Orientia tsutsugamushi dynamics in vectors and hosts: ecology and risk factors for foci of scrub typhus transmission in northern Thailand.

BACKGROUND: Scrub typhus is an important neglected vector-borne zoonotic disease across the Asia-Pacific region, with an expanding known distribution. The disease ecology is poorly understood, despite the large global burden of disease. The key determinants of high-risk areas of transmission to humans are unknown. METHODS: Small mammals and chiggers were collected over an 18-month period at three sites of differing ecological profiles with high scrub typhus transmission in Chiang Rai Province, northern Thailand. Field samples were identified and tested for Orientia tsutsugamushi by real-time PCR. The rates and dynamics of infection were recorded, and positive and negative individuals were mapped over time at the scale of single villages. Ecological analyses were performed to describe the species richness, community structure and interactions between infected and uninfected species and habitats. Generalised linear modelling (GLM) was applied to examine these interactions. RESULTS: The site with the highest rates of human infection was associated with the highest number of infected chigger pools (41%), individual chiggers (16%), proportion of the known vector species Leptotrombidium deliense (71%) and chigger index (151). Chigger species diversity was lowest (Shannon diversity index H': 1.77) and rodent density appeared to be high. There were no consistent discrete foci of infection identified at any of the study sites. The small mammals Rattus tanezumi and Bandicota indica and the chiggers L. deliense and Walchia kritochaeta emerged as central nodes in the network analysis. In the GLM, the end of the dry season, and to a lesser extent the end of the wet season, was associated with O. tsutsugamushi-infected small mammals and chiggers. A clear positive association was seen between O. tsutsugamushi-positive chigger pools and the combination of O. tsutsugamushi-positive chigger pools and O. tsutsugamushi-positive small mammals with lowland habitats. CONCLUSIONS: These findings begin to reveal some of the factors that may determine high-risk foci of scrub typhus at a fine local scale. Understanding these factors may allow practical public health interventions to reduce disease risk. Further studies are needed in areas with diverse ecology.

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.

Host Diversity Affects Parasite Diversity: A Case Study Involving Unionicola spp. Inhabiting Freshwater Mussels.

Water mites of the genus Unionicola are common parasites of freshwater mussels, living on the gills or mantle of their hosts and using these tissues as sites of oviposition. Although surveys of this mite fauna among North American unionid mussels indicate that these mites represent highly diverse assemblages, we know very little regarding the determinants of Unionicola species diversity among their molluscan hosts. The present study addresses the relationship between host diversity and mite diversity for Unionicola assemblages associated with unionid mussels of North America. The results of this study found a significantly positive relationship between host species richness and mite species richness, adding to a growing body of evidence that host diversity is an important determinant of parasite diversity. In recent years, molecular sequence data have discovered cryptic biodiversity among unionid mussels, yielding revisions in the nomenclature and systematic taxonomy of the group. DNA sequence variation has also revealed cryptic species complexes among Unionicola mites. Collectively, these findings suggest that the results of the present study may be underestimating species richness among mites and their host mussels. Unfortunately, human perturbations are known to have caused high recent rates of extinction in the mussel and mite faunas of North America and could play a major role in influencing patterns of species richness for this host-parasite system moving forward.

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.

A new species of Schoutedenichia Jadin & Vercammen-Grandjean, 1954 from Madagascar and a re-description of S. dutoiti (Radford, 1948) from South Africa (Acariformes: Trombiculidae).

A new chigger mite species, Schoutedenichia microcebi n. sp. is described from the grey mouse lemur Microcebus murinus (J.F. Miller) from Madagascar. The new species is closely related to S. dutoiti (Radford, 1948), a species described from a single specimen collected on a rodent in South Africa. Examination of the holotype and new material on S. dutoiti from South Africa enabled us to re-describe this species and provide new data on its hosts and geographical distribution.

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.

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.

The chiggers (Acari: Trombiculidae) on wild birds in Honduras.

The chiggers (Acari: Trombiculidae) Blankaartia sinnamaryi (Floch et Fauran, 1956), Parasecia soucouyanti (Brennan et Yunker, 1966), Eutrombicula lipovskyana (Wolfenbarger, 1952) and Neoschoengastia dalmati Brennan, 1951 were found in Honduras on a total of twelve bird species. Parasecia soucouyanti was recorded parasitising birds for the first time. All these mites are here reported from Honduras for the first time.

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 ß 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).

Combination of carvacrol and thymol against the poultry red mite (Dermanyssus gallinae).

Pest management by conventional pesticides has become progressively hindered by developing pest resistance and increase in consumers demand for safe and residue-free foodstuffs. This will create a considerable market opportunity for alternative products, including botanical pesticides. The present study was conducted to assess the combination of carvacrol and thymol, their repellent activity, and residual toxicity against Dermanyssus gallinae with the aim of designing a new strategy relying on natural compounds for the control of D. gallinae. Different ratios of carvacrol-thymol, 5:0, 4:1, 3:2, 2:3, 1:4, and 0:5 based on LD50 values, were tested for their toxicity on D. gallinae. For residual toxicity assay, mortality rate of mites recorded after being exposed to the surfaces 1, 3, 7, 14, 21, and 28 days post spraying by carvacrol-thymol preparation. In combination toxicity, carvacrol-thymol in 4:1 ratio showed the highest efficacy against D. gallinae. The highest repellent activity was observed in carvacrol-thymol 5:0 combination. Addition of thymol to carvacrol resulted in a decrease in repellent activity of carvacrol as was seen in carvacrol-thymol 3:2, 2:3, and 1:4 ratios (p < 0.05). Carvacrol-thymol in 4:1 ratio at 2 % concentration displayed good residual toxicity and was effective against D. gallinae till 14 days post spraying (p < 0.05). The present study showed that the combination of carvacrol-thymol particularly with a 4:1 ratio displayed improved acaricidal activity and good residual toxicity. However, combining the application of carvacrol and thymol did not show any synergistic effect on repellent activity. Overall, carvacrol-thymol can be suggested as an alternative strategy for the control of D. gallinae.

A new genus and species of chigger mite (Trombidiformes: Trombiculidae) from Loxodontomys pikumche (Rodentia: Cricetidae) in Chile.

The family Trombiculidae is one of the most diverse and cosmopolitan (Walter et al. 2009). In Chile, the family Trombiculidae is represented by six genera associated with reptiles: Eutrombicula Ewing; Microtrombicula Ewing; Paratrombicula Goff & Whitaker; Whartonacarus (Brennan & Jones); Diaguitacarus Stekolnikov & González-Acuña and Proschoengastia Vercammen-Grandjean and two genera associated with rodents Chilacarus Webb, Bennett & Loomis and Poliremotus Brennan & Goff (Stekolnikov & González-Acuña 2015).

Impeding movement of the poultry red mite, Dermanyssus gallinae.

The poultry red mite, Dermanyssus gallinae, is an economically important hematophagous parasite of commercial egg laying hens, also affecting domesticated birds and companion animals. Conventional control of D. gallinae through acaricidal spraying is often ineffective, creating an urgent need to identify alternative management strategies for commercial and domestic infestations. Whilst integrated pest management is being considered for D. gallinae, the potential of impeding mite 'migration' routes, to either prevent initial infestation or manage established populations, has not been researched. Here we demonstrate that barriers of insecticidal glue, double sided sticky tape and thyme oil can contain D. gallinae within a specified area of a petri dish (78-88% of total mite population) and this level of containment was significantly greater than for negative controls (p values <0.05). Further studies in poultry houses are recommended to investigate the efficacy of these barriers in real world application and identity potential for barriers as a strategy for mite control.

[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.

An updated distribution and hosts: trombiculid mites (Acari: Trombidiformes) associated with small mammals in Yunnan Province, southwest China.

Trombiculid mites (or chigger mites) are a large group of arthropods, and some of these species are vectors of Orientia tsutsugamushi, the causative agent of tsutsugamushi disease (scrub typhus). Yunnan Province is situated in the southwest of China, and its complicated topography, special altitude gradients, and high biodiversity have aroused the interest of many scientists to study the fauna and species diversity of plants and animals. To replenish our former faunal study, this paper listed all the scientific names of trombiculid mites in Yunnan Province, together with their hosts and collection sites (geographical distribution). A total of 120,138 individuals of trombiculid mites were collected from the body surface of 13,760 small mammal hosts (89.06 % of them are rodents) in 29 collection sites (counties) of Yunnan Province from 2001 to 2013. The 120,138 mites were identified as comprising 2 families (Trombiculidae and Leeuwenhoekiidae), 26 genera, and 274 species. The genus Leptotrombidium had the most abundant species (109 species) of 26 genera. Of the six main vectors of scrub typhus in China, five of them were found in Yunnan. Of the 274 chigger mite species, 23 were determined as the newly recorded species (new records), which were found in Yunnan Province for the first time. The identified 274 species of trombiculid mites in the present paper are much more than those from other provinces in China and even largely exceeded the species of trombiculid mites recorded from some other regions and countries in the world. Based on the formula of Chao 1, the total number of chigger mite species in Yunnan was approximately estimated to be 346 species, and about 72 species might have been missed in our sampling process.

Host-parasite association in trombiculid mites (Actinotrichida: Trombiculidae) of temperate zone - the case of Hirsutiella zachvatkini (Schluger, 1948); are we dealing with prolonged contact with the host?

BACKGROUND: The time-extended contact of trombiculid larvae with hosts poses a question of its ecological determinants. The phenomenon, which may facilitate the overwintering of larvae in the temperate zone, was previously observed in few parasitengone taxa, but not confirmed for mammal-associated trombiculids. The study aims at tracing the phenology of larvae of Hirsutiella zachvatkini and at verifying the hypothesis of contact with the host, extending beyond the parasitic phase. METHODS: Apodemus agrarius, Apodemus flavicollis and Myodes glareolus, trapped during 2-year studies, were checked for the presence of trombiculid larvae. Larvae of H. zachvatkini served for the studies. The degree of mites' engorgement was checked over time in order to estimate the duration of feeding phase and to measure the maximum size increase. The experimental rearing aimed at ascertaining the relations between the level of engorgement and successful transformation of larva into subsequent instar. RESULTS: The mass appearance of larvae on hosts fell on autumn and winter, with a decrease observed in spring, leading to an almost total absence in early and mid summer. The highest intensity, attained in late autumn or in winter, was not followed by further increase in the number of host-associated larvae. The percentage of unengorged larvae on hosts was disproportionately small, irrespective of the season. The size increase of larva was 12.6-fold at maximum. Engorged or partly engorged larvae, observed from the beginning of mass appearance over the entire period of host-parasite association in the field, transformed into subsequent instar when removed from host. CONCLUSIONS: An increase in intensity observed from the onset of appearance of larvae on hosts, through autumn and winter months, at rarity of observations of unengorged larvae and absence of engorged larvae off-host, indicates a prolonged contact with hosts, aimed at synchronisation of life cycle, conditioned by food resources available for active postlarval forms and constitutes a strategy enabling larvae to survive the unfavourable winter conditions. The proportion of engorged and partly engorged vs. unfed larvae, observed over the survey, along with their ability to transform into subsequent instars, indicates a relatively short feeding phase. The lack of continuous increase in abundance and intensity towards spring and summer suggests a gradual detachment of partly and fully engorged larvae which attained the readiness to subsequent development. The size increase of larvae during their parasitic phase does not corroborate the neosomy in H. zachvatkini. Host-associated differences in topic preferences of the chiggers become less obvious at maximum infection rates. Quantitative descriptors of parasite population place M. glareolus among the most infected hosts of H. zachvatkini in contrast to Apodemus mice collected in the same habitat.