Rickettsial diseases

Rickettsial diseases are important to consider 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 O 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 R 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 R typhi (murine typhus) which is rodent flea transmitted. The genus Orientia is mite transmitted.[1]Parola P, Paddock CD, Socolovschi C, et al. Update on tick-borne rickettsioses around the world: a geographic approach. Clin Microbiol Rev. 2013 Oct;26(4):657-702. [Erratum in: Clin Microbiol Rev. 2014 Jan;27(1):166.] https://cmr.asm.org/content/26/4/657.long http://www.ncbi.nlm.nih.gov/pubmed/24092850?tool=bestpractice.com

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