Detection of Orientia tsutsugamushi DNA in individual trombiculids using polymerase chain reaction in Korea

Abstract

In October 1995,field rodents and insectivores were captured at 5 localities in Chollanam-do and 3 localities in Choongchongnam-do, and a total of 81 field mice and shrews, including 64 Apodemus agrarius mice, were collected. The antibody positive rate of A. agrarius sera to Orientia tsutsugamushi was 52.4% in average. A total of 6,372 chigger mites were collected from the mice, and 10 species of 4 genera were identified. Leptotrombidium pallidum was predominant in Choong-chongnam-do, whereas L. scutellare was predominant in Chollanam-do. The chigger mites were individually dissected and internal contents were examined for O. tsutsugamushi infection applying IFA and PCR methods. Of 4,315 chigger mites screened by IFA, 115 positive and suspected cases were confirmed by consensus PCR. O. tsutsugamushi was found in 65 chiggers of 5 species, showing 1.51% infection rate in total. The infection rate of each 5 species was 1.64% in L. pallidum, 1.37% in L. scutellare, 1.77% in L. palpale, 1.60% in L. orientale and 1.41% in L. zetum. The detection of O. tsutsugamushi in L. orientale and L. zetum is the first finding in the world. The serotype of O. tsutsugamushi were also studied by analyzing the nucleotide sequences of the strain-specific region of 56 kDa protein, and all of the eight cases were of the F756-like type. This new sero-type was found from 4 species of Leptotrombidium, L. pallidum, L. scutellare, L. palpale and L. orientale.