Scrub typhus is a zoonotic bacterial disease caused by Orientia tsutsugamushi (Rickettsiales: Rickettsiaceae) and trombiculid mite larvae, also known as chigger, are known vector. Until recently, O. tsutsugamushi is the only species of the genus. However, two new species Candidatus O. chuto and Candidatus O. chiloensis that causes scrub typhus were reported recently in the Middle East, southern Chile, and Africa. In addition, Orientia spp. bacteria detected from field collected free-living Eutrombicula chigger mites in the United States. Despite these trends, research on new species is insufficient in the Republic of Korea. Therefore, we focused on finding the presence of novel species or strains from chiggers. Specimen chiggers harvested from rodents collected in 16 regions in October 2022 collaborating with the Regional Center for Vector Surveillance against Climate Change were selected. A total of 1,249 specimen belonging 4 genera and 14 species were identified by using a fluorescence microscope and 266 pools were produced by pooling up to 10 individuals per species chiggers. To detect Orientia spp., we screened by using a real-time PCR targeting the 16S rRNA gene. Overall minimum infection rate was 0.56% (7 pools/1,249 tested specimen). After screening, conventional nested-PCR for targeting 47-kDa htrA gene was conducted to obtain sequences, and four of the positive pools were amplified. Through phylogenetic analysis, three pools were clustered with O. tsutsugamushi Gilliam and UT221 strain, and the other pool was formed a clade that was distinct from O. tsutsugamushi. These results suggest that novel species of Orientia may exist in the Republic of Korea.

The purpose of this monitoring is to survey the geographical distribution of tick species using dry ice bait traps and flagging methods at each ten provinces (GangwonⅠ,GangwonⅡ, Gyeonggi, Chungbuk, Chungnam, Gyeongbuk, Gyeongnam, Jeonbuk, Jeonnam and Jeju area) and one Metropolitan area in the Republic of Korea for eight months from April through November, 2016. A total of 65,339 ixodid ticks (8,200 females, 1,988 males, 31,453 nymphs and 23,698 larvae) was collected, belonging to three genera (Haemaphysalis, Ixodes and Amblyomma). Haemaphysalis longicornis was the most commonly collected species, which is represented for 96.88% of all the collected ticks and followed by H. flava (2.69%), I. nipponensis (0.35%), A. testudinarium (0.05%) and H. japonica (0.03%) in the Republic of Korea for the study period. Haemaphysalis longicornis was a dominant species observed in these eleven areas.

We performed a survey for flavivirus infection and distribution of Aedes albopictus that known as Zika and Dengue virus vector using black–light trap and BG-sentinel trap around urban area in Korea. Mosquitoes were collected in 27 cities during March to November (twice a month) year 2016. Total numbers of mosquitoes collected 102,102 including 19 species 8 genera during collecting period. Total 21,467 Ae. albopictus was collected that 20,961(24.3%) by BG-sentinel trap and 506 (3.2%) by Black-light trap in urban area. Trap index(trap/night) of Ae. albopictus was showed highest in Hamyang (TI:992.3) and lowest in Taebaek (TI:0.3) there was only collected by Black-light trap. A total of 894 pools from all collecting Ae. albopictus were performed a Flavivirus detection. Flavivirus was not detected during study period. This study may provide basic information for surveillance of imported diseases (include Zika virus) and vectors in Korea.

The Ixodid ticks has been suspected to be the vector of severe fever with thrombocytopenia syndrome virus (SFTSV) in Korea. In order to confirm transovarial transmission of Ixodid ticks, a total of blood fed 284 ticks were collected from six host animals. They were identified as 3 genera and 4 species, Haemaphysalis longicornis (97.2%), H. flava (0.7%), Ixodes nipponensis (1.8%) and Amblyomma testudinarium (0.4%). Among them, 192 female adults hatched their eggs successfully. Our results showed a high prevalence of SFTSV among collected ticks (3.1%, 6/192 ticks), and we detected SFTSV from their larvae. This result suggests that the parent generation of H. longicornis can transmit SFTSV transovarially into their F1 progeny and H. longicornis might be one of major vectors of SFTSV in Korea.

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne zoonosis and SFTS virus is transmitted to humans by tick bites. The aim of this study was to monitor tick population and its SFTS virus infection. During March 2014 to October 2015, ticks were monthly sampled using dry-ice bait trap and flag method from 4 collecting points in Boeun-gun. A total of 16,500 ticks, including 14,646 Haemaphysalis longicornis (88.7%), 1,825 H. flava (11.1%), and 29 Ixodes nipponensis (0.2%), were collected. Ticks were pooled (5,156 ticks in 456 pools) and tested by RT-PCR and nested PCR and the minimum infection rate of ticks was 0.27% (14 pools) consisting of 0.13% H. longicornis (6 pools), 1.19% H. flava (8 pools). This annual surveillance study will be needed for long-term monitoring of ixodid ticks in Korea.

Ixodid ticks are notorious as the vector of severe fever with thrombocytopenia syndrome virus (SFTSV) in Korea. To confirm the transovarial transmission of SFTSV, we collected blood-fed adult ticks from animals in SFTS case reported area of Jeju island in 2015. A total of 476 ticks were collected from four host animal species, horse (81.3%), dog (9.0%), roe deer (7.1%) and wild boar (2.5%). They were identified as 1 genus and 2 species, Haemaphysalis longicornis (87.8%) and H. flava (12.2%). Among them, 131 adults hatched their eggs successfully. The body weight of females was highly correlated with the number of egg masses laid (P < 0.05). We confirmed that one adult H. flava was infected with SFTSV and its infection rate was 0.77%. The eggs of the SFTSV-infected adults also were infected with SFTSV and its transovarial transmission was confirmed. This result suggests that the parent generation of H. flava could transmit SFTSV transovarially into their F1 progeny and H. flava might be one of major vectors of SFTSV in Korea.

We investigated the distribution of ixodid ticks in severe fever with thrombocytopenia syndrome (SFTS) case reported areas using flagging method from May to November 2014 in Korea. We collected 13,471 ixodid ticks with 2 genera and 3 species. Among them, Genus Haemaphysalis and Ixodes accounted for 99.9% (13,455) and 0.1% (16), respectively. Genus Haemaphysalis consisted of 2 species, H. longicornis (96.2%) and H. flava (3.7%). I. nipponensis was only collected in Genus Ixodes. H. longicornis was the dominant species (over 90%) in most study areas. Ixodid ticks were evenly distributed at various environmental sites, such as residences, hills, grassfields, fields, graves, copses, other sites. The further study on SFTSV infection in ixodid ticks will be needed.

Trombiculid mites are known to be the vector of scrub typhus by transmitting rickettsial pathogen, Orientia tsutsugamushi, to human. In this study, we tried to establish a monitoring system for trombiculid mites using chigger mite collecting traps instead of the conventional rodent-capture method. For selection of collecting points, 10 environmental points were chosen from three regions (Taean, Jinan and Chungju) and two field collections were performed in spring (March-May) and autumn (October-November) seasons from 2013 to 2014. Among 10 environmental points, waterway (37.9%), grass field (28.0%), rice field and field near mountain side (11.4%) and reservoir/wet field (7.3%) showed high collecting rates and they should be included for the representative collecting points for surveillance using chigger mite collecting trap. In order to test the possibility that the dried chigger mites from collecting trap can be used for detection of O. tsutsugamushi, we pooled 30, 10 and 5 chigger mites separately and performed the nested PCR. The infection of O. tsutsugamushi was successfully detected from 5 chigger mites pooling sample. This study shows that chigger mite collecting trap could be an alternative method for monitoring system of scrub typhus vectors.

There are over 3,000 different species of mosquitoes throughout the world; currently 56 species are reported in Korea. Mosquitoes can act as vectors for many disease-causing viruses and parasites during blood sucking. Various species of mosquitoes are estimated to transmit various types of disease to more than 700 million people annually in Africa, South America, Central America, Mexico, Russia, and much of Asia, with millions of resultant deaths. At least two million people annually die of these diseases, and the morbidity rates are many times higher still. To prevent the spread of diseases, KNIH (Korea National Institute of Health) used three categorized methods; identifying or taxonomic analysis of mosquitoes, detecting virus caring mosquitoes, and detecting malaria from Anopheline mosquitoes. We have proved that taxonomic analysis using DNA barcording method (COI gene) is useful to complement identification of mosquito species. In detecting virus, we have reported Cx. orientalis as a new potential Japanese encephalitis virus (JEV) vector. We also reported that the Anopheline mosquito species composition and Plasmodium vivax infection rates in malaria hot spot in Korea.

Repellency of 20 plant essential oils to malaria main vector in the Republic of Korea (ROK), Anopheles kleini, was evaluated using skin direct contact bioassay. Anopheles kleini showed the highest repellency to Pelargonium graveolens with EC50 value of 0.244 mg/cm2, followed by Pinus sylvestris and Cinnamomum camphora with EC50 values of 0.484 mg/cm2 and 0.862 mg/cm2. The lowest repellency of An. kleini was revealed from Clary sage oil with EC50 value of 4.665 mg/cm2. Anopheles kleini did not demonstrated any repellency to Lemon, Orange, Neem, Coconut and Olive oil over 20 mg/cm2. Major repellent constituents of Geranium, Pine and Camphora oil were analyzed and identified using Mass-data, GC and GC-Mass. Major constituent of Geranium were β-citronellol (37.0%) and Camphora, 1,8-cineole (35.8%) and Pine, α-terpineol (39.5%). Anopheles kleini showed higher repellency to β-citronellol and 1,8-cineole than to DEET and IR3535 and did not showed any repellency to sabinene and γ-eudesmol over 20 mg/cm2. Residual repellent time of 1,8-cineole and β-citronellol were 26 and 41 min, respectively and DEET, 84 min and IR3535, 102 min. In the light of global efforts to reduce the level of highly toxic synthetic repellents, the three essential oils and their major constituents described merit further study as potential biorepellents for the control of An. kleini populations

Insecticide resistance and activation of the metabolic detoxification enzymes of female Culex pipiens pallens by the blood meal were assessed using a micro-application bioassay and micro-plate enzyme activity assays. Four group of Cx. pipiens pallens were used, a susceptible non-engorging group at seven days after emerging, SNE7 Cp; a resistant non-engorging group at seven days after emerging, RNE7 Cp; a resistant engorged group at one day after blood feeding and a resistant engorged group at seven days after blood feeding, REG7 Cp. Insecticide resistance of Cx. pipiens pallans was increased by the blood feeding. Based on LC50 values, SNE7 Cp demonstrated >50 fold of higher susceptibility to all tested insecticides when compared with RNE7 Cp. RNE7 Cp showed higher susceptibility to all tested insecticides than REG1 Cp and REG7 Cp with a relative susceptibility LC50 (SRLC50) of 25.8 to 50.0 and 25.0 to 48.8. In micro-plate enzyme assays, the metabolic detoxification enzyme activity of Cx. pipiens pallans adult females was increased by the blood feeding. Activation of non-specific esterases (EST), glutathione-S-transferase (GST) and mixed function oxidase (MFO) in RNE7 were higher than in SNE7 and the all tested enzymes in REG1 and REG7 demonstrated significantly higher enzyme activation than RNE7, except for activation of GST in REG1. Activation of MFO in REG1 and REG7 were 209.4- and 74.6- fold higher than in REG7, respectively. Non-specific esterases (EST) and glutathione-S-transferase exhibited < 10 fold of higher Rr values. These results may be significant in terms of the criteria that are used to evaluate resistance, because blood fed female mosquitoes may show enhanced expression of the resistance phenotype, possibly allowing for earlier detection of insecticide resistance.

Toxicities of 10 insecticides were examined against late third instars of Culex tritaeniorhynchus using the direct-contact mortality bioassay. Six geospatially distant field mosquitoes were collected from Chuncheon-si (designated CC-CT), Hwaseong (HS-CT), Seosan (SS-CT) Jeonju (JJ-CT), Daegu (DG-CT), and Busan (BS-CT) in the Republic of Korea (ROK). Marked regional variations of insecticide susceptibility were observed. Field populations of SS-CT, JJ-CT and DG-CT from agricultural areas showed higher to extremely higher insecticide susceptibility to pyrethroids than those of CC-CT, HS-CT and BS-CT strains from none agricultural areas. Extremely high to low levels of susceptibility were measured: bifenthrin, susceptible ratio (SR) = 2.7–896.3; β-cyfluthrin, SR = 1.8–633.3; α-cypermethrin, SR = 1.2–1,051.9; deltamethrin, SR = 1.3–711.1; permethrin, SR = 1.5–1,053.4 etofenprox, SR = 2.2–29.3; chlorfenapyr, SR = 5.1–103.6; chlorpyrifos, SR = 2.3–337.0; fenitrothion, SR = 2.0–142.3 and fenthion, SR = 1.4–186.2. Culex tritaeniorhynchus populations from rice paddies had been under heavy selection pressure due to the agricultural insecticides and that’s why the mosquito species demonstrated high resistance to pyrethroids which were used for a long time to control agricultural pests in the localities. These results indicate that careful selection and rotational use of these insecticides mayresult in continued satisfactory control against field populations of Japanese encephalitis vector mosquitoes.