• Korean Journal of Clinical Laboratory Science
• /
• v.52 no.4
• /
• pp.364-371
• /
• 2020

The Korea Centers for Disease Control and Prevention is conducting surveillance of climate change vectors across all regions in Korea to counteract the spread of these vectors. As a part of this surveillance project, wild rodents were captured using traps to investigate the spread of chigger mites, the vector of Tsutsugamushi disease, across Jeonbuk, Jinan region, and to conduct studies on pathogens. Twenty samplers were used to sample chigger mites weekly from September to November in four different locations. Six hundred and eleven chigger mites of eight varying types were captured. The largest number of captured chigger mites was N. tamiyai, with 434 samples (71.0%). With the addition of 66 wild rodents captured from traps, 3,050 chigger mites were sampled, which yielded a Chigger index of 46.2. The monthly Chigger index was highest in November with a value of 206.1. the result of the test conducted in the presence of pathogens showed two positive results, each from May and September, out of all 85 pools. This result was aligned with the increased frequency in tsutsugamushi disease cases in spring and fall seasons.

• Korean Journal of Clinical Laboratory Science
• /
• v.53 no.4
• /
• pp.317-325
• /
• 2021

In order to monitor the occurrence of chigger mites, collectors were installed at four places: rice field, field, waterway, and grass field. Totally, 207 chigger mites belonging to 7 species were collected. Starting with 2 mites in the 5 weeks of September, a maximum of 49 mites were collected during 3 weeks of November. Totally, 81, 52, 47 and 27 mites were collected from grass field, waterways, rice field, and field, respectively. Analysis of sampling and collecting chigger mites determined that the most encountered species was Neotrombicula kwangneun (73, 35.3%), followed by Leptotrombidium palpale (46, 22.2%), N. tamiyai (41, 19.8%) and N. asakawai (27, 13.0%). The grab results of 44 wild rodents revealed Apodemus agrarius (35, 79.5%), Crocidura spp. (5, 11.4%), Craseomys regulus (2, 4.5%), and A. peninsulae (2, 4.5%; which had not been detected previously). A total of 6,628 chigger mites were collected from rodents, and the chigger index was determined to be 150.6. Chigger index was found to be highest at 234.2 in October, followed by 223.3 in November, 75.6 in April, and 66.2 in May. PCR from all chigger mite samples tested negative for the Tsutsugamushi pathogen.

• The Korean Journal of Ecology
• /
• v.19 no.1
• /
• pp.31-37
• /
• 1996

The chigger mites known as the vectors of Tsutsugamushi disease seriously increased due to the expansion of their habitats by the change of farmland into idle land, arboreta and golf courses with the progress of industrialization. These mites were surveyed for their nymphs in soil of four areas located in the northern part of Kyonggido known as the outbreak areas of Tsutsugamushi disease. Total number of the chigger mites collected in the soil of four surveyed areas was 2576, and two genera and ten species including Leptotrombidium palpale were indentified. Among them L. pallidum was the dominant species with the highest occurrence rate of 62 percent. Nine species occurred on the bank of Changrungchon that has been idled for more than ten years, but six or seven species occurred in Wonhundong and Ilsandong that hans been idled for less than five years. The number of individuals collected was also higher in Changrungchon than the other sites. Seasonal occurrence of these mites showed a peak with 166 mites in November on the west slope and another with 192 mites in February on the east slope of the bank of Changrungchon, but none in June. Component ratio of individual numbers for L. palpale, L. pallidum, L. orientalis and L.scutelaris were 19, 62, 9 and 3 percent, respectively. Individual number of L. pallidum and L. scutelaris appeared to some extent of 397 and 23 mites, respetively.

• Parasites, Hosts and Diseases
• /
• v.58 no.4
• /
• pp.445-450
• /
• 2020

Trombiculid "chigger" mites (Acari) are ectoparasites that feed blood on rodents and another animals. A crosssectional survey was conducted in 7 ecosystems of southern Vietnam from 2015 to 2016. Chigger mites were identified with morphological characteristics and assayed by polymerase chain reaction for detection of rickettsiaceae. Overall chigger infestation among rodents was 23.38%. The chigger index among infested rodents was 19.37 and a mean abundance of 4.61. A total of 2,770 chigger mites were identified belonging to 6 species, 3 genera, and 1 family, and pooled into 141 pools (10-20 chiggers per pool). Two pools (1.4%) of the chiggers were positive for Orientia tsutsugamushi. Ricketsia spp. was not detected in any pools of chiggers. Further studies are needed including a larger number and diverse hosts, and environmental factors to assess scrub typhus.

• Parasites, Hosts and Diseases
• /
• v.55 no.5
• /
• pp.555-559
• /
• 2017

Chigger mites are parasites of rodents and other vertebrates, invertebrates, and other arthropods, and are the only vectors of scrub typhus, in addition to other zoonoses. Therefore, investigating their distribution, diversity, and seasonal abundance is important for public health. Rodent surveillance was conducted at 6 districts in Shandong Province, northern China ($114-112^{\circ}E$, $34-38^{\circ}N$), from January to December 2011. Overall, 225/286 (78.7%) rodents captured were infested with chigger mites. A total of 451 chigger mites were identified as belonging to 5 most commonly collected species and 3 genera in 1 family. Leptotrombidium scutellare and Leptotrombidium intermedia were the most commonly collected chigger mites. L. scutellare (66.2%, 36.7%, and 49.0%) was the most frequently collected chigger mite from Apodemus agrarius, Rattus norvegicus, and Microtus fortis, respectively, whereas L. intermedia (61.5% and 63.2%) was the most frequently collected chigger mite from Cricetulus triton and Mus musculus, respectively. This study demonstrated a relatively high prevalence of chigger mites that varied seasonally in Shandong Province, China.

• Parasites, Hosts and Diseases
• /
• v.52 no.2
• /
• pp.225-229
• /
• 2014

A total of 9,281 larval chigger mites were collected from small mammals captured at Hwaseong-gun, Gyeonggi-do (Province) (2,754 mites from 30 small mammals), Asan city, Chungcheongnam-do (3,358 mites from 48 mammals), and Jangseong-gun, Jeollanam-do (3,169 for 62 mammals) from April-November 2009 in the Republic of Korea (= Korea) and were identified to species. Leptotrombidium pallidum was the predominant species in Hwaseong (95.8%) and Asan (61.2%), while Leptotrombidium scutellare was the predominant species collected from Jangseong (80.1%). Overall, larval chigger mite indices decreased from April (27.3) to June (4.9), then increased in September (95.2) and to a high level in November (169.3). These data suggest that L. pallidum and L. scutellare are the primary vectors of scrub typhus throughout their range in Korea. While other species of larval chigger mites were also collected with some implications in the transmission of Orientia tsutsugamushi, they only accounted for 11.2% of all larval chigger mites collected from small mammals.

• The Korean Journal of Soil Zoology
• /
• v.11 no.1_2
• /
• pp.16-19
• /
• 2006

A checklist on 61 species of chigger mites belonging to 12 genera and 2 families from Korean peninsula is suggested with Korean names of each taxon.

• Parasites, Hosts and Diseases
• /
• v.59 no.5
• /
• pp.473-479
• /
• 2021

A nationwide survey of chigger mites causing scrub typhus and an investigation of epidemiologic factors for chigger mites was conducted at 16 localities in 8 provinces in Korea during autumn 2009, 2012, and 2013. A total of 233 Apodemus agrarius were captured, and all were infested with chigger mites. The chigger index was highest in Chungcheongbuk-do in 2009 (358.3) and 2012 (290.1) and Chungcheongnam-do in 2013 (294.4). The predominant chigger mite species was Leptotrombidium pallidum in the northern and central parts and L. scutellare in the southern and western parts, Korea. L. pallidum was not found in Jellanam-do and Gyeongsangnam-do and the distribution of L. scutellare had been expanded in the northern parts of Korea. The chigger index of L. pallidum was positively correlated with temperature and negatively correlated with humidity. The incidence of scrub typhus is dependent on L. scutellare index. These findings could be helpful to monitor the distribution of chigger mites and to develop a preventive measures for scrub typhus in Korea.

• Parasites, Hosts and Diseases
• /
• v.59 no.4
• /
• pp.377-392
• /
• 2021

This paper is to illustrate the infestation and related ecological characteristics of chigger mites on the Asian house rat (Rattus tanezumi). A total of 17,221 chigger mites were collected from 2,761 R. tanezumi rats, and then identified as 131 species and 19 genera in 2 families. Leptotrombidium deliense, the most powerful vector of scrub typhus in China, was the first major dominant species on R. tanezumi. All the dominant mite species were of an aggregated distribution among different individuals of R. tanezumi. The species composition and infestations of chiggers on R. tanezumi varied along different geographical regions, habitats and altitudes. The species-abundance distribution of the chigger mite community was successfully fitted and the theoretical curve equation was ${\hat{S}}(R)={37e^{-(0.28R)}}^2$. The total chigger species on R. tanezumi were estimated to be 199 species or 234 species, and this further suggested that R. tanezumi has a great potential to harbor abundant species of chigger mites. The results of the species-plot relationship indicated that the chig-ger mite community on R. tanezumi in Yunnan was an uneven community with very high heterogeneity. Wide geographi-cal regions with large host samples are recommended in the investigations of chigger mites.

• Parasites, Hosts and Diseases
• /
• v.59 no.3
• /
• pp.319-324
• /
• 2021

Incidence of tsutsugamushi disease (scrub typhus) caused by Orientia tsutsugamushi, is steadily increasing. It is a mite-borne disease transmitted by chigger mites. In this study, the chigger mites were collected from field small mammals in Hwaseong-si (city), Gyeonggi-do (province), Korea, 2019 and 2020. The field small mammals captured were 56 Apodemus agrarius (94.9%) and 3 Crocidura lasiura (5.1%). A total of 7,531 chigger mites were collected from the captured small mammals. Using PCR test, 153 chigger mite pools were examined and 17 pools were reported positive for O. tsutsugamushi. The O. tsutsugamushi were identified to 5 strains; Jecheon strain was most prevalent, followed by Boryong strain. The other strains were OI011, Taguchi, and Shimokoshi. Collectively, these results provide essential regional information on mite-borne tsutsugamushi disease in the Hwaseong-si, and further contribute to bring awareness and rapid diagnosis for the tsutsugamushi disease.