Emerging Tick-Borne Illnesses: Not Just Lyme Disease Part 4 RMSF

Rocky Mountain Spotted Fever (RMSF)

Epidemiology

Incidence:

• Overall annual incidence rose from 1.7 to 7 cases per million in the United States between 2000 and 2007 (Openshaw 2010)
• Annual incidence is highest in children aged 5-9 years of age (Amsden 2005)

Age:

• Median age is 42 years of age with greater than 87% of cases reported in Caucasian patients (Openshaw 2010)

Gender:

• Slight male to female predominance (Openshaw 2010)

Morbidity/Mortality: RMSF is the most common fatal rickettsial illness in the United States

• Overall hospitalization rates are noted be at 23.4% based on aggregated reviews of case reports (Openshaw 2010)
• Case fatality rate is estimated to be 5-10% overall (Biggs 2016)
  • If treatment is delayed, case-fatality rates of 40-50% have been described for patients treated on day 8 or 9 of their illness
  • Case fatality rate is highest in those over the age of 70 (Amsden 2005)
  • Without treatment, the case fatality rate is over 25% (Lacz 2006)

Geography and Seasonality (Openshaw 2010): Cases have been found in all continuous 48 states

• Five States account for over 64% of all reported cases:
  • North Carolina
  • Oklahoma
  • Arkansas
  • Tennessee
  • Missouri
• Seasonal distribution is concentrated in June (38 %) and July (38%).
  • Second smaller peak is noted in October and November when adult ticks are active

Poor Prognostic Factors (Biggs 2016):

• Age < 10 or > 40 years of age
• Alcohol abuse
• Glucose-6-phosphate dehydrogenase deficiency
• Delays in diagnosis and treatment
• Immunocompromised states
• Use of sulfonamide antimicrobial

Pathogenesis (Lacz 2006):

• Rickettsia has tropism for endothelial cells and is able to spread centripetally via filopodia propulsion.
• Invasion of endothelial and smooth muscle cells of various organs leads to dysfunction of microcirculation, host immune response, vascular tone, angiogenesis, and normal hemostasis.
• Multiple organ systems are infected including the brain, liver, skin, lungs, kidneys, as well as the gastrointestinal system.

History and Physical:

Symptoms (Biggs 2016):

• Symptoms typically appear 3-12 days after bite of an infected tick
• Classic Triad: Tick Bite, Rash, Fever
  • Present in only a minority of patients
• Rash: Absence of rash does not rule out this diagnosis
  • Timeline:
    • Typically appears 2-4 days after fever onset
  • Distribution:
    • Begin on the ankles, wrists, and forearms and subsequently spreads to the palms, soles, arms, legs, and trunk
    • Typically spares the face
  • Morphology:
    • Day 1: Initially seen as small, blanching macules
    • Over next several days, the rash becomes maculopapular, sometimes exhibiting central petechiae
    • Day 5 and 6: Rash becomes primarily petechial with involvement of the palms and soles
  • Initial Symptoms (< 5 days):
    • Fever
    • Headache
    • Chills
    • Malaise
    • Myalgia
    • Photophobia
    • Conjunctival Suffusion
    • Periorbital and Peripheral Edema
    • Calf Pain
    • Acute Transient Hearting Loss
    • Gastrointestinal Symptoms
  • Severe Manifestations: Most cases are self-limiting, but RMSF has been associated with the following severe disease manifestations:
    • Meningoencephalitis, Coma, Cerebral Edema
    • Renal Failure
    • ARDS
    • Seizures
    • Shock
    • Cutaneous Necrosis and Gangrene
    • Arrhythmias, Myocarditis

Diagnosis:

Labs: Characteristic laboratory findings are seen in RMSF along fever and non-specific flu-like illness:

• Thrombocytopenia
• Hyponatremia
• Mild Elevated Hepatic Transaminase
• Increased Number of Immature Neutrophils

Confirmatory Testing (Dantas-Torres 2007):

• Serological testing revealing four-fold change in IgG antibodies specific to R rickettsii using indirect immunofluorescence assay (IFA) in paired samples
  • Antibodies are not detected until 7-10 days after disease onset
• RT-PCR assays are also available for diagnosis
• ELISA testing is also available for diagnosis
• Immunohistochemical staining from skin or tissue biopsies has also been used for diagnosis

Guest Post By:

Akash Ray, DO
PGY-2 Emergency Medicine Resident Inspira Medical Center
Vineland, NJ
Twitter: @_kashray

References:

1. Biggs H et al. Diagnosis and Management of Tickborne Rickettsial Diseases: Rocky Mountain Spotted Fever and Other Spotted Fever Group Rickettsioses, Ehrlichioses, and Anaplasmosis – United States. MMWR Recomm Rep. 2016. PMID: 27172113
2. Openshaw J et al. Rocky mountain spotted fever in the United States, 2000-2007: interpreting contemporary increases in incidence. Am J Trop Med Hyg. 2010. PMID: 20595498
3. Amsden J et al. Tick-borne bacterial, rickettsial, spirochetal, and protozoal infectious diseases in the United States: a comprehensive review. Pharmacotherapy. 2005. PMID: 15767235
4. Lacz N et al. Rocky Mountain spotted fever. J Eur Acad Dermatol Venereol. 2006. PMID: 16643138
5. Dantas-Torres F. Rocky Mountain spotted fever. Lancet Infect Dis. 2007. PMID: 17961858

Post Peer Reviewed By: Salim R. Rezaie, MD (Twitter: @srrezaie)

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