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Rickettsia typhi - Typhus Fever

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

Epidemiology

Organism

Gram-negative coccobacilli which are obligate intracellular organisms
A characteristic feature of the Rickettsiae is that they multiply in an arthropod as part of their life cycle
With typhus (Rickettsia prowazekii and Rickettsia 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) – common in poor hygienic areas (jails)
- Endemic murine typhus (flea-borne) – caused by R. typhi, is common in close-quartered poverty
- Recrudescent typhus (Brill-Zinsser disease) – previously acquired disease that results from immunosuppression or old age

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) 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

Diagnosis

Laboratory testing
- IFA is one of the most sensitive serologic tools for confirming diagnosis

Differential Diagnosis

Treatment

Indications for Ordering

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: Indirect Fluorescent Antibody	Acute and convalescent titers are often necessary to document disease	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 more than 12 months post-infection	If test results are equivocal, repeat testing in 10-14 days
Febrile Antibodies Panel 0051638 Method: Direct Agglutination/Enzyme-Linked Immunosorbent Assay/Immunofluorescence Assay	Use to confirm presence of disease; not recommended for initial testing Panel includes IgM Rickettsia typhi antibody by ELISA testing, as well as testing for antibodies to Brucella, Rickettsia typhi, Salmonella O and H	Initial testing may not be helpful; base treatment decision on clinical and other laboratory assessments

Additional Tests Available

Click on number for test-specific information in the ARUP Laboratory Test Directory

Test Name and Number	Comments
Rickettsia typhi (Typhus Fever) Antibody, IgG by IFA 0050381 Method: Indirect Fluorescent Antibody
Rickettsia typhi (Typhus Fever) Antibody, IgM by IFA 0050383 Method: Indirect Fluorescent Antibody
Weil-Felix Test, DA 0093143 Method: Direct Agglutination

Additional Information

Antibody testing

If antibody test results are equivocal, consider retesting in 10-14 days
These tests are for antibodies to Rickettsia typhi. Any antibody reactivity to Rickettsia typhi antigen should also be considered group reactive for the typhus fever group (Rickettsia prowazekii)
The best evidence for infection is a significant change (4-fold difference in titer) on 2 appropriately timed specimens, where both tests are done in the same laboratory at the same time

Culture testing