Wook-Gyo Lee

Severe Fever with Thrombocytopenia Syndrome Virus in Ticks Collected from Humans, South Korea, 2013

We investigated the infection rate for severe fever with thrombocytopenia syndrome virus (SFTSV) among ticks collected from humans during May–October 2013 in South Korea. Haemaphysalis longicornis ticks have been considered the SFTSV vector. However, we detected the virus in H. longicornis, Amblyomma testudinarium, and Ixodes nipponensis ticks, indicating additional potential SFTSV vectors.

Detection of Japanese Encephalitis Virus Genotype V in Culex orientalis and Culex pipiens (Diptera: Culicidae) in Korea

Japanese encephalitis virus (JEV) causes significant viral encephalitis and is distributed throughout the Asian countries. The virus is known to be transmitted by Culex tritaeniorhynchus, which mainly breeds in rice paddies in Korea. In this study, we investigated the presence of other mosquito species that can transmit JEV as a second or regional vector. We selected five cities where patients have experienced JE in the last 5 years as mosquito-collecting locations and subdivided them into four collection sites according to the mosquito habitats (cowshed, downtown area, forest, and swamp). Mosquitoes were caught using the BG-Sentinel trap, CDC black-light trap, Fay-Prince trap, and Gravid trap. A total of 993 pools from 22,774 mosquitoes were prepared according to their species, collection date, and site. We performed a SYBR Green 1-based real-time RT-PCR assay to detect JEV from the mosquito pools. A total of six JEV-positive pools were detected from Culex orientalis and Culex pipiens caught in the Gangwon-do and Gyeonngi-do provinces. All the detected JEVs were revealed as genotype V by phylogenetic analysis of the envelope gene. Our findings confirm that a new genotype of JEV was introduced in Korea and suggest that two mosquito species may play a role in JEV transmission.

Susceptibility and Resistance of Field Populations of Anopheles sinensis (Diptera: Culicidae) Collected from Paju to 13 Insecticides

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.

Transovarial Transmission of Orientia tsutsugamushi in Leptotrombidium palpale (Acari: Trombiculidae)

Transovarial transmission of Orientia tsutsugamushi in colonies of Leptotrombidium palpale was studied in the parent and F1 and F2 generations. Both transovarial transmission and filial infection rates were 100% in the parent and F1 generations of Leptotrombidium palpale. The filial infection rate in the F1 generation was 100%, but it declined to 94.3% in the F2 progeny. The sex ratio of the F1 generation from infected L. palpale was 1∶0.8 (male:female) and the proportion of males was relatively high. This study is the first to report on the transovarial transmission of O. tsutsugamushi in L. palpale. High transovarial transmission rates in L. palpale suggest that this species might be one of the major vectors of tsutsugamushi disease in Korea.

Distribution of overwintering mosquitoes (Diptera: Culicidae) in grassy fields in the Republic of Korea, 2007–2008

Overwintering mosquitoes in a grassy field were surveyed at 13 different localities from December 2007 to February 2008 in the Republic of Korea (ROK). Mosquitoes were collected by putting a white colored tent on the grass, without the base, and heating the inside of the tent. A total of 784 female adults comprising seven species were collected during the study period, including 395 (45.6%) Anopheles pullus, 338 (43.2%) An. sinensis, 21 (2.7%) An. belenrae, 2 (0.3%) An. kleini, 43 (5.5%) Culex tritaeniorhynchus, 20 (2.5%) Cx. inatomii, and 1 (0.3%) Cx. pipiens complex. The mosquitoes showed different overwintering distributions by temperature zone and locality. Predominant species, the malaria vectors An. pullus and An. sinensis, showed different overwintering distributions. Anopheles pullus had a 90.9% collection rate except for Youngju and an average – 0.6°C temperature between December and February. Anopheles pullus showed >50% collection rate in most regions maintained below an average of −1.4°C, and the rate of An. sinensis showed more than 50% collection rate in all regions maintained at an average above −1.1°C. Other species showed regional characteristics; An. belenrae was distributed in the northwest part of the ROK, and An. kleini was collected rarely at one locality in the middle part of ROK. Culex tritaeniorhynchus, a Japanese encephalitis virus vector, was distributed in the southern and costal region and maintained at an above average of −1.0°C. Culex inatomii was collected on the coastal region of the ROK.

Prediction Forecast for Culex tritaeniorhynchus Populations in Korea

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 methods 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.

Seasonal Prevalence of Mosquitoes Collected from Light Traps in Gyeongsangnam Province, Republic of Korea (2013-2014): Seasonal Prevalence of Mosquitoes in Gyeongsangnam Province, South Korea

Adult mosquito surveillance was conducted from 2013 through 2014 at four cattle sheds, a wild bird refuge, and two residential areas located in Gyeongnam Province in the Republic of Korea. Adult mosquitoes were collected in black light traps from April 1, through November 30. Mosquito surveillance was conducted to figure out population densities of vector mosquitoes, possibly invaded mosquitoes and identify various virus infections at the selected sites. A total of 107,466 females comprising 14 species and 7 genera were collected from 2013 to 2014. The most common species collected were Culex tritaeniorhynchus Giles (63.8%), Anopheles sinensis s.l. (18.9%), Aedes vexans nipponii (Theobald) (7.7%), and Culex pipiens Coquillett (5.1%). Trap indices (TIs) varied widely for species over their range, due to geographical distribution and degree of association with rural and urban communities. The most collected An. sinensis s.l. and Cx. tritaeniorhynchus appeared at a cow shed in Hapcheon (TI 347.5) and a pigsty in Daejeo‐1‐dong, Busan (TI 1,040.8), respectively, due in part to their situation near breeding sites such as rice paddies. The bi‐weekly population densities for mosquito species were variable for each of the years, apparently as a result of variable annual weather conditions. None of the mosquito species collected tested for the flavivirus including Japanese Encephalitis Virus, West Nile Virus, Dengue Virus, and Zika Virus infections by polymerase chain reaction (PCR) assay were positive.

Investigation on the virologic vector-borne diseases by mosquito vector in Yeongnam, Korea

To prevent the influx, propagation and spread of epidemic vectors (vector borne disease) that are increasing due to global warming and climate change, we kept the mosquito vectors under constant surveillance from April (2nd week) to September (3rd week), 2011 in Yeongnam area. Samples were collected at Youngdo (Busan) for Dengue fever and Yellow fever and by support of Gimcheon, Gyeongju, Ulju(Ulsan), Jinju, Hapcheon public health center for Japanese encephalitis and malaria, and also at two sites in Eulsook‐do for Westnile.

Report on the rate of Orientia tsutsugamushi infection in Hapcheon and Miryang, Korea

Most of the epidemic spread is closely related to the growth environment of insects or rodents as mediators. Climate changes make their growth environment change resulting in an epidemic infection increase. Even though the incidence of scrub typhus is increasing, little is known about scrub typhus compared with other infectious diseases in Korea. The tsutsugamushi infection prevalence of Orientia tsutsugamushi carried by tick was projected for surveillance from April to September in 2011. Chigger mites were collected at Miryang (Mt. Gaji) and Hapcheon (Gaya‐myeon) by the Sherman live trap and hanging method. Each collected samples were identified by microscope. Genomic DNAs were purified using CTB extraction kit and amplified by PCR using INNOPLEX TSUTSU detection kit.

Black light trap collections in Wangging county and Yanji city, Jilin Province, China, August 2006–2007

Adult mosquito surveillance was conducted using black light traps in August of 2006 and 2007 at Wangging county and Yanji city, Jilin Province, China to identify the distribution of anopheline mosquitoes in northern China. A total of 2459 female mosquitoes comprising three genera and eight species including Anopheles (Anopheles) lesteri, An. (Ano.) kleini, An. (Ano.) pullus, Culex inatomii, Cx. orientalis, Cx. pipiens, Cx. bitaeniorhynchus and Aedes vexans nipponii were collected. The most commonly collected species was An. kleini which had not been previously reported from China. Anopheles sinensis sensu stricto is commonly collected throughout China, but was not collected from these areas.