What is scrub typhus?

Updated: Apr 19, 2018
  • Author: David J Cennimo, MD, FAAP, FACP, FIDSA, AAHIVS; Chief Editor: Russell W Steele, MD  more...
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Answer

Scrub typhus is an acute, febrile, infectious illness that was first described in China in 313 AD. It is caused by Orientia (formerly Rickettsia) tsutsugamushi, an obligate intracellular gram-negative bacterium, which was first isolated in Japan in 1930. Although scrub typhus was originally recognized as one of the tropical rickettsial diseases, O tsutsugamushi differs from the rickettsiae with respect to cell-wall structure and genetic composition.

The term scrub typhus derives from the type of vegetation (ie, terrain between woods and clearings) that harbors the vector. However, this term is not entirely accurate, in that scrub typhus can also be prevalent in areas such as sandy beaches, mountain deserts, and equatorial rain forests.

US cases have been imported from regions of the “tsutsugamushi triangle,” which extends from northern Japan and eastern Russia in the north to northern Australia in the south and to Pakistan and Afghanistan in the west, where the disease is endemic. The range includes tropical and temperate regions, extending to altitudes greater than 3200 meters in the Himalayas. Scrub typhus is often acquired during occupational or agricultural exposures [2] because active rice fields are an important reservoir for transmission. [3]

Western medicine became especially interested in scrub typhus during military campaigns fought in East Asia. During World War II, 18,000 cases were observed in Allied troops stationed in rural or jungle areas of the Pacific theatre. [3] Scrub typhus was the second or third most common infection reported in US troops stationed in Vietnam [4] and still infects troops in the region. [5, 6] The US military continues to work on vector control, more accurate diagnostic tests, better vaccines, and improved surveillance methods. [7]

Currently, it is estimated that about 1 million cases of scrub typhus occur annually and that as many as 1 billion people living in endemic areas may have been infected by O tsutsugamushi at some time. [6] Because of reports of O tsutsugamushi strains with reduced susceptibility to antibiotics, [8] as well as reports of interesting interactions between this bacterium and HIV, a renewed interest in scrub typhus has emerged. [9, 10]


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