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Trop. Med. Infect. Dis. 2017, 2(4), 63; doi:10.3390/tropicalmed2040063

The Historical Case for and the Future Study of Antibiotic-Resistant Scrub Typhus

Viral and Rickettsial Diseases Department, Naval Medical Research Center, Silver Spring, MD 20910, USA
Department of Evolution, Ecology and Organismal Biology, The Ohio State University, Columbus, OH 43210, USA
Author to whom correspondence should be addressed.
Received: 29 November 2017 / Revised: 6 December 2017 / Accepted: 11 December 2017 / Published: 15 December 2017
(This article belongs to the Special Issue The Past and Present Threat of Rickettsial Diseases)
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Scrub typhus is an acute, and sometimes fatal, human febrile illness, typically successfully treated using chloramphenicol or one of the tetracyclines. Over the past several years, descriptions of strains of Orientia tsutsugamushi with reduced susceptibility to antibiotics have appeared. Because case-fatality ratios approached 50% during the pre-antibiotic era, antibiotic-resistant scrub typhus is concerning. Herein, we review the data on resistant scrub typhus, describe how the theoretical existence of such resistance is affected by interpretation of treatment outcomes, and propose a plan to further identify whether true drug resistance is present and how to deal with drug resistance if it has evolved. Limited resistance is not unambiguous, if present, and antibiotic resistance in scrub typhus is not a dichotomous trait. Rather, evidence of resistance shows a continuous gradation of increasing resistance. The availability of genomes from isolates of O. tsutsugamushi allows the search for loci that might contribute to antibiotic resistance. At least eighteen such loci occur in all genomes of O. tsutsugamushi examined. One gene (gyrA) occurs as a quinolone-resistant form in the genome of all isolates of O. tsutsugamushi. At least 13 other genes that are present in some members of the genus Rickettsia do not occur within O. tsutsugamushi. Even though reports of scrub typhus not responding appropriately to chloramphenicol or a tetracycline treatment have been in the literature for approximately 23 years, the existence and importance of antibiotic-resistant scrub typhus remains uncertain. View Full-Text
Keywords: scrub typhus; Orientia; O. tsutsugamushi; antibiotic resistance; antibiotic resistance genes; genome comparison scrub typhus; Orientia; O. tsutsugamushi; antibiotic resistance; antibiotic resistance genes; genome comparison

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Kelly, D.J.; Fuerst, P.A.; Richards, A.L. The Historical Case for and the Future Study of Antibiotic-Resistant Scrub Typhus. Trop. Med. Infect. Dis. 2017, 2, 63.

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