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Ixodid ticks (Acarina, Ixodidae) are vectors of dangerous human infections. The main tick species that determine the epidemiological situation for tick-borne diseases in northern Europe are Ixodes ricinus and Ixodes persulcatus. In recent years, significant changes in the number and distribution of these species have been observed, accompanied by an expansion of the sympatric range. This work summarizes the data of long-term studies carried out in Karelia since 2007 on the infection of I. persulcatus and I. ricinus ticks with various pathogens, including new viruses with unclear pathogenic potential. As a result, tick-borne encephalitis virus (TBEV, Siberian genotype), Alongshan virus, several representatives of the family Phenuiviridae, Borrelia afzelii, Borrelia garinii, Ehrlichia muris, Candidatus Rickettsia tarasevichiae and Candidatus Lariskella arthropodarum were identified. Data were obtained on the geographical and temporal variability of tick infection rates with these main pathogens. The average infection rates of I. persulcatus with TBEV and Borrelia burgdorferi sensu lato were 4.4% and 23.4% and those of I. ricinus were 1.1% and 11.9%, respectively. We did not find a correlation between the infection rate of ticks with TBEV, B. burgdorferi s.l. and Ehrlichia muris/chaffeensis with the sex of the vector. In general, the peculiarities of the epidemiological situation in Karelia are determined by the wide distribution and high abundance of I. persulcatus ticks and by their relatively high infection rate with TBEV and B. burgdorferi s.l. in most of the territory, including the periphery of the range., Competing Interests: Declaration of Competing Interest The authors declare no conflict of interest., (Copyright © 2022. Published by Elsevier GmbH.)

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., (Copyright © 2014 Elsevier GmbH. All rights reserved.)

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., (Copyright © 2012 Elsevier GmbH. All rights reserved.)