Dermacentor reticulatus - a tick on its way from glacial refugia to a panmictic Eurasian population.

The ornate dog tick (Dermacentor reticulatus) shows a recently expanding geographic distribution. Knowledge on its intraspecific variability, population structure, rate of genetic diversity and divergence, including its evolution and geographic distribution, is crucial to understand its dispersal capacity. All such information would help to evaluate the potential risk of future spread of associated pathogens of medical and veterinary concern. A set of 865 D. reticulatus ticks was collected from 65 localities across 21 countries, from Portugal in the west to Kazakhstan and southern Russia in the east. Cluster analyses of 16 microsatellite loci were combined with nuclear (ITS2, 18S) and mitochondrial (12S, 16S, COI) sequence data to uncover the ticks' population structures and geographical patterns. Approximate Bayesian computation was applied to model evolutionary relationships among the found clusters. Low variability and a weak phylogenetic signal showing an east-west cline were detected both for mitochondrial and nuclear sequence markers. Microsatellite analyses revealed three genetic clusters, where the eastern and western cluster gradient was supplemented by a third, northern cluster. Alternative scenarios could explain such a tripartite population structure by independent formation of clusters in separate refugia, limited gene flow connected with isolation by distance causing a "bipolar pattern", and the northern cluster deriving from admixture between the eastern and western populations. The best supported demographic scenario of this tick species indicates that the northern cluster derived from admixture between the eastern and western populations 441 (median) to 224 (mode) generations ago, suggesting a possible link with the end of the Little Ice Age in Europe.

The Microbiota of Ixodes ricinus and Dermacentor reticulatus Ticks Collected from a Highly Populated City of Eastern Europe.

Recent investigations have examined, through sequencing the V6 region of 16S rRNA gene, the microbiota of questing Ixodes ricinus and Dermacentor reticulatus ticks collected from rural areas of Central (Dnipropetrovs'k (region D) and Poltava (region P)) and Northeastern (Kharkiv (region K)) Ukraine. In addition to defining the bacterial microbiota of both tick species, the previous investigations also revealed a high degree of inter-sex and inter-regional variations in the tick microbiota. As a continuation of the two studies, the present investigation has analyzed individual microbiota of questing I. ricinus (n = 50) and D. reticulatus (n = 50) ticks originating from Kyiv, the largest city of Ukraine. The Kyiv tick microbiota were compared between males and females for each tick species. Additionally, a cross-regional analysis was performed to compare the microbiota of Kyiv ticks to those from regions D, K, and P. Numerous statistically significant inter-sex and inter-regional variations were detected when alpha diversity, beta diversity, the bacterial relative and differential abundances were assessed. The overall results demonstrated that the microbiota of Kyiv ticks were statistically different compared to the ticks of the other three regions. Besides existing climatic and geographical differences between the four regions, the authors hypothesize that various anthropogenic factors of the megapolis (e.g., animal species translocation, land management, ecology) could have contributed to the distinct microbiota of Kyiv ticks observed in this study.

Extensive sex-specific and regional variations observed in the microbiome of Dermacentor reticulatus.

Recent progress in DNA sequencing technologies and advanced bioinformatic tools have enabled researchers to rapidly decipher the tick microbiome. To date, however, a number of microbiome studies performed on Dermacentor reticulatus ticks is still quite limited. Despite the importance of this ixodid tick for veterinary and human medicine, only two investigations have examined its microbiome. Moreover, these studies analyzed only a limited number of ticks/tick pools. Given the scarcity of microbiome data for D. reticulatus in general and the lack of microbiome studies on tick species from Eastern Europe in particular, the objective of the current investigation was to analyze the microbiome of D. reticulatus ticks collected from three geographical regions of Ukraine. A total of 88 individual tick microbiomes were analyzed by sequencing the V6 region of 16S rRNA. As a result, numerous significant differences in the bacterial relative abundance were detected between males and females of D. reticulatus for each region. The alpha diversity measures indicate that microbiomes were significantly different between females of D. reticulatus inter-regionally. In contrast, the collective results for male ticks are more suggestive of inter-regional microbiome homogeneity. The overall findings indicate that the composition and diversity of the D. reticulatus microbiome can be impacted by geographical and sex-related factors.

Metagenomic analysis of individually analyzed ticks from Eastern Europe demonstrates regional and sex-dependent differences in the microbiota of Ixodes ricinus.

Understanding the microbial ecology of disease vectors may be useful for development of novel strategies aimed at preventing transmission of vector-borne pathogens. Although Ixodes ricinus is one of the most important tick vectors, the microbiota of this tick has been examined for only limited parts of the globe. To date, the microbiota of I. ricinus ticks collected from Eastern Europe has not been defined. The objective of this study was to compare microbiota of I. ricinus ticks within (males vs. females) and between collection sites that represented three administrative regions of Ukraine, Dnipropetrovs'k (D), Kharkiv (K), and Poltava (P). A total of 89 questing I. ricinus adults were collected from region D (number of ticks, n = 29; 14 males and 15 females), region K (n = 30; 15 males and 15 females) and region P (n = 30; 15 males and 15 females). Each tick was subjected to metagenomic analysis by targeting the V6 region of 16S rRNA gene through the Illumina 4000 Hiseq sequencing. The alpha diversity analysis demonstrated that, regardless of tick sex, patterns of bacterial diversity in ticks from regions K and P were similar, whereas the microbiota of region D ticks was quite distinct. A number of inter-regional differences were detected by most beta diversity metrics for both males and females. The inter-regional variations were also supported by the principal coordinate analysis based on the unweighted UniFrac metrics with three region-specific clusters of female ticks and one distinct cluster of region D males. Lastly, numerous region- and sex-specific differences were also identified in the relative abundance of various bacterial taxa. Collectively, the present findings demonstrate that the microbiota of the I. ricinus tick can exhibit a high degree of variation between tick sexes and geographical regions.

Borrelia and Other Zoonotic Pathogens in Ixodes ricinus and Dermacentor reticulatus Ticks Collected from the Chernobyl Exclusion Zone on the 30th Anniversary of the Nuclear Disaster.

Background: The 26th of April 2016 marked 30 years since the Chernobyl accident has occurred in Ukraine. As a result, the uninhabited Chernobyl region has been directly exposed to ionizing radiation for >30 years. Most work has focused on identifying associations between levels of radiation and the abundance, distribution, and mutation rates of plants and animals. Much less, however, is known about microbial communities in this affected region. To date, there are no reports on the prevalence of any tick-borne pathogens in Ixodes ricinus ticks from the Chernobyl exclusion zone (CEZ). The objective of our study was to examine the abundance of I. ricinus and Dermacentor reticulatus ticks in the CEZ and to investigate the prevalence of Borrelia burgdorferi sensu lato (s.l.) and other zoonotic agents in these ixodid ticks. Methods: A total of 260 questing I. ricinus and 100 D. reticulatus adult ticks were individually polymerase chain reaction analyzed for the presence of Anaplasma phagocytophilum, Babesia spp., Bartonella spp., Borrelia burgdorferi s.l., Francisella tularensis, and/or Rickettsia spp. Results: The respective infections rates were identified and compared with those of ixodid ticks that were concurrently collected from Kyiv. The significant differences between the infection rates of the CEZ and Kyiv ticks were observed for Rickettsia raoultii in D. reticulatus ticks (53.0% vs. 35.7%, respectively; p < 0.05) and Bartonella spp. (8.1% vs. 2.7%; P < 0.05) in I. ricinus ticks. Conclusions: Although the current data clearly demonstrated that the prevalence of some zoonotic pathogens were significantly higher in the ixodid ticks from the CEZ, a more comprehensive systematic approach is required to examine the causal effect of long-term ionizing radiation on adaptive changes of tick-borne pathogens.

Diversity of Borrelia spirochetes and other zoonotic agents in ticks from Kyiv, Ukraine.

Lyme borreliosis (LB) is caused by tick-borne spirochetes of the Borrelia burgdorferi sensu lato complex. LB is the most prevalent vector-borne illness in Ukraine, but current data on the prevalence of LB pathogens in their tick vector, Ixodes ricinus, are lacking. I. ricinus ticks may also carry Borrelia miyamotoi, an emerging relapsing fever group spirochete that has been implicated in human illness. Despite its zoonotic potential, the prevalence of B. miyamotoi in ticks has not been examined in Ukraine. Similarly, data on the prevalence of other important tick-borne pathogens, Anaplasma phagocytophilum, Babesia spp., Bartonella spp., Francisella tularensis, and Rickettsia spp., in ixodid ticks are scarce or even absent. Thus, the overall objective of this study was to investigate the prevalence of these tick-borne pathogens in questing I. ricinus and Dermacentor reticulatus ticks collected in recreational parks of Kyiv, the most densely populated city of Ukraine. A total of 182 adult I. ricinus, 98 nymphal I. ricinus, and 98 adult D. reticulatus ticks were molecularly analyzed for the presence of these pathogens. As a result, the study shows a greater diversity of Borrelia genospecies in questing I. ricinus ticks than previously reported. The most prevalent genospecies in adult I. ricinus ticks were B. afzelii (7.7%), followed by B. burgdorferi sensu stricto (s.s.) (2.2%) and B. garinii (0.5%). In contrast, B. burgdorferi s.s. was most dominant in unfed I. ricinus nymphs (67.3%). Moreover, B. afzelii was detected in 11.2% of nymphs, but only 1.0% of nymphal ticks were positive for B. garinii and B. valaisiana. Importantly, this study provides the first record of B. miyamotoi detected in I. ricinus ticks from Ukraine (1.1%). Furthermore, the report is also the first to document other vector-borne pathogens, Bartonella henselae, Rickettsia conorii, and Rickettsia mendelii, in ixodid ticks from Ukraine. In summary, this work offers the latest data on the diversity and prevalence of the important zoonotic tick-borne agents in questing ticks from Kyiv, Ukraine. The data will help to better gauge the risk associated with vector-borne infections to which residents and guests of Ukraine's capital may be exposed.

Ixodid ticks in the megapolis of Kyiv, Ukraine.

The Ixodidae include the most common tick species encountered in Europe. The ticks transmit a variety of bacterial and protozoan agents of medical and veterinary significance. The aim of the current work was to investigate distribution of Ixodes ricinus and Dermacentor reticulatus ticks in Kyiv, the largest and most densely populated megapolis of Ukraine. Ticks were collected at various recreational areas by flagging during May, the month that showed the highest tick abundance in the past. Sex distribution among I. ricinus ticks was relatively equal, whereas females were collected in higher numbers for D. reticulatus. As opposed to western and central Europe where nymphal ticks had been more abundant, the nymph:adult ratio for I. ricinus was reversed. Also, this report documents detection of Rhipicephalus sanguineus sensu lato (s.l.) in Kyiv region, well outside of its historically documented distribution area. Previously thought to be restricted to the southern Ukraine, a single male specimen of R. sanguineus s.l. was collected just outside the city limits. Data on tick diversity over the past 30 years, however, indicates that this finding may only be incidental.