- Annual Fluctuation in Chigger Mite Populations and Orientia Tsutsugamushi Infections in Scrub Typhus Endemic Regions of South Korea
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Seong Yoon Kim, Byoungchul Gill, Bong Gu Song, Hyuk Chu, Won Il Park, Hee Il Lee, E-hyun Shin, Shin-Hyeong Cho, Jong Yul Roh
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Osong Public Health Res Perspect. 2019;10(6):351-358. Published online December 31, 2019
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DOI: https://doi.org/10.24171/j.phrp.2019.10.6.05
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2,877
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 Abstract
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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.
- Prevalence of Tick-Borne Encephalitis Virus in Ixodid Ticks Collected from the Republic of Korea During 2011–2012
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Seok-Min Yun, Bong Gu Song, WooYoung Choi, Won Il Park, Sung Yun Kim, Jong Yul Roh, Jungsang Ryou, Young Ran Ju, Chan Park, E-Hyun Shin
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Osong Public Health Res Perspect. 2012;3(4):213-221. Published online December 31, 2012
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DOI: https://doi.org/10.1016/j.phrp.2012.10.004
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1,515
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Abstract
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- Objectives
In this study, we demonstrated that TBEV-infected ticks have been distributed in the ROK, combined with our previous results. These results suggest that TBEV may exist in the ROK, and H. longicornis, H. flava, and I. nipponensis may be potential vectors of TBEV. In addition, these results emphasize the need for further epidemiological research of TBEV.
Methods
We examined for the presence of RNA of TBEV by reverse transcriptase-nested polymerase chain reaction (RT-nested PCR) using ixodid ticks captured in 25 localities of 10 provinces. Ticks were collected by the flagging and dragging method or using sentinel BG traps at forests, grass thickets, and grassland. A total of 13,053 ticks belonging to two genera and four species were collected and pooled (1292 pools), according to collection site, species of tick, and developmental stage.
Results
Among 1292 pools, the envelope (E) protein gene of TBEV was detected using RT-nested PCR in 10 pools (3 pools of the 1,331 adult ticks and 7 pools of the 11,169 nymph ticks) collected from Gangwon-do province, Jeonrabuk-do province, and Jeju Island. The minimum infection rates for TBEV of Haemaphysalis longicornis, Haemaphysalis flava, and Ixodes nipponensis were 0.06%, 0.17%, and 2.38%, respectively. Phylogenetic analysis based on the partial E protein gene was performed to identify relationships between the TBEV strains. This showed that 10 Korean strains clustered with the Western subtype.
Conclusion
In this study, we investigated the prevalence of tick-borne encephalitis virus (TBEV) in ixodid ticks from various regions of the Republic of Korea (ROK) during 2011–2012 to identify whether TBEV is circulating and to determine the endemic regions of TBEV.
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