Rocky Mountain Spotted Fever

1. See Also
   1. Vector Borne Disease
   2. Prevention of Tick-borne Infection
   3. Tick Removal
2. Pathophysiology
   1. Transmission
      1. Person to person transmission does not occur
      2. Tick bite (Ixodidae tick)
         1. Wood tick (Dermacentor andersoni) is vector in Western U.S.
         2. Dog tick (Dermacentor variabilis) is vector in Southern and Eastern U.S.
   2. Rickettsia rickettsii is causative organism
      1. Gram Negative Bacteria
      2. Small pleomorphic organism
      3. Obligate intracellular parasite
   3. Infects blood vessel walls
      1. Infects endothelial cells and smooth muscle cells,
      2. Spreads through Lymphatic System
      3. Secondary multiorgan Vasculitis ensues (especially involving skin and Adrenal Glands)
      4. Results in increased vascular permeability and decreased osmotic pressure
3. Epidemiology
   1. Most common Rickettsial disease in the United States
   2. Bimodal age distribution
      1. Ages 5 to 9 years old (most common age affected)
      2. Age over 60 years old
   3. Endemic area (only occurs in Western Hemisphere)
      1. North America
         1. Occurs in all states except Maine, Hawaii, Alaska
         2. Atlantic coast and south central states (most common)
         3. Midwest
      2. Central America
      3. South America
   4. Timing
      1. Most common April to September (90% of cases)
4. Presentation: Classic
   1. Recent tick bite
   2. Fever
   3. Headache
   4. Rash
5. Symptoms (follows 5-7 day incubation)
   1. Fever
   2. Frontal Headache
   3. Myalgias (back and leg muscles)
   4. Malaise
   5. Nausea or Vomiting
   6. Abdominal Pain (especially in children)
6. Signs: Rash (occurs in 90% of patients)
   1. Onset in first week of illness (follows fever by 2-5 days)
   2. Characteristics
      1. Initial: Pink blanching Macules 1 to 4 mm in diameter
      2. Later: Macules transition to Papules and Petechiae
      3. Final: Coalesce into large Ecchymoses and Ulcerations
   3. Distribution
      1. Onset: Wrists and ankles
      2. Next: Spreads distally to palms and soles (may be only rash in as many as 40% of patients)
      3. Next: Spreads proximally into upper arms and legs
      4. Later: Trunk, axilla, buttocks, neck
      5. Face is typically spared
7. Diagnosis
   1. Missed diagnosis initially in up to 75% of cases
   2. Based on clinical findings
   3. Specific testing is for confirmation only
      1. Skin biopsy with immunofluorescent Rickettsia stain
      2. Rickettsia Serology
8. Differential Diagnosis
   1. See Purpura Causes
   2. See Febrile Eruption
   3. Mycoplasma pneumonia
   4. Syphilis
   5. Lyme Disease
   6. Coxsachievirus
   7. Mononucleosis
   8. Parvovirus B19
   9. Kawasaki Disease
   10. Leptospirosis
   11. Roseola
   12. Rubeola
   13. Meningococcemia
   14. Toxic shock syndrome
   15. Scarlet Fever
   16. Immune Thrombocytopenic Purpura
9. Labs
   1. Complete Blood Count
      1. White Blood Cell count normal or slightly decreased
      2. Thrombocytopenia
   2. Liver transaminases increased
      1. Aspartate Aminotransferase (AST)
      2. Alanine Aminotransferase (ALT)
   3. Renal Function tests (Serum Creatinine and Blood Urea Nitrogen)
      1. Acute Renal Failure is a late finding
   4. Serum Sodium
      1. Hyponatremia
   5. Cerebrospinal Fluid (indicated for associated neurologuc changes)
      1. CSF Pleocytosis with monocytic predominance
   6. Skin Punch Biopsy with immunofluorescent stain for Rickettsia
      1. Used for confirmation, not for diagnosis
      2. Test Sensitivity: 60%
      3. Test Specificity: Very high
   7. Rickettsia Serology
      1. Positive 7 to 10 days after symptom onset
      2. Used for confirmation, not for diagnosis
10. Management
    1. Start treatment immediately when diagnosis suspected
       1. Do not delay treatment for diagnostic testing
       2. Treatment delayed >5 days after onset increases mortality by 3 fold
    2. Antibiotic Course
       1. Minimum course: 7 days
       2. Continue antibiotics until afebrile for 3 days
    3. Antibiotics
       1. Doxycycline
       2. Tetracycline
       3. Chloramphenicol (indicated in pregnancy)
11. Complications
    1. Encephalitis
    2. Noncardiac pulmonary edema
    3. Acute Respiratory Distress Syndrome (ARDS)
    4. Cardiac arrhythmia
    5. Coagulopathy
    6. Gastrointestinal Bleeding
    7. Skin Necrosis
12. Prognosis
    1. Untreated: 25% Mortality within 8 to 15 days
    2. Treated: 5% Mortality
    3. G6PD is associated with complications and poor outcome
13. Prevention
    1. See Prevention of Vector-borne Infection
14. Resources
    1. CDC Rocky Mountain Spotted Fever
       1. http://www.cdc.gov/ncidod/dvrd/rmsf
15. References
    1. Chapman (2006) MMWR Recomm Rep 55(RR-4):1-27
    2. Thorner (1998) Clin Infect Dis 27:1353-60