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Dermacentor reticulatus is a hard tick species with extraordinary biological features. It has a high reproduction rate, a rapid developmental cycle, and is also able to overcome years of unfavourable conditions. Dermacentor reticulatus can survive under water for several months and is cold-hardy even compared to other tick species. It has a wide host range: over 60 different wild and domesticated hosts are known for the three active developmental stages. Its high adaptiveness gives an edge to this tick species as shown by new data on the emergence and establishment of D. reticulatus populations throughout Europe. The tick has been the research focus of a growing number of scientists, physicians and veterinarians. Within the Web of Science database, more than a fifth of the over 700 items published on this species between 1897 and 2015 appeared in the last three years (2013–2015). Here we attempt to synthesize current knowledge on the systematics, ecology, geographical distribution and recent spread of the species and to highlight the great spectrum of possible veterinary and public health threats it poses. Canine babesiosis caused by Babesia canis is a severe leading canine vector-borne disease in many endemic areas. Although less frequently than Ixodes ricinus , D. reticulatus adults bite humans and transmit several Rickettsia spp., Omsk haemorrhagic fever virus or Tick-borne encephalitis virus. We have not solely collected and reviewed the latest and fundamental scientific papers available in primary databases but also widened our scope to books, theses, conference papers and specialists colleagues’ experience where needed. Besides the dominant literature available in English, we also tried to access scientific literature in German, Russian and eastern European languages as well. We hope to inspire future research projects that are necessary to understand the basic life-cycle and ecology of this vector in order to understand and prevent disease threats. We conclude that although great strides have been made in our knowledge of the eco-epidemiology of this species, several gaps still need to be filled with basic research, targeting possible reservoir and vector roles and the key factors resulting in the observed geographical spread of D. reticulatus .

Ticks are of medical importance owing to their ability to transmit pathogens to humans and animals. The Rocky Mountain wood tick, Dermacentor andersoni , is a vector of a number of pathogens, including Anaplasma marginale, which is the most widespread tick-borne pathogen of livestock. Although ticks host pathogenic bacteria, they also harbor bacterial endosymbionts that have a role in tick physiology, survival, as well as pathogen acquisition and transmission. The goal of this study was to characterize the bacterial microbiome and examine the impact of microbiome disruption on pathogen susceptibility. The bacterial microbiome of two populations of D. andersoni with historically different susceptibilities to A. marginale was characterized. In this study, the microbiome was disrupted and then ticks were exposed to A. marginale or Francisella novicida to determine whether the microbiome correlated with pathogen susceptibility. Our study showed that an increase in proportion and quantity of Rickettsia bellii in the microbiome was negatively correlated to A. marginale levels in ticks. Furthermore, a decrease in Francisella endosymbionts was associated with lower F. novicida infection levels, demonstrating a positive pathogen–endosymbiont relationship. We demonstrate that endosymbionts and pathogens have varying interactions, and suggest that microbiome manipulation may provide a possible method for biocontrol by decreasing pathogen susceptibility of ticks.

Extracellular vesicles are thought to facilitate pathogen transmission from arthropods to humans and other animals. Here, we reveal that pathogen spreading from arthropods to the mammalian host is multifaceted. Extracellular vesicles from Ixodes scapularis enable tick feeding and promote infection of the mildly virulent rickettsial agent Anaplasma phagocytophilum through the SNARE proteins Vamp33 and Synaptobrevin 2 and dendritic epidermal T cells. However, extracellular vesicles from the tick Dermacentor andersoni mitigate microbial spreading caused by the lethal pathogen Francisella tularensis . Collectively, we establish that tick extracellular vesicles foster distinct outcomes of bacterial infection and assist in vector feeding by acting on skin immunity. Thus, the biology of arthropods should be taken into consideration when developing strategies to control vector-borne diseases. Extracellular vesicles have been implicated in the transmission of pathogens from the arthropod to the human host. Here the authors show that tick-derived extracellular vesicles play a role in feeding and modulate the outcome of bacterial infection.

We collected 1,671 Dermacentor reticulatus ticks from 17 locations in the Czech Republic, Slovakia, and Hungary. We found 47.9% overall prevalence of Rickettsia species in ticks over all locations. Sequence analysis confirmed that all tested samples belonged to R. raoultii, the causative agent of tick-borne lymphadenopathy.

Dermacentor reticulatus ticks are sporadically removed from human skin and therefore the medical consequences of their feeding are neglected compared to Ixodes ricinus. We investigated the prevalence of pathogens in D. reticulatus removed from human skin and possible clinical manifestations suggestive of tick-borne diseases after a tick bite. A total of 2153 ticks were studied and of these only 34 were D. reticulatus . The mean prevalence of Rickettsia in D. reticulatus was 50.0% and R. raoultii was identified in 82.4% of infected D. reticulatus ticks. We confirmed the first case of R. aeschlimannii infection in D. reticulatus ticks. Among participants bitten by D. reticulatus , 13.3% reported reddening around the tick bite site and flu-like symptoms, including lymphadenopathy and 3.3% reported eschar on the tick site bite. All of the participants with flu-like symptoms after tick removal were bitten by ticks infected with R. raoultii. The results of this study indicate that even though D. reticulatus ticks bite humans sporadically, pathogenic Rickettsia have a remarkably high prevalence in this tick species . We can expect that the incidence of tick-borne lymphadenopathy might increase with the reported expansion of the D. reticulatus into new areas and its growing abundance in Central Europe.

Background Occurrence of tick-borne diseases (TBD) is often seasonal and associated with seasonal activity of appropriate tick vectors. As seasonal activity of ticks differs, the risk of contracting particular TBD should change between and within seasons. It is of key importance to monitor seasonal dynamic of tick vectors, especially in human-associated habitats. The aim of the current study was to compare activity and density of Ixodes ricinus and Dermacentor reticulatus during spring season in urban and suburban habitats. Methods Systematic tick collection by dragging was performed every 1–2 weeks between mid-March and mid-June 2021 at 15 sites: 6 in Warsaw (urban areas) and 9 in suburban areas. Results During 178 field collections of ticks, including 131 collections from urban sites and 47 collections from rural areas, 738 ticks (385 adult D. reticulatus and 353 I. ricinus ) were collected. Dermacentor reticulatus ticks are found from the beginning of spring, peaking in April and May, and I. ricinus ticks are present from early April, peaking in April and May as well. I. ricinus were abundant in rural and urban areas, including botanical garden and forest kindergarten area. Dermacentor reticulatus were found in urban fallow lands but were not collected in parks. These ticks were abundant in fallow lands, meadow, and mixed forest. DNA of B. burgdorferi s.l. and Rickettsia spp. was identified in ticks from urban areas. Conclusions Due to the marked differences in spring dynamic of D. reticulatus and I. ricinus , the sampling effort should be repeated at least three times per season for accurate estimation of tick occurrence (presence/absence) and density. Due to “exchange” of tick species, total tick density remains high through the spring season of activity, which may result in high transmission of tick-borne pathogens (TBPs). Tick densities are dependent on the habitat type and may be low in well-managed agricultural habitats (crop fields, pastures, chicken yard), but high in semi-natural habitats (fallow lands, rural forests). Numerous I. ricinus populations can be maintained in urban green areas such as botanical gardens. Ticks from urban areas can serve as vectors of important TBPs ( B. burgdorferi s.l., Rickettsia spp.). Graphical Abstract

The aim of this study was to characterize the bacterial microbiome of hard ticks with affinity to bite humans in La Rioja (North of Spain). A total of 88 adult ticks (22 Rhipicephalus sanguineus sensu lato, 27 Haemaphysalis punctata, 30 Dermacentor marginatus and 9 Ixodes ricinus) and 120 I. ricinus nymphs (CRETAV collection, La Rioja, Spain), representing the main anthropophilic species in our environment, were subjected to a metagenomic analysis of the V3-V4 region of the 16S rRNA gene using an Illumina MiSeq platform. Data obtained with Greengenes database were refined with BLAST. Four groups of samples were defined, according to the four tick species. Proteobacteria was the predominant phylum observed in all groups. Gammaproteobacteria was the most abundant class, followed by Alphaproteobacteria for R. sanguineus, H. punctata and D. marginatus but the relative abundance of reads for these classes was reversed for I. ricinus. This tick species showed more than 46% reads corresponding to 'not assigned' OTUs (Greengenes), and >97% of them corresponded to 'Candidatus Midichloriaceae' using BLAST. Within Rickettsiales, 'Candidatus Midichloria', Rickettsia, Ehrlichia, 'Candidatus Neoehrlichia' and Wolbachia were detected. I. ricinus was the most alpha-diverse species. Regarding beta-diversity, I. ricinus and H. punctata samples grouped according to their tick species but microbial communities of some R. sanguineus and D. marginatus specimens clustered together. The metagenomics approach seems useful to discover the spectrum of tick-related bacteria. More studies are needed to identify and differentiate bacterial species, and to improve the knowledge of tick-borne diseases in Spain.

Hard ticks of the order Ixodidae serve as vectors for numerous human pathogens, including the causative agent of Lyme Disease Borrelia burgdorferi . Tick-associated microbes can influence pathogen colonization, offering the potential to inhibit disease transmission through engineering of the tick microbiota. Here, we investigate whether B. burgdorferi encounters abundant bacteria within the midgut of wild adult Ixodes scapularis , its primary vector. Through the use of controlled sequencing methods and confocal microscopy, we find that the majority of field-collected adult I. scapularis harbor limited internal microbial communities that are dominated by endosymbionts. A minority of I. scapularis ticks harbor abundant midgut bacteria and lack B. burgdorferi . We find that the lack of a stable resident midgut microbiota is not restricted to I. scapularis since extension of our studies to I. pacificus, Amblyomma maculatum , and Dermacentor spp showed similar patterns. Finally, bioinformatic examination of the B. burgdorferi genome revealed the absence of genes encoding known interbacterial interaction pathways, a feature unique to the Borrelia genus within the phylum Spirochaetes. Our results suggest that reduced selective pressure from limited microbial populations within ticks may have facilitated the evolutionary loss of genes encoding interbacterial competition pathways from Borrelia .

Background Free-living ungulates are hosts of ixodid ticks and reservoirs of tick-borne microorganisms in central Europe and many regions around the world. Tissue samples and engorged ticks were obtained from roe deer, red deer, fallow deer, mouflon, and wild boar hunted in deciduous forests of south-western Slovakia. DNA isolated from these samples was screened for the presence of tick-borne microorganisms by PCR-based methods. Results Ticks were found to infest all examined ungulate species. The principal infesting tick was Ixodes ricinus, identified on 90.4% of wildlife, and included all developmental stages. Larvae and nymphs of Haemaphysalis concinna were feeding on 9.6% of wildlife. Two specimens of Dermacentor reticulatus were also identified. Ungulates were positive for A. phagocytophilum and Theileria spp. Anaplasma phagocytophilum was found to infect 96.1% of cervids, 88.9% of mouflon, and 28.2% of wild boar, whereas Theileria spp. was detected only in cervids (94.6%). Importantly, a high rate of cervids (89%) showed mixed infections with both these microorganisms. In addition to A. phagocytophilum and Theileria spp., Rickettsia helvetica , R. monacensis , unidentified Rickettsia sp., Coxiella burnetii , “ Candidatus Neoehrlichia mikurensis”, Borrelia burgdorferi ( s . l .) and Babesia venatorum were identified in engorged I. ricinus . Furthermore, A. phagocytophilum , Babesia spp. and Theileria spp. were detected in engorged H. concinna. Analysis of 16S rRNA and groEL gene sequences revealed the presence of five and two A. phagocytophilum variants, respectively, among which sequences identified in wild boar showed identity to the sequence of the causative agent of human granulocytic anaplasmosis (HGA). Phylogenetic analysis of Theileria 18S rRNA gene sequences amplified from cervids and engorged I. ricinus ticks segregated jointly with sequences of T. capreoli isolates into a moderately supported monophyletic clade. Conclusions The findings indicate that free-living ungulates are reservoirs for A. phagocytophilum and Theileria spp. and engorged ixodid ticks attached to ungulates are good sentinels for the presence of agents of public and veterinary concern. Further analyses of the A. phagocytophilum genetic variants and Theileria species and their associations with vector ticks and free-living ungulates are required.

Background Ticks are important vectors for the transmission of pathogens, including viruses, bacteria, and protozoa. This study investigated the microbial communities and the dominant tick-borne bacteria carried by ticks collected from Wenquan County and Gurtu Town, northwestern Xinjiang Uygur Autonomous Region (XUAR), China. Methods More than 600 questing ticks were collected each from Gurtu and Wenquan by using the flagging method in 2020. Genomic DNA was extracted from 100 ticks randomly selected from each collection site. High-throughput sequencing of the 16S rDNA V3-V4 region was performed to analyze the composition of the microbial communities. Subsequently, species-specific polymerase chain reaction (PCR) was conducted to confirm the presence of pathogenic bacteria. Results The ticks collected from Wenquan and Gurtu were identified as Dermacentor marginatus and Hyalomma asiaticum , respectively. High-throughput sequencing of the 16S rDNA V3-V4 region identified Acinetobacter , Rickettsia and Coxiella as the three genera with the highest relative abundance in D. marginatus , while Francisella was the most abundant genus in H. asiaticum. PCR detected the presence of spotted fever group rickettsiae (SFGR) (55/100), Borrelia burgdorferi (6/100), and B. miyamotoi (4/100) in D. marginatus , as well as B. miyamotoi (1/100) in H. asiaticum. Phylogenetic analysis revealed that SFGR were genotyped as Rickettsia raoultii (36/55) and R. sibirica (19/55). Borrelia burgdorferi was clustered with B. bavariensis (2/6), B. afzelii (2/6), and B. yangtzensis (2/6). Co-infections of B. burgdorferi and SFGR (3/100) as well as B. miyamotoi and SFGR (3/100) were detected in D. marginatus . Conclusions The present study demonstrated that SFGR were the dominant tick-borne bacteria in D. marginatus collected from Wenquan. Particularly, this study reported for the first time the presence of B. bavariensis , B. yangtzensis , and B. miyamotoi in D. marginatus in China. Extensive and comprehensive investigations into the prevalence of tick-borne pathogens in ticks, host animals, and local populations in XUAR should be conducted.