Rickettsia typhi - Typhus Fever

Diagnosis

Indications for Testing

Fever, headache, chills, rash, dry cough, nausea, and vomiting in at-risk individual (living in unsanitary conditions, close human contact, with potential for mouse/rat contact)

Laboratory Testing

• Clinical presentation and diagnosis recommendations (CDC)
• Nonspecific
  • CBC
  • Hepatic transaminases
  • Bilirubin
  • Blood urea nitrogen (BUN)
  • Creatinine
• IgG and IgM by indirect fluorescent antibody (IFA) – use to confirm diagnosis
  • Convalescent specimen usually required
  • IgG does not differentiate between primary infection and Brill-Zinsser disease
• Febrile antibody testing
  • More specific than Weil-Felix but still has cross-reactivity with Brucella and Salmonella
  • Must be used in conjunction with clinical presentation
• Weil-Felix
  • Not sensitive or specific
  • Outmoded
  • Should not be used
• Culture – not routinely available because of biosafety issues (research labs only)

Differential Diagnosis

• Other rickettsial diseases
• Tickborne diseases
• Plasmodium spp
• Salmonella typhi (typhoid fever)
• Leptospira spp
• Treponema pallidum (secondary syphilis)
• Dengue fever virus
• Toxoplasma gondii

Background

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