Importation and Transmission of SARS-CoV-2 B.1.1.529 (Omicron) Variant of Concern in Korea, November 2021

In November 2021, 14 international travel-related severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) B.1.1.529 (omicron) variant of concern (VOC) patients were detected in South Korea. Epidemiologic investigation revealed community transmission of the omicron VOC. A total of 80 SARS-CoV-2 omicron VOC-positive patients were identified until December 10, 2021 and 66 of them reported no relation to the international travel.There may be more transmissions with this VOC in Korea than reported.

Surveillance of Chigger Mite Vectors for Tsutsugamushi Disease in the Hwaseong Area, Gyeonggi-do, Republic of Korea, 2015

Owing to global climate change, the global resurgence of vector-borne infectious diseases and their potential to inflict widespread casualties among human populations has emerged as a pivotal burden on public health systems. Tsutsugamushi disease (scrub typhus) in the Republic of Korea is steadily increasing and was designated as a legal communicable disease in 1994. The disease is a mite-borne acute febrile disease most commonly contracted from October to December. In this study, we tried to determine the prevalence of tsutsugamushi disease transmitted by chigger mites living on rodents and investigated their target vector diversity, abundance, and distribution to enable the mapping of hotspots for this disease in 2015. A total of 5 species belonging to 4 genera (109 mites): Leptotrombidium scutellare 60.6%, L. pallidum 28.4% Neotrombicula tamiyai 9.2%, Euschoengastia koreaensis/0.9%), and Neoschoengastia asakawa 0.9% were collected using chigger mite collecting traps mimicking human skin odor and sticky chigger traps from April to November 2015. Chigger mites causing tsutsugamushi disease in wild rodents were also collected in Hwaseong for the zoonotic surveillance of the vector. A total of 77 rodents belonging to 3 genera: Apodemus agrarius (93.5%), Crocidura lasiura (5.2%), and Micromys minutus (1.3%) were collected in April, October, and November 2015. The most common mite was L. pallidum (46.9%), followed by L. scutellare (18.6%), and L. orientale (18.0%). However, any of the chigger mite pools collected from rodent hosts was tested positive for Orientia tsutsugamushi, the pathogen of tsutsugamushi disease, in this survey.

Four Year Surveillance of the Vector Hard Ticks for SFTS, Ganghwa-do, Republic of Korea

The seasonal abundance of hard ticks that transmit severe fever with thrombocytopenia syndrome virus was monitored with a collection trap method every April to November during 2015–2018 and with a flagging method every July and August during 2015–2018 in Ganghwa-do (island) of Incheon Metropolitan City, Republic of Korea. This monitoring was performed in a copse, a short grass field, coniferous forest and broad-leaved forest. A total of 17,457 ticks (8,277 larvae, 4,137 nymphs, 3,389 females, and 1,654 males) of the ixodid ticks comprising 3 species (Haemaphysalis longicornis, H. flava, and Ixodes nipponensis) were collected with collection traps. Of the identified ticks, H. longicornis was the most frequently collected ticks (except larval ticks) (94.26%, 8,653/9,180 ticks (nymphs and adults)), followed by H. flava (5.71%, 524/9,180) and Ix. nipponensis (less than 0.04%, 3/9,180). The ticks collected with collecting traps were pooled and assayed for the presence of SFTS virus with negative results. In addition, for monitoring the prevalence of hard ticks, a total of 7,461 ticks (5,529 larvae, 1,272 nymphs, 469 females, and 191 males) of the ixodid ticks comprising 3 species (H. longicornis, H. flava, and Ix. nipponensis) were collected with flagging method. H. longicornis was the highest collected ticks (except larval ticks) (99.53%, 1,908/1,917 ticks (nymphs and adults)), followed by H. flava (1.15%, 22/1,917).

Malaria Vector Surveillance in Ganghwa-do, a Malaria-Endemic Area in the Republic of Korea

We investigated the seasonality of Anopheles mosquitoes, including its species composition, density, parity, and population densities of mosquitoes infected with the parasite in Ganghwa-do (Island), a vivax malaria endemic area in the Republic of Korea. Mosquitoes were collected periodically with a dry-ice-tent trap and a blacklight trap during the mosquito season (April-October) in 2008. Anopheles sinensis (94.9%) was the most abundant species collected, followed by Anopheles belenrae (3.8%), Anopheles pullus (1.2%), and Anopheles lesteri (0.1%). Hibernating Anopheles mosquitoes were also collected from December 2007 to March 2008. An. pullus (72.1%) was the most frequently collected, followed by An. sinensis (18.4%) and An. belenrae (9.5%). The composition of Anopheles species differed between the mosquito season and hibernation seasons. The parous rate fluctuated from 0% to 92.9%, and the highest rate was recorded on 10 September 2008. Sporozoite infections were detected by PCR in the head and thorax of female Anopheles mosquitoes. The annual sporozoite rate of mosquitoes was 0.11% (2 of 1,845 mosquitoes). The 2 mosquitoes that tested positive for sporozoites were An. sinensis. Malarial infections in anopheline mosquitoes from a population pool were also tried irrespective of the mosquito species. Nine of 2,331 pools of Anopheles mosquitoes were positive. From our study, it can be concluded that An. sinensis, which was the predominant vector species and confirmed as sporozoite-infected, plays an important role in malaria transmission in Ganghwa-do.

Detection of vivax sporozoites naturally infected in Anopheline mosquitoes from endemic areas of northern parts of Gyeonggi-do (province) in Korea

We investigated population densities of mosquitoes infected with sporozoites in three highly epidemic areas of Josan-ri and Jangpa-ri (Paju City) and Dongjung-ri (Yeoncheon County) in Korea. Anopheline mosquitoes were collected from both indoors and outdoors by human baiting collection method during the period of the first week of June to the second week of September 1999. Total 13,296 female mosquitoes were collected and 8,650 (65.1%) were Anophelines. Thirty seven percent (3,199) of the Anopheline mosquitoes were captured outdoors and 63.9% (5,531) indoors. Employing a sandwich enzyme-linked immunosorbent assay (ELISA), we analyzed a total of 7,820 Anopheline mosquitoes and found that 7 Anopheline mosquitoes were infected with sporozoites. The positive rate in Josan-ri was 0.14% (5/3,500) and 0.15% (2/1,370) in Jangpa-ri. The total positive rate in all three surveyed areas was 0.09% (7/7,820). The mosquitoes infected with the sporozoites were detected on June 28th (n=2), July 5th (n=1), July 19th (n=1), August 9th (n=1), September 6th (n=1), and the last one on September 13th (n=1). They were all classified as Anopheles sinensis, which showed positive reaction in ELISA test. Therefore it might be concluded that A. sinensis plays an important role in re-emerging malaria transmission in Korea.

A mark-release-recapture experiment with Anopheles sinensis in the northern part of Gyeonggi-do, Korea

In order to study the range of flight and feeding activity of Anopheles sinensis, the dispersal experiment was conducted in Paju city, located in the northern part of Gyeonggi-do, Republic of Korea, during the period of 7th to 28th September 1998. Unfed females An. sinensis were collected in cowshed and released after being marked with fluorescent dye at 23:00 hours on the same day. Released female mosquitoes were recaptured everyday during 21 days using light traps, which were set at 10 sites in the cowsheds located 1, 3, 6, 9 and 12 km north-northwest and north-northeast and at 3 sites located 1, 6 and 9 km toward south-west from the release point. In addition, to study the longest flight distance in one night, we set the light traps at 16 and 20 km toward north-northeast from the release site. All the collected mosquitoes were placed on filter papers and observed on UV transilluminator after treatment with one drop of 100% ethanol. Out of 12,773 females of An. sinensis released, 194 marked females mosquitoes were recaptured, giving 1.52% recapture rate. Of 194, 72 mosquitoes (37.1%) were recaptured in light traps from three places set at 1 km from the release point, 57 mosquitoes (29.4%) from two places at 1-3 km, 41 mosquitoes (21.1%) from three places at 3-6 km, 20 mosquitoes (10.3%) from three places at 6-9 km, and 4 mosquitoes (2.1%) from two places at 9-12 km. Since 170 female mosquitoes (87.6%) out of 194 marked mosquitoes were captured within 6 km from the release point, this flight radius represents the main activity area. An sinensis was found to be able to fly at least 12 km during one night.