Article

Scrub Typhus: The Geographic Distribution of Phenotypic and Genotypic Variants of Orientia tsutsugamushi

Department of Evolution, Ecology, and Organismal Biology, The Ohio State University, Columbus, OH 43210, USA.
Clinical Infectious Diseases (Impact Factor: 9.42). 04/2009; 48 Suppl 3:S203-30. DOI: 10.1086/596576
Source: PubMed

ABSTRACT Orientia tsutsugamushi is the etiological agent of scrub typhus, an acute, mite-borne, febrile illness that occurs in the Asia-Pacific region. Historically, strain characterization used serological analysis and revealed dramatic antigenic diversity. Eyeing a recommendation of potential vaccine candidates for broad protection, we review geographic diversity and serological and DNA prevalences. DNA analysis together with immunological analysis suggest that the prototype Karp strain and closely related strains are the most common throughout the region of endemicity. According to serological analysis, approximately 50% of isolates are seroreactive to Karp antisera, and approximately one-quarter of isolates are seroreactive to antisera against the prototype Gilliam strain. Molecular methods reveal greater diversity. By molecular methods, strains phylogenetically similar to Karp make up approximately 40% of all genotyped isolates, followed by the JG genotype group (Japan strains serotypically similar to the Gilliam strain but genetically non-Gilliam; 18% of all genotyped isolates). Three other genotype groups (Kato-related, Kawasaki-like, and TA763-like) each represent approximately 10% of genotyped isolates. Strains genetically similar to the Gilliam strain make up only 5% of isolates. Strains from these groups should be included in any potential vaccine.

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    • "The three other strains are named Karp (AY956315), Kato (M63382) and Gilliam (DQ485289). Information of the time and place of isolation of the reference strains was collected from Kelly et al. (2009) "
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    • "are Leptotrombidium pallidum and Leptotrombidium scuttellare, which are endemic in Asia, the Pacific region and Australia. Accordingly, scrub typhus is highly prevalent in the Asia–Pacific region including Japan, Korea, the eastern part of Russia, India, Pakistan, the southwestern Pacific islands (Kelly et al., 2009), China (Zhan et al., 2013) and Australia (Graves and Stenos, 2009). Mortality rates of up to 40% have been reported (Tamura et al., 1995), more than one million cases are recorded annually and more than one billion people are estimated to be at risk (Kim et al., 2014). "
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    • "In addition to these prototype strains, more than 20 antigenically distinct serotypes have been recognized. In addition to the various antigenic types, at least 9 phylogenetic groups include 135 isolates of O. tsutsugamushi based upon the extremely variable 56-kD type-specific antigen (TSA) gene have been described (Kelly et al. 2009). Subunit vaccines based on the 47-kD high-temperature requirement A (HtrA) and 56-kD TSA proteins have been developed and evaluated (Chattopadhyay et al. 2007). "
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