Ectoparasitic insects and mites on Yunnan red-backed voles (Eothenomys miletus) from a localized area in southwest China

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.

Disease vector occurrence and ecological characteristics of chiggers on the chestnut white-bellied rat Niviventer fulvescens in Southwest China between 2001 and 2019

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.

Comparison of Chiggers (Acari: Trombiculidae, Leeuwenhoekiidae) on Two Sibling Mouse Species, Apodemus draco and A. ilex (Rodentia: Muridae), in Southwest China

Chigger mites (Acari) are common ectoparasites on rodents, and they are the exclusive vector of scrub typhus. South China field mouse (Apodemus draco) and Lantsang field mouse (A. ilex) are two sibling rodent species. Based on field investigations in southwest China (2001-2015), this paper compared the infestation of these two mouse species with chiggers. Of 42 chigger species identified from two mouse species, 36 were found on A. draco, 11 on A. ilex and 5 common species on both mice. Jaccard similarity index (J = 0.12, J < 0.25) showed a very different species composition of chiggers on two mouse species, and some parameters of the chigger community were also different. The overall mean intensity of chiggers on A. draco (MI = 4.26) was higher than that on A. ilex (MI = 3.91, p < 0.05). The dominant chigger species on A. draco were Trombiculindus yunnanus, Leptotrombidium scutellare (a major vector species in China) and L. sinicum with a total constituent ratio C_r = 42.9% (106/247). Leptorombidium sinicum and L. scutellare independently occurred on A. draco with an association coefficient V = 0.09 (V ≈ 0). The dominant chigger species on A. ilex were L. rusticum, L. densipunctatum and L. gongshanense, with a total C_r = 58.14% (25/43). Leptorombidium rusticum and L. densipunctatum on A. ilex had a slight positive association (V = 0.49, 0.5 < V < 1). All dominant chigger species were unevenly distributed among different individuals of two mouse species. Chigger infestation showed sex bias on different sexes of two mouse species. The species abundance of the chigger community on A. draco was revealed as a log-normal distribution pattern.

Analysis on infestation and related ecology of chigger mites on large Chinese voles (Eothenomys miletus) in five provincial regions of Southwest China

Based on a long-term field investigation in the five provincial regions of Southwest China between 2001 and 2019, the present paper studied the infestation and related ecology of chigger mites (chiggers) on the large Chinese vole (Eothenomys miletus), an endemic and dominant rodent species in the regions. A total of 52331 chiggers were collected from 2661 voles, and 52261 mites were identified as 185 species and 13 genera in the family Trombiculidae with very high species diversity. The identified 185 chigger species on E. miletus (a single rodent species) even exceeded those recorded in some countries. The overall infestation prevalence (P_m = 53.96%), mean abundance (MA = 19.64) and mean intensity (MI = 36.39) on E. miletus were much higher than those on some other rodent species in the same regions. Although the species composition showed a moderate similarity (J = 0.63) between male and female hosts (E. miletus), the infestation indices (P_m = 56.25%, MA = 21.67) of chiggers on male hosts were higher than those on the females (P_m = 51.23%, MA = 17.09) (P < 0.05). Two dominant chigger species, Leptotrombidium scutellare (C_r = 19.17%) and L. sinicum (C_r = 11.06%), showed an aggregated distribution pattern among different individuals of their host E. miletus, and a relatively high degree of positive association existed between the two dominant chigger species with PCC = 0.57, DI = 0.60 and OI = 0.62 (x² = 857.46, P < 0.001). Leptotrombidium densipunctatum, Walchia koi, Helenicula hsui, L. scutellare and W. ewingi showed a high degree of environmental adaptability to their environments with high niche breadths. The theoretical curve of the species abundance distribution of chigger community on E. miletus was successfully fitted with Preston's lognormal distribution model. Based on the theoretical curve fitting, the expected total number of chigger species on E. miletus was roughly estimated to be 223 species, and 38 chigger species were probably missed in the sampling investigation.

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Chiggers are the common ectoparasites of rodents and vector of scrub typhus, Eothenomys miletus is the reservoir host and infectious source of zoonoses.

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The dominant chigger specie, Leptotrombidium scutellare, is one of the main and powerful vectors of scrub typhus in China.

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To study the chigger mites of E. miletus voles in such a wide geographical region.

Preliminary Study on Species Diversity and Community Characteristics of Gamasid Mites on Small Mammals in Three Parallel Rivers Area of China

(1) Background: Gamasid mites are a large group of arthropods, and some of them are of medical importance. Besides directly biting humans and causing dermatitis, some gamasid mites are the vector of rickettsialpox and potential vector of hemorrhagic fever with renal syndrome (HFRS). The Three Parallel Rivers Area of China is one of the hotspots of biodiversity research in the world, with complicated topographic landforms, different types of vegetation, special elevation gradients and high biodiversity. (2) Methods: Species richness (S): the Shannon-Wiener diversity index (H), Simpson dominance index (D) and Pielou evenness index (E) were used to analyze the basic community structure. The β diversity (Cody index) was used to reflect the diversity difference between any two adjacent elevation gradients. The method based on Preston's lognormal model for species abundance distribution was used to estimate the total number of gamasid mite species. (3) Results: A total of 3830 small mammal hosts captured from the nine survey sites were identified as 44 species, 27 genera and nine families in five orders. Apodemus chevrieri, Eothenomys miletus and A. draco were the dominant host species with a total constituent ratio C_r = 52.037%. From the body surface of the hosts, 26,048 gamasid mites were collected and identified as 10 families, 21 genera and 82 species (excluding 847 unidentified specimens) with high species richness (S = 82) and diversity (H = 2.33). The three dominant mite species were Dipolaelaps anourosorecis, Laelaps nuttalli and L. echidninus, with a total C_r = 64.46% (16,791/26,048). There are significant differences in the species composition, species diversity and dominant species of gamasid mites on different hosts. The species diversity of the mite community fluctuated greatly in different elevation gradients. The highest peaks of species richness and β diversity appeared at altitudes of 3000-3500 m (S = 42) and 1500-2000 m (β = 17.5), respectively. The species abundance distribution of the mites was successfully fitted by Preston's lognormal model with S^(R)=19e-[0.22(R-0)]2 (α = 0.22, R² = 0.9879). Based on fitting the theoretical curve by Preston's model, the total number of gamasid mite species was estimated to be 153 species. (4) Conclusions: Gamasid mites on small mammals are abundant with complex community structures and high species diversity in the Three Parallel Rivers Area of China. There is an apparent community heterogeneity of the mites on different hosts and in different environments.

Infestation of chigger mites on Chinese mole shrew, Anourosorex squamipes, in Southwest China and ecological analysis

The Chinese mole shrew, Anourosorex squamipes Milne-Edwards, 1872, is a common species of insectivorous mammal in Southwest China. Based on field investigations between 2001 and 2019, the present study reports the infestation of chiggers (larvae of chigger mites) on the shrew in Southwest China and certain ecology parameters for the first time. A total of 3169 chiggers were collected from 1694 A. squamipes and they were identified into 72 species and 10 genera in the family Trombiculidae. The overall infestation prevalence (P_m), mean abundance (MA) and mean intensity (MI) of A. squamipes with chiggers reached 11.1%, 1.87 and 16.86, respectively. The species diversity, species composition and infestation of chiggers on A. squamipes fluctuated in different environments (latitudes, altitudes, habitats and landscapes) and on different sexes and ages of the shrew hosts with high heterogeneity and low species similarity. In the established linear regression equation (M* = 0.173 + 1.054 M) for dominant mite Leptotrombidium densipunctatum, both the α and β values (α = 0.173, β = 1.054) exceeded the boundary values (F = 4.67, p < 0.05), and therefore the spatial distribution pattern of this mite was determined as an aggregated distribution among different individuals of shrew hosts. The species abundance distribution of the chigger community on A. squamipes conformed to the lognormal distribution, and its curve showed a gradually descending tendency from the rare mite species to the dominant mite species. The curve tendency of species-sample relationship implies that more species of chiggers would be found if the host samples infinitely keep increasing.

Infestation and distribution of chigger mites on Chevrieri's field mouse (Apodemus chevrieri) in Southwest China

Based on a long-term field investigation on chigger mites in southwest China from 2001 to 2019, the present study analyzed the infestation and distribution of chigger mites on the Chevrieri's field mouse (Apodemus chevrieri) in the region. A total of 12,516 individuals of chigger mites were collected from 1981 A. chevrieri mice, and 12,281 chiggers were identified as 107 species, 11 genera and 3 subfamilies in 2 families, which revealed a high species diversity of the mites on A. chevrieri mice. Of 1981 A. chevrieri mice, 633 ones were infested with chiggers with a relatively high overall prevalence (P M  = 31.95%), mean abundance (MA = 6.32) and mean intensity (MI = 19.77). Of the 107 chigger species identified from A. chevrieri mice, three ones were the most dominant and they were Leptrombidium scutellare, L. densipunctatum and L. cricethrionis, which showed aggregated distribution among different individuals of the mice. A slightly positive association existed between every two dominant chigger species, which implied that the dominant chigger species tend to co-exist on A. chevrieri. The infestations of A. chevrieri with chiggers varied in different latitudes, altitudes and landscapes and they showed some heterogeneity along different environmental gradients. The logistic regression analysis showed that the risk factors for chigger infestations on A. chevrieri were landscapes, ages and altitudes, which implied that the environmental factors and host ages could influence the infestations of the mice with the mites. A theoretical curve of the species abundance distribution of chigger mites on A. chevrieri was successfully fitted by Preston's lognormal model, suggesting that the species abundance distribution conforms to the lognormal distribution pattern. The expected total species of chigger mites on A. chevrieri was roughly estimated to be 136 species and about 29 rare chigger species were probably missed in the sampling field investigation.

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.

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 Ŝ (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.

Molecular detection of Rickettsia species and host associations of Laelaps mites (Acari: Laelapidae) in Taiwan

Various rickettsiae have recently been detected in Laelaps mites (Acari: Laelapidae), which are common ectoparasites of rodents; however, investigations on this topic remain very scarce, particularly in Asia. In the present study, shrews and rodents were trapped from 2006 to 2010 in eight lowland regions of Taiwan (< 500 m in elevation) to collect associated Laelaps mites, from which Rickettsia-a group of emerging pathogens-were detected and identified by assaying the gltA and ompB genes. A total of 853 Laelaps mites of at least four species were collected from a sample of 1004 small mammals that included one shrew and 10 rodent species. Rattus losea was the most common species (44.9% of total hosts) and hosted the highest percentage of mites (76.6% of total mites). Laelaps nuttalli was the most abundant mite species (51.7% of total mites), followed by Laelaps echidninus (24.2%), Laelaps sedlaceki (23.1%), and Laelaps myonyssognathus (0.2%). Notably, Rickettsia species with the highest similarity to spotted fever group (SFG) rickettsiae were identified from seven of the 72 pools of Laelaps mites. The presence of SFG rickettsiae in hematophagous Laelaps mites, particularly including species that are closely associated with commensal rodents in frequent contact with humans, calls for further investigation on the competence of Laelaps mites in transmitting rickettsiae.

Circulation of Rickettsia species and rickettsial endosymbionts among small mammals and their ectoparasites in Eastern Slovakia

Bacteria belonging to the genus Rickettsia are known as causative agents of vector-borne zoonotic diseases, such as spotted fevers, epidemic typhus and endemic typhus. Different species of ticks, mites and fleas could act as reservoirs and arthropod vectors of different pathogenic Rickettsia species. The aim of this work was to establish active surveillance of Rickettsia spp. in mites, ticks and fleas collected from small mammals (rodents and shrews) in Eastern Slovakia. A total of 964 animal ear biopsies, 871 mites, 667 ticks and 743 fleas were collected from small mammals in the Košice region, Eastern Slovakia. All specimens were identified using specialized taxonomic keys, and were conserved in ethanol until DNA extraction was performed. After DNA extraction, identification of Rickettsia species was performed by PCR-based methods. The total prevalence of rickettsiae from ear biopsies was 4.6% (95% CI, 3.2-5.9), in tested mites 9.3% (95% CI, 7.4-11.2), 17.2% (95% CI, 14.3-20.1) in I. ricinus ticks and 3.5% (95% CI, 2.2-4.8) in fleas. Sequence analysis of the partial gltA gene and Rickettsia helvetica-, Rickettsia slovaca-, Rickettsia raoultii- species specific real-time PCR tests revealed the presence of R. helvetica, R. slovaca, unidentified Rickettsia and rickettsial endosymbionts. These pathogenic and symbiotic species were confirmed in the following ectoparasite species-Laelaps jettmari, Haemogamasus nidi, Laelaps agilis and Eulaelaps stabularis mites, Ixodes ricinus ticks, Ctenophthalmus solutus, C. assimilis and Megabothris turbidus fleas infesting host-Apodemus agrarius, A. flavicollis, Microtus arvalis and Myodes glareolus small mammals. These results confirm the circulation of R. helvetica, R. slovaca, unidentified Rickettsia and rickettsial endosymbionts in mites, ticks and fleas collected on small mammals in the Košice region, Eastern Slovakia.

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 (P_M=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.

Co-Infection of Scrub Typhus and Human Granulocytic Anaplasmosis in Korea, 2006

BACKGROUND

Scrub typhus, severe fever with thrombocytopenia syndrome (SFTS) and human granulocytic anaplasmosis (HGA) are important arthropod-borne infectious diseases in Korea and share a common point that they are transmitted by arthropod bites mostly during outdoor activities and there are considerable overlaps of epidemiologic and clinical features at presentation. We investigated the co-infection of these infections.

METHODS

The study subjects were patients with laboratory-confirmed scrub typhus who were enrolled retrospectively in 2006. SFTS virus (SFTSV) infection was confirmed by a reverse transcriptase polymerase chain reaction (PCR) to amplify partial L segment of SFTSV for molecular diagnosis. HGA was confirmed by a nested PCR to amplify 16S rRNA gene of Anaplasma phagocytophilum. Direct sequencing of the positive PCR products was performed. Clinical features of co-infected subjects were described.

RESULTS

One-hundred sixty-seven patients with scrub typhus were included in the analysis. Co-infection of A. phagocytophilum was identified in 4.2% of scrub typhus patients (7/167). The route of co-infection was uncertain. The co-infected patients had not different clinical manifestations compared to the patients with scrub typhus only. All the study subjects were negative for SFTSV.

CONCLUSION

We found retrospective molecular evidence of the co-infection of scrub typhus and HGA in Korea. HGA may be more prevalent than expected and need to be considered as an important differential diagnosis of febrile patients in Korea.

Severe fever with thrombocytopenia syndrome: comparison with scrub typhus and clinical diagnostic prediction

Background

Severe fever with thrombocytopenia syndrome (SFTS) is emerging in Asian 3 countries, China, Japan and Korea, which are scrub typhus endemic areas, and its incidence is increasing. As the two infections overlap epidemiologically and clinically and the accessibility or sensitivity of diagnostic tests is limited, early clinical prediction may be useful for diagnostic and therapeutic purposes.

Methods

Patients aged ≥16 years who were clinically suspected and laboratory-confirmed to be infected with Orientia tsutsugamushi or the SFTS virus in South Korea were enrolled. Clinical and laboratory parameters were compared. Scrub typhus was further subclassified according to the status of eschar and skin rash. An SFTS prediction scoring tool was generated based on a logistic regression analysis of SFTS compared with scrub typhus.

Results

The analysis was performed on 255 patients with scrub typhus and 107 patients with SFTS. At initial presentation, subjective symptoms except for gastrointestinal symptoms, were more prominent in scrub typhus patients. In addition to the characteristic eschar and skin rash, headache was significantly more prominent in scrub typhus, while laboratory abnormalities were more prominent in SFTS. Leukopenia (white blood cell count < 4000/mm³; odds ratio [OR] 30.13), thrombocytopenia (platelet count < 80,000 /mm³; OR 19.73) and low C-reactive protein (< 1 mg/dL; OR 67.46) were consistent risk factors for SFTS (all P < 0.001). A prediction score was generated using these 3 variables, and a score ≥ 2 had a sensitivity of 93.1% (95% confidence interval [CI], 87.9–96.4%) and a specificity of 96.1% (95% CI, 93.8–97.6%) for SFTS.

Conclusion

This prediction scoring tool may be useful for differentiating SFTS from eschar- or skin rash-negative scrub typhus. It is a simple and readily applicable tool with potential for use in primary care settings.

Prevalence and diversity of Rickettsia species in ectoparasites collected from small rodents in Lithuania

BACKGROUND

Rickettsiae are emerging pathogens causing public health problems in many countries around the world. Rickettsia spp. are found in association with a wide range of arthropods which feed on different species of animals. However, the distribution and natural cycle of Rickettsia species and their association with different arthropod vectors are not fully established. The aim of this study was to investigate the presence and prevalence of Rickettsia spp. in ticks, mites and fleas parasitizing different species of small mammals in Lithuania and to molecularly characterize the Rickettsia spp. obtained from different ectoparasites.

RESULTS

A total of 1261 ectoparasites (596 Ixodes ricinus ticks, 550 mites of five species and 115 fleas of eight species) collected from 238 rodents in Lithuania during 2013-2014 were investigated for the presence of Rickettsia pathogens. Infection rates were calculated as the maximum likelihood estimation (MLE) with 95% confidence intervals (CI). The infection rate varied among ectoparasites and was found highest in fleas 43.5%, followed by I. ricinus ticks (MLE = 26.5%; 95% CI: 22.2-31.3%) and then mites (MLE = 9.3%; 95% CI: 7.0-12.2%). Sequence analysis of partial gltA and 17kDa genes revealed the presence of Rickettsia helvetica, R. felis, R. monacensis, Rickettsia sp. and rickettsial endosymbionts. Four Rickettsia spp. were identified in fleas, while three Rickettsia spp. were identified in Laelapidae mites and only one (R. helvetica) in I. ricinus ticks.

CONCLUSIONS

To our knowledge, this is the first report of the occurrence and molecular characterization of Rickettsia spp. in 11 species of ectoparasites of small rodents in Lithuania. The present data extend the knowledge on the distribution of Rickettsia spp. and their association with different arthropod vectors. Prior to our study, R. felis had never been identified in Lithuania. To our knowledge, this is also the first report of R. felis in L. agilis and H. microti mites and in Ct. agyrtes and H. talpae fleas, as well as the first detection of R. monacensis in Ct. agyrtes fleas.

Species diversity of ectoparasitic chigger mites (Acari: Prostigmata) on small mammals in Yunnan Province, China

Chigger mites are a large group of arthropods and the larvae of mites are ectoparasites. Some species of ectoparasitic mites (larvae) can be the transmitting vectors of tsutsugamushi disease (scrub typhus). Yunnan Province is located in the southwest of China with complicated topographic landform and high biodiversity, where there are five zoogeographical subregions. Rodents and some other small mammals were trapped and examined for ectoparasitic chigger mites in 29 investigation sites in Yunnan during 2001-2013. From 13,760 individuals and 76 species of small mammal hosts, we collected 274 species of mites, which were identified as comprising 26 genera in two families. The species diversity of chigger mites (274 species) in the present study were not only much higher than that from other provinces of China but also largely exceeded that recorded from other regions and countries in the world. Of the five zoogeographical subregions, both the species diversity and Shannon-Weiner's diversity of mites were the highest in subregion II (southern subregion of Hengduan Mountains) with middle altitudes and middle latitude. Both the species diversity of mites and Shannon-Wiener diversity index showed a parabolic tendency from the low altitude (<500 m) to the high altitude (>3500 m) along the vertical gradients with the peak occurring in the middle-altitude regions (2000-2500 m). Of four dominant hosts, the species richness of mites was highest on Eothenomys miletus (S = 165) and Shannon-Wiener diversity index was highest on Rattus norvegicus (H = 3.13). Along latitude gradients, species richness of chigger mites increased first and then decreased, peaking at 25° to 26° N with 193 mite species. The geographical location, complex topography, and landscape with diverse small mammal hosts in Yunnan Province have contributed to the extremely high species diversity of mites in the province. The large sampling size of small mammal hosts in a wide geographical scope within a long time span also made it possible to have collected so many species of chigger mites.

Analysis of ectoparasites (chigger mites, gamasid mites, fleas and sucking lice) of the Yunnan red-backed vole (Eothenomys miletus) sampled throughout its range in southwest China

The Yunnan red-backed vole Eothenomys miletus (Rodentia: Cricetidae) is an endemic rodent species and reservoir host of zoonoses in southwest China. Based on a large host sample (2463 voles collected from 39 localities between 2001 and 2013), a general analysis of four categories of ectoparasite (fleas, sucking lice, chigger mites and gamasid mites) on E. miletus across its entire range of distribution was made. This analysis identified a total of 71 895 ectoparasites belonging to 320 species (30 species of flea, 9 of sucking louse, 106 of gamasid mite and 175 of chigger mite) with a high prevalence (87%), mean abundance (29.19) and mean intensity (33.69). Of the 18 vector species of zoonoses found on E. miletus, the flea Ctenophthalmus quadratus (Siphonaptera: Hystrichopsyllidae) and chigger mite Leptotrombidium scutellare (Trombidiformes: Trombiculidae) were the dominant species; these are the main vectors of zoonoses in China. All of the dominant parasite species showed an aggregated distribution pattern. Male voles harboured more species of parasite than females. Chigger mites represented the most abundant species group on voles and their prevalence was positively correlated with mean abundance (r = 0.73; P < 0.05). As a single rodent species, E. miletus has a high potential to harbour abundant ectoparasites with high species diversity and high rates of infestation. The sex of the vole affects ectoparasite infestation.

Faunal analysis of chigger mites (Acari: Prostigmata) on small mammals in Yunnan province, southwest China

This paper studied the species diversity and fauna distribution of chigger mites on small mammals in Yunnan province, southwest Yunnan. In total, 120,138 individuals of chigger mites were collected from 13,760 individual small mammals, and these mites were identified as comprising two families, 26 genera, and 274 species. Of the five zoogeographical subregions, the mite species diversity in subregions I and II was higher than that in subregions III, IV, and V. Four mite species (Leptotrombidium scutellare, Leptotrombidium sinicum, Leptotrombidium deliense, and Helenicula simena) were the most dominant species in the whole province. Several vector species of chigger mites co-existed in Yunnan, and L. deliense (a main vector of scrub typhus in China) was mainly distributed in subregions IV and V with lower latitude and average altitude whereas L. scutellare (also a main vector in China) was mainly distributed in subregions I, II, and III with higher latitude and average altitude. Some geographically widely distributed mite species were also the mites with wide host ranges and low host specificity. The dominant mite species and their clustering tendency in the dendrogram of hierarchical clustering analysis were highly in accordance with the zoogeographical divisions. The species diversity of chigger mites showed a parabolic tendency from the low altitude (<500 m) to the high altitude (>3,500 m) along the vertical gradients and reached the highest value in the middle altitude regions in 2,000-2,500 m. The highest species diversity of the mites and their small mammal hosts happened in the regions around the Hengduan Mountains, which is a hotspot of biodiversity in Asia continent. The host and its sample size, geographical scope, landscape, topography, and some other factors comprehensively influence the species diversity and faunal distribution of chigger mites. A systematic field investigation with a wide geographical scope and large host sample is strongly recommended in the fauna study of chigger mites and other ectoparasites.