Rocky Mountain spotted fever

Alternative names

Spotted fever

Definition

Rocky Mountain spotted fever is an infectious disease caused by Rickettsia rickettsii transmitted to humans by the bite of a tick.

Causes, incidence, and risk factors

In the western U.S., the causative agent, R. rickettsii, is transmitted by the wood tick, and in the eastern U.S., by the dog tick. Other ticks transmit the infection in the southern U.S. and in Central and South America.

Contrary to the name "Rocky Mountain," most recent cases have been reported in the eastern United States: North and South Carolina, Virginia, Maryland, Georgia, Tennessee, and Oklahoma. Most cases occur in the spring and summer with about 1,000 cases reported per year. Most of the reported cases have been in children.

The risk factors include recent hiking or exposure to ticks in an area where the disease is known to occur.

Symptoms

• fever
  
• chills
  
• incubation period of 2 to 14 days
  
• severe headache
  
• muscle pain
  
• mental confusion
  
• rash, first appearing on wrists and ankles, then spreading to most of the body, usually starts a few days after fever starts; up to 20% of people do not get a rash
  

Additional symptoms that may be associated with this disease:

• excessive thirst
  
• nausea and Vomiting
  
• hallucinations
  
• diarrhea
  
• appetite, loss
  
• abnormal sensitivity to light
  

Signs and tests

• low platelets
  
• low red blood cell count in 30% of patients
  
• possible renal failure, elevated creatinine
  
• possible clotting problems, elevated PT and PTT
  
• Blood in the urine and protein in the urine
  
• Antibody titer by complement fixation or immunofluorescence that indicates the presence of infection