Genetic Typing, Based on the 56-Kilodalton Type-Specific Antigen Gene, of Orientia tsutsugamushi Strains Isolated from Chiggers Collected from Wild-Caught Rodents in Taiwan

Abstract

Orientia tsutsugamushi is the etiological agent of scrub typhus, a mite-borne, febrile illness that occurs in the Asia-Pacific region. We conducted strain characterization of O. tsutsugamushi isolates from chiggers obtained from rodents based the nucleotide sequence of the 56-kDa outer membrane protein gene. With the use of PCR, a total of 68 DNA sequences of 56-kDa antigen genes were amplified. Phylogenetic analysis revealed that there were at least six definable clusters among the 68 isolates: 37% Karp-related strains (25/68), 27% TA763 strains (18/68), 12% JG-related strains (8/68), 19% Kato-related strains (13/68), 4% divergent strains (3/68), and 1% representing a Gilliam prototype strain (1/68). Overall, the O. tsutsugamushi genotypes exhibited a high degree of diversity, similar to that seen in strains from the rest of the areas where scrub typhus is endemic. Orientia tsutsugamushi is an obligate intracellular, Gramnegative bacterium that causes scrub typhus, an acute febrile illness characterized by a typical primary lesion (eschar), lymphadenopathy, and nonspecific symptoms such as chills, headache, and malaise (10, 24). The disease is endemic in Asian countries, including Japan, South Korea, China, Thailand, and Taiwan (6, 13). An estimated 1 million cases occur annually (22). However, the precise incidence of this disease is unknown, as the available diagnostic facilities in most of the region of endemicity are limited (32). In nature, the bacterial agent is maintained within a life cycle involving wild mammals and a mite vector, primarily of the Leptotrombidium genus (14). Humans are accidentally infected by the bites of a larval mite, known as a chigger, during feeding (30).The 56-kDa type-specific antigen (TSA) gene encodes a dominant membrane protein, which accounts for 10% to 15% of the total protein of O. tsutsugamushi (17). The deduced size of the 56-kDa protein varies from 516 to 541 amino acids, according to gene sequences deposited in the GenBank (11). It is highly immunogenic, and the sera of most patients with scrub typhus are reactive. Serological analyses show that the antigenicity of the 56-kDa protein is diverse and includes variants such as the representative Karp-, Gilliam-, and Kato-type strains and other isolates (2,8,18). The immune responses to the 56-kDa protein provide protection against Scrub typhus, suggesting that it is a potential candidate for vaccine development (3,16,33). No commercially licensed vaccine for scrub typhus is currently available.In the present study, we cloned and sequenced the 56-kDa TSA gene of O. tsutsugamushi isolated from the chigger mite obtained from a rodent in order to understand the genetic types as well as the relationships with other known strains. Our results demonstrated that the genotypes of O. tsutsugamushi isolates appeared highly diverse and widely and geographically distributed in Taiwan. MATERIALS AND METHODSStudy site and arthropod collection. All the arthropods used in this study were collected from rodents captured by randomly settin...

Molecular Epidemiology and Genetic Diversity ofOrientia tsutsugamushifrom Patients with Scrub Typhus in 3 Regions of India

“…Overall, 80 (61.5%) of 130 samples were Kato-like strains, which have previously been found by serologic testing and genotyping in other locations, primarily Japan and Cambodia, but not as a predominant strain ( 1 , 4 , 27 , 28 ). The strains we identified were largely similar to the Hualien-3 reference sample, which was originally reported from Taiwan ( 6 ). However, some Kato-like strains showed closer similarity to the TA678 strain from South Korea.…”

“…Currently, the most widely used method for strain classification is sequence analysis of the 56-kDa type-specific antigen (TSA), an immunodominant outer membrane protein unique to O. tsutsugamushi . With an open reading frame (ORF) of ≈1,600 bp, the 56-kDa TSA contains 516–541 amino acids and is involved in host cell invasion through the binding of fibronectin ( 6 ). Four hypervariable domains in this region, variable domains (VD) I–IV, are responsible for the large degree of antigenic variation in this gene.…”

Scrub Typhus, a Disease with Increasing Threat in Guangdong, China

“…Twenty samples were amplified with PCR and their sequences were analyzed. The Karp genotype was the most common at a rate of 40%, which is consistent with the rates in Cambodia (43.5%) and Taiwan (37%), but differs with the rate in Korea (the Boryong 76.6%) [ 25 , 26 , 27 ]. China/GDst33G and China/GDyj13016 strains showed 99.7%-100% similarity to the KM08 strain (GU120153), which was identified as TA763 in Taiwan [ 26 ] and the first genotype reported in Guangdong.…”

“…Multiple serotypes of O. tsutsugamushi have been identified in China, including Gilliam, Kato, Karp, Kuroki, Shimokoshi, TA763, and Kawasaki strains. The Karp, Kato and TA763 serotypes are prevalent in Taiwan [ 26 ] and the Gilliam serotype is mainly in southern China. The aim of this study was to clarify the previously unknown genotypes of O. tsutsugamushi in Guangdong Province.…”

Prevalence of antibodies against Ehrlichia spp. and Orientia tsutsugamushi in small mammals around harbors in Taiwan

“…Scrub typhus is endemic to Asia, northern Australia, and the western Pacific regions [ 1 , 2 ]. Diverse strains of Orientia tsutsugamushi , the etiological agent of scrub typhus, have been isolated from humans and its vectors, larval-stage trombiculid mites (chiggers) [ 3 , 4 ]. Epidemiological surveys have suggested considerably high prevalence of O. tsutsugamushi infections in wild rodents, ranging from 69.1 % to over 90 %, on the offshore and main islands of Taiwan [ 5 , 6 ].…”