Rickettsial diseases

Overview 
Theory 
Diagnosis 
Management 
Follow up 
Resources 

Last reviewed: 20 Apr 2025

Last updated: 01 Aug 2023

Rickettsial diseases are important to consider in acutely unwell patients who recall having been "bitten by something" and/or live in 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.

Definition

Rickettsial infections (rickettsioses) occur worldwide and are associated with the patient having been bitten by an ectoparasite such as a louse, mite, flea, mosquito, or most commonly, a 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, where patients present with fever and spots, and the typhus group. Some scholars also include an ancestral group but this is not yet widely accepted.

The spotted fever group 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 spotted fever group are mainly tick transmitted.

The typhus group 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]

This topic focuses on spotted fever group, typhus group, and scrub typhus group rickettsioses. See Rocky Mountain spotted fever for more detailed information on this condition

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History and exam

Key diagnostic factors

fever >38°C
rash
eschar
lymphadenopathy associated with eschar

Full details

Other diagnostic factors

headache
myalgia
fatigue
nausea/vomiting
abdominal pain
hepatosplenomegaly
tachypnoea

Full details

Risk factors

exposure to human body lice
exposure to rodents (rats and mice) and their fleas
tick bites
mite bites
travel to the tropics
exposure to natural vegetation, forests, scrub, bush
exposure to cat or dog fleas

Full details

Diagnostic investigations

1st investigations to order

FBC
LFTs
serum electrolyte levels
CRP
serology
polymerase chain reaction (PCR)

Full details

Investigations to consider

chest x-ray
trial of doxycycline therapy
cell cultures
immunohistochemistry

Full details

Treatment algorithm

ACUTE

suspected or confirmed rickettsial infection: not pregnant or breastfeeding

suspected or confirmed rickettsial infection: pregnant or breastfeeding

Contributors

Authors

Christopher A. Ohl, MD

Professor of Medicine

Section on Infectious Diseases

Wake Forest University School of Medicine

Winston-Salem

Disclosures

CAO declares that he has no competing interests.

Acknowledgements

Professor Christopher A. Ohl would like to gratefully acknowledge Dr Stephen R. Graves, a previous contributor to this topic.

Disclosures

SRG is the author of a reference cited in this topic.

Peer reviewers

S.A.M. Kularatne, MD, FRCP (Lond)

Professor

Department of Medicine

University of Peradeniya

Peradeniya

Sri Lanka

Disclosures

SAMK declares that he has no competing interests.

Louis Weiss, MD, MPH

Professor of Medicine and Pathology

Albert Einstein College of Medicine

New York City

Disclosures

LW's laboratory research programme is supported by NIH (NIAID) grants. He performs infectious diseases consultation at Montefiore (Weiler Hospital).

References

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Key articles

Biggs HM, Behravesh CB, Bradley KK, et al. Diagnosis and management of tickborne rickettsial diseases: Rocky Mountain spotted fever and other spotted fever group rickettsioses, ehrlichioses, and anaplasmosis - United States. MMWR Recomm Rep. 2016 May 13;65(2):1-44.Full text Abstract

Reference articles

A full list of sources referenced in this topic is available to users with access to all of BMJ Best Practice.

Differentials
- Rocky mountain spotted fever
- Malaria infection
- Dengue fever
More Differentials
Guidelines
- CDC Yellow Book: health information for international travel - rickettsial diseases
- Tick bite diseases and symptoms attributed to tick bites
More Guidelines
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Rickettsial diseases

Summary

Definition

History and exam

Key diagnostic factors

Other diagnostic factors

Risk factors

Diagnostic investigations

1st investigations to order

Investigations to consider

Treatment algorithm

suspected or confirmed rickettsial infection: not pregnant or breastfeeding

suspected or confirmed rickettsial infection: pregnant or breastfeeding

Contributors

Authors

Christopher A. Ohl, MD

Disclosures

Acknowledgements

Disclosures

Peer reviewers

S.A.M. Kularatne, MD, FRCP (Lond)

Disclosures

Louis Weiss, MD, MPH

Disclosures

References

Key articles

Reference articles

A full list of sources referenced in this topic is available to users with access to all of BMJ Best Practice.

Differentials

Guidelines

Log in or subscribe to access all of BMJ Best Practice

Log in or subscribe to access all of BMJ Best Practice

Log in to access all of BMJ Best Practice