It is important to consider rickettsial infection in acutely unwell patients who recall having been “bitten by something” and/or have travelled to an endemic area.
Patients usually present with a fever and may have a rash (usually maculopapular) or an eschar (the bite site of the ectoparasite).
Epidemic typhus ( Rickettsia prowazekii ) is now rare but may occur in situations of mass crowding, poverty, famine, and war where there is an increased risk of human body louse infestation.
Doxycycline is the drug of choice for treatment in all patients.
Rickettsial infections (rickettsioses) occur worldwide and are associated with the patient having been bitten by an ectoparasite such as a louse, mite, flea, or tick. Rickettsioses of humans are caused by several related genera of bacteria including Rickettsia species, Orientia tsutsugamushi and Orientia chuto , Anaplasma species, Ehrlichia species, and Neoehrlichia species.
The genus Rickettsia is usually divided into the spotted fever group (SFG), where patients present with fever and spots, and the typhus group (TG). Some scholars also include an ancestral group but this is not yet widely accepted.
The SFG consists of many species, about 20 of which can cause human infection. Different species occur in geographically different parts of the world: for example, Mediterranean spotted fever caused by Rickettsia conorii and Queensland tick typhus caused by Rickettsia australis . The SFG are mainly tick transmitted. See our separate Rocky Mountain spotted fever topic for detailed information on this condition.
The TG consists of two species: Rickettsia prowazekii (epidemic louse-borne typhus) which is human body louse transmitted, and Rickettsia typhi (murine typhus) which is rodent flea transmitted. The genus Orientia is mite transmitted. 
Professor of Medicine
Section on Infectious Diseases
Wake Forest University School of Medicine
CAO declares that he has no competing interests.
Professor Christopher A. Ohl would like to gratefully acknowledge Dr Stephen R. Graves, a previous contributor to this topic. SRG is the author of a reference cited in this topic.
Department of Medicine
University of Peradeniya
SAMK declares that he has no competing interests.
Professor of Medicine and Pathology
Albert Einstein College of Medicine
New York City
LW's laboratory research programme is supported by NIH (NIAID) grants. He performs infectious diseases consultation at Montefiore (Weiler Hospital).
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