Rickettsia typhi - Typhus Fever

Diagnosis

Indications for Testing

  • Febrile illness in setting of unhygienic environments

Laboratory Testing

  • Clinical presentation and diagnosis recommendations (CDC)
  • Nonspecific
    • CBC
    • Hepatic transaminases
    • Bilirubin
    • Blood urea nitrogen (BUN)
  • IgG and IgM by IFA – method of confirming 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

Clinical Background

Rickettsia typhi is the etiologic agent of both epidemic and endemic typhus.

Epidemiology

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

Organism

  • Gram-negative coccobacilli of the Rickettsiaceae family (obligate intracellular organisms)
  • Characteristic feature of Rickettsia – life cycle requires multiplying in an arthropod
  • With typhus (Rickettsia 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:

Risk Factors

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

Clinical Presentation

  • The incubation period for most rickettsioses ranges from 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, but chills, myalgias, arthralgias, malaise, and anorexia also are noted
    • Rash (maculopapular, nonconfluent, and blanching areas) is a hallmark of infection, but it usually follows systemic symptoms
      • Its 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

Treatment

  • Antibiotic treatment is curative

Indications for Laboratory Testing

  • Tests generally appear in the order most useful for common clinical situations
  • Click on number for test-specific information in the ARUP Laboratory Test Directory
Test Name and Number Recommended Use Limitations Follow Up
Rickettsia typhi (Typhus Fever) Antibodies, IgG & IgM by IFA 0050384
Method: Semi-Quantitative Indirect Fluorescent Antibody

Confirm presence of Rickettsia typhi

Initial testing may not be helpful; base treatment on clinical and other laboratory assessment 

While the presence of IgM antibodies suggests current or recent infection, low levels of IgM antibodies may occasionally persist for >12 months postinfection

Any antibody reactivity to Rickettsia typhi antigen should also be considered group reactive for the typhus fever group (R. prowazekii)

If test results are equivocal, repeat testing in 10-14 days

Febrile Antibodies Identification Panel 2010805
Method: Semi-Quantitative Agglutination/Semi-Quantitative Indirect Fluorescent Antibody/Qualitative Immunoblot

Use to confirm presence of disease; not recommended for initial testing

Includes Brucella Antibody (Total) by Agglutination; Rickettsia rickettsii Antibody, IgM; Rickettsia rickettsii antibody, IgG; Rickettsia typhi Antibody, IgG by IFA; Rickettsia typhi Antibody, IgM by IFA, and Salmonella typhi and paratyphi Antibodies

Base treatment decision on clinical and other laboratory assessments

Cross reactivity with Brucella and Salmonella

 
CBC with Platelet Count and Automated Differential 0040003
Method: Automated Cell Count/Differential

Nonspecific testing for R. typhi

Shows thrombocytopenia in 40% of cases

   
Urea Nitrogen, Serum or Plasma 0020023
Method: Quantitative Spectrophotometry

Nonspecific testing for R. typhi

Elevated in ~30% of cases

   
Hepatic Function Panel 0020416
Method: Quantitative Enzymatic/Quantitative Spectrophotometry

Nonspecific testing for R. typhi

Bilirubin elevated in ~20% of cases

   
Creatinine, Serum or Plasma 0020025
Method: Quantitative Enzymatic

Nonspecific testing for R. typhi

   
Additional Tests Available
 
Click the plus sign to expand the table of additional tests.
Test Name and NumberComments
Rickettsia typhi (Typhus Fever) Antibody, IgG by IFA 0050381
Method: Semi-Quantitative Indirect Fluorescent Antibody
Rickettsia typhi (Typhus Fever) Antibody, IgM by IFA 0050383
Method: Semi-Quantitative Indirect Fluorescent Antibody