Genotype Diversity and Distribution of Orientia tsutsugamushi Causing Scrub Typhus in Thailand

Abstract

Scrub typhus, caused by antigenically disparate isolates of Orientia tsutsugamushi, is a widely distributed mite-borne human disease in the Asia Pacific region. Information regarding the heterogeneity of the immunodominant 56-kDa type-specific antigen (TSA) gene is crucial for the design and evaluation of scrub typhusspecific diagnostic assays and vaccines. Using indirect immunofluorescence assays (IFA) and PCR assays, O. tsutsugamushi was detected samples from rodents and patients with fever of unknown origin obtained from six provinces of Thailand during 2004 to 2007. Sequences were determined for a fragment of the 56-kDa TSA gene, and the relationship between these sequences and those previously determined were assessed. The phylogenetic analyses of partial 56-kDa TSA gene sequences demonstrated wide diversity and distribution of O. tsutsugamushi genotypes in Thailand. Furthermore, the genetic diversity grouped the scrub typhus agents into two commonly and five infrequently found genotypes within six provinces of Thailand. The two most commonly found genotypes of O. tsutsugamushi described in this study do not associate with the prototype strains that are widely used for the design and evaluation of diagnostic assays and vaccine candidates. Thus, these new genotypes should be considered for future scrub typhus assay and vaccine development.

Scrub Typhus Outbreak, Northern Thailand, 2006–2007

“…Multiple alignment and phylogenetic analysis demonstrated that the 4 O. tsutsugamushi isolates from Ban Pongyeang fell into 4 clusters. Sequences for 3 of the isolates clustered with Gilliam, LA, and TA, 3 genotypes that are commonly found in Southeast Asia ( 10 , 11 ); the sequence of the fourth isolate presented as a divergent distinct genotype (Figure 2). Most of the children were infected with a strain genetically similar to the LA cluster (Figure 2).…”

Underrecognized Arthropod-Borne and Zoonotic Pathogens in Northern and Northwestern Thailand: Serological Evidence and Opportunities for Awareness

“…Recent studies have established the impact of scrub typhus and murine typhus as causes of acute febrile illness in Thailand (Blacksell et al 2008, Thitivichianlert et al 2009, Ruang-Areerate et al 2011) and adjacent countries (Phongmany et al 2006, Chheng et al 2013, Mayxay et al 2013, McGready et al 2014). Although pathogens like Orientia tsutsugamushi and Rickettsia typhi are well described, only limited evidence is available for other zoonotic pathogens contributing to the burden of undifferentiated febrile illness.…”

Characterization Based on the 56-Kda Type-Specific Antigen Gene of Orientia tsutsugamushi Genotypes Isolated from Leptotrombidium Mites and the Rodent Host Post-Infection

“…The resulting genotypes exhibited much lower similarity to the prototype strains than previously described. 17,18 In the current study, we also use the 56-kDa TSA gene sequence (700 basepairs [bp]) to characterize O. tsutsugamushi from 12 naturally infected, laboratory-reared Leptotrombidium colonies (comprising three Leptotrombidium species: L. deliense, L. imphalum, and L. chiangraiensis) located at the Armed Forces Research Institute of Medical Sciences in Bangkok, Thailand (AFRIMS). As knowledge regarding the transmission dynamics of O. tsutsugamushi and chigger-host interactions is limited, we evaluated the degree to which the composition of O. tsutsugamushi genotype(s) found in an individual chigger is maintained in the rodent host post-infection.…”