Rickettsia typhi

Background

• Causes murine typhus, flea-borne typhus, or endemic typhus

Microbiology

• Flea-borne Gram-negative intracellular bacterium

Life Cycle

• Flea bites, flea poops, feces get rubbed into the bite wound
• Flea acquires infection from feeding on a rickettsemic host

Epidemiology

• Flea vector (Xenopsylla cheopis) with a rat reservoirs (Rattus)
  • Also, cat flea vector (Ctenocephalides felis) in southern US
  • Possibly opossums as reservoirs
• Worldwide distribution
• In the US, most cases are in southern Texas and California

Clinical Manifestations

• Incubation period of 1 to 2 weeks, but rarely remember flea exposure
• Fever, headache, nausea and vomiting are common, as well as myalgias
• Rash develops over the course in about 50%
  • Usually described as macular or maculopapular rash, sometimes with petechiae
  • On trunk, but can involve extremities
  • Rarely on palms and soles
• May have leukopenia and thrombocytopenia early in the course
• Elevated AST is common, as well as other liver enzymes
• Further nausea/vomiting and anorexia, cough, and hepatosplenomegaly may all develop
• Neurologic complications include confusion, seizures, and ataxia
• They often develop hypoalbuminemia and electrolyte abnormalities such as hyponatremia and hypocalcemia
• CSF shows aseptic meningitis
• 1 to 4% mortality
• Sort of like a milder version of Rickettsia prowazekii

Diagnosis

• Based on acute and convalescent serology looking for a 4-fold risk after about 4 weeks
• Possibly PCR of skin biopsy

Management

• doxycycline 100 mg PO bid for 7 to 10 days
• Should be treated empirically, since cannot confirm diagnosis quickly