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Skin-nontumor / Clinical Dermatology

Infectious disorders

Scrub typhus


Reviewer: Mowafak Hamodat MB.CH.B, MSc., FRCPC (see Reviewers page)
Revised: 5 September 2010, last major update September 2010
Copyright: (c) 2002-2010, PathologyOutlines.com, Inc.

Definition
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● Chigger-borne zoonosis of tropical Asia and western Pacific islands, caused by Orientia (formerly Rickettsia) tsutsugamushi

Terminology
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● Formerly called Rickettsia tsutsugamushi, but now distinguished from Rickettsiaceae family by differences in cell wall
● Similar in presentation to other forms of typhus, but caused by agent in a different genus (Wikipedia)
● "Scrub" refers to the type of vegetation (ie, terrain between woods and clearings) that harbors the vector, but name is not entirely correct because endemic areas can be sandy and semiarid (eMedicine)

Epidemiology
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● Infected large number of soldiers in World War II
● Today, a frequent cause of febrile illness leading to hospital admissions in indigenous populations in eastern Asia, the southwestern Pacific (Korea to Australia) and from Japan to India and Pakistan

Etiology
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● Caused by Orientia (formerly Rickettsia) tsutsugamushi, an obligate intracellular gram-negative bacteria
● Maintained in nature by trombiculid mites (Wikipedia), transmitted to humans by larval mite (chigger) during feeding
Orientia is grouped with the Rickettsial infections (Centers for Disease Control), but distinguished from Rickettsiaceae family by differences in cell wall (Int J Syst Bacteriol 1995;45:589)

Clinical features
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● Travelers with imported disease often become sick before or within a few days of return from an endemic region; unlikely diagnosis if illness begins >18 days after return (Curr Infect Dis Rep 2009;11:66)

Treatment
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● Doxycycline (eMedicine)
● Death rates up to 30% without treatment; death is now rare with treatment

Clinical images
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Adult trombiculid mite

     
Chigger


Eschar

Micro description
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● Lymphocytic vasculitis of arterioles (not post-capillary venules) causes cutaneous findings
● Variable thrombosis of vessels
● Microorganisms are detected in endothelium of skin and other organs using fluorescein-labelled antiserum; also present in macrophages as fine granules on high power
● Eschar exhibits necrotic ulceration, due to coagulative necrosis of of the epidermis and underlying dermis
● Often only few neutrophils in the inflammatory infiltrate

Micro images
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Various images


Immunostains

Positive stains
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● Immunohistochemical staining of Orientia tsutsugamushi, particularly in eschars, is confirmatory (Am J Clin Pathol 2008;130:543)

Molecular / cytogenetics
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● PCR is useful for confirmation

Additional references
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Mod Pathol 2001;14:752

End of Skin-nontumor / Clinical Dermatology > Infectious disorders > Scrub typhus


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