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Rocky Mountain Spotted Fever
Aka: Rocky Mountain Spotted Fever, Rickettsia rickettsii
- See Also
- Tick-Borne Disease
- Vector Borne Disease
- Prevention of Tick-borne Infection
- Tick Removal
- Epidemiology
- Rocky Mountain Spotted Fever is the most common Rickettsial Disease in the United States
- Up to 6000 cases per year of RMSF and related Rickettsial spotted fevers (see below)
- RMSF is the most lethal of Tick Borne Illnesses (5-10% mortality)
- Bimodal age distribution
- Ages 5 to 9 years old (highest mortality)
- Age over 40-60 years old
- Timing
- Most common April to September (90% of cases)
- Endemic area (only occurs in Western Hemisphere)
- Central America
- South America
- North America
- Occurs in all states except Maine, Hawaii, Alaska
- Midwest
- Atlantic coast and south central states (account for 60% of cases in U.S.)
- North Carolina
- Oklahoma
- Arkansas
- Tennessee
- Missouri
- Other similar Rickettsial spotted fevers
- Respond to similar antibiotics as those used in Rocky Mountain Spotted Fever
- In U.S.
- Rickettsial Pox (R. akari in North America)
- American Boutonneuse fever (R. parkeri in southeast U.S.)
- Finders Island Spotted Fever (R. honei in northwest U.S. as well as Australia and southeast Asia)
- Non-U.S.
- Mediterranean Spotted Fever or Boutonneuse Fever (R. connori in the Mediterranean)
- Queensland Tick Typhus (R. australis in australia)
- African Tick BiteFever (R. africae in africa)
- Siberian Tick Typhus (R. sibirica in China)
- Pathophysiology
- Transmission
- Tick to human transmission
- Transmission may occur as early as 2 hours after Tick Bite
- Tick engorgement need not be present for transmission to have occurred
- Person to person transmission does not occur
- Tick Bite (Ixodidae tick)
- Wood tick (Dermacentor andersoni) is vector in Western U.S.
- Dog tick (Dermacentor variabilis) is vector in Southern and Eastern U.S.
- Other ticks transmitting spotted fever group Bacteria
- Rhipicephalus
- Amblyomma Maculatum (Gulf Coast Tick)
- Rickettsia rickettsii is causative organism
- Gram Negative Bacteria
- Small pleomorphic organism
- Obligate intracellular Parasite
- Infects blood vessel walls
- Infects endothelial cells and Smooth Muscle Cells,
- Spreads through Lymphatic System
- Secondary multiorgan Small Vessel Vasculitis ensues (especially involving skin and Adrenal Glands)
- Results in increased vascular permeability and decreased osmotic pressure
- Presentation: Classic
- Classic presentation in <18% of patients
- Initial
- Recent Tick Bite in endemic areas
- Fever and flu-like illness in spring and summer
- Headache
- Later (day 6)
- Erythematous, Macular rash (transitions to Petechiae)
- Symptoms (follows 5-7 day incubation)
- Fever
- Frontal Headache
- Myalgias (back and leg Muscles)
- Malaise
- Nausea or Vomiting
- Abdominal Pain (especially in children)
- Signs: Rash (occurs in 90-95% of patients)
- Onset in first week of illness (follows fever by 2-5 days)
- Characteristics
- Initial: Pink blanching Macules 1 to 4 mm in diameter
- Later: Macules transition to Papules and Petechiae (seen in 40-50% of patients)
- Final: Coalesce into large Ecchymoses and ulcerations (eschar may form)
- Distribution: Centripetal Rash - peripheral to central spread
- Onset: Wrists and ankles
- Next: Spreads distally to palms and soles (may be only rash in as many as 40% of patients)
- Next: Spreads proximally into upper arms and legs
- Later: Trunk, axilla, buttocks, neck
- Face is typically spared
- Diagnosis
- Missed diagnosis initially in up to 75% of cases
- Delayed onset of rash until day 6 makes initial diagnosis more difficult
- Start empiric management immediately on suspicion
- Based on clinical findings
- Do not rely on rash or Thrombocytopenia to make diagnosis
- Specific testing is for confirmation only
- Skin biopsy with immunofluorescent Rickettsia stain
- RickettsiaSerology
- Differential Diagnosis
- See Purpura Causes
- See Febrile Eruption
- See Tick Borne Illness
- Ehrlichiosis
- Mycoplasma pneumonia
- Syphilis
- Lyme Disease
- Coxsachievirus
- Mononucleosis
- Parvovirus B19
- Kawasaki Disease
- Leptospirosis
- Roseola
- Rubeola
- Meningococcemia
- Toxic Shock Syndrome
- Scarlet Fever
- Immune Thrombocytopenic Purpura
- Labs
- Complete Blood Count
- White Blood Cell Count normal or slightly decreased (Leukopenia)
- Thrombocytopenia
- Liver Function Test abnormalities
- Serum Bilirubin increased (Hyperbilirubinemia)
- Liver transaminases increased
- Aspartate Aminotransferase (AST) increased
- Alanine Aminotransferase (ALT) increased
- Renal Function tests (Serum Creatinine and Blood Urea Nitrogen)
- Acute Renal Failure is a late finding
- Serum Sodium
- Hyponatremia
- Cerebrospinal Fluid (indicated for associated neurologuc changes)
- CSF Pleocytosis with monocytic predominance
- Diagnosis
- Skin Punch Biopsy with immunofluorescent stain for Rickettsia
- Used for confirmation, not for diagnosis
- Test Sensitivity: 60%
- Test Specificity: Very high
- RickettsiaSerology
- Positive 7 to 10 days after symptom onset
- Used for confirmation, not for diagnosis
- IgG increases 4 fold from baseline when re-tested 2-4 weeks later
- Management
- Start empiric treatment immediately when diagnosis suspected
- Do not delay treatment for diagnostic testing
- Treatment delayed >5 days after onset increases mortality by 3 fold
- Treatment is ideally started before rash onset (typically develops day 6)
- Antibiotic Course
- Minimum course: 7 days
- Continue antibiotics until afebrile for 3 days
- Antibiotics
- Doxycycline for 7 days
- Adult: 100 mg oral or IV twice daily
- Child (<45 kg) 2.2 mg/kg (max 100 mg) twice daily
- Children of any age and pregnant women should be treated with Doxycycline despite dental risks
- Only effective treatment available for a condition with high risk for mortality
- Chloramphenicol (only if Doxycycline contraindicated)
- Dose: 12.5 mg/kg orally four times daily for 7 days
- Higher mortality than with Doxycycline
- Complications
- Encephalitis (and cerebral edema)
- Noncardiac Pulmonary Edema and Pulmonary Hemorrhage
- Acute Respiratory Distress Syndrome (ARDS)
- Acute Renal Failure
- Myocarditis
- Cardiac Arrhythmia
- Disseminated Intravascular Coagulation
- Gastrointestinal Bleeding
- Skin Necrosis
- Prognosis
- Untreated: 20-25% Mortality within 7 to 15 days (median 7 days)
- Treated: 4-5% Mortality
- Children have a higher mortality rate than adults
- G6PD is associated with complications and poor outcome
- Prevention
- See Prevention of Vector-borne Infection
- Resources
- CDC Rocky Mountain Spotted Fever
- http://www.cdc.gov/ncidod/dvrd/rmsf
- References
- (2016) Sanford Guide to Antibiotics, IOS App accessed 4/14/2016
- Chapman (2006) MMWR Recomm Rep 55(RR-4):1-27 [PubMed]
- Cunha (2008) Lancet Infect Dis 8(3): 143-4 [PubMed]
- Huntington (2016) Am Fam Physician 94(7): 551-7 [PubMed]
- Pace (2020) Am Fam Physician 101(9): 530-40 [PubMed]
- Thorner (1998) Clin Infect Dis 27:1353-60 [PubMed]