Study on vector mites of tsutsugamushi disease in Cheju Island, Korea

Because no reference on trombiculid mites (Acarina: Trombiculidae) in Cheju Island where tsutsugamushi disease is highly endemic had been available, studies on trombiculid mites in Cheju Island were implemented during the period of August 1991-April 1992, and the results obtained are summarized as follows: (1) The species and numbers of the field rodents collected were 143 Apodemus agrarius chejuensis (92.3%), 11 Crocidura lasiura (7.1%) and 1 Micromys minutus (0.6%). From total 12,075 chiggers harvested, 9 species of 4 genera in Trombiculidae were identified. (2) The predominant species through all seasons was L. zetum (43.3%), followed by L. orientale (27.4%) and L. scutellare (26.6%). However, in autumn when the most cases of tsutsugamushi disease occur, L. scutellare was prominently predominant, having 79.8% of the collected chiggers. (3) Among 1,142 L. scutellare examined for Rickettsia tsutsugamushi by means of IFA test, 6 individuals were found positive showing 0.5% of infection rate. This is the first finding that L. scutellare is the second vector species of tsutsugamushi disease in Korea. (4) Antibody positive rate of A. agrarius chejuensis sera were 31.2% (44/139), and 1 M. minutus serum was also found positive. The seropositive rates by season were not so significantly different.