| E-hyun Shin | 6 Articles |
<sec>
<b>Objectives</b>
<p>Chigger mites are vectors for scrub typhus. This study evaluated the annual fluctuations in chigger mite populations and <italic>Orientia tsutsugamushi</italic> infections in South Korea.</p></sec>
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<b>Methods</b>
<p>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 <italic>Orientia tsutsugamushi</italic>.</p></sec>
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<b>Results</b>
<p>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 <italic>Leptotrombidium pallidum</italic> (43.5%), <italic>L. orientale</italic> (18.9%), <italic>L. scutellare</italic> (18.1%), <italic>L. palpale</italic> (10.6%), and <italic>L. zetum</italic> (3.6%). <italic>L. scutellare</italic> and <italic>L. palpale</italic> populations, were relatively higher in Autumn. Monthly <italic>O. tsutsugamushi</italic> infection rates in wild rodents (average: 4.8%) and chigger mites (average: 0.7%) peaked in Spring and Autumn.</p></sec>
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<b>Conclusion</b>
<p>The findings demonstrated a bimodal pattern of the incidence of <italic>O. tsutsugamushi</italic> 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.</p></sec>
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<b>Objectives</b><br/>
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 <i>Culex tritaeniorhynchus</i> to all the species of mosquitoes present in the study regions.<br/><b>Methods</b><br/>
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.<br/><b>Results</b><br/>
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 <i>Cx. tritaeniorhynchus</i> for 2013. However, the actual frequency of this species showed an increase in frequency. By contrast, the frequency rate of all the mosquitoes including <i>Cx. tritaeniorhynchus</i> gradually decreased.<br/><b>Conclusion</b><br/>
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.
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<b>Objectives</b><br/>
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, <i>Anopheles</i> 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.<br/><b>Methods</b><br/>
The insecticide resistance of <i>Anopheles sinensis</i> 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.<br/><b>Results</b><br/>
Based on median lethal dose (LC<sub>50</sub>) values, <i>An. sinensis</i> s.s. were most susceptible to the insecticides bifenthrin, cyfluthrin, and etofenprox in that order, and least susceptible to permethrin. <i>An. sinensis</i> showed higher susceptibility to pyrethroids than organophosphates, except for fenthion and permethrin. In a comparative resistance test, the resistance ratios (RRs) of <i>An. sinensis</i> collected in 2012 (AS12) to the 13 insecticides were compared to the RRs of two strains of <i>An. sinensis</i> 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.<br/><b>Conclusion</b><br/>
These results indicate that careful selection and rotation of these insecticides may result in continued satisfactory control of field populations of <i>An. sinensis</i> s.s. for effective malaria management in Paju.
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<b>Objective</b><br/>
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.<br/><b>Method</b><br/>
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.<br/><b>Results</b><br/>
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 cm<sup>2</sup> 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, <i>Haemaphysalis japonica</i> and <i>Haemaphysalis flava</i>, were identified. PCR and culture were performed on ticks. However, <i>Borrelia burgdo rferi</i> sensu lato was not isolated from any collected ticks.<br/><b>Conclusions</b><br/>
This study is significant to confirm Lyme borreliosis officially at first by the national surveillance system, although identification of the mites and pathogens failed.
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<b>Objectives</b><br/>
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 <i>H. longicornis, H. flava</i>, and <i>I. nipponensis</i> may be potential vectors of TBEV. In addition, these results emphasize the need for further epidemiological research of TBEV.<br/><b>Methods</b><br/>
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.<br/><b>Results</b><br/>
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 <i>Haemaphysalis longicornis, Haemaphysalis flava</i>, and <i>Ixodes nipponensis</i> 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.<br/><b>Conclusion</b><br/>
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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