • Rickettsia parkeri rickettsiosis, caused by R. parkeri
  • Pacific Coast tick fever, caused by R. philipii
  • Rickettsialpox, caused by R. akari
Microscopic sample of human cells infected with Rocky Mountain Spotted Fever.
Skin infected with Rocky Mountain Spotted Fever
Image courtesy of MicroscopeWorld
Rocky Mountain Spotted Fever rash on foot
Image courtesy of the CDC

Signs and Symptoms

  • eschar (dark scab at the site of tick or mite bite)
  • muscle aches
  • fever
  • headache
  • rash
  • In cases of RMSF, rashes can appear as pinpoint dots, and typically spread centripetally up the arms and legs​
  • Vomiting​
  • Stomach pain
  • Lack of appetite