Origins, Importance and Genetic Stability of the Prototype Strains Gilliam, Karp and Kato of Orientia tsutsugamushi

Abstract

Scrub typhus, a chigger-borne febrile illness, occurs primarily in countries of the Asia-Pacific rim and islands of the Western Pacific. The etiologic agent is the obligate intracellular rickettsial bacterium Orientia tsutsugamushi. Research on O. tsutsugamushi has relied on the availability of several prototype strains, which were isolated from human cases of scrub typhus in the 1940s and 1950s. We review the history of the three original, and most important, prototype strains, Gilliam, Karp and Kato, including information on their isolation, their culture history, their clinical characteristics, their importance within the research literature on scrub typhus, and recent advances in elucidating their molecular genomics. The importance of these strains to the research and development of clinical tools related to scrub typhus is also considered. Finally, we examine whether the strains have been genetically stable since their isolation, and whether prototype strains maintained in separate laboratories are identical, based on pairwise comparisons of several sequences from four genes. By using genetic information archived in international DNA databases, we show that the prototype strains used by different laboratories are essentially identical, and that the strains have retained their genetic integrity at least since the 1950s. The three original prototype strains should remain a standard by which new diagnostic procedures are measured. Given their fundamental position in any comparative studies, they are likely to endure as a critical part of present and future research on scrub typhus and Orientia.

A Brief History of the Major Rickettsioses in the Asia–Australia–Pacific Region: A Capstone Review for the Special Issue of TMID

“…The vast majority of the rickettsioses reported within the AAP appear to be scrub typhus, caused by Orientia tsutsugamushi . Consistent with this finding, scrub typhus is part of the focus in 10 of the 19 papers within this special issue in which rickettsial diseases in the AAP are examined [ 4 , 6 , 9 , 10 , 11 , 12 , 13 , 14 , 15 ]. Specific instances in which scrub typhus in the AAP is a focus include Naoi et al [ 13 ], who describe recent disparate clinical syndromes associated with scrub typhus in Japan.…”

“…The sensitive genotyping methods that became available included restriction fragment length polymorphism (RFLP), single-gene sequencing of highly variable genes, such as the 56-kD type-specific antigen (TSA56) of O. tsutsugamushi , multilocus sequence typing/analysis (MLST/MLSA), multispacer typing (MST), and whole-genome sequencing [ 64 ]. Gene sequence analysis forms an important tool for the comparison of standard strain of O. tsutsugamushi presented by Kelly et al [ 12 ] in the special issue.…”

“…Both were evaluated in the field and were found to not be significantly better than controls in preventing disease or death [ 105 , 106 ]. Immediately following the WWII era, the scrub typhus vaccine development efforts utilized O. tsutsugamushi isolates that were transported from Malaya to Britain [ 12 , 107 ]. Efforts in vaccine production up to the present run the gamut of inactivated and live-attenuated microorganisms and include recombinant protein-derived vaccines as well as DNA-plasmid vaccines, which are currently under investigation [ 108 , 109 ].…”

Scrub Typhus: Historic Perspective and Current Status of the Worldwide Presence of Orientia Species

“…Subsequently, a study by Maitra and Sen Gupta showed the presence of scrub typhus and murine typhus (OXK and OX19 positive, respectively) in Burma [ 85 ]. The famous prototype, O. tsutsugamushi Gilliam, was contracted by Dr. Gilliam in 1944 on the equally famous Stillwell Road, in Burma [ 67 ]. Nicholls reported OXK-positive cases of tsutsugamushi (rural typhus) in nearby Ceylon [ 86 ].…”

Representative Genotyping, Recombination and Evolutionary Dynamics Analysis of TSA56 Gene Segment of Orientia tsutsugamushi

“…O. tsutsugamushi is a Gram-negative, obligate intracellular bacteria known as the etiological agent of scrub typhus with many strains. The genotyping method based on the 56-kDa type-specific antigen ( TSA56 ) gene has been widely recognized as an effective approach for genotyping O. tsutsugamushi (Kelly et al, 2019 ). In recent decades, new genotypes have been continuously discovered and confirmed, and more researches have been conducted on the biological characteristics of TSA56 .…”