Winter activity of questing ticks (Ixodes ricinus and Dermacentor reticulatus) in Germany - Evidence from quasi-natural tick plots, field studies and a tick submission study.

Changing climatic conditions and other anthropogenic influences have altered tick distribution, abundance and seasonal activity over the last decades. In Germany, the two most important tick species are Ixodes ricinus and Dermacentor reticulatus, the latter of which has expanded its range across the country during the past three decades. While I. ricinus was rarely found during the colder months in the past, D. reticulatus is known to be active at lower temperatures. To quantify tick appearance during winter, specimens were monitored in quasi-natural tick plots three times a week. Additionally, the questing activities of these two tick species were observed throughout the year at nine field collection sites that were regularly sampled by the flagging method from April 2020 to April 2022. Furthermore, tick winter activity in terms of host infestation was analysed as part of a nationwide submission study from March 2020 to October 2021, in which veterinarians sent in ticks mainly collected from dogs and cats. All three study approaches showed a year-round activity of I. ricinus and D. reticulatus in Germany. During the winter months (December to February), on average 1.1% of the inserted I. ricinus specimens were observed at the tops of rods in the tick plots. The average questing activity of I. ricinus amounted to 2 ticks/100 m² (range: 1-17) in the flagging study, and 32.4% (211/651) of ticks found infesting dogs and cats during winter 2020/21 were I. ricinus. On average 14.7-20.0% of the inserted D. reticulatus specimens were observed at the tops of rods in the tick plots, while the average winter questing activity in the field study amounted to 23 specimens/100 m² (range: 0-62), and 49.8% (324/651) of all ticks collected from dogs and cats during winter 2020/21 were D. reticulatus. Additionally, the hedgehog tick Ixodes hexagonus was found to infest dogs and cats quite frequently during the winter months, accounting for 13.2% (86/651) of the collected ticks. A generalized linear mixed model identified significant correlations of D. reticulatus winter activity in quasi-natural plots with climatic variables. The combined study approaches confirmed a complementary main activity pattern of I. ricinus and D. reticulatus with climate change-driven winter activity of both species. Milder winters and a decrease of snowfall, and consequently high winter activity of D. reticulatus, among other factors, may have contributed to the rapid spread of this tick species throughout the country. Therefore, an effective year-round tick control is strongly recommended to not only efficiently protect dogs and cats with outdoor access from ticks and tick-borne pathogens (TBPs), but also to limit the further geographical spread of ticks and TBPs to so far non-endemic regions. Further measures, including information of the public, are necessary to protect both, humans and animals, in a One Health approach.

The Eurasian shrew and vole tick Ixodes trianguliceps: geographical distribution, climate preference, and pathogens detected.

The Eurasian shrew and vole tick Ixodes trianguliceps Birula lives in the nests and burrows of its small mammalian hosts and is-along with larvae and nymphs of Ixodes ricinus or Ixodes persulcatus-one of the most commonly collected tick species from these hosts in its Eurasian range. Ixodes trianguliceps is a proven vector of Babesia microti. In this study, up-to-date maps depicting the geographical distribution and the climate preference of I. trianguliceps are presented. A dataset was compiled, resulting in 1161 georeferenced locations in Eurasia. This data set covers the entire range of I. trianguliceps for the first time. The distribution area between 8[Formula: see text] W-105[Formula: see text] E and 40-69[Formula: see text] N extends from Northern Spain to Western Siberia. To investigate the climate adaptation of I. trianguliceps, the georeferenced locations were superimposed on a high-resolution map of the Köppen-Geiger climate classification. The Köppen profile for I. trianguliceps, i.e., a frequency distribution of the tick occurrence under different climates, shows two peaks related to the following climates: warm temperate with precipitation all year round (Cfb), and boreal with warm or cold summers and precipitation all year round (Dfb, Dfc). Almost 97% of all known I. trianguliceps locations are related to these climates. Thus, I. trianguliceps prefers climates with warm or cold summers without dry periods. Cold winters do not limit the distribution of this nidicolous tick species, which has been recorded in the European Alps and the Caucasus Mountains up to altitudes of 2400 m. Conversely, I. trianguliceps does not occur in the Mediterranean area with its hot and dry summers.

Atlas of ticks (Acari: Argasidae, Ixodidae) in Germany: 1st data update.

The first data update of the atlas of ticks in Germany published in 2021 is presented here. This atlas provides maps based on georeferenced tick locations of 21 species endemic in Germany as well as three tick species that are regularly imported to Germany. The data update includes the following numbers of newly georeferenced tick locations: 17 Argas reflexus, 79 Carios vespertilionis, 2 Dermacentor marginatus, 43 Dermacentor reticulatus, 4 Haemaphysalis concinna, 3 Haemaphysalis punctata, 3 Hyalomma rufipes, 3 Ixodes apronophorus, 9 Ixodes arboricola, 1 Ixodes ariadnae, 30 Ixodes canisuga, 3 Ixodes frontalis, 80 Ixodes hexagonus, 3 Ixodes lividus, 497 Ixodes ricinus/inopinatus, 1 Ixodes rugicollis, 17 Ixodes trianguliceps, 14 Ixodes vespertilionis, and 45 Rhipicephalus sanguineus sensu lato. Old and new tick findings were mapped, such as the northernmost occurrence of D. marginatus in Germany observed in 2021, but also the historical records from the first descriptions of I. apronophorus and I. arboricola, which were georeferenced here for the first time. The digital dataset of tick locations available for Germany is supplemented by 854 new tick locations. These records increase the number of tick species mapped in the federal states Bavaria, Brandenburg and Mecklenburg Western Pomerania by five each, those in Berlin and Schleswig-Holstein by four each, those in Hamburg by three, those in Baden-Wuerttemberg, Bremen, Lower Saxony, Northrhine-Westphalia, Rhineland Palatinate and Thuringia by two each, and those in Hesse, Saxony and Saxony-Anhalt by one each. Thus, the first data update of the tick atlas in Germany and the underlying digital dataset significantly improve our knowledge of the distribution of these tick species and helps to investigate the effects of climate change and habitat changes on them.

The biology of Ixodes ricinus with emphasis on its ecology.

Prior to its identification as the vector of Lyme borreliosis spirochaetes in Europe in 1983, interest in Ixodes ricinus (L.) was moderate and mainly concerned the transmission of pathogens to farm animals and of tick-borne encephalitis virus to humans. The situation now is very different, and more papers have been published on I. ricinus than on any other ixodid tick species. However, this large literature is scattered and in recent years has become dominated by the molecular detection and characterization of the many pathogens that I. ricinus transmits. Several decades have now elapsed since a review addressing its basic biology and ecology appeared, and the present publication seeks to present basic aspects of its biology and ecology that are related to its role as a vector of disease agents, including its life cycle, feeding behaviour, host relations, survival off the host, and the impact of weather and climate.

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.

Preliminary study on the seasonal questing of Ixodes ricinus group ticks in Ain Draham forest (north-western Tunisia) with analyses of their phylogenetic diversity.

The present study aimed to investigate the activity dynamics of Ixodes ricinus group ticks in a forest located in north-western Tunisia (Aïn Draham, Jendouba District) and assess the variation of abiotic factors (temperature, Normalized Difference Vegetation Index and relative humidity) during one year survey from September 2016 to August 2017 using the dragging sampling method. A total of 116 questing ticks was collected from the vegetation consisting of 47 adults (19 females and 28 males, sex ratio M:F = 1.47), 45 nymphs and 24 larvae representing 40.5, 38.8 and 20.7% of the total collected specimens, respectively. Adult I. ricinus were collected during October-May, nymphs during May-August and larvae during July-September. There were statistically significant correlations between adult tick numbers and mean daily relative humidity (Pearson r = 0.77; p = 0.003) and mean daily temperature (r = -0.74; p = 0.006). The comparison of 16S rDNA sequences from 20 adult ticks of approximately 444 bp length showed variability among 11 sequences. There was a low genetic variability (<1%) among the I. ricinus isolates collected from the forest. The amplicons showed >99% identity with I. ricinus and Ixodes inopinatus sequences from different countries and published in GenBank. These results should be complemented by further surveys in other Tunisian regions to better understand the influence of environmental factors on the biology of I. ricinus and the occurrence of sympatric I. inopinatus ticks. Different molecular markers should be used for better understanding of their taxonomic status.

Ticks in the metropolitan area of Berlin, Germany.

A high-resolution city map showing the geographic distribution of 12 tick species (Acari: Argasidae, Ixodidae) that have been recorded from the metropolitan area of Berlin, Germany is presented. A total of 237 tick locations was mapped. These include ten ixodid tick species: Dermacentor reticulatus, Haemaphysalis concinna, Hyalomma rufipes, Ixodes ricinus, Ixodes canisuga, Ixodes hexagonus, Ixodes arboricola, Ixodes frontalis, Ixodes trianguliceps and Rhipicephalus sanguineus sensu lato. The two tick species Hy. rufipes and R. sanguineus s.l. are not endemic to Berlin. Hyalomma rufipes ticks are introduced in Europe with migratory birds from Africa every spring. Rhipicephalus sanguineus s.l. are introduced to Central Europe with dogs that had travelled to or were imported from countries where this tick is endemic. In Germany, they are able to develop and reproduce inside heated buildings. Occurrences of two soft tick species, the pigeon tick Argas reflexus and the short-legged bat tick Carios vespertilionis were also mapped. Other tick species that are likely to be endemic to Berlin and its environs, but for which documented findings or geographical coordinates are lacking, are mentioned. These include the long-legged bat tick I. vespertilionis and the marten tick I. rugicollis documented in Brandenburg, the federal state surrounding Berlin. It can be assumed that if appropriate field studies are carried out, these tick species will also be found in the metropolitan area of Berlin. The high-resolution mapping of all tick species found in a city (like Berlin) forms the basis for further investigations into the impact of climate change and changing land use on ticks and tick-borne diseases, precisely in those habitats where most people will live in the future.

Some new findings on the endophilic vector tick Ixodes hexagonus in Germany.

The authors of the present study received a number of hard ticks (Acari: Ixodidae) from different regions of Germany in 2018-2021. In most cases, the ticks were removed from pet dogs or cats. In one case, engorged and detached ticks were found in a house, and it was unclear how they had gained entrance. Morphological examination revealed that all the specimens (n = 18, larvae, nymphs, and adults) were hedgehog ticks, Ixodes hexagonus. Morphological identification for two larvae was confirmed by 16S rRNA gene amplification. These two larvae were also examined for tick-borne encephalitis virus RNA, but were found to be negative. In a previous, unreported study by one of the authors, which commenced in the late 1980s, it was observed that unfed larvae of I. hexagonus were extremely long-lived. They were still alive 5 years after the engorged female had detached from the host when maintained at a moderate temperature under controlled not too warm laboratory conditions (constant 15 °C, 91% relative humidity, and darkness).

Borrelia Infections in Ageing Ticks: Relationship with Morphometric Age Ratio in Field-Collected Ixodes ricinus Nymphs.

In Europe, Ixodes ricinus plays a major role as a vector of Borrelia burgdorferi sensu lato (s.l.) spirochaetes, the causative agents of Lyme borreliosis, among other pathogens. In unfed ticks, Borrelia spirochaetes experience prolonged nutrient restriction. However, only few studies exist with regard to Borrelia infections in unfed ticks of different physiological ages. Changing body dimensions of unfed ticks, due to the consumption of energy reserves, allow physiological age estimation. The present study investigated the relationship of morphometric age with Borrelia prevalence and spirochaete load in 1882 questing I. ricinus nymphs, collected at two different locations in northern Germany in 2020. In addition, Borrelia species composition was investigated by employing a reverse line blot (RLB) probe panel suitable for the detection of ten different B. burgdorferi s.l. species, as well as the relapsing-fever spirochaete B. miyamotoi. Overall, Borrelia prevalence was 25.8% (485/1882). Whilst there was no statistically significant difference in Borrelia prevalence between the different morphometric age groups, Borrelia infection intensity as determined by probe-based quantitative real-time PCR significantly declined with increasing morphometric age. Borrelia species differentiation by RLB was successful in 29.5% of positive ticks, and revealed B. afzelii as the dominating species (65.0% of the differentiated infections). Additionally, B. garinii, B. valaisiana, B. burgdorferi sensu stricto, B. spielmanii, and B. miyamotoi were detected.

Beech tree masting explains the inter-annual variation in the fall and spring peaks of Ixodes ricinus ticks with different time lags.

BACKGROUND: The tick Ixodes ricinus is an important vector of tick-borne diseases including Lyme borreliosis. In continental Europe, the nymphal stage of I. ricinus often has a bimodal phenology with a large spring peak and a smaller fall peak. There is consensus about the origin of the spring nymphal peak, but there are two alternative hypotheses for the fall nymphal peak. In the direct development hypothesis, larvae quest as nymphs in the fall of the same year that they obtained their larval blood meal. In the developmental diapause hypothesis, larvae overwinter in the engorged state and quest as nymphs one year after they obtained their larval blood meal. These two hypotheses make different predictions about the time lags that separate the larval blood meal and the density of questing nymphs (DON) in the spring and fall. METHODS: Inter-annual variation in seed production (masting) by deciduous trees is a time-lagged index for the density of vertebrate hosts (e.g., rodents) which provide blood meals for larval ticks. We used a long-term data set on the masting of the European beech tree and a 15-year study on the DON at 4 different elevation sites in western Switzerland to differentiate between the two alternative hypotheses for the origin of the fall nymphal peak. RESULTS: Questing I. ricinus nymphs had a bimodal phenology at the three lower elevation sites, but a unimodal phenology at the top elevation site. At the lower elevation sites, the DON in the fall was strongly correlated with the DON in the spring of the following year. The inter-annual variation in the densities of I. ricinus nymphs in the fall and spring was best explained by a 1-year versus a 2-year time lag with the beech tree masting index. Fall nymphs had higher fat content than spring nymphs indicating that they were younger. All these observations are consistent with the direct development hypothesis for the fall peak of I. ricinus nymphs at our study site. Our study provides new insight into the complex bimodal phenology of this important disease vector. CONCLUSIONS: Public health officials in Europe should be aware that following a strong mast year, the DON will increase 1 year later in the fall and 2 years later in the spring. Studies of I. ricinus populations with a bimodal phenology should consider that the spring and fall peak in the same calendar year represent different generations of ticks.

Ticks on the turf: investigating the presence of ixodid ticks on and around football fields in Germany.

Ixodes ricinus is the most abundant tick species and an important vector of pathogens in Germany and in large parts of Europe. A few other ixodid tick species, e.g., Dermacentor reticulatus, may also be of eco-epidemiological relevance. As ticks are not only found in natural but also in suburban areas (parks, gardens), the present study investigated whether ticks occur on and near football grounds thus posing a potential risk to players and visitors. Thirty-two football grounds from all 16 German federal states were selected, mainly situated adjacent to a green area (forest, park). Ticks were collected by the conventional flagging method in spring 2018, and nymphs and adults were counted and morphologically determined. Altogether 807 nymphal and adult ticks were collected from 29 football grounds: 714 I. ricinus, 64 Ixodes inopinatus, 2 Ixodes frontalis, 24 Ixodes sp. ticks, and 3 D. reticulatus. Ixodes inopinatus was found in 13 out of 16 German states. Three ticks were even found on the turf of two football fields. It can be concluded that ticks occur quite frequently and sometimes in high abundance near football grounds situated close or adjacent to a forest or a park.

Atlas of ticks (Acari: Argasidae, Ixodidae) in Germany.

An updated and increased compilation of georeferenced tick locations in Germany is presented here. This data collection extends the dataset published some years ago by another 1448 new tick locations, 900 locations of which were digitized from literature and 548 locations are published here for the first time. This means that a total of 3492 georeferenced tick locations is now available for Germany. The tick fauna of Germany includes two species of Argasidae in the genera Argas and Carios and 19 species of Ixodidae in the genera Dermacentor, Haemaphysalis, and Ixodes, altogether 21 tick species. In addition, three species of Ixodidae in the genera Hyalomma (each spring imported by migratory birds) and Rhipicephalus (occasionally imported by dogs returning from abroad with their owners) are included in the tick atlas. Of these, the georeferenced locations of 23 tick species are depicted in maps. The occurrence of the one remaining tick species, the recently described Ixodes inopinatus, is given at the level of the federal states. The most common and widespread tick species is Ixodes ricinus, with records in all 16 federal states. With the exception of Hamburg, Dermacentor reticulatus was also found in all federal states. The occurrence of the ixodid ticks Ixodes canisuga, Ixodes frontalis, Ixodes hexagonus and I. inopinatus were documented in at least 11 federal states each. The two mentioned argasid tick species were also documented in numerous federal states, the pigeon tick Argas reflexus in 11 and the bat tick Carios vespertilionis in seven federal states. The atlas of ticks in Germany and the underlying digital dataset in the supplement can be used to improve global tick maps or to study the effects of climate change and habitat alteration on the distribution of tick species.

What do we still need to know about Ixodes ricinus?

In spite of many decades of intensive research on Ixodes ricinus, the castor bean tick of Europe, several important aspects of its basic biology remain elusive, such as the factors determining seasonal development, tick abundance and host specificity, and the importance of water management. Additionally, there are more recent questions about the geographical diversity of tick genotypes and phenotypes, the role of migratory birds in the ecoepidemiology of I. ricinus, the importance of protective immune responses against I. ricinus, particularly in the context of vaccination, and the role of the microbiome in pathogen transmission. Without more detailed knowledge of these issues, it is difficult to assess the likely effects of changes in climate and biodiversity on tick distribution and activity, to predict potential risks arising from new and established tick populations and I. ricinus-borne pathogens, and to improve prevention and control measures. This review aims to discuss the most important outstanding questions against the backdrop of the current state of knowledge of this important tick species.

Vectors of disease at the northern distribution limit of the genus Dermacentor in Eurasia: D. reticulatus and D. silvarum.

The two ixodid tick species Dermacentor reticulatus (Fabricius) and Dermacentor silvarum Olenev occur at the northern distribution limit of the genus Dermacentor in Eurasia, within the belt of [Formula: see text] latitude. Whilst the distribution area of D. reticulatus extends from the Atlantic coast of Portugal to Western Siberia, that of D. silvarum extends from Western Siberia to the Pacific coast. In Western Siberia, the distribution areas of the two Dermacentor species overlap. Although the two tick species are important vectors of disease, detailed information concerning the entire distribution area, climate adaptation, and proven vector competence is still missing. A dataset was compiled, resulting in 2188 georeferenced D. reticulatus and 522 D. silvarum locations. Up-to-date maps depicting the geographical distribution and climate adaptation of the two Dermacentor species are presented. To investigate the climate adaptation of the two tick species, the georeferenced locations were superimposed on a high-resolution map of the Köppen-Geiger climate classification. The frequency distribution of D. reticulatus under different climates shows two major peaks related to the following climates: warm temperate with precipitation all year round (57%) and boreal with precipitation all year round (40%). The frequency distribution of D. silvarum shows also two major peaks related to boreal climates with precipitation all year round (30%) and boreal winter dry climates (60%). Dermacentor silvarum seems to be rather flexible concerning summer temperatures, which can range from cool to hot. In climates with cool summers D. reticulatus does not occur, it prefers warm and to a lesser extent hot summers. Lists are given in this paper for cases of proven vector competence for various agents of both Dermacentor species. For the first time, the entire distribution areas of D. reticulatus and D. silvarum were mapped using georeferenced data. Their climate adaptations were quantified by Köppen profiles.

Long-term monitoring of the seasonal density of questing ixodid ticks in Vienna (Austria): setup and first results.

The first long-term monitoring to document both activity and density of questing ixodid ticks in Vienna, Austria, is introduced. It was started in 2017 and is planned to run over decades. Such long-term monitorings are needed to quantify possible effects of climate change or to develop tick density forecast models. The monthly questing tick density at three sites has been observed by using a standardized sampling method by dragging an area of [Formula: see text] at each occasion. Popular recreational areas were chosen as study sites. These are the Prater public park, the wooded Kahlenberg, and a wildlife garden in Klosterneuburg. First results show a 3-year time series of nymphs and adults of the Ixodes ricinus species complex and Haemaphysalis concinna for the period 2017-2019. Whereas questing nymphs of the I. ricinus species complex were collected from February to November, H. concinna nymphs were only dragged from May to October. The peak of nymphal activity of the I. ricinus species complex was in May, that of H. concinna in August. In addition, a brief overview is given about ticks and tick-borne pathogens occurring in urban and suburban areas of Vienna.

Isolation of known and potentially pathogenic tick-borne microorganisms from European ixodid ticks using tick cell lines.

Ticks harbour and, in many cases transmit to their vertebrate hosts, a wide variety of pathogenic, apathogenic and endosymbiotic microorganisms. Recent molecular analyses have greatly increased the range of bacterial species potentially associated with ticks, but in most cases cannot distinguish between surface contaminants, microorganisms present in the remains of the previous blood meal and truly intracellular or tissue-associated bacteria. Here we demonstrate how tick cell lines, primary cell cultures and organ cultures can be used to isolate and propagate bacteria from within embryonic and adult Ixodes ricinus, Dermacentor marginatus and Dermacentor reticulatus ticks originating from different parts of Europe. We isolated and partially characterised four new strains of Spiroplasma from The Netherlands, Spain and Poland, two new strains of Rickettsia raoultii from Russia and Poland, one strain of Rickettsia slovaca from Spain and a species of Mycobacterium from the UK. Comparison with published sequences showed that the Spiroplasma strains were closely related to Spiroplasma ixodetis and the Mycobacterium isolate belonged to the Mycobacterium chelonae complex, while the R. raoultii and R. slovaca strains were similar to previously-validated species.