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Public Health Weekly Report 2020; 13(14): 817-831

Published online April 2, 2020

© The Korea Disease Control and Prevention Agency

Geographical Distribution of Chigger Mites as Scrub Typhus Vectors in the Republic of Korea, 2019

Song Bong Goo, Lee Wook-Gyo, Lee Hee Il, Cho Shin-Hyeong

Division of Vectors and Parasitic Diseases, Center for Laboratory Control of Infectious Diseases, KCDC

*교신저자 : cho4u@korea.kr, 043-719-8520

This is an Open Access aritcle distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/) which permits unrestricted distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Sections

Scrub typhus is an acute infectious febrile disease caused by Orientia tsutsugamushi with increased cases observed in autumn. Scrub typhus is spread to people through bites of infected chiggers (larval mites). The symptoms are fever, body ache, headache, and sometimes rash. Annually, more than 4,000 scrub typhus cases are reported in Korea. Therefore, it is important to recognize any nationwide changes in the density and prevalence of chigger mites. To that end, this study conducted a survey. The survey was conducted in 32 regions (160 locations) across Korea in April and November. A total of 49,301 mites representing 6 genera and 18 species were collected from 515 trapped rodents. Among the rodents, the majority were Apodemus agrarius (striped field mouse) (85%, n=437), The predominant chigger species was Leptotrombidium pallidum (53.9%, n=13,278), followed by L. orientale (13.2%, n=3,239), and L. scutellare (9.5%, n=2,348). Leptotrombidium pallidum, confirmed as the dominant species, showed similar density in spring (April) and autumn (November) at 55.1% and 53.1%, respectively. However, L. scutellare showed a relatively high share of 16.1% (n=2,341) in autumn. In particular, the distribution of L. scutellare, known as the main vector for scrub typhus, expanded northward to the central region of Korea, which was highly correlated with the cases of Scrub typhus patient occurrence in 2019. Thus, the results required monitoring of chigger mites and further epidemiological analysis between patients and vectors.

Key words Scrub typhus, Chigger mites, L. scutellare, Density survey

Sections
Table 1. Total number of rodents and chigger mites collected from 32 localities, 2019
RegionsSpringAutumnTotal
RodentsChigger mitesClRodentsChigger mitesClRodentsChigger mitesCl
GWGangneung-si192,475130.3131,541118.5324,016125.5
Samcheok-si620033.35786157.21198689.6
Sokcho-si549298.41232026.71781247.8
Cheorwon-gun1465446.7941846.4231,07246.6
Chuncheon-si718526.4919221.31637723.6
Pyeongchang-gun152,037135.8141,687120.5293,724128.4
Subtotal666,04391.6624,94479.712810,98785.8
GGGanghwa-gun44110.348220.5812315.4
Yeoju-si51,000200.0132,860220.0183,860214.4
Paju-si71,121160.171,959279.9143,080220.0
Hwaseong-si101,202120.2132,278175.2233,480151.3
Subtotal263,364129.4377,179194.06310,543167.3
CBCheongju-si533066.072,558365.4122,888240.7
Chungju-si5888177.61690256.4211,79085.2
Subtotal101218121.8233460150.4334,678141.8
CNNonsan-si151,585105.7638964.8211,97494.0
Boryeong-si731344.7757482.01488763.4
Yesan-gun5605121.091,619179.9142,224158.9
Subtotal27250392.7222,582117.4495,085103.8
JBGimje-si517434.8527755.41045145.1
Namwon-si1266255.251,012202.4171,67498.5
Jeongeup-si527655.2651185.21178771.5
Jinan-gun5722144.471,443206.1122,165180.4
Subtotal27183467.9233,243141.0505,077101.5
JNMuan-gun35719.07926132.31098398.3
Boseong-gun171,900111.841,052263.0212,952140.6
Jangseong-gun700.0544689.21244637.2
Haenam-gun1012612.61165359.42177937.1
Subtotal37208356.3273077114.064516080.6
GBGimcheon-si518136.259719.41027827.8
Andong-si726437.7510721.41237130.9
Yeongdeok-gun51,440288.061,048174.7112,488226.2
Subtotal171,885110.9161,25278.3333,13795.1
GNGeoje-si519038.07913130.4121,10391.9
Miryang-si710.15214.212221.8
Ulsan-si811113.981,247155.9161,35884.9
Hapcheon-gun958665.181,509188.6172,095123.2
Subtotal2988830.6283,690131.8574,57880.3
JJSeogwipo-si7182.6891.115271.8
Jeju-si17291.7600.023291.3
Subtotal24472.01490.638561.5
Grand total26319,86575.525229,436116.851549,30195.7

※ GW: Gangwon province, GG: Gyeonggi province, CB: Chungcheongbuk province, CN: Chungcheongnam province, GB: Gyeongsangbuk province, GN: Gyeongsangnam province, JB: Jeollabuk province, JN: Jeollanam province, JJ: Jeju island

※ CI (chigger index): no. of chigger mites per rodent

Table 2. Total number of chigger mites and species ratio, 2019
GenusSpeciesSpringAutumnTotal
No. of chigger mites%No. of chigger mites%No. of chigger mites%
Cheladontaikaoensis120.1110.1230.1
Euschoengastiakoreaensis620.64032.84651.9
Leptotrombidiumfulleri30.0--30.0
gemiticulum10.0880.6890.4
hiranumai20.0--20.0
orientale2,36923.68706.03,23913.2
pallidum5,52955.17,74953.113,27853.9
palpale6426.41,3529.31,9948.1
scutellare70.12,34116.12,3489.5
subintermedium60.170.0130.1
zetum8848.82701.91,1544.7
Neotrombiculagardellai--440.3440.2
japonica--1260.91260.5
kwangneungensis10.08145.68153.3
nagayoi40.01090.71130.5
tamiyai5125.13932.79053.7
Walchiafragilis10.020.030.0
Shunseniahertigi40.040.080.0
Total10,039100.014,583100.024,622100.0

※ Main vector of Scrub Typhus: E. koreaensis, L. orientale, L. pallidum, L. palpale, L. scutellare, L. zetum, N. japonica

Figure 1. Distribution of rodent species (A) and the environment of chigger mites (B)
※ CI (chigger index): No. of chigger mites per rodent

Figure 2. Seasonal density distribution of chigger mites, 2019 (A: Spring, B: Autumn)

Figure 3. Geographical distribution of major chigger mites by season, 2019 (A: Spring, B: Autumn)

Figure 4. Annual regional distribution variation (A: No. of patients B: CI of L. scutellare)

References

Sections
  1. 국가생물종목록. National Species list of Korea. 2019. 환경부, 국립생물자원관. National Institute of Biological Resources, online at http://kbr.go.kr, accessed on(2020. 03. 01.)
    Self
  2. Lee Hee Il, Shim Soo Kyoung, Song Bong Gu, Choi Eun Na, et al. et al. Detection of Orientia tsutsugamushi , the Causative Agent of Scrub Typhus, in a Novel Mite Species, Eushoengastia koreaensis , in Korea. VECTOR-BORNE AND ZOONOTIC DISEASES 2011;11(3):209-214.
    Pubmed CrossRef
  3. Park Sang-Won, Ha Na-Young, Ryu Boyeong, Bang Ji Hwan, Song Hoyeon, et al. Urbanization of Scrub Typhus Disease in South Korea. PLoS Negl Trop Dis 2015;9(5):e0003814. doi:10.1371/journal.pntd.0003814.
    Pubmed KoreaMed CrossRef
  4. 노종열, 신이현, 주영란. 쯔쯔가무시증 매개 털진드기의 전국 분포조사. 주간 건강과 질병 2014;7(51):1146-1148.
    Self
  5. 박원일, 노종열, 조신형. 2016년 쯔쯔가무시증 매개 털진드기 감시 현황. 주간 건강과 질병 2017;10(39):1058-1061.
    Self
  6. Kim Seong Yoon, Gill Byoungchul, Song Bong Gu, et al. Annual Fluctuation in Chigger Mite Populations and Orientia tsutsugamushi Infections in Scrub Typhus Endemic Regions of South Korea. Osong Public Health Res Perspect 2019;10(6):351-358.
    Pubmed KoreaMed CrossRef
  7. Ivo Elliott, Isabelle Pearson, Prabin Dahal, Nigel V. Thomas, Tamalee Roberts and Paul N. Newton Scrub typhus ecology: a systematic review of Orientia in vectors and hosts. Parasites Vectors. 2019;12:513
    Pubmed KoreaMed CrossRef
  8. Korea Centers for Disease Control and Prevention (KCDC). Disease Web Statistics System. Cheongju-si, Republic of Korea.
    CrossRef

Epidemiology and Surveillance

Public Health Weekly Report 2020; 13(14): 817-831

Published online April 2, 2020

Copyright © The Korea Disease Control and Prevention Agency.

Geographical Distribution of Chigger Mites as Scrub Typhus Vectors in the Republic of Korea, 2019

Song Bong Goo, Lee Wook-Gyo, Lee Hee Il, Cho Shin-Hyeong

Division of Vectors and Parasitic Diseases, Center for Laboratory Control of Infectious Diseases, KCDC

Correspondence to:*교신저자 : cho4u@korea.kr, 043-719-8520

This is an Open Access aritcle distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/) which permits unrestricted distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Scrub typhus is an acute infectious febrile disease caused by Orientia tsutsugamushi with increased cases observed in autumn. Scrub typhus is spread to people through bites of infected chiggers (larval mites). The symptoms are fever, body ache, headache, and sometimes rash. Annually, more than 4,000 scrub typhus cases are reported in Korea. Therefore, it is important to recognize any nationwide changes in the density and prevalence of chigger mites. To that end, this study conducted a survey. The survey was conducted in 32 regions (160 locations) across Korea in April and November. A total of 49,301 mites representing 6 genera and 18 species were collected from 515 trapped rodents. Among the rodents, the majority were Apodemus agrarius (striped field mouse) (85%, n=437), The predominant chigger species was Leptotrombidium pallidum (53.9%, n=13,278), followed by L. orientale (13.2%, n=3,239), and L. scutellare (9.5%, n=2,348). Leptotrombidium pallidum, confirmed as the dominant species, showed similar density in spring (April) and autumn (November) at 55.1% and 53.1%, respectively. However, L. scutellare showed a relatively high share of 16.1% (n=2,341) in autumn. In particular, the distribution of L. scutellare, known as the main vector for scrub typhus, expanded northward to the central region of Korea, which was highly correlated with the cases of Scrub typhus patient occurrence in 2019. Thus, the results required monitoring of chigger mites and further epidemiological analysis between patients and vectors.

Keywords: Scrub typhus, Chigger mites, L. scutellare, Density survey

Body

Total number of rodents and chigger mites collected from 32 localities, 2019
RegionsSpringAutumnTotal
RodentsChigger mitesClRodentsChigger mitesClRodentsChigger mitesCl
GWGangneung-si192,475130.3131,541118.5324,016125.5
Samcheok-si620033.35786157.21198689.6
Sokcho-si549298.41232026.71781247.8
Cheorwon-gun1465446.7941846.4231,07246.6
Chuncheon-si718526.4919221.31637723.6
Pyeongchang-gun152,037135.8141,687120.5293,724128.4
Subtotal666,04391.6624,94479.712810,98785.8
GGGanghwa-gun44110.348220.5812315.4
Yeoju-si51,000200.0132,860220.0183,860214.4
Paju-si71,121160.171,959279.9143,080220.0
Hwaseong-si101,202120.2132,278175.2233,480151.3
Subtotal263,364129.4377,179194.06310,543167.3
CBCheongju-si533066.072,558365.4122,888240.7
Chungju-si5888177.61690256.4211,79085.2
Subtotal101218121.8233460150.4334,678141.8
CNNonsan-si151,585105.7638964.8211,97494.0
Boryeong-si731344.7757482.01488763.4
Yesan-gun5605121.091,619179.9142,224158.9
Subtotal27250392.7222,582117.4495,085103.8
JBGimje-si517434.8527755.41045145.1
Namwon-si1266255.251,012202.4171,67498.5
Jeongeup-si527655.2651185.21178771.5
Jinan-gun5722144.471,443206.1122,165180.4
Subtotal27183467.9233,243141.0505,077101.5
JNMuan-gun35719.07926132.31098398.3
Boseong-gun171,900111.841,052263.0212,952140.6
Jangseong-gun700.0544689.21244637.2
Haenam-gun1012612.61165359.42177937.1
Subtotal37208356.3273077114.064516080.6
GBGimcheon-si518136.259719.41027827.8
Andong-si726437.7510721.41237130.9
Yeongdeok-gun51,440288.061,048174.7112,488226.2
Subtotal171,885110.9161,25278.3333,13795.1
GNGeoje-si519038.07913130.4121,10391.9
Miryang-si710.15214.212221.8
Ulsan-si811113.981,247155.9161,35884.9
Hapcheon-gun958665.181,509188.6172,095123.2
Subtotal2988830.6283,690131.8574,57880.3
JJSeogwipo-si7182.6891.115271.8
Jeju-si17291.7600.023291.3
Subtotal24472.01490.638561.5
Grand total26319,86575.525229,436116.851549,30195.7

※ GW: Gangwon province, GG: Gyeonggi province, CB: Chungcheongbuk province, CN: Chungcheongnam province, GB: Gyeongsangbuk province, GN: Gyeongsangnam province, JB: Jeollabuk province, JN: Jeollanam province, JJ: Jeju island.

※ CI (chigger index): no. of chigger mites per rodent.

Total number of chigger mites and species ratio, 2019
GenusSpeciesSpringAutumnTotal
No. of chigger mites%No. of chigger mites%No. of chigger mites%
Cheladontaikaoensis120.1110.1230.1
Euschoengastiakoreaensis620.64032.84651.9
Leptotrombidiumfulleri30.0--30.0
gemiticulum10.0880.6890.4
hiranumai20.0--20.0
orientale2,36923.68706.03,23913.2
pallidum5,52955.17,74953.113,27853.9
palpale6426.41,3529.31,9948.1
scutellare70.12,34116.12,3489.5
subintermedium60.170.0130.1
zetum8848.82701.91,1544.7
Neotrombiculagardellai--440.3440.2
japonica--1260.91260.5
kwangneungensis10.08145.68153.3
nagayoi40.01090.71130.5
tamiyai5125.13932.79053.7
Walchiafragilis10.020.030.0
Shunseniahertigi40.040.080.0
Total10,039100.014,583100.024,622100.0

※ Main vector of Scrub Typhus: E. koreaensis, L. orientale, L. pallidum, L. palpale, L. scutellare, L. zetum, N. japonica.

Figure 1. Distribution of rodent species (A) and the environment of chigger mites (B)
※ CI (chigger index): No. of chigger mites per rodent

Figure 2. Seasonal density distribution of chigger mites, 2019 (A: Spring, B: Autumn)

Figure 3. Geographical distribution of major chigger mites by season, 2019 (A: Spring, B: Autumn)

Figure 4. Annual regional distribution variation (A: No. of patients B: CI of L. scutellare)

Fig 1.

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Figure 1.Distribution of rodent species (A) and the environment of chigger mites (B)
※ CI (chigger index): No. of chigger mites per rodent
Public Health Weekly Report 2020; 13: 817-831

Fig 2.

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Figure 2.Seasonal density distribution of chigger mites, 2019 (A: Spring, B: Autumn)
Public Health Weekly Report 2020; 13: 817-831

Fig 3.

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Figure 3.Geographical distribution of major chigger mites by season, 2019 (A: Spring, B: Autumn)
Public Health Weekly Report 2020; 13: 817-831

Fig 4.

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Figure 4.Annual regional distribution variation (A: No. of patients B: CI of L. scutellare)
Public Health Weekly Report 2020; 13: 817-831
Total number of rodents and chigger mites collected from 32 localities, 2019
RegionsSpringAutumnTotal
RodentsChigger mitesClRodentsChigger mitesClRodentsChigger mitesCl
GWGangneung-si192,475130.3131,541118.5324,016125.5
Samcheok-si620033.35786157.21198689.6
Sokcho-si549298.41232026.71781247.8
Cheorwon-gun1465446.7941846.4231,07246.6
Chuncheon-si718526.4919221.31637723.6
Pyeongchang-gun152,037135.8141,687120.5293,724128.4
Subtotal666,04391.6624,94479.712810,98785.8
GGGanghwa-gun44110.348220.5812315.4
Yeoju-si51,000200.0132,860220.0183,860214.4
Paju-si71,121160.171,959279.9143,080220.0
Hwaseong-si101,202120.2132,278175.2233,480151.3
Subtotal263,364129.4377,179194.06310,543167.3
CBCheongju-si533066.072,558365.4122,888240.7
Chungju-si5888177.61690256.4211,79085.2
Subtotal101218121.8233460150.4334,678141.8
CNNonsan-si151,585105.7638964.8211,97494.0
Boryeong-si731344.7757482.01488763.4
Yesan-gun5605121.091,619179.9142,224158.9
Subtotal27250392.7222,582117.4495,085103.8
JBGimje-si517434.8527755.41045145.1
Namwon-si1266255.251,012202.4171,67498.5
Jeongeup-si527655.2651185.21178771.5
Jinan-gun5722144.471,443206.1122,165180.4
Subtotal27183467.9233,243141.0505,077101.5
JNMuan-gun35719.07926132.31098398.3
Boseong-gun171,900111.841,052263.0212,952140.6
Jangseong-gun700.0544689.21244637.2
Haenam-gun1012612.61165359.42177937.1
Subtotal37208356.3273077114.064516080.6
GBGimcheon-si518136.259719.41027827.8
Andong-si726437.7510721.41237130.9
Yeongdeok-gun51,440288.061,048174.7112,488226.2
Subtotal171,885110.9161,25278.3333,13795.1
GNGeoje-si519038.07913130.4121,10391.9
Miryang-si710.15214.212221.8
Ulsan-si811113.981,247155.9161,35884.9
Hapcheon-gun958665.181,509188.6172,095123.2
Subtotal2988830.6283,690131.8574,57880.3
JJSeogwipo-si7182.6891.115271.8
Jeju-si17291.7600.023291.3
Subtotal24472.01490.638561.5
Grand total26319,86575.525229,436116.851549,30195.7

※ GW: Gangwon province, GG: Gyeonggi province, CB: Chungcheongbuk province, CN: Chungcheongnam province, GB: Gyeongsangbuk province, GN: Gyeongsangnam province, JB: Jeollabuk province, JN: Jeollanam province, JJ: Jeju island.

※ CI (chigger index): no. of chigger mites per rodent.
Total number of chigger mites and species ratio, 2019
GenusSpeciesSpringAutumnTotal
No. of chigger mites%No. of chigger mites%No. of chigger mites%
Cheladontaikaoensis120.1110.1230.1
Euschoengastiakoreaensis620.64032.84651.9
Leptotrombidiumfulleri30.0--30.0
gemiticulum10.0880.6890.4
hiranumai20.0--20.0
orientale2,36923.68706.03,23913.2
pallidum5,52955.17,74953.113,27853.9
palpale6426.41,3529.31,9948.1
scutellare70.12,34116.12,3489.5
subintermedium60.170.0130.1
zetum8848.82701.91,1544.7
Neotrombiculagardellai--440.3440.2
japonica--1260.91260.5
kwangneungensis10.08145.68153.3
nagayoi40.01090.71130.5
tamiyai5125.13932.79053.7
Walchiafragilis10.020.030.0
Shunseniahertigi40.040.080.0
Total10,039100.014,583100.024,622100.0

※ Main vector of Scrub Typhus: E. koreaensis, L. orientale, L. pallidum, L. palpale, L. scutellare, L. zetum, N. japonica.

References

  1. 국가생물종목록. National Species list of Korea. 2019. 환경부, 국립생물자원관. National Institute of Biological Resources, online at http://kbr.go.kr, accessed on(2020. 03. 01.)
    Self
  2. Lee Hee Il, Shim Soo Kyoung, Song Bong Gu, Choi Eun Na, et al. et al. Detection of Orientia tsutsugamushi , the Causative Agent of Scrub Typhus, in a Novel Mite Species, Eushoengastia koreaensis , in Korea. VECTOR-BORNE AND ZOONOTIC DISEASES 2011;11(3):209-214.
    Pubmed CrossRef
  3. Park Sang-Won, Ha Na-Young, Ryu Boyeong, Bang Ji Hwan, Song Hoyeon, et al. Urbanization of Scrub Typhus Disease in South Korea. PLoS Negl Trop Dis 2015;9(5):e0003814. doi:10.1371/journal.pntd.0003814.
    Pubmed KoreaMed CrossRef
  4. 노종열, 신이현, 주영란. 쯔쯔가무시증 매개 털진드기의 전국 분포조사. 주간 건강과 질병 2014;7(51):1146-1148.
    Self
  5. 박원일, 노종열, 조신형. 2016년 쯔쯔가무시증 매개 털진드기 감시 현황. 주간 건강과 질병 2017;10(39):1058-1061.
    Self
  6. Kim Seong Yoon, Gill Byoungchul, Song Bong Gu, et al. Annual Fluctuation in Chigger Mite Populations and Orientia tsutsugamushi Infections in Scrub Typhus Endemic Regions of South Korea. Osong Public Health Res Perspect 2019;10(6):351-358.
    Pubmed KoreaMed CrossRef
  7. Ivo Elliott, Isabelle Pearson, Prabin Dahal, Nigel V. Thomas, Tamalee Roberts and Paul N. Newton Scrub typhus ecology: a systematic review of Orientia in vectors and hosts. Parasites Vectors. 2019;12:513
    Pubmed KoreaMed CrossRef
  8. Korea Centers for Disease Control and Prevention (KCDC). Disease Web Statistics System. Cheongju-si, Republic of Korea.
    CrossRef

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