What causes 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 caused by O tsutsugamushi, an obligate intracellular gram-negative bacterium that lives primarily in L akamushi and L deliense mites . This organism is found throughout the mite’s body but is present in the greatest number in the salivary glands. When the mite feeds on rodents (eg, rats, moles, and field mice, which are the secondary reservoirs) or humans, the parasites are transmitted to the host. Only larval Leptotrombidium mites (chiggers) transmit the disease.

O tsutsugamushi is very similar to the rickettsiae and indeed meets all of the classifications of the genus Rickettsia; this connection is demonstrated by the high degree of homology (90-99%) on 16S ribosomal sequencing. However, the cell walls are quite different, in that those of O tsutsugamushi lack peptidoglycan and lipopolysaccharide. [3] This pathogen does not have a vacuolar membrane; thus, it freely grows in the cytoplasm of infected cells.

There are numerous serotypes, [19] of which 5—Karp, Gilliam, Kawazaki, Boryon, and Kato—are helpful in serologic diagnosis. About half of isolates are seroreactive to Karp antisera, and approximately one-quarter of isolates are seroreactive to antisera against the prototype Gilliam strain. [20]


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