Scrub typhus
Peer reviewed by Patient clinician teamLast updated by Dr Gurvinder Rull, MBBSLast updated 25 Aug 2010
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This disease is notifiable in the UK.
An infection caused by Orientia tsutsugamushi - a small intracellular bacterium related to the family of Rickettsiaceae - the organism is classified on its own and not with other rickettsiaceae as it has differences in genes and cell wall structure.1 The name scrub typhus was applied after discovery of increased frequency of the disease in scrub or wasteland areas.2
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Transmission of scrub typhus
Orientia tsutsugamushi is transmitted by the ovaries of trombiculid mites. The offspring mites or larvae are then infected and these are known as "chiggers". These mites then pass the infection to humans by feeding on the fluid in skin cells.
Any surrounding which supports the chiggers will be rife in infection eg near riverbanks (especially if forest cleared close by). It follows that infections are greatest in the rainy season.
Epidemiology
Scrub typhus is endemic in Eastern and Southern Asia, Northern Australia but is also found in other regions eg India, Thailand, Tibet, Japan, Russia and mountainous regions of Nepal.
Scrub typhus can cause outbreaks of pyrexia of unknown origin eg in a school in India.3
Not surprisingly, infection is commonest in the indigenous population and immunity after infection varies and may last 1 - 3 years. However, people visiting endemic areas may also be infected.
In endemic areas up to 5% of the population are infected.
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Presentation
Infection with scrub typhus is most often self-limiting but can occasionally be severe and even fatal.
The incubation period is up to ten days and the commonest features are:
Papule followed by an eschar at the site of chigger feeding (only in 50%)
Fever
Headache
Myalgia
Cough
Abdominal pain, nausea and vomiting
Regional lymphadenopathy
Maculopapular rash
Indigenous patients do not commonly develop rash or lymphadenopathy which is thought to be related to previous exposure.3
Severe cases can develop encephalitis and interstitial pneumonia and this may be fatal. If concomitant G6PD deficiency is present then the severity is increased.
Investigations
Indirect immunofluorescence
PCR for Orientia tsutsugamushi from blood of feverish patients
Some studies have used PCR (polymerase chain reaction) on specimens obtained from eschars.45 This involves obtaining a small piece of the eschar and then amplifying the DNA to look for the genetic sequence of scrub typhus.
CXR may show lower zone lung infiltrates in interstitial pneumonia
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Complications
Pneumonitis
Hepatitis
Myocarditis
Meningoencephalitis
Disseminated intravascular coagulation6
Multi-organ failure
Management
Antibiotics: doxycycline orally or chloramphenicol in more severe cases.
There may be antibiotic resistance in some areas eg Thailand.
Azithromycin has been used in resistant cases and may be better than doxycycline - especially in children and pregnant women.5
Prognosis
Fatality of untreated cases is between 5-10 % and is even higher in adults.6
Prevention
Vector control and systemic acaracides have been used. No vaccine or chemoprophylaxis is available.
Further reading and references
- Tamura A, Ohashi N, Urakami H, et al; Classification of Rickettsia tsutsugamushi in a new genus, Orientia gen. nov., as Orientia tsutsugamushi comb. nov.; Int J Syst Bacteriol. 1995 Jul;45(3):589-91.
- Brown GW; Recent studies in scrub typhus: a review.; J R Soc Med. 1978 Jul;71(7):507-10.
- Sharma A, Mahajan S, Gupta ML, et al; Investigation of an outbreak of scrub typhus in the himalayan region of India.; Jpn J Infect Dis. 2005 Aug;58(4):208-10.
- Liu YX, Cao WC, Gao Y, et al; Orientia tsutsugamushi in eschars from scrub typhus patients.; Emerg Infect Dis. 2006 Jul;12(7):1109-12.
- Lee SH, Kim DM, Cho YS, et al; Usefulness of eschar PCR for diagnosis of scrub typhus.; J Clin Microbiol. 2006 Mar;44(3):1169-71.
- Pavithran S, Mathai E, Moses PD; Scrub typhus.; Indian Pediatr. 2004 Dec;41(12):1254-7.
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Article history
The information on this page is written and peer reviewed by qualified clinicians.
25 Aug 2010 | Latest version

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