Variation in Populations of Chigger Vectors of Scrub Typhus in Developing Oil Palm Areas of Different Ages

Dohany, A. L.; Shirai, Akira; Lim, B. L.; Huxsoll, David L.

doi:10.7883/yoken1952.33.263

Cited by 4 publications

(3 citation statements)

References 6 publications

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“…Remarks: unengorged larvae of L. vivericola Vercammen-Grandjean and Langston, 1976 found in Malaysia by Dohany et al [ 128 ] were also reported as O. tsutsugamushi -associated, however, the subsequent revision of the material proved the first species determination wrong and larvae were then assigned to L. umbricola [ 127 ].…”

Section: Resultsmentioning

confidence: 99%

Not Only Leptotrombidium spp. an Annotated Checklist of Chigger Mites (Actinotrichida: Trombiculidae) Associated with Bacterial Pathogens

2022

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Mites of the family Trombiculidae are known for playing a role in maintaining and spreading the scrub typhus etiologic agent, an intracellular Gram-negative bacterium, Orientia tsutsugamushi. Species of the genus Leptotrombidium are investigated most thoroughly, particularly in SE Asia, and a few are proven vectors for the pathogen. The mentioned association, however, is not the only one among trombiculids. Here, we present a list of chiggers indicated in the literature as positive for bacterial pathogens, tested throughout almost 100 years of research. Taxonomic identities of trombiculids follow recent revisions and checklists. Results point at 100 species, from 28 genera, evidenced for association with 31 bacterial taxa. Pathogen-positive mites constitute around 3.3% of the total number of species comprising the family. Discussed arachnids inhabit six biogeographic realms and represent free-living instars as well as external and internal parasites of rodents, soricomorphs, scadents, lagomorphs, peramelemorphs, bats, passerine birds, reptiles and humans. A variety of so far detected bacteria, including novel species, along with the mites’ vast geographical distribution and parasitism on differentiated hosts, indicate that revealing of more cases of Trombiculidae-pathogens association is highly probable, especially utilizing the newest techniques enabling a large-scale bacterial communities survey.

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Section: Resultsmentioning

confidence: 99%

Not Only Leptotrombidium spp. an Annotated Checklist of Chigger Mites (Actinotrichida: Trombiculidae) Associated with Bacterial Pathogens

2022

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“…Due to increased vector abundance in the dry season, the risk of chigger bites and scrub typhus is likely to be higher at that time of year, and plantations bordering forest may support particularly large vector populations. Reducing small-mammal populations and relative humidity near the ground level (e.g., by grass cutting) are possible options to manage scrub typhus risk to plantation workers and Orang Asli living near these sites [ 22 ]. Further work in Malaysia is warranted to understand the fine-scale dynamics of O. tsutsugamushi in chigger–host networks in anthropized habitats across space and seasons, especially as our study was underpowered in the rice paddy, forest border, and rubbish dumpsite (probably because these habitats were not matched between states).…”

Section: Discussionmentioning

confidence: 99%

“…Malaysia lacks a national reporting system for scrub typhus and there have been no large-scale analyses of disease risk in the country using modern statistical methods. However, focalised studies over the past century have shown a high seroprevalence of scrub typhus among agricultural workers, including those employed in oil palm or rubber plantations [ 19 , 20 , 21 ], and Orientia infections have been detected in chiggers and small mammals in oil palm estates [ 22 , 23 ]. The native indigenous people of Malaysia, known locally as the “Orang Asli”, who either maintain their nomadic lifestyle or inhabit the forests of Peninsular Malaysia, exhibit particularly high exposure to scrub typhus, with one study from the 1970s reporting a seroprevalence of >70% in deep forests [ 24 ].…”

Section: Introductionmentioning

confidence: 99%

Habitat and Season Drive Chigger Mite Diversity and Abundance on Small Mammals in Peninsular Malaysia

et al. 2022

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Chigger mites are vectors of the bacterial disease scrub typhus, caused by Orientia spp. The bacterium is vertically transmitted in the vector and horizontally transmitted to terrestrial vertebrates (primarily wild small mammals), with humans as incidental hosts. Previous studies have shown that the size of the chigger populations is correlated with the density of small mammals in scrub typhus-endemic regions. Here, we explore interactions between the small mammals and chiggers in two oil palm plantations located in the Perak and Johor states of Peninsular Malaysia. The location in Perak also contained an aboriginal (Orang Asli) settlement. A ~5% sub-sample from 40,736 chigger specimens was identified from five species of small mammals (n = 217), revealing 14 chigger species, including two new records for Malaysia. The abundance and species richness of chiggers were significantly affected by habitat type (highest in forest border), state (highest in Perak), and season (highest in dry). The overall prevalence of Orientia tsutsugamushi DNA in small-mammal tissues was 11.7% and was not significantly affected by host or habitat characteristics, but in Johor, was positively associated with infestation by Leptotrombidium arenicola. These findings highlight the risk of contracting scrub typhus in oil palm plantations and associated human settlements.

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Occurrence ofOrientia tsutsugamushiin Chiggers (Acari: Trombiculidae) and Small Animals in an Orchard Near Bangkok, Thailand

et al. 1999

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The ecology of Orientia tsutsugamushi (Hayashi) was studied in chiggers and small animals in an orchard near Bangkok, Thailand. Small animals were trapped monthly between July and November 1992 and examined for the presence of O. tsutsugamushi and ectoparasitic chiggers. A total of 40 Rattus rattus (L.) and 16 Tupaia glis (Diard) was trapped. O. tsutsugamushi was isolated from liver and spleen samples of 30.8% of R. rattus and 18.6% of T. glis. Antibodies to O. tsutsugamushi were detected in 95% of R rattus, and IgG antibodies persisted for up to 10 mo after removing rats from potential reinfection in the field. A total of 1,133 chiggers was identified and examined for the presence of O. tsutsugamushi using a direct fluorescent antibody test, and 2.6% Leptotrombidium deliense Walch, 5.1% Aschoshoengastia indica Hirst, 2.6% A. (Laurentella) sp. #2 and 0.9% A. (Laurentella) sp. #4 were infected. Forty-four pools of chiggers from these animals were triturated and injected into mice. Seven pools were obtained from T. glis and 1 was positive for O. tsutsugamushi, and 3 of 37 pools from R. rattus were positive. A proportion of the engorged chiggers collected was reared to the adult stage, and the progeny of these adults tested for the presence of O. tsutsugamushi. The progeny of 186 females was tested, and the progeny of 2 L. deliense was found to be naturally infected with O. tsutsugamushi.

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Variation in Populations of Chigger Vectors of Scrub Typhus in Developing Oil Palm Areas of Different Ages

Cited by 4 publications

References 6 publications

Not Only Leptotrombidium spp. an Annotated Checklist of Chigger Mites (Actinotrichida: Trombiculidae) Associated with Bacterial Pathogens

Not Only Leptotrombidium spp. an Annotated Checklist of Chigger Mites (Actinotrichida: Trombiculidae) Associated with Bacterial Pathogens

Habitat and Season Drive Chigger Mite Diversity and Abundance on Small Mammals in Peninsular Malaysia

Occurrence ofOrientia tsutsugamushiin Chiggers (Acari: Trombiculidae) and Small Animals in an Orchard Near Bangkok, Thailand

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