Epidemiological studies on host animals of tsutsugamushi disease in Korea

Epidemiological studies on host rodents of tsutsugamushi disease were carried out during the period of July-September 1990 at nine localities of central Korea. Among total 111 wild rodents trapped by the modified Sherman live traps, 103 were Apodemus agrarius (92.8%), seven were Crocidura lasiura (6.3%) and one was Microtus fortis (0.9%), showing 24.0% of trapping rate in winter, 11.7% in spring, 11.2% in summer and 12.0% in autumn. Out of 103 A. agrarius 84 were parasitized by chiggers, showing 81.6% of the infestation rate and 43.0 of the chigger index. The antibody positive rate of A. agrarius sera to Rickettsia tsutsugamushi was significantly variable by locality, being in the range of 0-78.6%. The seasonal change of the antibody positive rate at Dorai 5-ri, Goyang-gun was 75.8% in average during November-March, decreased to 30.3% in April and further decreased to 13.3% in average during May-August. Among 33 antibody positives, 31 were Karp strain and two were Gilliam. Seven Crocidura lasiura sera showed all negative. R. tsutsugamushi organisms were isolated from three A. agrarius out of 94 mice tested, showing 3.2% of the infection rate.