Determination and geographical distribution of Orientia tsutsugamushi serotypes in Korea by nested polymerase chain reaction

Field rodents and chigger mites were collected at 30 locations in Korea in October and November 1997-1999 to determine the serotypes of Orientia tsuts ugamushi and their geographical distribution. A nested polymerase chain rea ction was performed with the spleen tissues from 546 field-striped mice (Ap odemus agrarius) and 104 pools of chigger mites. The positivity rate of O. tsutsugamushi was 45.6% in A. agrarius and 39.4%. in the chigger mite pools . Two serotypes, Boryong and Karp, were found in these samples; the former was predominant (78.3% in the mice and 82.9%, in the chigger mite pools), w ith wide distribution throughout the country, including Cheju-do. The latte r was confined to the middle of the Korean peninsula, with positivity rates of 15.7% in the mice and 12.2% in the chigger mite pools. The double infec tion of Karp and Boryong serotypes was found in 15 (6.0%) A. agrarius mice. Gilliam serotype was not detected at any of the study locations. The Boryo ng and Kuroki serotypes were identical in amino acid sequence of the 56-kDa protein, although they differed in virulence to BALB/c mice.