Epidemilogical Study on Orientia tsutsugamushi Infection of Wild Rodents in Korea

This study was carried out to determine the seropositivity for Orientia tsutsugamushi infection among wild rodents captured in farms and mountains of Korea. A total 965 wild rodents of 7 species and 48 Crocidura laciura were captured in farms and mountains of 6 province during 1997~2000 in Korea. Serological evidence for O. tsutsugamushi infection was obtained using O. tsutsugamushi antigens by indirect immunofluorescent antibody technique (IFA). Four hundred eighty four Apodemus agrariusus, 246 Apodemus peninsulae, 179 Eothenomys regulus, 44 Microtus fortis, 6 Micromys minutus, 5 Mus musculus, and 1 Cricetula triton were captured in Gyeonggi, Gangwon, Chungnam, Gyeongbuk, Gyeongnam, and Jeonbuk province. Among them, 59 (12.2%) A. agrariusus, 22 (8.9%) A. peninsulae, 12 (6.7%) E. regulus, 5 (11.4%) M. fortis and 1 (16.7%) M. minutus were IF antibody positive against O. tsutsugamushi Gilliam or Karp strain.

Seroprevalence and Phylogenetic Analysis of Orientia tsutsugamushi from Apodemus peninsulae in Korea

To investigate the seroprevalence of the Orientia tsutsugamushi infection of Apodemus peninsulae and genomic variations in O. tsutsugamushi isolates, 246 A. peninsulae were trapped in 14 mountainous areas approximately 500 meter above sea level in Korea during the period of 1997 and 2000. Seropositive rate of O. tsutsugamushi among A. peninsulae was 31.8% in Kyunggi, 8.2% in Chunbuk and 7.1% in Kangwon provinces by microimmunofluorescent test. The 56 kDa protein gene was amplified by PCR in the spleens of seropositive A. peninsulae. Two amplicons from seropositive A. peninsulae were sequenced and their phylogeny was analysed on the basis of sequence homology. The 56 kDa genes of A. peninsulae 98-12 strain and A. peninsulae 98-16 strain showed 98.7% nucleotide homology and 96.6% amino acid similarity. A. peninsulae 98-12 and A. peninsulae 98-16 strain were related to Kuroki, Boryong and Karp strains showing 93.3~92.2%, and 87.1~84.6% homologies in nucleotide and amino acids levels, respectively. In the phylogenetic analysis, A. peninsulae 98-12 and A. peninsulae 98-16 strain formed a distinct group with Boryong, Kuroki and Nishino strains and were clearly distinguished from other genetic groups. The results suggest that A. peninsulae might be an important reservoir of O. tsutsugamushi in Korea.