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)

Cite this article as: Muhammad Durrani, "Emerging Tick-Borne Illnesses: Not Just Lyme Disease Part 4 RMSF", REBEL EM blog, November 5, 2020. Available at: https://rebelem.com/emerging-tick-borne-illnesses-not-just-lyme-disease-part-4-rmsf/.
The following two tabs change content below.

Muhammad Durrani

Assistant Clerkship Director & Assistant Research Director at Inspira Medical Center

Like this article?

Share on facebook
Share on Facebook
Share on twitter
Share on Twitter
Share on linkedin
Share on Linkdin
Share on email
Share via Email

Want to support rebelem?

Leave a Comment

Time limit is exhausted. Please reload CAPTCHA.

Sponsored

0