• Parasites, Hosts and Diseases
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• v.50 no.4
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• pp.327-331
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• 2012

Monthly surveys were conducted to investigate the occurrence of chigger mites and seroprevalence of scrub typhus among small mammals in Jeollanam-do, the southwestern part of Korea, from November 2006 through October 2007. Fifty-eight small mammals, including 57 Apodemus agrarius (98.3%) and 1 Crocidura lasiura (1.7%), were captured, and a total of 4,675 chigger mites representing 4 genera and 8 species were collected from them. The chigger infestation rate among small mammals was 69.0%. The most predominant species in A. agrarius was Leptotrombidium scutellare (54.0%), followed by Leptotrombidium pallidum (39.4%), Leptotrombidium orientale (4.4%), Leptotrombidium palpale (1.1%), Neotrombicula tamiyai (0.6%), Eushoengastia koreaensis (0.3%), Neotrombicula gardellai (0.3%), and Cheladonta ikaoensis (<0.1%). The chigger index of A. agrarius was the highest in October (740.0), followed by November (242.0), September (134.6), March (98.3), February (38.2), January (35.3), December (34.5), April (30.8), and May (1.7). The average antibody positive rate of scrub typhus in wild rodents was 50.0%. The seropositive rates were high in October (100.0%) and November (83.3%), whereas those in other months were relatively low (28.6-57.1%). The chigger index of L. scutellare rapidly increased in September to form an acuminate peak in October, followed by a gradual decline. These results suggest that the outbreak of scrub typhus in the southwestern part of Korean peninsula is mostly due to L. scutellare.

• Parasites, Hosts and Diseases
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• v.47 no.4
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• pp.381-386
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• 2009

A survey to determine the geographical distribution and relative abundance of potential vectors of scrub typhus was conducted from October to November 2006 at 13 localities throughout the Republic of Korea. Apodemus agrarius accounted for 97.6% (80/82) of all rodents, while only 2 Myodes regulus (2/82) were collected. A total of 10,860 chiggers were collected from A. agrarius belonging to 4 genera and 8 species, while only Walehia fragilis (40) was collected from Myodes regulus. Leptotrombidium pallidum (8,137; 74.9%), a vector of scrub typhus, was the predominant species collected from A. agrarius followed by Leptotrombidium scutellare (2,057, 18.9%), Leptotrombidium palpale (279; 2.7%), Leptotrombidium orientale (232; 2.1%), and Leptotrombidium zetum (79; 0.7%), Neotrombicula tamiyai (58; 0.5%), Euschoengastica koreaensis (16; 0.1%), and Cheladonta ikaoensis (2; < 0.1 %). L. pallidum was the predominant chigger collected at collection sites in Gangwon (100%), Gyeonggi (87.2%), Chungnam (100%), Chungbuk (100%), Jeonbuk (73.9%), Jeonnam (77.0%), and Gyeongbuk (66.1%) provinces, whereas L. scutellare was the predominant chigger collected in Gyeongnam province (77.9%) and Jeju Island (62.3%). Data suggest a correlation between chigger population abundance and human cases of scrub typhus in Korea.

• Parasites, Hosts and Diseases
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• v.56 no.4
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• pp.313-324
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• 2018

This article reviews Leptotrombidium deliense, including its discovery and nomenclature, morphological features and identification, life cycle, ecology, relationship with diseases, chromosomes and artificial cultivation. The first record of L. deliense was early in 1922 by Walch. Under the genus Leptotrombidium, there are many sibling species similar to L. deliense, which makes it difficult to differentiate L. deliense from another sibling chigger mites, for example, L. rubellum. The life cycle of the mite (L. deliense) includes 7 stages: egg, deutovum (or prelarva), larva, nymphochrysalis, nymph, imagochrysalis and adult. The mite has a wide geographical distribution with low host specificity, and it often appears in different regions and habitats and on many species of hosts. As a vector species of chigger mite, L. deliense is of great importance in transmitting scrub typhus (tsutsugamushi disease) in many parts of the world, especially in tropical regions of Southeast Asia. The seasonal fluctuation of the mite population varies in different geographical regions. The mite has been successfully cultured in the laboratory, facilitating research on its chromosomes, biochemistry and molecular biology.

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

• Parasites, Hosts and Diseases
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• v.55 no.5
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• pp.555-559
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• 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
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• v.59 no.1
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• pp.1-8
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• 2021

Leptotrombidium scutellare is one of the 6 main vectors of scrub typhus in China. It has been found in more than 15 provinces of China. Especially in Yunnan, it was found to be mainly distributed in some mountainous areas with high altitude, low temperature and low precipitation. Rodents and some other small mammals were the most common hosts of L. scutellare. To date, more than 40 host species of L. scutellare have been recorded with very low host specificity, and the main hosts varied in different geographical regions. L. scutellare had a strong resistance against the cold environment, and the temperature and humidity were 2 important factors affecting its growth and development. Among different individuals of their rodent hosts, L. scutellare mites often showed an aggregated distribution pattern, which reflected the interspecific cooperation of the mites. The chromosome karyotype of L. scutellare was 2n=16 and all the 8 pairs of chromosomes were short rod-shaped with metacentric or sub-metacentric types. The isozyme spectrum supported that L. scutellare, L. deliense and L. rubellum were in the same species group. Based on the natural infection, experimental transmission and epidemiological evidence, L. scutellare has been eventually confirmed as the second major vector of scrub typhus in China, which is second only to L. deliense.

• Parasites, Hosts and Diseases
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• v.61 no.3
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• pp.272-281
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• 2023

Chigger mites are the vector of scrub typhus. This study estimates the infestation status and ecological characteristics of chiggers on the chestnut white-bellied rat Niviventer fulvescens in Southwest China between 2001 and 2019. Chiggers were identified under the microscope, and infestation indices were calculated. The Preston's log-normal model was used to fit the curve of species abundance distribution. A total of 6,557 chiggers were collected in 136 of 342 N. fulvescens rats, showing high overall infestation indices (prevalence=39.8%, mean abundance=19.2, mean intensity=48.2) and high species diversity (S=100, H'=3.0). Leptotrombidium cangjiangense, Neotrombicula japonica, and Ascoschoengastia sifanga were the three dominant chigger species (constituent ratio=42.9%; 2,736/6,384) and exhibited an aggregated distribution among different rat individuals. We identified 100 chigger species, with 3 of them (Leptotrombidium scutellare, Leptotrombidium wenense, and Leptotrombidium deliense) as the main vectors of scrub typhus in China and nine species as potential vectors of this disease. Disease vector occurrence on N. fulvescens may increase the risk of spreading scrub typhus from rats to humans. Chigger infestation on N. fulvescens varied significantly in different environments. The species abundance distribution showed a log-normal distribution pattern. The estimated number of chigger species on N. fulvescens was 126 species.

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

• The Korean Journal of Soil Zoology
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• v.11 no.1_2
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• pp.1-6
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• 2006

The chigger is of importance to humans and animals as an irritating pest and a crucial vector of disease. We observed stylostome formation by larvae of Leptotrombidium pallidum in parasitized striped-field mouse (Apodemus agarius) pinna skin. The stylostome formations were also examined in detail by electron microscopy. The proximal and middle parts of the stylostome were formed as a rod-like structure containing a canal. The stylostome was coated with thick degenerated epidermal cells, and seemed to be formed a hyperplastic epidermis. The stylostome formation may result from an interaction between larval secretions and the host tissue. According to histological and morphological characteristics, the stylostome exhibited considerable inflammation in the epidermis and similar reactivity.

• Journal of Ecology and Environment
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• v.41 no.3
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• pp.107-113
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• 2017

Background: As the habitat changes in Korea due to climate change, the emergence of disease-mediated vectors is increasing rapidly. Thus for the surveillance of mosquito- and chigger mite-borne disease, their seasonal prevalence and species composition were investigated at seven locations in Daegu, Gunwi and Sangju. Methods: Mosquitoes were collected twice every month from five collection sites using a black light and BG sentinel traps in Daegu and Gunwi from April through November. Chigger mites were investigated twice per month from wild rodents caught with Sherman live traps in Gunwi and Sangju from April through May and September through November. Results: A total of 2,361 female mosquitoes were collected. Cowshed (626 individuals, Trap index (TI) 44.7) and Kyungpook National University campus (846 individuals, TI 60.4) in Daegu had the highest number of mosquitoes in the black light and BG sentinel trap, respectively. The mosquitoes were collected more by BG sentinel trap than the black light trap. Nine mosquito species were trapped, and the Culex pipiens complex was the most commonly mosquito (1,397 individuals, 59.2%), followed by Anopheles sinensis (554 individuals, 23.5%). Anopheles sinensis (531 individuals, 51.9%) and Culex pipiens complex (1,142 individuals, 85.4%) were the most mosquitoes from black light and BG sentinel trap, respectively. In terms of seasonal prevalence, the highest abundance was in July, with 824 individuals collected. In chigger mites, eighty-one wild rodents of five species that are hosts of chigger mites were collected; among them, 53 and 25 individuals of Apodemus agrarius and Crocidura suaveolens, respectively were trapped. Leptotrombidium pallidum was a dominant species, with 2,467 individuals collected (67.8%). Conclusions: The mosquito was the dominant species in Culex pipiens complex and the highest in July and August. Apodemus agrarius was most abundant in wild rats and Leptotrombidium pallidum was dominant in the collected chigger mites.