Bimonthly surveillance of wild rodents and chigger mites in urban parks in Daegu from 2018 to 2019

Tsutsugamushi disease is caused by Orientia tsutsugamushi, which is transmitted to humans via chigger mites in wild rodents, among other animal hosts. It has become a recurring health problem in South Korea with increasing numbers of cases since 2010s and most cases occurring in October through December. However, studies on chigger mites and wild rodents in urban areas in South Korea are inadequate. Thus, this study aimed to analyze the species composition of chigger mites and wild rodents, their seasonal distribution, and pathogen rates of chigger mites via a 2-year surveillance study at six urban parks in Daegu. Monthly surveillance of wild rodents and chigger mites was conducted at urban parks in Daegu from 2018 to 2019. Chigger mites were isolated from the collected rodents bimonthly. A total of 31 rodents were collected, with a trap rate and percentage of chigger mite infection of 0.52 and 61.3%, respectively. A total of 273 chigger mites were collected, with a chigger index (CI) of 14.4. Six species of chigger mites from two genera were collected, with Leptotrombidium pallidum being the most common (n = 127, 31.8%). Chigger mites were most frequent at riverside parks (n = 95, 34.8%). To detect O. tsutsugamushi in chigger mites, 40 pools of chigger mites (n = 273) were analyzed. All analyzed pools showed negative results. In conclusion, the populations of chigger mites and wild rodents in the six parks surveyed were smaller than those in the other regions in South Korea. Both the population and minimum positive rates of chigger mites in urban Daegu indicated a low threat of Tsutsugamushi disease. However, attention should still be paid to preventing this disease.