Rickettsia typhi - Typhus Fever

Epidemiology

• Incidence – <100 cases annually in the U.S.
• Transmission – louse or flea

Organism

• Gram-negative coccobacilli of the Rickettsiaceae family (obligate intracellular organisms)
• Characteristic feature of Rickettsia – life cycle requires multiplying in an arthropod
• With typhus (R. prowazekii and R. typhi), the invertebrate hosts are both reservoirs and vectors
• Rickettsia are part of a family of organisms responsible for the following rickettsial diseases
  • Spotted fever and typhus (vector – tick, louse, flea, or gamasid mite)
  • Scrub typhus (vector – chigger)
  • Ehrlichiosis (vector – tick)
  • Neorickettsiosis
  • Q-fever

Risk Factors

• Epidemic typhus (louse borne) – residence in poor hygienic areas (eg, jails) in cold months
• Endemic murine typhus (flea borne) – residence in close-quartered poverty in warm climates
• Recrudescent typhus (Brill-Zinsser disease) – previously acquired disease combined with immunosuppression or old age
• Flying squirrel typhus (louse or flea borne) – contact with flying squirrels, particularly in southern U.S.

Clinical Presentation

• Incubation period – 3-14 days
• Most patients develop nonspecific symptoms and signs
• Onset of disease is sudden in about half of the cases
  • Fever and headache are the most commonly reported symptoms
  • Chills, myalgias, arthralgias, malaise, and anorexia can be present
  • Rash (maculopapular, nonconfluent, and blanching areas)
    • Hallmark of infection
    • Usually follows systemic symptoms
    • Often transient and difficult to observe in murine typhus
    • Absence should not rule out a possible rickettsial etiology
• Pulmonary involvement is frequent in murine typhus
• Serious central nervous system impairment can also be seen with typhus
  • Meningitis
  • Seizures
  • Hearing loss
  • Multiorgan failure may occur