Discovery of a novel spotted fever group Rickettsia, "Candidatus Rickettsia kedanie," in unfed larval chigger mites, Leptotrombidium scutellare.

Spotted fever group (SFG) rickettsia, the causative agent of SFG rickettsiosis, is predominantly carried by ticks, whereas Orientia tsutusgamushi, the causative agent of scrub typhus, is primarily transmitted by chigger mites in Japan. In this study, we attempted to isolate intracellular eubacteria from Leptotrombidium scutellare, a major vector of O. tsutsugamushi; moreover, we isolated an SFG rickettsia using a mosquito-derived cell line. Draft genome sequences of this unique isolate, by applying criteria for species delimitation, classified this isolate as a novel strain, proposed as "Rickettsia kedanie." Further genetic analysis identified conserved virulence factors, and the isolate successfully propagated in mammalian cells, suggesting its ability to cause diseases in humans. The presence of SFG rickettsia in unfed larvae implies potential dual-pathogen carriage and reflects a symbiotic relationship similar to that between the mites and O. tsutsugamushi, indicating possibility of its transovarial transmission from female adults. Furthermore, conserved genomic similarity of the novel isolate to known SFG rickettsia suggests potential multiple hosts, including chiggers and ticks. In the natural environment, ticks, chigger mites, and wild animals may carry new isolates, complicating the infection cycle and increasing the transmission risks to humans. This discovery challenges the conventional association of SFG rickettsia with ticks, emphasizing its implications for research and disease control. However, this study was confined to a particular species of chigger mites and geographic area, underscoring the necessity for additional studies to comprehend the ecological dynamics, host interactions, and health implications linked to this newly identified SFG rickettsia.

Microscopic Menaces: The Impact of Mites on Human Health.

Mites are highly prevalent arthropods that infest diverse ecological niches globally. Approximately 55,000 species of mites have been identified but many more are yet to be discovered. Of the ones we do know about, most go unnoticed by humans and animals. However, there are several species from the Acariformes superorder that exert a significant impact on global human health. House dust mites are a major source of inhaled allergens, affecting 10-20% of the world's population; storage mites also cause a significant allergy in susceptible individuals; chiggers are the sole vectors for the bacterium that causes scrub typhus; Demodex mites are part of the normal microfauna of humans and their pets, but under certain conditions populations grow out of control and affect the integrity of the integumentary system; and scabies mites cause one of the most common dermatological diseases worldwide. On the other hand, recent genome sequences of mites provide novel tools for mite control and the development of new biomaterial with applications in biomedicine. Despite the palpable disease burden, mites remain understudied in parasitological research. By better understanding mite biology and disease processes, researchers can identify new ways to diagnose, manage, and prevent common mite-induced afflictions. This knowledge can lead to improved clinical outcomes and reduced disease burden from these remarkably widespread yet understudied creatures.

Parasite infestation patterns differ between ticks and chigger mites on two rodent host species in Taiwan.

Parasites are typically concentrated on a few host individuals, and identifying the mechanisms underlying aggregated distribution can facilitate a more targeted control of parasites. We investigated the infestation patterns of hard ticks and chigger mites on two rodent species, the striped field mouse, Apodemus agrarius, and the lesser ricefield rat, Rattus losea, in Taiwan. We also explored abiotic and biotic factors that were important in explaining variation in the abundance of ticks and chiggers on rodent hosts. Ticks were more aggregated than chiggers on both rodent species. Factors important for the variation in parasitic loads, especially biotic factors, largely differed between ticks and chiggers. Variation partitioning analyses revealed that a larger proportion of variation in chiggers than in ticks can be explained, especially by abiotic factors. If, as proposed, the higher number of parasites in males is due to a larger range area or immunity being suppressed by testosterone, when A. agrarius males host more ticks, they are expected to also host more chiggers, given that chiggers adopt a similar host finding approach to that of ticks. Instead, the similar abundance of chiggers in male and female A. agrarius implies that a large home range or suppressed immunity does not predispose males to inevitably host more parasites. More variations were explained by abiotic than biotic factors, suggesting that controlling practices are more likely to be successful by focusing on factors related to the environment instead of host traits. Our study indicated that the extent of parasitism is rarely determined by a sole factor, but is an outcome of complex interactions among animal physiology, animal behavior, characteristics of parasites, and the environments.

Detection of Orientia spp. Bacteria in Field-Collected Free-Living Eutrombicula Chigger Mites, United States.

Scrub typhus, a rickettsial disease caused by Orientia spp., is transmitted by infected larval trombiculid mites (chiggers). We report the molecular detection of Orientia species in free-living Eutrombicula chiggers collected in an area in North Carolina, USA, to which spotted fever group rickettsiae infections are endemic.

Molecular Detection of Candidatus Orientia chuto in Wildlife, Saudi Arabia.

Scrub typhus is a zoonosis caused by 3 species of Orientia bacteria, including Candidatus Orientia chuto. This species is known only from a human case in Dubai and infections in wildlife in Kenya. We report molecular detection of Candidatus O. chuto in 2 wild rodent species from Saudi Arabia.

Species diversity and related ecology of chiggers on small mammals in a unique geographical area of Yunnan Province, southwest China.

Chiggers are common ectoparasites and the exclusive vector of scrub typhus. Based on previous investigations from a unique geographical area in Yunnan Province of southwest China, the Three Parallel Rivers Area, we retrospectively studied the species diversity and related ecology of chiggers on rodents and other small mammals. A very high species diversity of 120 chigger species was identified. Five dominant chigger species accounted for 59.4% (5238/8965) of total chiggers, and among them Leptotrombidium scutellare is the second major vector of scrub typhus in China. Species diversity of the chigger community fluctuates greatly in different altitudinal and latitudinal gradients. There are significant differences in species composition, species diversity and dominant species of chiggers among hosts with apparent community heterogeneity. Based on the species abundance distribution, the expected total number of chigger species was estimated to be 170, 50 more than the number of actually collected species; this further indicates a very high chigger species diversity in this area. The bipartite ecological network analysis revealed the intricate relationships between chigger and host species-positive and negative correlations existed among some species of dominant and vector chiggers.

Emerging trends of scrub typhus disease in southern Rajasthan, India: A neglected public health problem.

Scrub typhus is the oldest known vector-borne zoonotic infectious disease in the world which is life-threatening for all age groups as it presents acute febrile illness along with multi-organ involvements and spread with the biting of infectious 'Trombiculid mite' (chigger mite). The pathogen of this disease is an obligatory coccobacillus gram-negative rickettsial bacteria Orientia tsutsugamushi. Scrub typhus disease was previously confined geographically only to the Asia Pacific region (tsutsugamushi triangle), but in recent years it has crossed its limit and has spread in other countries beyond the tsutsugamushi triangle and has become more hazardous for the community. The objective of this study is to explore the scrub typhus disease outbreak trends with existing information in southern Rajasthan state, India. This study concluded that scrub typhus disease is being re-emerged again and again in various Indian geographical regions with new species of vectors. The disease has been raised in tremendous amounts in Rajasthan within the last five years especially in the hilly zone and has led to major public health problems with other zoonotic diseases.

Vector and rodent surveillance for Orientia tsutsugamushi in north India.

BACKGROUND & OBJECTIVES: Scrub typhus or chigger borne typhus, caused by Orientia tsutsugamushi is an emerging vector-borne disease as large numbers of cases have been reported in various tropical countries. It is transmitted to humans through bites of infected chiggers (larval mites). The knowledge about the vector, its distribution, density and habitat are important so as to understand the epidemiology of scrub typhus in a given area. To control rickettsial infections, regular rodent-vector surveillance should be planned in areas where the disease transmission is occurring and it will also help to strengthen the existing entomological data related to the vector of scrub typhus in northern India. METHODS: In the present study, rodent-vector surveillance was planned for one whole year, covering both mite active and non-active seasons (October 2019-December 2020) in selected areas of Chandigarh and Punjab in north India. Rodent tissues and mites were also examined for the presence of O. tsutsugamushi by nested PCR for 56 kDa gene and real-time PCR for 47 kDa outer membrane protein gene. 18S gene PCR was performed for molecular identification of mites. RESULTS: In the surveillance, three types of ectoparasite, viz. mites, fleas and ticks were obtained in rodents. All mites found were of Laelapidae family. None of the pooled rodent tissue samples as well as mite samples were found positive for O. tsutsugamushi by nested PCR for rickettsial DNA. INTERPRETATION & CONCLUSION: In the present study, we did not get any evidence of carriage of O. tsutsugamushi in either mites or rodents collected and sampled in selected regions in Chandigarh and Punjab. We need to strengthen the entomological surveillance over a broader region and increase the frequency of trapping rodents to increase clarity on vector-reservoir dynamics in this geographical region.

Screening and genotyping of Orientia tsutsugamushi from field-collected on-host chiggers (Acari: Prostigmata) recovered from a positive scrub typhus locality in Kelantan, Malaysia.

Orientia tsutsugamushi is the causative agent of scrub typhus vectored by larval stages of trombiculid mites (chiggers) that occur in most tropical regions of Southeast Asia. A total of 242 chiggers extracted from eight small mammals captured from a positive scrub typhus locality in Kelantan, Malaysia, were screened for the presence of O. tsutsugamushi. The chiggers were grouped in 16 pools for extraction of DNA prior to screening of O. tsutsugamushi based on the nucleotide sequence of 56-kDa type specific antigen (TSA) gene using nested polymerase chain reaction. Two species of on-host chiggers were identified, the one, Leptotrombidium deliense, much more dominant (94.8%) than the other, Ascoshoengastia sp. (5.2%). The pathogen was detected in two pools (12.5%) of L. deliense recovered from Rattus rattus and Tupaia sp. The 56-kDa TSA gene sequence analysis revealed the O. tsutsugamushi harboured in those chiggers were Karp prototype strain with high similarity (99.3%). Findings of this study strongly supported the existence of scrub typhus infections in certain parts of Malaysia which agrees with previous local reports. Moreover, this study highlighted the pressing need of a large-scale close observation of O. tsutsugamushi DNA sequences from chiggers that can probably be collected from other positive scrub typhus localities to precisely provide the distribution and prevalence of this zoonotic pathogen.

Monitoring Chigger Mites for Orientia tsutsugamushi in Field Small Mammals in Hwaseong-si, Gyeonggi-do, Korea, 2019-2020.

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.

Infestation and Related Ecology of Chigger Mites on the Asian House Rat (Rattus tanezumi) in Yunnan Province, Southwest China.

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 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 chigger mite community on R. tanezumi in Yunnan was an uneven community with very high heterogeneity. Wide geographical regions with large host samples are recommended in the investigations of chigger mites.

Research Advances of Leptotrombidium scutellare in China.

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.

A Report of Chigger Mites on the Striped Field Mouse, Apodemus agrarius, in Southwest China.

Based on the field investigations in 91 investigation sites (counties) in southwest China between 2001 and 2019, the present paper reported the chigger mites on A. agrarius mice in southwest China for the first time by using a series of statistical methods. From 715 striped field mice captured in 28 of 91 investigated sites, only 255 chiggers were collected, and they were identified as 14 species, 6 genera in 3 subfamilies under 2 families. Of 715 A. agrarius mice, only 24 of them were infested with chigger mites with low overall prevalence (PM=3.4%), overall mean abundance (MA=0.36 mites/host) and overall mean intensity (MI=10.63 mites/host). The species diversity and infestation of chiggers on A. agrarius were much lower than those previously reported on some other rodents in southwest China. On a certain species of rodent, A. agrarius mouse in southwest China seems to have a very low susceptibility to chigger infestations than in other geographical regions. Of 14 chigger species, there were 3 dominant species, Leptotrombidium sialkotense, L. rupestre and Schoengastiella novoconfuciana, which were of aggregated distribution among different individuals of A. agrarius hosts. L. sialkotense, one of 6 main vectors of scrub typhus in China, was the first dominant on A. agrarius. The species similarity of chigger mites on male and female hosts was low with CSS=0.25, and this reflects the sex-bias of different genders of A. agrarius mice in harboring different chigger species.

Batmanacarus robini, n. gen., n. sp. (Trombidiformes: Trombiculidae) collected parasitizing a ghost-faced bat (Chiroptera: Mormoopidae) from a cave in Trinidad and Tobago.

Trinidad and Tobago, a neotropical country, has 38 reported chigger species. Of these species, 18 were parasitizing bats. Here, we describe a new genus and species parasitizing a ghost-faced bat in this country.

Identification of Trombiculid Chigger Mites Collected on Rodents from Southern Vietnam and Molecular Detection of Rickettsiaceae Pathogen.

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.

Epidemiological Characteristics of Rodents and Chiggers with Orientia Tsutsugamushi in the Republic of Korea.

A survey of rodents and chiggers associated with Orientia tsutsugamushi was conducted in a rural region of the Republic of Korea (Korea) between 2014 and 2018. Overall Apodemus agrarius 15.2% had the highest seropisitive for O. tsutsugamushi, followed by Myodes regulus 11.4%. Monthly risk factors using logistic regression analysis were not associated with O. tsutsugamushi infections in rodents. The overall prevalence rate of O. tsutsugamushi among chiggers was 0.3%. The chigger (Leptotrombidium scutellare) and monthly (October) risk factors were associated with O. tsutsugamushi human infections (P<0.05). Orientia tsutsugamushi infections are endemic in rodents in Korea and people, for example, soldiers who are active outdoors, must employ preventive measures, especially during October (P<0.05). When there are many reports of O. tsutsugamushi infections in Korea. The Boryong strain 85.7% (2/14) was the most common strain detected in chiggers, followed by the Shimokoshi 7.1% (1/14) and Karp 7.1% strains.

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.

Relative Abundance of a Vector of Scrub Typhus, Leptotrombidium sialkotense, in Southern Yunnan Province, China.

The chigger mite Leptotrombidium sialkotense is one of the 6 main vectors of scrub typhus in China. Before present study, L. sialkotense was found in some parts of Hunan province, China with a narrow geographical distribution. During field investigation 2016-2017, we found L. sialkotense in Jingha, southern Yunnan, China. Of 15 small mammal host species, L. sialkotense were collected from 6 species of the hosts. Rattus brunneusculus was a dominant host of L. sialkotense, from which 98.3% of the mites were collected. The chigger mite showed a relatively high infestation prevalence (PM=11.7%) and mean abundance (MA=0.5) in comparison with the rest 5 host species. These results reveal a certain host specificity of L. sialkotense to a rat R. brunneusculus. The mite L. sialkotense showed an aggregated distribution on the host (P<0.05). A positive correlation observed between L. sialkotense and the body length of hosts. There was a positive interspecific association between L. sialkotense and 2 other dominant vectors, L. deliense and L. scutellare.

Geographical distribution of Orientia tsutsugamushi strains in chiggers from three provinces in Korea.

Chiggers were collected from the central and southern parts of South Korea between April and November, 2009 with the aim of investigating the seasonal and geographical distribution of Or. A total of 1136 chiggers were identified. They included eight species belonging to four genera, as follows: Leptotrombidium scutellare (27.2%, n = 309), L. pallidum (54.6%, n = 621), L. orientale (6.25%, n = 71), L. palpale (1.59%, n = 18), L. zetum (2.0%, n = 23), Euschoengastia koreaensis (1.5%, n = 17), Cheladonta ikaoensis (0.08%, n = 1) and Neotrombicula japonica (1.05%, n = 12). The density of L. pallidum was high from April to May, whereas L. scutallare was not found in spring, being observed from October. Serotype-specific nested PCR targeting the 56 kDa protein gene and sequencing analysis identified that the strains of 1136 O. tsutsugamushi in the chiggers as Boryong (6.8%), Kanda (0.4%), Oishi (0.3%), Jecheon (0.1%), Youngworl (0.1%) and Wonju (0.1%). Our findings indicate that L. pallidum and L. scutellare are dominant species in Korea and have geographical and seasonal variations.

Research Progress on Leptotrombidium deliense.

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.