Osong Public Health Res Perspect.  2019 Dec;10(6):351-358. 10.24171/j.phrp.2019.10.6.05.

Annual Fluctuation in Chigger Mite Populations and Orientia Tsutsugamushi Infections in Scrub Typhus Endemic Regions of South Korea

Affiliations
  • 1Division of Vectors and Parasitic Diseases, Korea Centers for Disease Control and Prevention, Cheongju, Korea. rohling@korea.kr
  • 2Division of Laboratory Diagnosis Management, Korea Centers for Disease Control and Prevention, Cheongju, Korea.
  • 3Division of Bacterial Disease Research, Korea Centers for Disease Control and Prevention, Cheongju, Korea.

Abstract


OBJECTIVES
Chigger mites are vectors for scrub typhus. This study evaluated the annual fluctuations in chigger mite populations and Orientia tsutsugamushi infections in South Korea.
METHODS
During 2006 and 2007, chigger mites were collected monthly from wild rodents in 4 scrub typhus endemic regions of South Korea. The chigger mites were classified based on morphological characteristics, and analyzed using nested PCR for the detection of Orientia tsutsugamushi.
RESULTS
During the surveillance period, the overall trapping rate for wild rodents was 10.8%. In total, 17,457 chigger mites (representing 5 genera and 15 species) were collected, and the average chigger index (representing the number of chigger mites per rodent), was 31.7. The monthly chigger index was consistently high (> 30) in Spring (March to April) and Autumn (October to November). The mite species included Leptotrombidium pallidum (43.5%), L. orientale (18.9%), L. scutellare (18.1%), L. palpale (10.6%), and L. zetum (3.6%). L. scutellare and L. palpale populations, were relatively higher in Autumn. Monthly O. tsutsugamushi infection rates in wild rodents (average: 4.8%) and chigger mites (average: 0.7%) peaked in Spring and Autumn.
CONCLUSION
The findings demonstrated a bimodal pattern of the incidence of O. tsutsugamushi infections. Higher infection rates were observed in both wild rodents and chigger mites, in Spring and Autumn. However, this did not reflect the unimodal incidence of scrub typhus in Autumn. Further studies are needed to identify factors, such as human behavior and harvesting in Autumn that may explain this discordance.

Keyword

mites; Orientia tsutsugamushi; rodents; scrub typhus
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