Murine typhus

also known as "endemic typhus" and "fleaborne typhus"

Background

• Caused by Rickettsia typhi
  • Gram negative, obligate, intracellular bacterium
  • Replicates in epithelial cells of flea's midgut

Vector

• Infection is transmitted by fleas
  • Typically rat fleas
  • Also Rickettsia felis (indistinguishable from R. typhi) carried by fleas on opossum and cats
• Feces containing R. typhi are deposited into wound made by flea bites

• Found in areas with large populations of urban rats
  • United States
    • Southern Texas
    • Southern California
  • Internationally: Tropical/Subtropical urban seaboard regions

• Seasonal predilection for summer months
  • Texas: Spring to summer
  • California: Summer to fall

Clinical Features

• Incubation period: 7-14 days

Rash of Murine Typhus

Symptoms

• Variable and non-specific
• Often presents as acute, self-limited illness, with no complications

Most Common Symptoms

• Fever- can last ~1 week
• Rash
  • Macular or maculopapular, blanching, non-pruritic
  • Starts centrally and moves to the extremities
  • Can involve palms/soles but usually sparing
  • Starts 6-7 days after symptom onset (fever onset)
• Headache
• Arthralgias

Other Symptoms

• Hepatomegally
• Splenomegally
• Cough
• Diarrhea
• Nausea/Vomiting
• Abdominal pain
• Confusion

Differential Diagnosis

• Non-specific viral illness
• Most common admitting diagnosis in one case study was "fever of unknown origin"

Tick Borne Illnesses

• Babesiosis
• Colorado tick fever
• Ehrlichiosis
• Heartland virus
• Lyme
• Murine typhus
• Rocky mountain spotted fever
• Southern tick-associated rash illness (STARI)
• Tick paralysis
• Tularemia

Fever in traveler

• Normal causes of acute fever!
• Malaria
• Dengue
• Leptospirosis
• Typhoid fever
• Typhus
• Viral hemorrhagic fevers
  • Ebola virus disease
  • Marburg virus disease
  • Lassa fever
  • Crimean-Congo hemorrhagic fever
• Chikungunya
• Yellow fever
• Rift valley fever
• Q fever
• Amebiasis
• Zika virus

Diagnosis

Work up

• Infectious work up
  • Not sensitive or specific
  • CBC- can show anemia and thrombocytopenia
  • LFTs- often elevated 3-5x normal
  • Lumbar Puncture- resembles aseptic meningitis

Diagnostic labs

• Immunofluorescent assay is the gold standard
  • Becomes diagnostic with time. Rarely positive at onset of illness.
• PCR

Management

• Doxycycline 100mg BID continue for 3 days after resolution of symptoms
  • Children - 2.2mg/kg BID
• Chloramphenicol 50-100 mg/kg/day div Q6hr (Max dose = 4g/day)