Osong Public Health and Research Perspectives

Original Articles

Annual Fluctuation in Chigger Mite Populations and Orientia Tsutsugamushi Infections in Scrub Typhus Endemic Regions of South Korea: 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; Osong Public Health Res Perspect. 2019;10(6):351-358. Published online December 31, 2019; DOI: https://doi.org/10.24171/j.phrp.2019.10.6.05

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Abstract PDF: 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.

Prediction Forecast for Culex tritaeniorhynchus Populations in Korea: Nam-Hyun Kim, Wook-Gyo Lee, E-Hyun Shin, Jong Yul Roh, Hae-Chun Rhee, Mi Yeoun Park; Osong Public Health Res Perspect. 2014;5(3):131-137. Published online June 30, 2014; DOI: https://doi.org/10.1016/j.phrp.2014.04.004

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Abstract PDF: Objectives
Japanese encephalitis is considered as a secondary legal infectious disease in Korea and is transmitted by mosquitoes in the summer season. The purpose of this study was to predict the ratio of Culex tritaeniorhynchus to all the species of mosquitoes present in the study regions.
Methods
From 1999 to 2012, black light traps were installed in 10 regions in Korea (Busan, Gyeonggi, Gangwon, Chungbuk, Chungnam, Jeonbuk, Jeonnam, Gyeongbuk, Gyeongnam, and Jeju) to capture mosquitoes for identification and classification under a dissecting microscope. The number of mosquitoes captured/week was used to calculate its daily occurrence (mosquitoes/trap/night). To predict the characteristics of the mosquito population, an autoregressive model of order p (AR(p)) was used to execute the out-of-sample prediction and the in-sample estimation after presumption.
Results
Compared with the out-of-sample method, the sample-weighted regression method's case was relatively superior for prediction, and this method predicted a decrease in the frequency of Cx. tritaeniorhynchus for 2013. However, the actual frequency of this species showed an increase in frequency. By contrast, the frequency rate of all the mosquitoes including Cx. tritaeniorhynchus gradually decreased.
Conclusion
The number of patients with Japanese encephalitis has been strongly associated with the occurrence and density of vector mosquitoes, and the importance of this infectious disease has been highlighted since 2010. The 2013 prediction indicated an increase after an initial decrease, although the ratio of the two mosquito species decreased. The increase in vector density may be due to changes in temperature and the environment. Thus, continuous prevalence prediction is warranted.

Susceptibility and Resistance of Field Populations of Anopheles sinensis (Diptera: Culicidae) Collected from Paju to 13 Insecticides: Kyu-Sik Chang, Dae-Hyun Yoo, E-Hyun Shin, Wook-Gyo Lee, Jong Yeol Roh, Mi Yeoun Park; Osong Public Health Res Perspect. 2013;4(2):76-80. Published online April 30, 2013; DOI: https://doi.org/10.1016/j.phrp.2013.02.001

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Abstract PDF: Objectives
Over 20% of all malaria cases reported annually in the Republic of Korea (ROK) occur in Paju, Gyeonggi Province. Vector control for malaria management is essential, but the insecticide resistance of the vector, Anopheles mosquitoes, has been a major obstacle in implementing effective control. In this study, the insecticide resistance of the vector mosquitoes was evaluated and compared with that of vector mosquitoes collected from the same locality in 2001 and 2009.
Methods
The insecticide resistance of Anopheles sinensis s.s. collected from Paju, Gyeonggi Province in the ROK was evaluated under laboratory conditions with a micro-application method using 13 insecticides currently used by local public health centers and pest control operators in the ROK.
Results
Based on median lethal dose (LC₅₀) values, An. sinensis s.s. were most susceptible to the insecticides bifenthrin, cyfluthrin, and etofenprox in that order, and least susceptible to permethrin. An. sinensis showed higher susceptibility to pyrethroids than organophosphates, except for fenthion and permethrin. In a comparative resistance test, the resistance ratios (RRs) of An. sinensis collected in 2012 (AS12) to the 13 insecticides were compared to the RRs of two strains of An. sinensis collected from the same locality in 2001 (AS01) and 2008 (AS08). With some exceptions, AS12 demonstrated higher resistance to all tested insecticides compared to AS01 and AS08, and less resistance to bifenthrin, cyfluthrin, and cypermethrin compared to AS01.
Conclusion
These results indicate that careful selection and rotation of these insecticides may result in continued satisfactory control of field populations of An. sinensis s.s. for effective malaria management in Paju.

Autochthonous Lyme Borreliosis in Humans and Ticks in Korea: Shinje Moon, Jin Gwack, Kyu Jam Hwang, Donghyuk Kwon, Suyeon Kim, Yoontae Noh, Jongyul Roh, E-hyun Shin, Kyungjin Jeong, Wonseok Seok, Seung-Ki Youn; Osong Public Health Res Perspect. 2013;4(1):52-56. Published online February 28, 2013; DOI: https://doi.org/10.1016/j.phrp.2012.12.001

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Abstract PDF: Objective: This study aimed at finding epidemiological and clinical features of autochthonous Lyme borreliosis in humans through epidemiological investigations and identifying its vectors and pathogens through analysis of ticks.
Method
Epidemiological investigations, including review of the retrospective medical records and patient interviews, were conducted in two cases that occurred in 2012. To identify the vectors and pathogens, ticks were collected between September 23 and October 6, 2012 from the area where the tick bite in the first patient occurred. The ticks were classified, and polymerase chain reaction (PCR) tests and cultures were performed.
Results
The first patient, a 46-year-old female, visited a forest in Gangwon province, which was 900 m above sea level, where the tick bite occurred. Two weeks after the tick bite, erythema migrans (12 × 6 cm² in size) appeared on the site of tick bite, along with fever, chill, fatigue, myalgia, and arthralgia on shoulders, knees, and hips. The second patient, a 44-year-old male, visited a mountain in Gangwon province, which was 1200 m above sea level, where a tick bite occurred. One month after the tick bite, erythema migrans appeared at the site of the tick bite, along with fatigue, myalgia, and arthralgia on the right shoulder and temporomandibular joint. Indirect fluorescent antibody testing and Western blotting were carried out in these two cases for diagnosis, and positive findings were obtained. As a result, Lyme borreliosis could be confirmed. To estimate the pathogens and vectors, the ticks were collected. A total of 122 ticks were collected and only two species, Haemaphysalis japonica and Haemaphysalis flava, were identified. PCR and culture were performed on ticks. However, Borrelia burgdo rferi sensu lato was not isolated from any collected ticks.
Conclusions
This study is significant to confirm Lyme borreliosis officially at first by the national surveillance system, although identification of the mites and pathogens failed.

Articleses

Prevalence of Tick-Borne Encephalitis Virus in Ixodid Ticks Collected from the Republic of Korea During 2011–2012: 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; Osong Public Health Res Perspect. 2012;3(4):213-221. Published online December 31, 2012; DOI: https://doi.org/10.1016/j.phrp.2012.10.004

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Abstract PDF: 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.

Management and Surveillance of Disease Vectors in the Republic of Korea: E-Hyun Shin; Osong Public Health Res Perspect. 2011;2(Suppl 1):S7-S7. Published online December 31, 2011; DOI: https://doi.org/10.1016/j.phrp.2011.11.028

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