| Jong Yul Roh | 3 Articles |
<sec>
<title>Objectives</title>
<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>
<sec>
<title>Methods</title>
<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>
<sec>
<title>Results</title>
<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>
<sec>
<title>Conclusion</title>
<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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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 <i>Culex tritaeniorhynchus</i> 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 <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. 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. Citations
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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 <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. 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 <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. 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. Citations
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