Seasonal Activity of Adult Ticks Ixodes persulcatus (Acari, Ixodidae) in the North-West of the Distribution Area.

The taiga tick Ixodes persulcatus (Schulze, 1930) (Acari, Ixodidae) is the main vector of the tick-borne encephalitis virus and one of the most widespread species of ixodid ticks in the Palaearctic. In this paper, we present long-term data on the seasonal activity of adult ticks in the north-west of their distribution. The seasonal activity of Ixodes persulcatus was studied from 1982 to 1990 and from 2012 to 2023 in the middle taiga subzone of Karelia (N62.0697, E33.961). In the study area, adult ticks I. persulcatus demonstrate a pronounced spring-summer activity with a unimodal curve of abundance change. A comparison of the monitoring data from the 1980s and the 2010s showed a significant increase in the abundance of I. persulcatus in the study area. A tendency towards an earlier start of the tick activity, as compared to the 1980s, is now being observed.

Differentiation of Laboratory-Obtained Ixodes ricinus × Ixodes persulcatus Hybrid Ticks: Selection of Suitable Genes.

Ixodes ricinus and Ixodes persulcatus ticks are the main vectors of tick-borne encephalitis virus and some bacterial pathogens. The regions where these tick species live overlap, forming large sympatric areas. It has previously been shown that these tick species have no morphological barrier, and interspecies crossing is possible with the appearance of sterile hybrids. It has also been shown that hybrid larvae and nymphs can be differentiated using discriminant functions based on a set of morphological features. However, such an approach is laborious and rather ineffective with adult ticks, making a molecular approach necessary. In the current work, we tested the ability of different systems to differentiate laboratory-obtained hybrid ticks. Our data suggest that commonly used primer sets that target rRNA are unsuitable for hybrid tick determination, likely due to the rRNA region being linked with the X chromosome in I. ricinus and I. persulcatus ticks. We tested several primer sets targeting different non rRNA genes to assess their ability to determine hybrids. The best primer set, Toll_R, targeting the putative Toll gene, showed little to no bias when used for DNA amplification from hybrid ticks. Thus, Toll gene can be further used for hybrid detection.

Mark-release-recapture of ticks: A case study of estimating the abundance of Ixodes persulcatus (Acari, Ixodidae).

In this study, we tested the applicability of three common methods of absolute abundance estimation-Peterson, Bailey and Jolly-Seber-to Ixodes persulcatus ticks based on mark-release-recapture data. The ticks were collected by flagging during the seasonal activity peak of the ticks in the mid-taiga zone of Karelia (62.0697°N, 33.9614°E). In total, 108 females and 92 males of I. persulcatus were marked. The marked individuals were captured 161 times before the end of the study period with their proportion in the samples reaching 50%. Females were recaptured more often than males, 105 versus 56 times. Estimates of adult tick abundance ranged from 0.4 to 2 specimens per m2 depending on the calculation method. The obtained estimates of absolute abundance varied unpredictably depending on the length of the intervals between capture sessions and showed no significant correlations with the number of ticks collected by flagging. The choice of the method of tick abundance estimation mainly depends on the study aims. The Petersen method may be useful for quick estimates of local tick abundance, whereas the Jolly-Seber method allows an estimation of the absolute abundance during the entire period of the tick activity. Individual marking of ticks may improve the accuracy of the estimates.

Geographical and Tick-Dependent Distribution of Flavi-Like Alongshan and Yanggou Tick Viruses in Russia.

The genus Flavivirus includes related, unclassified segmented flavi-like viruses, two segments of which have homology with flavivirus RNA-dependent RNA polymerase NS5 and RNA helicase-protease NS3. This group includes such viruses as Jingmen tick virus, Alongshan virus, Yanggou tick virus and others. We detected the Yanggou tick virus in Dermacentor nuttalli and Dermacentor marginatus ticks in two neighbouring regions of Russia. The virus prevalence ranged from 0.5% to 8.0%. We detected RNA of the Alongshan virus in 44 individuals or pools of various tick species in eight regions of Russia. The virus prevalence ranged from 0.6% to 7.8%. We demonstrated the successful replication of the Yanggou tick virus and Alongshan virus in IRE/CTVM19 and HAE/CTVM8 tick cell lines without a cytopathic effect. According to the phylogenetic analysis, we divided the Alongshan virus into two groups: an Ixodes persulcatus group and an Ixodes ricinus group. In addition, the I. persulcatus group can be divided into European and Asian subgroups. We found amino acid signatures specific to the I. ricinus and I. persulcatus groups and also distinguished between the European and Asian subgroups of the I. persulcatus group.

Baltic Group Tick-Borne Encephalitis Virus Phylogeography: Systemic Inconsistency Pattern between Genetic and Geographic Distances.

Tick-Borne Encephalitis Virus (TBEV) is a dangerous arbovirus widely distributed in Northern Eurasia. The area of this pathogen changes over time. At the beginning of the 2000s, the Ixodes tick populations in Karelia increased. At the same time, the area of I. persulcatus, the main vector of the Siberian TBEV subtype, also expanded. Herein, we sequenced 10 viruses isolated from ticks collected in three locations from the Karelia region in 2008-2018. PCR positive samples were passaged in suckling mice or pig embryo kidney cells (PEK). After the second passage in suckling, mice viral RNA was isolated and E-gene fragment was sequenced. Viral sequences were expected to be similar or nearly identical. Instead, there was up to a 4.8% difference in nucleotide sequence, comparable with the most diverse viruses belonging to the Baltic subgroup in Siberian TBEV subtype (Baltic TBEV-Sib). To reveal whether this was systemic or incidental, a comprehensive phylogeographical analysis was conducted. Interestingly, viruses within each geographic region demonstrated comparable diversity to the whole Baltic TBEV-Sib. Moreover, Baltic TBEV-Sib has a distribution area limited by three ecological regions. This means that active virus mixing occurs in the vast geographic area forming one common virus pool. The most plausible explanation is the involvement of flying animals in the TBEV spread.

Phlebovirus sequences detected in ticks collected in Russia: Novel phleboviruses, distinguishing criteria and high tick specificity.

Phlebovirus is an abundant and rather heterogeneous genus within the Phenuiviridae family (order Bunyavirales). The genus Phlebovirus is divided into two antigenic complexes, which also correspond to the main vector: sandflies/mosquitoes and ticks. Previously, only sandfly/mosquito-borne phleboviruses were associated with human disease, such as Rift Valley fever virus, Toscana virus, Sicilian and Naples Sandfly fever viruses and others. Until recently, tick-borne phleboviruses were not considered as human pathogens. After the discovery of severe fever with thrombocytopenia syndrome, interest to tick-borne phleboviruses has increased dramatically. In the last decade, many novel phleboviruses have been reported in different regions. Despite this, the diversity, ecology and pathogenicity of these viruses still remain obscure. The aim of this work was to study the diversity of phleboviruses in ticks collected in several regions of Russia. We used pan-phlebovirus RT-PCR assays based on multiple degenerate primers targeting the polymerase gene fragment. Arthropod specimens were collected from 2005 to 2018. A total of 5901 Ixodidae ticks combined into 1116 pools were screened. A total of 160 specific amplicons were produced. In three cases RT-PCR assays amplified two distinct viruses from same tick pools. Direct sequencing of amplicons and subsequent phylogenetic analysis revealed twelve representatives of divergent phlebovirus groups. Based on the distribution of pairwise nucleotide sequence identity values, a cut-off (88%) was suggested to distinguish tick-borne phleboviruses. According to this provisional criterion, two viruses found here could be termed novel, while ten viruses have been described in previous studies. Detected phleboviruses demonstrated almost perfect specificity to a tick species or, at least, a genus. The same pattern was observed for tick-borne phleboviruses found in different studies around the world. Viruses that grouped together on a phylogenetic tree and differed less than this sequence identity threshold suggested above were hosted by ticks from the same genus.

Isolation and Characterisation of Alongshan Virus in Russia.

In recent decades, many new flavi-like viruses have been discovered predominantly in different invertebrates and, as was recently shown, some of them may cause disease in humans. The Jingmenvirus (JMV) group holds a special place among flaviviruses and flavi-like viruses because they have a segmented ssRNA(+) genome. We detected Alongshan virus (ALSV), which is a representative of the JMV group, in ten pools of adult Ixodes persulcatus ticks collected in two geographically-separated Russian regions. Three of the ten strains were isolated in the tick cell line IRE/CTVM19. One of the strains persisted in the IRE/CTVM19 cells without cytopathic effect for three years. Most ALSV virions purified from tick cells were spherical with a diameter of approximately 40.5 nm. In addition, we found smaller particles of approximately 13.1 nm in diameter. We obtained full genome sequences of all four segments of two of the isolated ALSV strains, and partial sequences of one segment from the third strain. Phylogenetic analysis on genome segment 2 of the JMV group clustered our novel strains with other ALSV strains. We found evidence for the existence of a novel upstream open reading frame in the glycoprotein-coding segment of ALSV and other members of the JMV group.

Geographical distribution and hosts of the cestode Paranoplocephala omphalodes (Hermann, 1783) Lühe, 1910 in Russia and adjacent territories.

Paranoplocephala omphalodes is a widespread parasite of voles. Low morphological variability within the genus Paranoplocephala has led to erroneous identification of P. omphalodes a wide range of definitive hosts. The use of molecular methods in the earlier investigations has confirmed that P. omphalodes parasitizes four vole species in Europe. We studied the distribution of P. omphalodes in Russia and Kazakhstan using molecular tools. The study of 3248 individuals of 20 arvicoline species confirmed a wide distribution of P. omphalodes. Cestodes of this species were found in Microtus arvalis, M. levis, M. agrestis, Arvicola amphibius, and also in Chionomys gud. Analysis of the mitochondrial gene cox1 variability revealed a low haplotype diversity in P. omphalodes in Eurasia.

First record of natural Baylisascaris transfuga (Ascaridoidea, Nematoda) infection in wild rodents.

The intestinal parasitic nematode, Baylisascaris transfuga, was recorded in wild rodents for the first time. Representatives of four murid species (15 Myodes rufocanus, 10 M. rutilus, 3 M. glareolus and 27 Microtus oeconomus) were collected in the White Sea coastal habitats in the south of the Kola Peninsula, Russia in July 2015 and examined for parasites. Encapsulated nematode larvae were detected in the mesentery and the large intestine wall of one grey-sided vole (M. rufocanus) and one tundra vole (M. oeconomus). Based on morphology, the larvae were identified as belonging to the genus Baylisascaris Sprent 1968. The partial 18S rDNA sequence of the larvae from the voles was obtained and fully corresponded to the sequence of Baylisascaris transfuga in the NCBI GenBank. The ITS rDNA and CoxI mtDNA sequences these larvae were also similar to the respective B. transfuga sequences in GenBank. The presence of B. transfuga in wild rodents suggests that rodents can participate in the B. transfuga life cycle.

Comparison of Helminth Infection among the Native Populations of the Arctic and Subarctic Areas in Western Siberia Throughout History: Parasitological Researches on Contemporary and the Archaeological Resources.

The aim of this parasitological study is examining contemporary (the late 20th century) specimens of the arctic or subarctic areas in Western Siberia and comparing them with the information acquired from archaeological samples from the same area. In the contemporary specimens, we observed the parasite eggs of 3 different species: Opisthochis felineus, Ascaris lumbricoides, and Enterobius vermicularis. Meanwhile, in archaeoparasitological results of Vesakoyakha, Kikki-Akki, and Nyamboyto I burial grounds, the eggs of Diphyllobothrium and Taenia spp. were found while no nematode (soil-transmitted) eggs were observed in the same samples. In this study, we concluded helminth infection pattern among the arctic and subarctic peoples of Western Siberia throughout history as follows: the raw fish-eating tradition did not undergo radical change in the area at least since the 18th century; and A. lumbricoides or E. vermicularis did not infect the inhabitants of this area before 20th century. With respect to the Western Siberia, we caught glimpse of the parasite infection pattern prevalent therein via investigations on contemporary and archaeoparasitological specimens.

Morphological features of Ixodes persulcatus and I. ricinus hybrids: nymphs and adults.

Our aim was to reveal morphological features of first-generation Ixodes persulcatus and I. ricinus hybrids (nymphs and adults) obtained under laboratory conditions for further study of natural populations of these species in sympatry foci. In 65 nymphs of three groups I. ricinus (23 specimens), I. persulcatus (21 specimens), and hybrids (21 specimens), 16 parameters were evaluated (length/width of the scutum and capitulum, length of the hypostome, palp, tarsus I, coxa I, sternal setae, and various scutal and alloscutal setae) and discrimination analysis was performed allowing differentiation of hybrid nymphs from original species. General effectiveness of classification of I. ricinus, I. persulcatus, and hybrids was >95 %. Discriminant functions are presented allowing classification of I. persulcatus, I. ricinus, and hybrid nymphs. For description of morphology, 27 adult hybrids (13 males and 14 females) were examined under a stereo microscope at 14-28× (without preparation of permanent mounts). The following morphological distinctions of hybrids from original species were described: posterior marginal groove is not clear (as in I. ricinus) and absence of syncoxa on coxa I (as in I persulcatus). In hybrid males, simultaneous absence of syncoxa on coxa I (as in I. persulcatus) and a long internal spur on coxa I (as in I. ricinus) can be used as a diagnostic feature. Based on the detected characteristics, 10 of 157 ticks collected in Karelia in I. ricinus and I. persulcatus sympatry area were classified as hybrids.

Morphological differentiation of Ixodes persulcatus and I. ricinus hybrid larvae in experiment and under natural conditions.

The objective of the study was detection of hybrid larvae in Ixodes persulcatus and Ixodes ricinus cohabitation sites. To this end, the following three tasks were solved: interspecies crossing of ticks, evaluation of typical morphological signs of the hybrid larvae, and analysis of collected specimens from sites of sympatry. Under experimental conditions, hybrid larvae of I. persulcatus (female) and I. ricinus (male) were obtained that differed from the parental species by the size of setae on the scutum and alloscutum. Discriminant analysis yielded 87.5% classification accuracy for the priory set groups of I. persulcatus, I. ricinus, and hybrids. Of 88 hybrid larvae, 13 (15%) were classified as I. persulcatus and 4 (5%) as I. ricinus. We measured larvae of Ixodes ticks (n=141) collected from small mammals in 1950-1970 in Karelia in cohabitation sites of these species that were previously classified as I. persulcatus or I. ricinus. According to the results of discriminant analysis, 31 larvae (22%) were classified as hybrids with probability p≥0.52; for 10 larvae (7%), the probability of placement to the hybrid group was >0.95.

Distribution of Ixodes ricinus and I. persulcatus ticks in southern Karelia (Russia).

The northern boundary of the sympatric zone of Ixodes persulcatus and I. ricinus (Acari: Ixodidae) passes through Karelia. Studies carried out in the 1950s showed that these Ixodes species were mostly found in southern Karelia. I. ricinus inhabited the west of the region, I. persulcatus the east, with a zone of sympatry in the centre. Here, we describe the present distribution of these species in southern Karelia and provide a retrospective assessment of potential changes in the sympatric zone. Tick distribution and abundance were investigated during transect samplings, conducted in May-June 2006-2010. Additional information was obtained during examination of pet dogs and cats. Overall, 4561 adult ticks were collected. Since the 1950s, there has been a significant increase in the abundance of I. persulcatus, and a decrease in I. ricinus. Currently, southern Karelia can be considered as a zone of sympatry for I. ricinus and I. persulcatus, without a clear geographic boundary between the 2 species. In most areas, except to the west of Lake Ladoga, I. persulcatus is more abundant. Possible reasons for this trend are discussed.