The diversity and distribution of chigger mites associated with rodents in the South African savanna

Chigger mites (Trombiculidae) are temporary habitat-specific ectoparasites that often occur on rodents. Little ecological data are available on chiggers associated with rodents in South Africa. The study aims were to (1) record the chigger species associated with rodents in the savanna, (2) assess if chigger species display parasitope preference on the rodent body and (3) compare the distribution of chigger species in natural, agricultural and urban habitats. Rodents (n = 314) belonging to eight genera were trapped in the savanna biome during 2014 and 2015. Twelve chigger species, of which five are recently described species, were recorded from 161 rodent hosts. The data include three new country locality records. Microtrombicula mastomyia was the most prevalent species across sampling seasons and habitat types. Significant parasitope preference was recorded for two species, with the ear, face and tail base some of the preferred attachment sites. Sampling season and habitat type had a significant effect on chigger communities with summer and agricultural habitats recording the highest species richness, while the highest species diversity was recorded in natural habitats. The study contributes to our current knowledge regarding rodent-associated chigger diversity and distribution in South Africa and further highlights the importance of environmental characteristics in shaping chigger communities.

Severe Trombiculiasis in Hunting Dogs Infested With Neotrombicula inopinata (Acari: Trombiculidae)

This study records the clinical findings in nine hunting dogs showing systemic illness associated with trombiculids and identifies the mite species involved. In fall, coinciding with the seasonality of mites, all dogs were infested with mites and had been in the risk area (Sierra Cebollera Natural Park, La Rioja, Spain) a few hours before the onset of symptoms. The symptoms included vomiting, anorexia, weakness and lethargy, diarrhea, and even stupor. The clinical picture was fast-acting and potentially fatal. The infestations varied from low to severe. Molecular analysis of mites that fed on the dogs confirmed that they were larvae of Neotrombicula inopinata (Oudemans, Acari, Trombiculidae). This is the first time that N. inopinata has been identified as feeding on dogs and implicated in canine systemic illness associated with trombiculids. In contrast to other chiggers, N. inopinata does not seem to cause dermatitis. Likewise, the clinical and epidemiological similarity between the clinical symptoms we describe herein and the occurrence of seasonal canine illness (SCI) led us to suspect that this illness may be caused by infestation with these mites. The condition could be the consequence of severe infestation from large numbers of feeding mites, especially N. inopinata. Whether or not the cases were due to a severe allergic host response to salivary proteins or the result of the transmission of a new or emerging trombiculid-borne pathogen is not known.

Risk factors for acquisition of scrub typhus in children admitted to a tertiary centre and its surrounding districts in South India: a case control study

BACKGROUND

Scrub typhus is a mite borne zoonosis common in the tropics with no good preventive strategy. Children are also affected leading to considerable morbidity and mortality. We conducted a case control study and a vector survey to determine the risk factors for acquisition of scrub typhus.

METHODS

A case control study with a 1:2 case control ratio was conducted over a 2 year period at a tertiary care centre and its surrounding districts in South India. Cases were children < 15 years with confirmed scrub typhus. Controls were age and locality matched community controls without fever. Demographic, environmental and behavioural risk factors were obtained in cases and controls by an interview and an environmental survey. A vector survey was also undertaken in the immediate vicinity of the cases.

RESULTS

Case Control study: 101 cases and 167 controls were analysed. On multivariate analysis, significant association was observed with environmental factors such as the presence of a water body within 100 m of the house (OR 3.56(1.36,9.75); p 0.011), cooking outside the house (OR 5.61 (1.51,23.01); p 0.011), owning pets (OR 3.33(1.16,9.09); p 0.031), and the presence of bushes within 5 m of the house (OR 2.78 (1.11,7.69); p 0.033). Of the behavioural factors, the child going to school by a vehicle (OR 3.12 (2.29,8.37); p 0.006) was associated with an increased risk. Drying clothes on a clothesline showed a trend towards protection from acquiring scrub typhus (OR 0.31 (0.08, 1.08); p 0.077). Vector survey:26 rodents were trapped in as many houses. Trombiculid mites were isolated in 24 houses with 9(34.6%) being able to transmit scrub typhus. 254 trombiculid mites belonging to four species and two genera were collected. Leptotrombidium deliense, (33.5%). Schoengastiella ligula, (11.0%) of the total mite specimens collected. S. ligula always co-existed with L. deliense. The estimated Chigger index for Leptotrombidium deliense and Schoengastiella ligula was 3.27and 1.08 per animal respectively.

CONCLUSIONS

Our study highlights risk factors for scrub typhus, some of which may be modifiable. A clean peri-domestic environment free of vegetation, drying clothes on a clothesline and cooking indoors may decrease the risk of scrub typhus.

Evidence for co-invasion events: different chigger species (Actinotrichida, Trombidioidea: trombiculidae) share a host

Cases of co-invasion of various chigger species parasitizing murids and cricetids in various habitats were analysed using morphological and molecular approaches. Here we provide evidence for 25 new cases of co-parasitism of chigger mites on rodent hosts (Myodes glareolus, Apodemus flavicollis, Apodemus agrarius) accounting for 8.6% of all host-parasite associations observed in this study. The results confirm higher incidence of co-parasitism in vertebrate-associated Parasitengona mites compared to arthropod-associated ones. Among factors influencing the occurrence of co-parasitism in Trombiculidae the body constitution and year-round availability of hosts associated with lower host specificity of larvae should be considered.

Heterogeneity of Orientia tsutsugamushi genotypes in field-collected trombiculid mites from wild-caught small mammals in Thailand

Trombiculid mites are the vectors of scrub typhus, with infected larval mites (chiggers) transmitting the causative agent, Orientia tsutsugamushi, during feeding. Co-existence of multiple O. tsutsugamushi strains within infected mites has previously been reported in naturally infected, laboratory-reared mite lines using molecular methods to characterize the 56-kDa type-specific antigen (TSA) gene. In the current study, more advanced next-generation sequencing technology was used to reveal the heterogeneity of O. tsutsugamushi genotypes in field-collected trombiculid mites from rodents and small mammals in scrub typhus-endemic areas of Thailand. Twenty-eight trombiculid mites collected from 10 small mammals were positive for O. tsutsugamushi, corresponding to a prevalence rate of 0.7% within the mite population. Twenty-four of the infected mites were Leptotrombidium spp., indicating that this genus is the main vector for O. tsutsugamushi transmission in Thailand. In addition, O. tsutsugamushi was detected in the mite genera Ascoschoengastia, Blankaartia, Gahrliepia, and Lorillatum. Of the 10 infested small animal hosts, six had 2-10 infected mites feeding at the time of collection. Deep sequencing was used to characterize mixed infections (two to three O. tsutsugamushi genotypes within an individual mite), and 5 of the 28 infected mites (17.9%) contained mixed infections. Additionally, 56-kDa TSA gene sequence analysis revealed identical bacterial genotypes among co-feeding mites with single or mixed infections. These results suggest that co-feeding transmission may occur during the feeding process, and could explain the occurrence of mixed infections in individual mites, as well as the recovery of multiple infected mites from the same host. This study also revealed highly diverse within-host O. tsutsugamushi genotypes. The occurrence of multiple O. tsutsugamushi genotypes within individual mites has important implications, and could provide a mechanism for pathogen evolution/diversification in the mite vector.

Landscapes with different biodiversity influence distribution of small mammals and their ectoparasitic chigger mites: A comparative study from southwest China

From a previous field investigation in Yunnan, southwest China between 2001 and 2015, we selected two types of landscapes to make a retrospectively comparative study on the distribution of small mammals and their ectoparasitic chigger mites. One landscape is "mountainous uncultivated land (MUL)" with higher biodiversity, which is located in a famous "World Nature Heritage Site", the Three-Parallel-Rivers Region in the northwest of Yunnan. The other is "cultivated flatland landscape (CFL)" with lower biodiversity, which is located in the south of Yunnan. The landscapes with different biodiversity apparently influenced the distribution of small mammals and their ectoparasitic chigger mites. Much more species of small mammals and mites were found in MUL than in CFL. A total of 3,177 small mammals captured from MUL were identified as 55 species, 30 genera and 10 families in five orders. From these small mammal hosts, 5,882 chigger mites were collected and identified as 127 species, 15 genera and 3 subfamilies in two families. A total of 1,112 small mammals captured from CFL were identified as 19 species, 12 genera and 5 families in three orders. From these hosts, 17,742 chiggers were collected and identified as 86 species, 12 genera and 3 subfamilies in two families. Both the species diversity (S = 55) and community diversity (H = 2.673) of small mammals in MUL were much higher than those in CFL (S = 19; H = 0.926). There were also higher values of β diversity in MUL than in CFL. Different main reservoir rodent hosts of zoonoses (including tsutsugamushi disease) were found in two types of landscapes. Rattus tanezumi (one main reservoir host) was most abundant in CFL, which accounted for 80.22% of all the small mammals. Another two main reservoir hosts, Eothenomys miletus and Apodemus chevrieri were the dominant species in MUL, but they were not as abundant as R. tanezumi in CFL. Different vector species of chigger mites also existed in MUL and CFL. Leptotrombidium deliense (a main and powerful vector of tsutsugamushi disease in China) and Ascoschoengastia indica (a potential vector of tsutsugamushi disease) were the dominant species of chigger mites in CFL (Cr = 25.81% for A. indica; Cr = 23.47% for L. deliense). Leptotrombidium scutellare (also a main vector of tsutsugamushi disease in China) was the dominant chigger species in MUL (Cr = 26.09%). Higher infestation of vector mites on small mammals was found in the simple landscape with lower biodiversity (CFL) than in the complex landscape with higher biodiversity (MUL). The overall prevalence (P), mean abundance (MA) and mean intensity (MI) of chigger mites on small mammals were much higher in CFL than in MUL. The main vector mite species on their main rodent hosts also showed a higher P, MA and MI in CFL than in MUL.

Comparative stylostome ultrastructure of Hirsutiella zachvatkini (Trombiculidae) and Trombidium holosericeum (Trombidiidae) larvae

Stylostomes (feeding tubes) of Hirsutiella zachvatkini (Schluger) (Trombiculidae), feeding on bank voles [Myodes glareolus (Schreber)], and of Trombidium holosericeum (L.) (Trombidiidae), feeding on larvae of Stenodemini sp. (Heteroptera, Miridae), were studied by TEM methods and on semi-thin sections. The stylostome of H. zachvatkini is a homogeneous structure of low electron density and without strict margins. It extends within the concave host epidermis, undergoing hyperplasia and hyperkeratosis. TEM does not reveal any obvious stratification in the stylostome walls. The cheliceral movable digits are moved apart by 5-6 µm and tightly applied/adhered to the stylostome substance. A local area beneath the open end of the stylostome canal is not empty but contains a nearly homogeneous substrate, which can pass into the central stylostome canal. The latter is mostly free of contents. In contrast to H. zachvatkini, larvae of T. holosericeum form a root-like stylostome chaotically branching within the clear space underneath the host cuticle free of tissue elements. Tubules of the distal stylostome branches become progressively thinner and disappear blindly. As in H. zachvatkini, the stylostome walls of T. holosericeum are devoid of stratification but show moderate to high electron density. The cheliceral movable digits are moved apart by the same distance, as in H. zachvatkini, and tightly applied to the stylostome substance. The lumen of the central canal is either electron lucent, in the distal portions, or filled with a fine granular or homogeneous substrate of low electron density in the proximal portions forming a type of ampoule. This study shows that Trombiculidae and Trombidiidae share similar initial stages of stylostome formation but the resultant stylostome of each family is distinctly different.

Description of Blankaartia shatrovi n. sp. (Acari: Trombiculidae) From Brazil

The chigger mite genus Blankaartia includes 28 known species, of which 10 are distributed in the Nearctic and Neotropical regions. These species preferentially parasitize birds, but occasionally they can also be found on rodents, bats, and reptiles, showing low host selectivity. In the present study, we report the presence of this genus in Brazil for the first time, including the first report of Blankaartia sinnamaryi (Floch and Fauran) and the description of a new species of Blankaartia collected from birds (Order Passeriformes).

[ECOLOGICAL AND GEOGRAPHIC ANALYSIS OF THE SPREAD OF MITES OF THE FAMILY TROMBICULIDAE IN MONGOLIA]

The paper gives data on the fauna of chigger mites (Thrombiculinae), the ectoparasites of small mammals in Mongolia. The ecological and geographic analysis could reveal the major abiotic and biotic determinants of the spread of the chigger mites and make a map of their potential area.

Resistance to Arrenurus spp. Parasitism in Odonates: Patterns Across Species and Comparisons Between a Resistant and Susceptible Host

Some adult odonates resist parasitism by larval water mites (Arrenurus spp.) with melanotic encapsulation, in which the mite's stylestome is clogged and the mite starves. In summer 2014, we counted the engorged and resisted mites on 2,729 adult odonates sampled by aerial net at 11 water bodies in Greenville Co. and Pickens Co., SC, and tested the hypothesis that the frequency and intensity of resistance correlates with parasite prevalence (the percentage of parasitized hosts). Resistance prevalence (the percentage of parasitized hosts that resisted at least one mite) varied significantly among host species, exceeding 60% for Argia fumipennis(Burmeister) and Celithemis fasciata Kirby but less than 20% for other species. However, neither resistance prevalence nor mean resistance intensity (mean percentage of resisted mites on resisting hosts) correlated with parasite prevalence. We described potential effects of parasitism on host development ofA. fumipennis and Pachydiplax longipennis(Burmeister) by comparing the percent asymmetry of forewing lengths between parasitized and unparasitized individuals. There was no significant difference in asymmetry for either males or females of A. fumipennis, or males of Pa. longipennis(females were not sampled). We also evaluated differences in melanotic encapsulation between A. fumipennis, which readily encapsulates mites in nature, and Pa. longipennis We inserted a 2.0-mm piece of sterile monofilament line into the thorax of captured individuals for 24 h and compared mean gray value scores of inserted and emergent ends using Image-J software. There was no difference in melanotic encapsulation between species.

Host-associated differences in morphometric traits of parasitic larvae Hirsutiella zachvatkini (Actinotrichida: Trombiculidae)

Examination of host-associated variation in the chigger mite Hirsutiella zachvatkini (Schluger) revealed morphological differences among larvae infesting sympatric hosts: Apodemus agrarius, Apodemus flavicollis and Myodes glareolus. The analysis included 61 variables of larvae obtained from their gnathosoma, idiosoma and legs (measurements and counts). Statistically significant differences were observed for metric characters of the legs as opposed to the scutum. In view of the conspecificity of the mites, supported by comparison of COI gene products obtained from larvae and laboratory-reared deutonymphs, the observed variation is attributed to phenotypic plasticity. The knowledge of larval morphology, including intraspecific variation of metric characters, supported by molecular and host range data, places H. zachvatkini among the most comprehensively defined members of Trombiculidae.

Stylostome organization in feeding Leptotrombidium larvae (Acariformes: Trombiculidae)

The stylostome of larvae of the trombiculids Leptotrombidium scutellare (Nagayo et al.), Leptotrombidium fletcheri (Womersley et Heaslip) and Leptotrombidium deliense (Walch) was studied experimentally at different time intervals after larval attachment using the histological method. The stylostome of these species has the same organization and belongs to the epidermal combined with the mixed type, developing more in width than in length. Neither transverse nor conspicuous longitudinal layers are present within the stylostome walls, which stain predominantly in red with Azan, also showing longitudinal portions with blue staining. Larvae tend to attach closely to each other and scabs, consisting of the hyperkeratotic epidermal layers fusing with migrating inflammatory cells, develop around the attachment sites. The dermis shows inflammatory foci with dilated capillaries and inflammatory cells inserting in the connective tissue layer underneath the stylostome. The feeding cavity, which is moderately expressed, may be found either in the epidermis or in the dermis. It contains inflammatory cells and their debris in the liquefied host tissues. The stylostome length depends on the character of the attachment site (the thicker epidermis or scab the longer the stylostome), and does not directly correspond to the stages of larval feeding. Nevertheless, at the 48-h time interval, nearly all attached larvae are found to be fully fed and their midgut cells are filled with nutritional globules.

Chigger mites (Actinotrichida: Parasitengona, Trombiculidae) of Poland. An updated distribution and hosts

The existing body of knowledge regarding the Trombiculidae of Poland is summarized and supplemented with the results of our recent studies. Although around 3000 nominal species are known worldwide, only 18 have been recorded in Poland. Due to the medical and veterinary importance of parasitic larvae, and the complex life cycle which presents difficulties in finding habitats occupied by postlarval forms, most species have been described exclusively from their larvae. This review provides updated information on the host spectrum and distribution of all the trombiculid species hitherto recorded in Poland, supplemented with data on their general distribution and biology.

[Geographical distribution of chigger mites on Rattus flavipectus in Yunnan Province]

OBJECTIVE

To investigate species composition of chigger mites on Rattus flavipectus in different zoogeographical subregion of Yunnan Province.

METHODS

The field investigation was carried out in 25 counties of Yunnan Province during 2001-2012. Some conventional statistical methods were adopted to calculate the species of collected chigger mites, constituent ratio (Dr), mite infestation rate (RM), mean abundance (MA), mean intensity (MI), species richness (S) and species diversity index (H') of chigger mites in five zoogeographical subregions. The hierarchical cluster analysis was used to compare the similarity of chigger mite communities on the rats in the subregions.

RESULTS

A total of 2 118 R. flavipectus were captured. 11 040 individuals of chigger mites were identified as 3 subfamilies, 17 genera and 114 species. The overall RM, MA and MI of chigger mites were 19.6% (416/2 118), 5.2 mites per examined rat and 26.5 mites per infested rat, respectively. The species richness, species composition and dominant species of chigger mites on R. flavipectus were not identical among the subregions. The RM (28.9%, 179/620), MA (10.6) and MI (36.6) of chigger mites in the mountainous subregion of southern Yunnan were the highest among the five subregions. There was a significantly linear positive correlation between the number of R. flavipectus and the species of chigger mites (r = 0.942, P < 0.05). The similarity of chigger mite communities between plateau subregion of western Yunnan and mountainous subregion of southern Yunnan was the highest, and the dominant species of chigger mites was Leptotrombidium deliense. The main dominant species of chigger mites in middle subregion and southern subregion of Hengduan Mountains, and eastern plateau subregion of Yunnan were Ascoschoengastia indica and Schoengastiella ligula.

CONCLUSION

The infestation of chigger mites on R. flavipectus is common with a high species diversity. The composition of chigger mite community in different geographical subregions is significantly different.

Abundances and host relationships of chigger mites in Yunnan Province, China

This paper reports on ectoparasitic chigger mites found on small mammals in Yunnan Province, southwest China. Data were accumulated from 19 investigation sites (counties) between 2001 and 2009. A total of 10 222 small mammal hosts were captured and identified; these represented 62 species, 34 genera and 11 families in five orders. From the body surfaces of these 10 222 hosts, a total of 92 990 chigger mites were collected and identified microscopically. These represented 224 species, 22 genera and three subfamilies in the family Trombiculidae (Trombidiformes). Small mammals were commonly found to be infested by chigger mites and most host species harboured several species of mite. The species diversity of chigger mites in Yunnan was much higher than diversities reported previously in other provinces of China and in other countries. A single species of rodent, Eothenomys miletus (Rodentia: Cricetidae), carried 111 species of chigger mite, thus demonstrating the highest species diversity and heaviest mite infestation of all recorded hosts. This diversity is exceptional compared with that of other ectoparasites. Of the total 224 mite species, 21 species accounted for 82.2% of all mites counted. Two species acting as major vectors for scrub typhus (tsutsugamushi disease), Leptotrombidium scutellare and Leptotrombidium deliense, were identified as the dominant mite species in this sample. In addition to these two major vectors, 12 potential or suspected vector species were found. Most species of chigger mite had a wide range of hosts and low host specificity. For example, L. scutellare parasitized 30 species of host. The low host specificity of chigger mites may increase their probability of encountering humans, as well as their transmission of scrub typhus among different hosts. Hierarchical clustering analysis showed that similarities between different chigger mite communities on the 18 main species of small mammal host did not accord with the taxonomic affinity of the hosts. This suggests that the distribution of chigger mites may be strongly influenced by the environment in which hosts live.

Repellency of cassia bark, eucalyptus, and star anise oils and their major constituents to Leptotrombidium pallidum (Acari: Trombiculidae)

Leptotrombidium pallidum (Nagoya, Miyagawa, Mitamura & Tamiya) is a primary vector of Orientia tsutsugamushi (Hyashi), the causative agent of scrub typhus. An assessment is made of the repellency to L. pallidum larvae (chiggers) of cassia bark, eucalyptus, and star anise oils and major constituents (E)-cinnamaldehyde, 1,8-cineole, and (E)-anethole of the corresponding oils. Results were compared with those of conventional repellents DEET (N,N-diethyl-3-methylbenzamide), IR3535 [(ethyl 3-[acetyl(butyl)amino]propanoate)], and permethrin. Based on the median repellent concentration (RC50) values, (E)-cinnamaldehyde, (E)-anethole, cassia bark oil, and star anise oil (RC50, 0.95-1.52 mg/cm2) exhibited significantly more potent repellency than DEET (3.85 mg/cm2). (E)-cinnamaldehyde, (E)-anethole, cassiabark oil, 1,8-cineole, and star anise oil were approximately 43, 16, 11, 8, and 4 times more effective than IR3535 (CC5, 6.51%) as judged by the median climbing distance-disturbing concentration (CC50) values. The median residual duration time of repellency (RT50) was significantly more pronounced in DEET (RT50, 323 min) than in all essential oils and constituents (108-167 min). In the light of global efforts to reduce the level of highly toxic synthetic repellents, the three essential oils and their major constituents described merit further study as potential biorepellents for the control of L. pallidum populations.

[Research on the area distribution and host selection of Leptotrombidium scutellare in 19 counties of Yunnan Province]

In order to investigate the area distribution and host selection of Leptotrombidium scutellare in Yunnan Province, a field survey was carried out during 2001 to 2009, based on different geographic location, topography, climate and ecological characteristics. A total of 16 491 L. scutellare were captured from the body surface of 9 838 small mammal hosts of 7 families, 18 genera, and 30 species in 4 orders, accounted for 17.73% (16,491/92,990) of all chigger mites collected. L. scutellare distributed in 12 counties, more in the northwest and south of the Province. Although L. scutellare could parasitize on different small mammal species, most of them were on Eothenomys miletus and Apodemus chevrieri.

[Possible evolutionary scenarios in the parasitengona mites (Acariformes: Parasitengona) based on anatomical peculiarities of their digestive system]

Five possible evolutionary scenarios of the higher acariform mites from the cohort Parasitengona are proposed on the basis of the detailed examination of anatomy of the excretory organ and midgut in the representatives of terrestrial mite families Trombiculidae and Microtrombidiidae, and in freshwater mite families Teutoniidae and Pionidae, on different developmental stages including parasitic larva. These scenarios explain possible ways of evolutionary transformation within the Parasitengona from one or several ancestor with the open digestive tract.

Stylostome formation in trombiculid mites (Acariformes: Trombiculidae)

Stylostomes of the trombiculid mite larvae Neotrombicula pomeranzevi (Schluger), Hirsutiella zachvatkini (Schluger), Miyatrombicula esoensis (Sasa and Ogata) and Euschoengastia rotundata (Schluger) (Acariformes: Trombiculidae), formed in the host skin during feeding of the parasites on their natural hosts (voles) were studied histologically and histochemically. A stylostome is a variously shaped tube formed of solidified mite saliva that extends from the mouthparts of the parasite through the epidermis into the dermis of the host, and allows the mite to obtain its liquid food. The first step of stylostome formation is deposition of an eosinophilic cone, to which the larva's chelicerae are glued. Organization of the stylostome depends on the mite species, and its walls may show weakly expressed longitudinal or transverse stratification. Histochemically, the stylostome is composed of complex glycoprotein with varying tinctorial properties through the width or the length of the stylostome's walls. Beneath the distal end of the stylostome, irrespectively of its localization either in the epidermis or in the dermis of the host, a feeding cavity is formed as a result of the action of the hydrolytic components of the mite's saliva forced through the stylostome into the wound. An inflammatory dermal reaction of moderate intensity is evolved during larval feeding and stylostome formation. It is manifested by the infiltration of the foci with neutrophiles, lymphocytes and macrophages and by dilation of capillaries of the terminal vessel bed and filling them by erythrocytes and other blood elements. Around the stylostome, necrosis of the epidermal cells occurs, leucocytes come to the damaged area and fuse with the necrotic epidermal cells, leading to the formation of the large scabs on the surface of the host's skin. In the case of E. rotundata, single capsules having a terminal opening and containing feeding larva are formed on the abdomen of the hosts. The walls of the capsules are composed of the mite's saliva flowing upon the surface of the host's skin. At the bottom of the capsule, a stylostome perforating the epidermis is also present.

[Study of chigger communities on major species of rodents in Yunnan Province]

OBJECTIVE

To understand the characteristics of the chigger communities on the major species of rodent hosts.

METHODS

Rats were captured in 16 counties (or towns) of Yunnan. All the mites on the two auricles of the host were collected and identified. Shannon-Weiner's indices (H,E), the richness indices and dominance indices were adopted to judge the diversity and community structure of chiggers on their hosts (7 species of rodents).

RESULTS

From the 7 species of dominant rodent hosts, 131 species of chiggers were identified, belonging to 17 genera of Trombiculidae. Among them, abundant individuals were collected from 6 species which were considered to be dominant chigger species. Shannon-Weiner's indices (H) of the chigger communities showed the following sequence: Rattus norvegicus>Apodemus chevrieri>Eothenomys miletus>Mus pahari>Rattus nitidus>Rattus flavipectus>Mus caroli, and the richness indices were similar to this tendency. The niche breadth of the 6 dominant chigger species showed the following tendency: Herpetacarus hastoclavus>Leptotrombidium scutellare>Leptotrombidium sinicum>Helenicula siena>Leptotrombidium hiemalis>Leptotrombidium eothenomydis. There was a wide niche overlap between any two chigger species with all indices beyond 0.76. Slight positive association existed between each two dominant species of chigger mites by the coefficient of association (V).

CONCLUSION

The community structure of chigger mites on the 7 major species of rodent hosts is complex, reflecting a high diversity of mite species. The niche breadth of the 6 dominant chigger species is different with a wide niche overlap.

Multiple environmental factor analysis in habitats of the harvest mite Neotrombicula autumnalis (Acari: Trombiculidae) suggests extraordinarily high euryoecious biology

The harvest mite Neotrombicula autumnalis (Trombiculidae) has become a great nuisance in various vegetated areas in Germany over the last 15 years. According to reports of dermatologists, this species appears to have propagated and spread significantly. Moreover, cases of severe trombidiosis or trombidiosis-like skin reactions have been noticed at unusually early times of the year. Due to the lack of scientific studies, little is known about the ecology of N. autumnalis and its distribution, and preferred habitats cannot be predicted. A four-year study was conducted to identify trombiculid foci in different areas of Bonn in order (1) to determine the timing of larvae appearance in different years, (2) to identify the factors that lead to high larvae abundances at the mite foci ('multiple factor analysis'), and (3) to develop an ecological control strategy. By means of the 'tile catch method' (TCM) which turned out to be most appropriate to collect data on the distribution and abundances of trombiculid mites, larvae of N. autumnalis were caught from mid July until the end of October/beginning of November. The distribution of the mites was patchy, supporting the hypothesis that certain factors cause a concentration in foci. Most of the mite foci had a fixed location for at least three years. Efforts to isolate nymphs and adults in larger quantities to gain knowledge about their preferred soil areas and soil depths failed. Only some nymphs of N. autumnalis could be found living 10-40 cm deep in the soil. Due to the restriction that the nymphs and adults can only rarely be isolated in the ground, the analysis of environmental factors was executed based on abundances of questing larvae on the soil surface. The detailed analysis of soil-physical, soil-chemical and meso-faunistic factors could not finally explain the unequal distribution of the mites, although the porosity of the soil had a statistically significant slight influence on the abundance of larvae, and soil pH bordered significance, also suggesting a slight influence. Furthermore, soil temperatures during the winter seasons in three subsequent years appeared too high to affect the harvest mite. The field experiments suggest that N. autumnalis and particularly its larval stages are extremely euryoecious (meaning tolerating very different environmental conditions). Further studies are necessary: additional investigations on the influence of certain abiotic environmental factors on N. autumnalis, the search for factors underlying the rhythmicity of its life cycle ('zeitgeber'), and the reasons and mechanisms for heterogeneous distribution of soil fauna in general. Ecological control of the mite is, in principle, possible but only after identifying the foci and ascertaining their approximate dimensions with the TCM. This control strategy is the most promising one, albeit very laborious, emphasising the need of further research on the ecology of the harvest mite.

[Geographical variation in the species Montivagum dihumerale and speciation in chigger mites (Acari: Trombiculidae)]

Intraspecific morphological variation of the chigger mite species Montivagum dihumerale (Traub et Nadchatram, 1967) is studied. Eco-geographic rules of the variation are revealed. General size of mites is found to be increased along with the rise of the high-mountain character of the landscape in the collection localities. The numbers of idiosomal setae are varied independently from the size parameters and geographically close populations are proved to be the most similar by these characters. At the same time, numbers of the setae of different types play the leading role in the discrimination of closely related Montivagum species, while the eco-geographical rules have not been found in this genus at the level of interspecific differences. As a result, the hypothesis is set up, that a significant degree of isolation of local populations separated from each other by high mountain ranges of the Central Asia is the main factor of speciation in the genus Montivagum. Regional character of this speciation mode is confirmed by the comparison with other chigger mites taxa.

Electron microscopic observations of Orientia tsutsugamushi in salivary gland cells of naturally Infected Leptotrombidium pallidum larvae during feeding

We performed a detailed electron microscopic observation on the escaping process of Orientia tsutsugamushi from the salivary gland cells of naturally infected trombiculid larvae into the acinar lumen of the gland during feeding on mice. In unfed larvae, many O. tsutsugamushi were intermingled with secretory granules in the cytoplasm of the salivary gland cell. O. tsutsugamushi was neither found in the acinar lumen nor observed escaping from the apical surface of the gland cell. In contrast, in the larvae fed on mice, many O. tsutsugamushi were observable in the acinar lumen. They were enveloped with the host glandular cell membrane. In salivary gland cells, secretory granules changed the distribution and accumulated in the apical region. In such cells, the majority of O. tsutsugamushi were found at the base of the cell. Some O. tsutsugamushi were pushing the glandular cell membrane outward in various degrees, showing different stages of escape. These findings suggest that larval feeding induced O. tsutsugamushi escape from salivary gland cells, that the escape was by budding, during which O. tsutsugamushi were enveloped in the host cell membrane, and that O. tsutsugamushi would be injected into the mouse skin as a mixture with mite saliva. The study also revealed the presence of many small vesicles that had the same cell wall structure as O. tsutsugamushi in the cytoplasm of the salivary gland cell. Most of them seemed to be products from degenerated Orientia.

Life cycle and parasitic interaction of the lizard-parasitizing mite Ophionyssus galloticolus (Acari: Gamasida: Macronyssidae), with remarks about the evolutionary consequences of parasitism in mites

Wild-caught specimens of the lacertid lizard Gallotia galloti eisentrauti from the Canary Island of Tenerife were checked for ectoparasites. The parasitic gamasid mite Ophionyssus galloticolus Fain and Bannert (2000) was very abundant on these lizards. Additionally, parasitism by larvae of two species of Trombiculidae (Prostigmata: Parasitengona) was observed. O. galloticolus was reared in the laboratory on its natural host in order to investigate its life cycle, reproductive biology, and development. The life history of O. galloticolus is documented in detail and compared to literature data of other Ophionyssus species. O. galloticolus was found to be similar to other species of the same genus with respect to the duration of development, the precopulatory association of protonymphs, and the arrhenotokous development of eggs. However, it seems to be more tolerant towards low relative humidity and longer starvation periods than other Ophionyssus species. Evolutionary transformations of the life-history pattern of this genus and other parasitic mites in comparison to its predatory precursors involve a reduction or partial suppression of ontogenetic instars in order to decrease mortality during host-seeking phases, and a compensating increase in growth capacity of the remaining feeding instars facilitated by replacement of sclerites through elastic cuticle or by growth of new cuticle unrelated to a moult (neosomy).

Transmission of Orientia tsutsugamushi, the aetiological agent for scrub typhus, to co-feeding mites

Experiments were conducted to investigate the potential for transmission of Orientia tsutsugamushi, the aetiological agent for scrub typhus, when naturally infected mite larvae were co-feeding with uninfected larvae. Larvae from colonies of Leptotrombidium deliense and L. imphalum infected with O. tsutsugamushi were used. Transmission of O. tsutsugamushi to previously uninfected L. deliense and Blankaartia acuscutellaris co-fed with infected L. deliense was shown to occur. The overall minimum rate of acquisition was 1.6% (4/258) for L. deliense and 2.5% (3/119) for B. acuscutellaris. When individual infected L. deliense were co-fed with B. acuscutellaris acquisition of O. tsutsugamushi was not detected. However, when 4 and 8 infected larvae were co-fed with B. acuscutellaris acquisition of O. tsutsugamushi was detected. Transmission of O. tsutsugamushi was not observed when uninfected L. deliense were co-fed with infected L. imphalum. This novel transmission route may explain the occurrence of rickettsiae in genera other than Leptotrombidium spp, which are considered to be the main vectors of O. tsutsugamushi.

Seasonal occurrence of Leptotrombidium deliense (Acari: Trombiculidae) attached to sentinel rodents in an orchard near Bangkok, Thailand

Leptotrombidium deliense Walch that attached to sentinel laboratory mice and the roof rat, Rattus rattus (L.), placed in an orchard habitat near Bangkok, Thailand, were studied between April 1993 and April 1995. A single L. deliense larva was attached to only 1 of 51 laboratory mice placed in the study area between April and September 1993. Overall, 89/202 (44.1%) R. rattus had 1 or more L. deliense larvae attached, and Orientia tsutsugamushi (Hayashi), the etiologic agent for scrub typhus, was isolated from liver/spleen samples of 2/202 (1.0%) rats placed in an endemic area for a single night. A total of 474 L. deliense attached to sentinel R. rattus, of which 314 larvae successfully fed to repletion and were recovered, and 2 (0.6%) of these were naturally infected with O. tsutsugamushi. The occurrence of L. deliense was influenced by rainfall, with more chiggers attached to rodents in the wetter months of the year. The study showed that the risk of exposure to infection with O. tsutsugamushi is greater during the wetter months of the year, and that only a relatively small number of chigger attachments are needed to infect potential hosts.

Trombiculid fauna and seasonal abundance of Leptotrombidium scutellare (Acari: Trombiculidae) in an endemic area of scrub typhus (Tsutsugamushi disease) in Yamakita Town, Kanagawa Prefecture, Japan

Using the Tullgren funnel method, we surveyed for trombiculid larvae around dwellings and in mandarin orange groves on the slopes of Sengenyama and Maruyama, Yamakita Town, Kanagawa Prefecture, Japan, during the period between 8 October 1992 and 8 January 1993. In total, 6,690 trombiculid larvae, consisting of 6,669 Leptotrombidium scutellare (Nagayo, Mitamura, Tamiya & Tenjin), 13 L. fuji Kuwata, Berge & Philip, two L. himizu (Sasa, Kumada, Hayashi, Enomoto, Fukuzumi & Obata), two Neotrombicula japonica (Tanaka, Kaiwa, Teramura & Kagaya), one Gahrliepia saduski Womersley, and three Walchia ogatai Sasa & Teramura, were taken from 240 soil samples (40 samples, six times at intervals of 2-4 wk). From the above species composition, L. scutellare is suspected to be the sole vector of scrub typhus in the survey area, where the disease is known to be caused by two serotypic strains of Rickettsia tsutsugamushi Ogata, Kawasaki and Kuroki. L. scutellare larvae rapidly increased in number in late October to form an acuminate peak of abundance in early November, followed by a gradual wane.

An ultrastructural study of vertical transmission of Rickettsia tsutsugamushi during oogenesis and spermatogenesis in Leptotrombidium pallidum

Rickettsia tsutsugamushi in Leptotromibidium pallidum was observed by electron microscopy and rickettsiae were found in the various tissues and organs of both larvae and adults. Budding of rickettsiae, a manner of release from the host cells, was observed only in the rudiments of the reproductive organs in larvae. Oogonia and maturing oocytes in adult females and eggs after oviposition contained the microorganisms. In adult males, rickettsiae were also found in the spermatogonia, spermatocytes, and spermatids in the early stage of spermatogenesis, but were eliminated from these cells during maturation. Only the maturing spermatids, but not the eliminated rickettsiae, migrated to another rickettsia-free area of the testis, resulting in the separation of spermatids from rickettsiae and in the production of rickettsia-free spermatophores. Based on these observations, the mechanism of vertical transmission of the rickettsiae to the progeny occurs only in the female parents. Most rickettsiae in the somatic cells of larvae and adults were coccoid, but some rickettsiae in the ovary and the testis of adult mites showed bacillary forms and were enveloped by a membrane of unknown origin.

Duration of attachment of the chigger, Eutrombicula lipovskyana (Trombiculidae) in mite pockets of Yarrow's spiny lizard, Sceloporus jarrovii (Phrynosomatidae) from Arizona

Duration of attachment was determined for the chigger, Eutrombicula lipovskyana in mite pockets of the phrynosomatid lizard, Sceloporus jarrovii from Arizona. Eutrombicula lipovskyana remained attached in mite pockets for as long as 52 days. Infestations in other body areas were of shorter duration. The mite Geckobiella texana was also found to infest S. jarrovii.

Distribution and seasonal and diurnal activity patterns of Eutrombicula alfreddugesi (Acari: Trombiculidae) in a forest edge ecosystem

Microclimatic and vegetative effects on the population size and activity patterns of larval Eutrombicula alfreddugesi Oudemans, 1910 (Acari: Trombiculidae), were investigated in Nebraska between latitude 40 degrees 0'0" N and 40 degrees 1'21" N. Larval population densities along a forest edge were greatest in areas of high relative humidity, moderate temperature, low incident sunlight, and increasing substrate vegetation. Although chigger populations existed throughout the forest edge, larger populations concentrated in short- to tall-grass transition zones. Chiggers were rarely found in the undergrowth beneath the tree canopy. Chigger activity correlated with a microclimatically driven diurnal rhythm. Activity was greatest during the late afternoon-early evening, between 1530 and 1930 hours (CDST). Larval activity dropped to low levels and remained so until sunrise; this period of reduced activity occurred between 1930 and 0530 hours. Small increases in larval activity occurred around sunrise (approximately 0600-0700 hours). Between about 0700 and 1530 hours, larval E. alfreddugesi were inactive and did not respond to normal sampling stimuli. Larval populations appeared in late April through early May, peaked in abundance in late June and early July, diminished through late summer, and disappeared in midautumn as the ground began to freeze.

Duration of attachment by mites and ticks on the iguanid lizards Sceloporus graciosus and Uta stansburiana

Duration of attachment was determined for the mites Neotrombicula californica and Geckobiella texana and the tick Ixodes pacificus on the iguanid lizards Sceloporus graciosus and Uta stansburiana from southern California. Neotrombicula californica infestations lasted approximately 1 wk. Attachment of Ixodes pacificus larvae and nymphs lasted approximately 8 days on S. graciosus and 16 days on U. stansburiana. Geckobiella texana remained attached to S. graciosus for 5 days and to U. stansburiana for 28 days.

Characterization of Rickettsia tsutsugamushi strains in two species of naturally infected, laboratory-reared chiggers

The strains of Rickettsia tsutsugamushi found in naturally infected, laboratory-reared Leptotrombidium (Leptotrombidium) arenicola and L. (L.) fletcheri chiggers were characterized by direct immunofluorescence (FA) and by mouse and monkey virulence tests. The strains existing in the L. (L.) arenicola chiggers consisted of different combinations of TA716, TA763, TA686, Karp, and Kato. In addition to these five strains, Gilliam was found in the L. (L.) fletcheri chiggers. Results indicate that individual chiggers can be simultaneously infected with several antigenic strains of R. tsutsugamushi. Although these antigens appear to remain stable within familial lines when several generations were viewed, the antigenic patterns observed in two succeeding generations did not always correlate. This variable expression of antigens was considered to be due to a quantitative fluctuation from one generation to the next in the strains of rickettsiae combined with a lack of sensitivity of the direct FA test in detecting small numbers of antigenically different rickettsiae. Phenotypic variation was considered to be a less probable explanation. Morbidity and mortality were minimal in ICR mice fed upon by individual chiggers of either species, but infection rates were 85-99%. Tissue suspensions prepared from mice infected by L. (L.) arenicola produced higher mortality and longer duration of illness in mice than those prepared from L. (L.) fletcheri-infected mice. Silvered leaf and cynomolgus monkeys were fed upon by the two species of chiggers or inoculated with the mouse tissue suspensions. In both cases, minimal clinical responses were observed.

[Harvest mite Neotrombicula autumnalis in the Leipzig area]

The paper describes an isolated population of the plague-causing harvest mite, Neotrombicula autumnalis autumnalis (Trombiculidae) in the Leipzig area. The focus has an area of about 20 km2 and extends from the eastern outskirts of the city to the built-up sections with a strong anthropogenic impact. It seems to have existed within these limits for at least five decades, with some variation in space and time. The surrounding area is free from Neotrombicula autumnalis, except for two unstable and temporary small populations 7 and 14 km away, respectively. The leipzig population of harvest mites does not prefer river courses, and it does not settle in valley plains with wet soils and woods nor does it prefer the margins of stagnant waters.

[Morphofunctional characteristics of the larval mouth apparatus of the chigger, Neotrombicula pomeranzevi (Trombiculidae)]

Gnathostoma of larvae of the chigger mite N. pomeranzevi is situated terminally on the trunk. The base of the gnathostoma is gnathocoxa represented by conglutinated coxae of pedipalps. Gnathocoxa narrows apically and passes into hypostome protruding up to the cheliceral blades. Lateral borders of the hypostome are bent dorsally thus forming a groove in which cheliceral blades are located. The cheliceral blades have a small groove in their internal surface. Larval chelicerea are free because their tactum is missing. Cheliceral apodemes which serve for the insertion of muscles, elevators of chelicerae, are jointed to the base of inner walls of basal cheliceral joints. Lateral gnathostoma bears five-jointed palps which have strong three-apical claws on tibia. Palps do not take part in the attachment of larvae to the host. The dorsal wall of gnathostoma is formed by the epistoma and caudal subcheliceral plate which further is branched into two cheliceral apodemes. Subcheliceral plate and apodemes serve as an attachment place of muscles, dilatators of the pharynx. The mouth opening is situated not far from the apical end of hypostome and goes into a large pharynx passing along the bottom of gnathosoma. On the whole, the mouth parts of larvae are adapted well for sucking liquid food.

Vectors of scrub typhus and their hosts on a mature oil palm estate

L. (L.) deliense was the predominant vector of scrub typhus in a mature oil palm estate, but a small number of L. (L.) fletcheri (0.1% from rodents) and L. (L.) vivericola (0.02% from rodents and 8.0% from black plates) was also collected. Although good correlation between L. (L.) deliense collected from rodents and from black plates was not established, either method may serve as a general indicator of population fluctuations over a period of time. For the most part, the vectors of scrub typhus were limited to litter piles, and thus, the possibility of contracting scrub typhus within this type of habitat was minimal.