Prevalence of tick-borne encephalitis virus (TBEV) RNA in Dermacentor reticulatus ticks from natural and urban environment, Poland

Identification of New Microfoci and Genetic Characterization of Tick-Borne Encephalitis Virus Isolates from Eastern Germany and Western Poland

(1) Background: Tick-borne encephalitis (TBE) is the most important tick-borne viral disease in Eurasia, although effective vaccines are available. Caused by the tick-borne encephalitis virus (TBEV, syn. Orthoflavivirus encephalitidis), in Europe, it is transmitted by ticks like Ixodes ricinus and Dermacentor reticulatus. TBEV circulates in natural foci, making it endemic to specific regions, such as southern Germany and northeastern Poland. Our study aimed to identify new TBEV natural foci and genetically characterize strains in ticks in previously nonendemic areas in Eastern Germany and Western Poland. (2) Methods: Ticks were collected from vegetation in areas reported by TBE patients. After identification, ticks were tested for TBEV in pools of a maximum of 10 specimens using real-time RT-PCR. From the positive TBEV samples, E genes were sequenced. (3) Results: Among 8400 ticks from 19 sites, I. ricinus (n = 4784; 56.9%) was predominant, followed by D. reticulatus (n = 3506; 41.7%), Haemaphysalis concinna (n = 108; 1.3%), and I. frontalis (n = 2; <0.1%). TBEV was detected in 19 pools originating in six sites. The phylogenetic analyses revealed that TBEV strains from Germany and Poland clustered with other German strains, as well as those from Finland and Estonia. (4) Conclusions: Although there are still only a few cases are reported from these areas, people spending much time outdoors should consider TBE vaccination.

Perspectives of vector management in the control and elimination of vector-borne zoonoses

The complex transmission profiles of vector-borne zoonoses (VZB) and vector-borne infections with animal reservoirs (VBIAR) complicate efforts to break the transmission circuit of these infections. To control and eliminate VZB and VBIAR, insecticide application may not be conducted easily in all circumstances, particularly for infections with sylvatic transmission cycle. As a result, alternative approaches have been considered in the vector management against these infections. In this review, we highlighted differences among the environmental, chemical, and biological control approaches in vector management, from the perspectives of VZB and VBIAR. Concerns and knowledge gaps pertaining to the available control approaches were discussed to better understand the prospects of integrating these vector control approaches to synergistically break the transmission of VZB and VBIAR in humans, in line with the integrated vector management (IVM) developed by the World Health Organization (WHO) since 2004.

Co-Circulation of West Nile, Usutu, and Tick-Borne Encephalitis Viruses in the Same Area: A Great Challenge for Diagnostic and Blood and Organ Safety

Viral infections caused by viruses from the family Flaviviridae such as Zika (ZIKV), Dengue (DENV), yellow fever (YFV), tick-borne encephalitis (TBEV), West Nile (WNV), and Usutu (USUV) are some of the most challenging diseases for recognition in clinical diagnostics and epidemiological tracking thanks to their short viremia, non-specific symptoms, and high cross-reactivity observed in laboratory techniques. In Central Europe, the most relevant endemic flaviviruses are mosquito-borne WNV and USUV, and tick-borne TBEV. All three viruses have been recognised to be responsible for human neuroinvasive diseases. Moreover, they are interrupting the blood and transplantation safety processes, when the great efforts made to save a patient's life could be defeated by acquired infection from donors. Due to the trend of changing distribution and abundance of flaviviruses and their vectors influenced by global change, the co-circulation of WNV, USUV, and TBEV can be observed in the same area. In this perspective, we discuss the problems of flavivirus diagnostics and epidemiology monitoring in Slovakia as a model area of Central Europe, where co-circulation of WNV, USUV, and TBEV in the same zone has been recently detected. This new situation presents multiple challenges not only for diagnostics or surveillance but particularly also for blood and organ safety. We conclude that the current routinely used laboratory diagnostics and donor screening applied by the European Union (EU) regulations are out of date and the novel methods which have become available in recent years, e.g., next-gene sequencing or urine screening should be implemented immediately.

Tick-borne pathogens in Dermacentor reticulatus collected from dogs in eastern Poland

In recent years, the distribution of Dermacentor reticulatus ticks has expanded into new territories in many European countries, including Poland, with increased population densities in areas of their regular occurrence. The spread of D. reticulatus enhances the risk of exposure of domestic animals and their owners to tick-borne diseases. The objective of this study was to assess the prevalence of infection of D. reticulatus ticks feeding on dogs with the pathogens Borrelia burgdorferi sensu lato and Anaplasma phagocytophilum. The study material comprised 152 D. reticulatus ticks collected from dogs in the northeastern part of Lublin Province (eastern Poland). A ready-made AmpliSens® TBEV, B.burgdorferi sl, A.phagocytophilum, E.chaffeensis/E.muris-FRT PCR kit was used for qualitative detection and differentiation of tick-borne infections. The assessment of the degree of infection of the analyzed ticks with the two pathogens revealed that 9.2% (14/152) of the examined ticks were infected with one of the pathogens. No co-infections with the pathogens were detected in any of the ticks. The highest specific percentage of infections (8.6%, 13/152) was associated with A. phagocytophilum. The presence of B. burgdorferi s.l. was detected in only one of the examined ticks (0.7%). The spread of D. reticulatus to new territories and the increase in population density in areas of their regular occurrence implies the need for further studies of the prevalence of pathogens with medical and veterinary importance in order to assess the risk of tick-borne diseases.

Similar Trajectories in Current Alcohol Consumption and Tick-Borne Diseases: Only Parallel Changes in Time or Links Between?

In a modern world, both tick-borne diseases and alcohol consumption are among major public health threats. In the present opinion article, we pose the question, whether these two health problems: alcohol consumption and tick-borne diseases prevalence can be related. We hypothesize that it is possible due to at least three factors: outdoor places chosen for alcohol consumption, behavioral changes induced by alcohol, and possible stronger attraction of human hosts after alcohol consumption to ticks. Many important clues are coming from social studies about people’s preference of places to consume alcohol and from studies regarding the attraction of people consuming alcohol to mosquitos. These data, however, cannot be directly transferred to the case of alcohol consumption and ticks. Therefore, we suggest that more detailed studies are needed to better understand the possible individual attractiveness of people to ticks and ways alcohol may influence it.

Climate and the seasonal abundance of the tick Dermacentor reticulatus

Dermacentor reticulatus (Ixodida: Ixodidae, Fabricius 1794) is one of the most widely distributed and abundant tick species in central Europe and is a vector for a range of pathogens. Nevertheless, many aspects of its ecology and distribution remain poorly understood. To quantify the seasonal abundance of this species in the U.K. and the environmental factors that determine this, weekly sampling at sites throughout Wales and southern England was undertaken for 12 months. This showed that the activity of adult D. reticulatus peaked February and March and that no individuals were collected between May and mid-October; no questing tick activity was observed when the 5-day average temperature was greater than 15 °C. A single nymph was collected by dragging, confirming speculation over the nidicolous status of larval and nymphal stadia. Laboratory analysis found that D. reticulatus were able survive cold shock and the lower lethal temperature was estimated to be between -18 and -20 °C. Habitat was significantly associated with tick activity, with higher numbers of ticks collected from low lying vegetation in marsh environments than from exposed grassland or woodland. A strong association was observed between activity and saturation deficit suggesting that the seasonal pattern of activity seen in the field, within the sites where it was abundant, is more strongly determined by temperature than humidity. Range expansion within the U.K. should be expected, bringing with it an elevated disease risk for animal and human hosts.

Molecular detection and phylogenetic analysis of tick-borne encephalitis virus in ticks in northeastern China

Tick-borne encephalitis virus (TBEV) is an important causative agent that causes neurological infections in humans and animals. In recent years, only few epidemiological surveys on TBEV have been conducted in China. The purpose of this study was to determine the prevalence and subtype of TBEV in ticks in northeastern (NE) China. A total of 3799 questing ticks were collected in NE China between April 2015 and June 2016. Ticks were pooled and tested for TBEV RNA using semi-nested reverse transcriptase-polymerase chain reaction. Positive pools were used to isolate the virus and amplify complete sequences, followed by sequence identity and phylogenetic analysis. TBEV RNA was detected in Ixodes persulcatus ticks at a total prevalence of 2.9% (6/143; 95% confidence interval: 1.2%-5.9%). Three TBEV strains were isolated (JL-T75, HLB-T74, and DXAL-T83) and showed 93.9%-99.1% nucleotide identities and 97.1%-99.5% amino acid identities in Far Eastern (FE) TBEV subtypes, and 82.9%-87.6% nucleotide identities and 92.9%-96.4% amino acid identities in other subtypes. For polyprotein, the JL-T75, HLB-T74, and DXAL-T83 strains showed 29, 50, and 55 amino acid residues, respectively, different from those in the TBEV vaccine (Senzhang) strain in China. Phylogenetic analysis revealed that these viruses were clustered in the FE-TBEV branch but formed distinct clades depending on the natural foci. The results of this study suggest that the FE-TBEV subtype is still endemic in I. persulcatus ticks in NE China, and the viruses in different natural foci in NE China are more likely to have genetic differences.

Prevalence of tick-borne encephalitis virus in questing Dermacentor reticulatus and Ixodes ricinus ticks in Lithuania

The Baltic States are the region in Europe where tick-borne encephalitis (TBE) is most endemic, with one-third of the European TBE cases detected in Lithuania, Latvia and Estonia. With the Czech Republic and Germany, Lithuania has among the highest population incidences of TBE. Ticks from the Ixodidae family are the main vectors of the TBE virus (TBEV) in Europe. However, there is still a lack of data on the prevalence of TBEV in ticks in different parts of Lithuania. This study analysed the current prevalence of TBEV in the two most common tick species distributed in Lithuania: Ixodes ricinus and Dermacentor reticulatus. Questing I. ricinus (n = 7170) and D. reticulatus (n = 1676) ticks were collected from 81 locations in all ten counties of Lithuania between 2017 and 2019. The presence of TBEV was analysed using a real-time reverse transcription polymerase chain reaction (RT-PCR) and TBEV prevalence in ticks was calculated as the minimum infection rate (MIR). TBEV was detected in the three developmental stages (adults, nymphs and larvae) of I. ricinus and in D. reticulatus adults. The MIR of TBEV in the total sample of I. ricinus was 0.4 % (28/7170) and for D. reticulatus was also estimated to be 0.4 % (6/1676). TBEV-infected ticks were found in 16 locations in seven counties, with MIR ranging from 0.1 % to 1.0 %. The TBEV strains detected belong to the European subtype. To the best of the authors' knowledge, this is the first report on the prevalence of TBEV in unfed D. reticulatus ticks and in I. ricinus unfed larvae in Lithuania.

Complete mitogenome of the ixodid tick Dermacentor reticulatus (Acari: Ixodida)

Here, we present the complete mitochondrial DNA sequence of Dermacentor reticulatus. The mitogenome is 14,806 bp and contains 13 protein-coding, 2 rRNA, and 22 tRNA genes, along with 2 control regions. Dermacentor reticulatus mitogenome has the common mitochondrial gene order of Metastriata ticks. It is phylogenetically close to the mitogenomes of Dermacentor ticks, of which D. everestanus mitogenome is the closest with 85.7% similarity. These data provide insights into the phylogenetic relations among Dermacentor ticks.

Collection of immature Dermacentor reticulatus (Fabricius, 1794) ticks from vegetation and detection of Rickettsia raoultii in them

It is commonly assumed that Dermacentor reticulatus immature life stages are nidicolous and therefore cannot be collected from vegetation. However, in June and July of 2018 and 2019, a total of 47 questing D. reticulatus larvae and two nymphs were collected by the flagging method in two different sites close to the city of Leipzig, Germany. To confirm their role in the transmission of tick-borne pathogens, 45 larvae (pooled by 2 in 21 pools and 1 pool with three individuals) and one nymph were tested either by conventional or real-time PCR for the presence of Bartonella spp., Neoehrlichia mikurensis, Rickettsia spp., and Babesia spp. All samples tested negative for Bartonella spp., N. mikurensis, and Babesia spp.; while the minimal infection rate of larvae for Rickettsia spp. was 42%, and the one tested nymph was also positive. Sequencing partial ompB genes revealed the presence of Rickettsia raoultii in larvae and nymph. Further research needs to be done to determine under which circumstances immature D. reticulatus ticks are found outside the burrows of their hosts and can be collected from vegetation.

Prevalence of tick-borne encephalitis virus and Borrelia burgdorferi sensu lato in Ixodes ricinus ticks in Lower Bavaria and Upper Palatinate, Germany

Lyme borreliosis and tick-borne encephalitis (TBE) are the most common tick-borne diseases in Germany. We collected Ixodes ricinus ticks from 16 high-risk and four low-risk sites distributed in Lower Bavaria and Upper Palatinate based on the number of human TBE cases recorded at the Robert Koch Institute from 2001 to 2009. A total of 8805 questing ticks (8203 nymphs, 602 adults) were collected in 2010 and examined in pools for the presence of tick-borne encephalitis virus (TBEV) using real-time RT-PCR. Overall TBEV prevalence evaluated as the minimum infection rate (MIR) was 0.26 % (23 positive pools/8805 ticks in 1029 pools). TBEV was detected at seven of the 16 high-risk sites, where MIR ranged from 0.16 to 2.86 %. A total of 3969 ticks were examined by PCR for infection with Borrelia burgdorferi sensu lato (s.l.) targeting the 5 S-23 S rRNA intergenic spacer (IGS) region. IGS nucleotide sequences were used to determine genospecies. Selected positive Borrelia samples were subjected to PCR and sequencing targeting the OspA gene, providing 46 sequences for molecular phylogenetic analysis. Of the 3969 questing ticks, 506 (12.7 %) were positive for B. burgdorferi s.l. Seven B. burgdorferi s.l. genospecies were identified: B. afzelii (41.3 %), B. garinii (19 %), B. valaisiana (13.8 %), B. burgdorferi sensu stricto (11.1 %), B. spielmanii (0.4 %), B. lusitaniae (0.2 %), and Candidatus B. finlandensis (0.6 %). Mixed infections were identified in 13.6 % of the ticks. The rate of infection in questing ticks varied among sites from 5.6 % (72 examined, four positive) to 29.5 % (88 examined, 26 positive). B. burgdorferi s.l. occurred at all 20 sites, whereas TBEV was detected only at the high-risk sites where more human TBE cases were reported compared to low-risk sites.

Exploring the Reservoir Hosts of Tick-Borne Encephalitis Virus

Tick-borne encephalitis virus (TBEV) is an important arbovirus, which is found across large parts of Eurasia and is considered to be a major health risk for humans. Like any other arbovirus, TBEV relies on complex interactions between vectors, reservoir hosts, and the environment for successful virus circulation. Hard ticks are the vectors for TBEV, transmitting the virus to a variety of animals. The importance of these animals in the lifecycle of TBEV is still up for debate. Large woodland animals seem to have a positive influence on virus circulation by providing a food source for adult ticks; birds are suspected to play a role in virus distribution. Bank voles and yellow-necked mice are often referred to as classical virus reservoirs, but this statement lacks strong evidence supporting their highlighted role. Other small mammals (e.g., insectivores) may also play a crucial role in virus transmission, not to mention the absence of any suspected reservoir host for non-European endemic regions. Theories highlighting the importance of the co-feeding transmission route go as far as naming ticks themselves as the true reservoir for TBEV, and mammalian hosts as a mere bridge for transmission. A deeper insight into the virus reservoir could lead to a better understanding of the development of endemic regions. The spatial distribution of TBEV is constricted to certain areas, forming natural foci that can be restricted to sizes of merely 500 square meters. The limiting factors for their occurrence are largely unknown, but a possible influence of reservoir hosts on the distribution pattern of TBE is discussed. This review aims to give an overview of the multiple factors influencing the TBEV transmission cycle, focusing on the role of virus reservoirs, and highlights the questions that are waiting to be further explored.

Comparative proteomics of the vector Dermacentor reticulatus revealed differentially regulated proteins associated with pathogen transmission in response to laboratory infection with Rickettsia slovaca

BACKGROUND

Tick-borne rickettsial diseases are caused by pathogens acquired from hard ticks. In particular, Rickettsia slovaca, a zoonotic infectious bacterium causing tick-borne lymphadenopathy (TIBOLA), is transmitted by the vectors Dermacentor spp. that can be found all over Europe. Although recent studies point out the extreme complexity of bacteria-induced effects in these blood-feeding vectors, the knowledge of individual molecules involved in the preservation and transmission of the pathogen is still limited. System biology tools, including proteomics, may contribute greatly to the understanding of pathogen-tick-host interactions.

METHODS

Herein, we performed a comparative proteomics study of the tick vector Dermacentor reticulatus that was experimentally infected with the endosymbiotic bacterium R. slovaca. Rickettsia-free ticks, collected in the southern region of Slovakia, were infected with the bacterium by a capillary tube-feeding system, and the dynamics of infection was assessed by quantitative PCR method after 5, 10, 15 and 27 days.

RESULTS

At the stage of controlled proliferation (at 27 dpi), 33 (from 481 profiled) differentially abundant protein spots were detected on a two-dimensional gel. From the aforementioned protein spots, 21 were successfully identified by tandem mass spectrometry.

CONCLUSIONS

Although a few discovered proteins were described as having structural or housekeeping functions, the vast majority of the affected proteins were suggested to be essential for tick attachment and feeding on the host, host immune system evasion and defensive response modulation to ensure successful pathogen transmission.

Ixodid ticks and tick-borne encephalitis virus prevalence in the South Asian part of Russia (Republic of Tuva)

The most significant processes of arbovirus evolution can be expected to occur in the territories where ticks of different species cohabitate and at the boundaries of virus occurrence, where the probability of the appearance of new virus variants is high due to the possible shift in the main vectors and/or vertebrate hosts. One of the most interesting regions in this regard is the Republic of Tuva. Since most of its territory is covered by mountain ranges and intermountain basins, we were able to study the distribution of vectors and viruses in geographically isolated areas at different altitudes and in various landscapes. From 2008 to 2017, we conducted six expeditions to Tuva and collected 3,077 adult ticks and 24 nymphs. The distribution of tick species was confined to specific landscapes, as follows: Dermacentor nuttalli occurred in steppes, D. silvarum inhabited forest-steppe areas, and Ixodes persulcatus inhabited mixed forests. All three species of ticks were collected on plains and mountain slopes. The range of D. silvarum was shown to be lower than 1300 m above sea level (a.s.l.). Only D. nuttalli and I. persulcatus were collected at higher altitudes. According to our observations, single nymphs of D. nuttalli appear on animals one month before larvae appear. This finding confirms the hypothesis that the immature forms of D. nuttalli are able to overwinter under favourable conditions. We isolated 9 strains and 3 isolates of tick-borne encephalitis virus (TBEV) from I. persulcatus, one strain from D. nuttalli and one strain from D. silvarum. The TBEV strain from D. nuttalli was isolated from the territory inhabited only by Dermacentor ticks. All isolated strains belong to the Siberian subtype of TBEV. TBEV was detected in ticks from all the investigated altitudes. There were no statistically significant differences in the virus prevalence between the Dermacentor and Ixodes ticks. The results of our work provide additional support for the hypothesis of the existence of TBEV foci in areas with an absolute dominance of D. nuttalli.

Tick-borne encephalitis in Europe: a brief update on epidemiology, diagnosis, prevention, and treatment

Tick-borne encephalitis (TBE) is an emerging health threat that is spreading in many parts of Europe. The mix of socio-economical, ecological and climatic factors as well as the presence of more susceptible hosts is actively contributing to the increasing number of TBE reported cases. TBE is an important cause of central nervous system (CNS) infection that can result in long-term neurological sequelae and even death. Diagnosis of TBE relays mainly on high clinical suspicion confirmed by serological and molecular assays both on serum and cerebrospinal fluid (CSF) with an ancillary role for neuroimaging in supporting the diagnosis. No specific antiviral treatment is currently available for TBE; indeed, supportive treatment as well as intensive care and assisted ventilation in severe forms may be needed. Because of limited option for TBE treatment, of crucial importance is effective vaccination to prevent disease-related morbidity and mortality. Due to expanding proportion of subject possibly exposed to TBE (and new populations such as: unaware travellers to TBE-endemic areas and immunocompromised patients), we performed a comprehensive review of TBE epidemiology, clinical presentation, current available diagnostic tools and treatment.

Repeated isolation of tick-borne encephalitis virus from adult Dermacentor reticulatus ticks in an endemic area in Germany

Background

Tick-borne encephalitis (TBE) virus is transmitted to humans and animals through tick bites and is thought to circulate in very strictly defined natural environments called natural foci. The most common tick serving as a vector for the TBE virus in central Europe is Ixodes ricinus; it is rarely found in other tick species and in Dermacentor reticulatus it has, so far, only been reported in Poland.

Methods

Between autumn 2016 and spring 2018 ticks were collected by the flagging method in a new TBE focus in the district of northern Saxony, Germany, outside the known risk areas as defined by the national Robert Koch Institute. Ticks were morphologically identified and tested in pools for the presence of TBE virus using a real-time RT-PCR. TBE virus from positive pools was isolated in A549 cells, and the E gene sequences were determined after conventional RT-PCR, followed by a phylogenetic comparison.

Results

TBE virus was detected in 11 pools, 9 times in flagged adults D. reticulatus (n = 1534; MIR: 0.59%, CI: 0.29–11.3%) and only twice in I. ricinus nymphs (n = 349; MIR: 0.57%, CI: 0.02–2.2%). All other ticks, I. ricinus males (n = 33), females (n = 30) and larvae (n = 58), as well as 5 I. inopinatus (2 females, 3 males) and 14 Haemaphysalis concinna (3 females, 11 nymphs), tested negative for TBE virus. TBE virus was not detected in I. ricinus during the summer, when D. reticulatus is not active. Sequence comparison of the entire E gene of the isolated virus strains resembled each other with only 3 nucleotide differences. The most closely related viral sequences belong to TBE virus strains from Poland and Neustadt an der Waldnaab (county of Neustadt an der Waldnaab, Bavaria), approximately 200 km east and 200 km south-west of the new focus, respectively.

Conclusions

TBE virus was found in northern Saxony, Germany, with similar MIRs in D. reticulatus and I. ricinus, indicating that D. reticulatus plays an equal role to I. ricinus in virus circulation when both tick species are sympatric.

Phylogenetics of tick-borne encephalitis virus in endemic foci in the upper Rhine region in France and Germany

Objective

Tick-borne encephalitis (TBE) caused by the tick-borne encephalitis virus (TBEV) is the most important tick-borne arboviral disease in Europe and Asia. The Upper Rhine Valley is thought to be the very western border of TBEV distribution in Europe. The aim of our study was to identify natural foci and isolate TBEV from ticks, to determine the prevalence of TBEV in local tick populations and to study the phylogenetic relatedness of circulating TBEV strains in this region.

Material and methods

Ticks were collected between 2016, 2017 and 2018 by flagging. TBEV was isolated from collected ticks and phylogenetic analyses were performed. Minimal infection rates (MIR) of the collected ticks were calculated.

Results

At 12 sampling sites, a total of 4,064 Ixodes ticks were collected in 2016 and 2017 –(and one single collection 2018). 953 male, 856 female adult ticks and 2,255 nymphs were identified. The MIR rates were 0,17% (1/595) for Schiltach (Germany) and 0,11% (1/944) for Foret de la Robertsau (France), respectively. Overall, the three newly described TBEV strains, isolated in the years 2016 and 2017 from the Upper Rhine Valley have no close phylogenetic relation and show a genetic relationship with strains from eastern Europe. The 2018 TBEV strain from Aubachstrasse (Germany), however, is closely related to the TBEV found in Schiltach (Germany).

Conclusion

In conclusion, we demonstrate, to our knowledge for the first time, the phylogenetic relations of the newly isolated TBEV strains on both sides of the upper Rhine river.

Dermacentor reticulatus ticks (Acari: Ixodidae) distribution in north-eastern Poland: an endemic area of tick-borne diseases

Dermacentor reticulatus is the second most important tick species in Poland. Although the north-eastern region of Poland is considered typical for D. reticulatus and is treated as a contiguous area of Eastern populations of the meadow ticks, the occurrence of this tick species in this region to date has been recorded as separate foci. The present report supplements data on the geographical distribution of D. reticulatus in urban and natural biotopes of north-eastern Poland (Warmia and Mazury province). In 2015-2017 (during the springtime activity of ticks) adult questing D. reticulatus were found in 13 of 25 monitored localities. Six sites are located in urbanized areas, within the administrative borders of the city of Olsztyn and seven sites are in natural biotopes in the central part of Warmia and Mazury. A total of 398 adult D. reticulatus ticks, including 257 females and 141 males, were collected. A comparison of data grouped according to urban and natural type of area revealed no statistical differences between them. Taking into account the habitat type, the mean tick density was the highest in open landscapes. The identification of new foci D. reticulatus in the endemic areas of Lyme borreliosis, tick-borne encephalitis and canine babesiosis is crucial for determining the risk of diseases transmitted by ticks and taking proper preventive measures.

Prevalence of different Rickettsia spp. in Ixodes ricinus and Dermacentor reticulatus ticks (Acari: Ixodidae) in north-eastern Poland

In two surveys conducted in April and May 2013, a total of 1148 unfed ticks belonging to two species, Ixodes ricinus and Dermacentor reticulatus, were collected by flagging lower vegetation in 15 different localities throughout the Białowieża Primeval Forest (Podlaskie voivodship; north-eastern Poland) and in its buffer zone. In order to establish their infection rate with Rickettsia spp. individual adult ticks and pooled nymphs were tested by real-time PCR targeting the gltA gene. For the further identification of rickettsial species, positive samples were subjected for nested and semi-nested PCR targeting ompA and 16S rRNA genes, respectively, followed by sequencing analysis. Rickettsial DNA was detected in at least 279 ticks (minimum infection rate [MIR], 23.9%), including 52 nymphal and adult I. ricinus (MIR 8.6%) and 222 adult D. reticulatus (41%). Three species of SFG rickettsiae were identified: Rickettsia helvetica and 'Candidatus R. mendelii' in I. ricinus and R. raoultii in D. reticulatus and I. ricinus. Moreover, unidentified Rickettsia spp. which showed 99.4% identity, among others, with the uncultured Rickettsia sp. isolated from Cicadella viridis leafhopper, Rickettsia endosymbiont of Lasioglossum semilucens bee and R. bellii, were detected in I. ricinus, while Rickettsia sp. 98.3-98.4% homologous to Rickettsia secondary endosymbionts of Curculio spp. weevils was found in D. reticulatus. These results confirm the diversity of rickettsiae occurring in Poland. Further studies are needed to expand the knowledge on the species spectrum, prevalence and epidemiology of SFG rickettsiae in the country.

Prevalence and Detection of Flaviviruses Occurring in Slovakia

The tick-borne encephalitis virus (TBEV) and West Nile virus (WNV) are arboviruses of the genus Flavivirus in the family Flaviviridae. Their hosts are vertebratesof which rodents are the reservoirs of TBEV and birds are the reservoirs of WNV. Both viruses are transmitted from reservoirs to mammals by vectors. TBEV is transmitted by ticks (mostly Ixodes spp.) and WNV by mosquitoes (mostly Culex spp.). Both viruses are capable of infecting mammals, including man. TBEV and WNV are neurotropic, however infection is, in most cases, subclinical or accompanied by only moderate general signs. However, in some cases they can cause serious disturbances of the CNS. Our study focused on the detection of the genomes of TBEV and WNV in vectors by means of the reverse-transcription polymerase chain reaction (RT-PCR). The flavivirus genome was detected by means of oligonucleotides delineating the sequence in NS5 gene that encodes viral RNA-dependent RNA-polymerase. For the detection of TBEV, we used the oligonucleotide pair detecting the structural envelope protein. The positive samples were subjected to the sequence and phylogenetic analysis. The WNV was not detected in any of the pooled samples prepared from 616 mosquitoes captured in the vicinity of the village Drienovec, district Košice-surroundings. The investigation of 676 ticks demonstrated the presence of one strain of TBEV. One blood-fed I. ricinus female was obtained from a goat grazing in a pasture in the Dúbrava area close to Prešov. The genetic analysis revealed the presence of a strain close to the endemic strainsof TBEV Hypr and Neudörfl. The results of our study can become a motivation for additional studies in model locations oriented on ecology and circulation of these important zoonotic flaviviruses.

Seasonal dynamics of adult Dermacentor reticulatus in a peri-urban park in southern Europe

Studies on the human-biting pathogen vectors Dermacentor reticulatus and Ixodes ricinus have been scarce in southern Europe. The aims of the present study were to determine the abundance of these ticks in a peri-urban park in northern Italy, describe the seasonal activity of D. reticulatus and examine the correlation between tick occurrence and environmental factors. Ticks were collected monthly from April 2015 to May 2016 using both dragging and flagging techniques. Various climatic variables (mean temperature, relative humidity and evapotranspiration for the collection dates; and 30-day moving averages preceding each collection date were calculated for rainfall, temperature, relative humidity and saturation deficit) also were recorded. Overall, 444 adults of D. reticulatus and 10 adults of I. ricinus were collected. Males of D. reticulatus appeared earlier in the year than females, but overall females were collected more frequently than males (1:1.25). Statistical analysis showed significant differences in the density of D. reticulatus among sampling transects and among months. The seasonal dynamic of D. reticulatus was characterized by a single peak of activity in the early spring. Tick density was associated with climatic variables: the 30-day moving average saturation deficit was particularly significant as most ticks (83%) were collected at values below 5.2mmHg. At the level of individual sampling transects, seasonal dynamics could be influenced by habitat type and host availability. We found D. reticulatus to be most abundant in mixed forests dominated by oaks and rich in ponds. As to I. ricinus, though found in a small number, its presence can be confirmed by our investigation. In light of the results of this study, the risk for encounters with D. reticulatus and I. ricinus may be higher than previously thought in northern Italy.

Dermacentor reticulatus: a vector on the rise

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.

The transstadial persistence of tick-borne encephalitis virus in Dermacentor reticulatus ticks in natural conditions

There are a number of reports regarding natural infection of Dermacentor reticulatus ticks with TBE virus; however, the transmission mode of TBE virus in this tick population has not been investigated. This study was conducted in Białowieża Primeval Forest, east Poland. Forty fully engorged nymphs of D. reticulatus were sampled from root voles (Microtus oeconomus). Ticks were kept until molting. All ticks were screened for the presence of TBE virus by nested RT-PCR. Three adult ticks were positive for infection with TBE virus. The present study for the first time demonstrates the possibility of transstadial mode of TBEV transmission in D. reticulatus ticks.

The first detection of the tick-borne encephalitis virus (TBEV) RNA in Dermacentor reticulatus ticks collected from the lowland European bison (Bison bonasus bonasus L.)

Tick borne encephalitis virus (TBEV) (Flaviviridae, Flavivirus) is the causative agent of tick-borne encephalitis (TBE), a potentially fatal neurological infection. The disease is endemic in a large region in Eurasia, where is transmitted mainly by hard ticks: Ixodes ricinus and I. persulcatus. It is known that also Dermacentor reticulatus is involved in a circulation of TBEV, but the knowledge of its importance in the TBE epidemiology is still insufficient. The Białowieża Primeval Forest is located in eastern Poland and it is a well-known endemic focus of tick-borne encephalitis. The aim of this study was to identify the prevalence of tick-borne encephalitis virus (TBEV) in Dermacentor reticulatus ticks collected from European bison (Bison bonasus bonasus), an important host of hard ticks in the Białowieża Primeval Forest. In the years 2008-2009, a total of 114 adult D. reticulatus ticks were collected from 7 European bison and examined individually for the presence of TBEV RNA using nested RT-PCR assay. Positive results were noted in 18.42% of ticks. This is the first record of TBEV infection in ticks collected from European bison.

Geographical distribution of Dermacentor marginatus and Dermacentor reticulatus in Europe

The goal of this paper is to present up-to-date maps depicting the geographical distribution of Dermacentor species in Europe based on georeferenced sampling sites. Therefore, a dataset was compiled, resulting in 1286 D. marginatus (Sulzer, 1776) and 1209 D. reticulatus (Fabricius, 1794) locations. Special emphasis is given to the region of the European Alps depicting a presumable climate barrier of the mountains and to overlaps in the distribution of both species as well as on the situation in eastern European countries. For the latter newly described Dermacentor findings comprise 59 locations in Romania and 62 locations in Ukraine. The geographical distributions of both species in Europe range from Portugal to Ukraine (and continue to the east of Kazakhstan). Although it is well known that D. marginatus is adapted to a warmer and drier climate at more southern latitudes and D. reticulatus to a moderately moist climate at more northern latitudes, the distribution limits of both species were not well known. Here, the northern and southern distribution limits for both species in Europe, as determined from the georeferenced database, were specified for D. marginatus by the belt of 33-51° N latitude and for D. reticulatus by the belt of 41-57° N latitude. Thus, overlapping species distributions were found between 41° N and 51° N.

Pathogens vectored by the tick, Dermacentor reticulatus, in endemic regions and zones of expansion in Poland

Background

Dermacentor reticulatus plays an important role in the maintenance of pathogens of medical and veterinary importance in the environment. Currently two isolated populations of D. reticulatus are present in Poland –Western and Eastern. The range of the Eastern population covers endemic areas in eastern Poland but this population is expanding westwards creating an expansion zone in the centre of the country. The expansion zone in western Poland is occupied by the recently discovered Western population, spreading eastwards.

Methods

Questing adult ticks (n = 2585) were collected in 2012–2014 in endemic regions of north-eastern (Warmińsko-Mazurskie Voivodeship) and central Poland (Masovian Voivodeship) and in the expansion zones in central and western Poland, in the region between the Vistula River and the western border of the country. Amplification of Babesia, Rickettsia spp. and Borrelia burgdorferi sensu lato DNAs was performed using specific starters. RNA of the TBE virus was detected using RT-PCR and representative PCR products were sequenced and compared with sequences deposited in GenBank.

Results

Of the total 2585 examined ticks, 1197 (46.3 %) were infected with at least one pathogen. Overall prevalence of pathogens was 4.18 % (108/2585) for Babesia spp., 44.10 % (1140/2585) for Rickettsia spp., 0.09 % (1/1107) for Borrelia afzelii and 7.6 % (7/92) for TBEV. Sequence analysis of DNA showed 99.86 % similarity to R. raoulti and 99.81 % to B. canis. One male from north-eastern Poland was infected with B. microti.

Prevalence of R. raoulti was highest in the Western population (52.03 %) and lowest in the Eastern population in north-eastern Poland (34.18 %). Babesia canis was not detected in 592 ticks collected in the Western population, while in the Eastern population overall prevalence was 5.42 %. There were significant differences in the prevalence of B. canis between tick samples from northern (0.68 %), central (1.18 %) and southern (14.8 %) areas of the expansion zone in central Poland.

Conclusions

Our study found significant differences between the range and prevalence of vectored pathogens in D. reticulatus from the endemic areas and newly inhabited expansion zones. The differences were likely associated with the different time of settlement or ‘source’ of ticks populations, the Eastern and the Western one.

Novel foci of Dermacentor reticulatus ticks infected with Babesia canis and Babesia caballi in the Netherlands and in Belgium

Background

Autochthonous populations of Dermacentor reticulatus ticks in the Netherlands were discovered after fatal cases of babesiosis occurred in resident dogs in 2004. The presence of D. reticulatus in the Netherlands has also linked with the emergence of piroplasmosis in the resident horse population. The aim of this study was to put together results of continued surveillance of field sites and hosts for this tick in the Netherlands and also in Belgium and determine their infection status for Babesia and Theileria species.

Methods

Ticks were collected from the vegetation at 11 locations between 2011 and 2013. D. reticulatus ticks were also collected from different hosts between 2007 and 2013. Ticks were screened by PCR and reverse line blot (RLB).

Results

A total of 1368 D. reticulatus ticks were collected from 4 previously known field locations and from 5 new locations in the Netherlands and from 2 sites in Belgium (one old and one new location). A total of 855 ticks collected from 8 locations in the Netherlands and 2 locations in Belgium were tested. Fourteen ticks (1,64%) collected at 4 field locations (Dintelse Gorzen, Rozenburg, Slikken van de Heen and St. Philipsland) were positive for Babesia canis, whereas two ticks were positive for Babesia caballi, one tick in the Dintelse Gorzen in the Netherlands and one tick was found positive in De Panne in Belgium.

A further 1092 D. reticulatus ticks were collected between 2007 and 2013 from 40 dogs (132 ticks), two ticks from two humans, 51 ticks from 15 horses, two ticks from two cats, one tick from a roe deer, whereas most ticks (904) were collected from cattle (n = 25). Ticks were found throughout the year on dogs in nearly all provinces of the Netherlands. None of the ticks collected from these hosts were infected.

Conclusions

D. reticulatus is continuing its spread into novel areas. The finding that some autochthonous ticks are infected with B. canis and B. caballi poses a threat to the resident dog and horse population and justifies year-round tick control measures.

Ixodes ricinus and Its Transmitted Pathogens in Urban and Peri-Urban Areas in Europe: New Hazards and Relevance for Public Health

Tick-borne diseases represent major public and animal health issues worldwide. Ixodes ricinus, primarily associated with deciduous and mixed forests, is the principal vector of causative agents of viral, bacterial, and protozoan zoonotic diseases in Europe. Recently, abundant tick populations have been observed in European urban green areas, which are of public health relevance due to the exposure of humans and domesticated animals to potentially infected ticks. In urban habitats, small and medium-sized mammals, birds, companion animals (dogs and cats), and larger mammals (roe deer and wild boar) play a role in maintenance of tick populations and as reservoirs of tick-borne pathogens. Presence of ticks infected with tick-borne encephalitis virus and high prevalence of ticks infected with Borrelia burgdorferi s.l., causing Lyme borreliosis, have been reported from urbanized areas in Europe. Emerging pathogens, including bacteria of the order Rickettsiales (Anaplasma phagocytophilum, "Candidatus Neoehrlichia mikurensis," Rickettsia helvetica, and R. monacensis), Borrelia miyamotoi, and protozoans (Babesia divergens, B. venatorum, and B. microti) have also been detected in urban tick populations. Understanding the ecology of ticks and their associations with hosts in a European urbanized environment is crucial to quantify parameters necessary for risk pre-assessment and identification of public health strategies for control and prevention of tick-borne diseases.

Ixodes ricinus and Its Transmitted Pathogens in Urban and Peri-Urban Areas in Europe: New Hazards and Relevance for Public Health

Tick-borne diseases represent major public and animal health issues worldwide. Ixodes ricinus, primarily associated with deciduous and mixed forests, is the principal vector of causative agents of viral, bacterial, and protozoan zoonotic diseases in Europe. Recently, abundant tick populations have been observed in European urban green areas, which are of public health relevance due to the exposure of humans and domesticated animals to potentially infected ticks. In urban habitats, small and medium-sized mammals, birds, companion animals (dogs and cats), and larger mammals (roe deer and wild boar) play a role in maintenance of tick populations and as reservoirs of tick-borne pathogens. Presence of ticks infected with tick-borne encephalitis virus and high prevalence of ticks infected with Borrelia burgdorferi s.l., causing Lyme borreliosis, have been reported from urbanized areas in Europe. Emerging pathogens, including bacteria of the order Rickettsiales (Anaplasma phagocytophilum, "Candidatus Neoehrlichia mikurensis," Rickettsia helvetica, and R. monacensis), Borrelia miyamotoi, and protozoans (Babesia divergens, B. venatorum, and B. microti) have also been detected in urban tick populations. Understanding the ecology of ticks and their associations with hosts in a European urbanized environment is crucial to quantify parameters necessary for risk pre-assessment and identification of public health strategies for control and prevention of tick-borne diseases.