Isolation of a New Orientia Tsutsugamushi Strain in Hualien
2002 Vol.18 NO.6
Background and purpose：Scrub typhus is an acute febrile disease caused by Orientia tsutsugamushi. The disease occurs mainly in the large triangular region extending from Japan in the north to Australia in the southwest and the South Pacific Islands in the southeast. Humans are infected by the bite of the larva of the trombiculid mite harbouring O. tsutsugamushi. This pathogen attacks endothelial cells resulting in vasculitis. The clinical manifestations are characterized by a papular rash, headache, fever, chills, and an eschar at the site of the chigger bite. The disease can be tested serologically. R. tustsugamushi can be subdivided into various serotypes and subtypes and the antigenic variation depends on a 56 Kda protein called major surface antigenic components on the cell surface. Furthermore there are great variations in virulence among the variants. Unfortunately the current vaccines are effective only against homologous strains and no single antigen that induces protection against all of the strains has been found. The purpose of this study is to investigate the specific serotype(s) of O. tsutsugamushi in Hualien. Better knowledge concerning O. tsutsugamushi in this part of our country is important in the process of classifying the possible variants and to ensure better preventive medicine. Materials and Methods：Homogenate of mites from field rodents in Hualien region were inoculated onto L929 cell monolayer. Cultivation was continued until the growth of O. tsutsugamushi was established. Genotyping was performed using nested polymerase chain reaction（PCR）to amplify of a portion of the gene of the major surface antigenic components on the cell surface. Results：A strain with unique sequences named Hualien-A was found. Conclusions：due to geographic isolation, there may be unique strains with distinct pathogenicity and immunogenicity in this part of our country. Future work should include studies of infectivity, immunogenicity, and vaccine designs.