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

Disparate dynamics of pathogen prevalence in Ixodes ricinus and Dermacentor reticulatus ticks occurring sympatrically in diverse habitats

Ixodes ricinus and Dermacentor reticulatus ticks are important reservoirs and vectors of pathogens. The aim of the present study was to investigate the dynamic of the prevalence and genetic diversity of microorganisms detected in these tick species collected from two ecologically diverse biotopes undergoing disparate long-term climate condition. High-throughput real time PCR confirmed high prevalence of microorganisms detected in sympatrically occurring ticks species. D. reticulatus specimens were the most often infected with Francisella-like endosymbiont (FLE) (up to 100.0%) and Rickettsia spp. (up to 91.7%), while in case of I. ricinus the prevalence of Borreliaceae spirochetes reached up to 25.0%. Moreover, pathogens belonging to genera of Bartonella, Anaplasma, Ehrlichia and Babesia were detected in both tick species regardless the biotope. On the other hand, Neoehrlichia mikurensis was conformed only in I. ricinus in the forest biotope, while genetic material of Theileria spp. was found only in D. reticulatus collected from the meadow. Our study confirmed significant impact of biotope type on prevalence of representatives of Borreliaceae and Rickettsiaceae families. The most common co-infection detected in D. reticulatus was Rickettsia spp. + FLE, while Borreliaceae + R. helvetica was the most common in I. ricinus. Additionally, we found significant genetic diversity of R. raoultii gltA gene across studied years, however such relationship was not observed in ticks from studied biotopes. Our results suggest that ecological type of biotope undergoing disparate long-term climate conditions have an impact on prevalence of tick-borne pathogens in adult D. reticulatus and I. ricinus.

Distribution of ticks in the Western Palearctic: an updated systematic review (2015-2021)

BACKGROUND

The distributions of ticks and tick-borne pathogens are thought to have changed rapidly over the last two decades, with their ranges expanding into new regions. This expansion has been driven by a range of environmental and socio-economic factors, including climate change. Spatial modelling is being increasingly used to track the current and future distributions of ticks and tick-borne pathogens and to assess the associated disease risk. However, such analysis is dependent on high-resolution occurrence data for each species. To facilitate such analysis, in this review we have compiled georeferenced tick locations in the Western Palearctic, with a resolution accuracy under 10 km, that were reported between 2015 and 2021 METHODS: The PubMed and Web of Science databases were searched for peer-reviewed papers documenting the distribution of ticks that were published between 2015 and 2021, using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The papers were then screened and excluded in accordance with the PRISMA flow chart. Coordinate-referenced tick locations along with information on identification and collection methods were extracted from each eligible publication. Spatial analysis was conducted using R software (version 4.1.2).

RESULTS

From the 1491 papers identified during the initial search, 124 met the inclusion criteria, and from these, 2267 coordinate-referenced tick records from 33 tick species were included in the final dataset. Over 30% of articles did not record the tick location adequately to meet inclusion criteria, only providing a location name or general location. Among the tick records, Ixodes ricinus had the highest representation (55%), followed by Dermacentor reticulatus (22.1%) and Ixodes frontalis (4.8%). The majority of ticks were collected from vegetation, with only 19.1% collected from hosts.

CONCLUSIONS

The data presented provides a collection of recent high-resolution, coordinate-referenced tick locations for use in spatial analyses, which in turn can be used in combination with previously collated datasets to analyse the changes in tick distribution and research in the Western Palearctic. In the future it is recommended that, where data privacy rules allow, high-resolution methods are routinely used by researchers to geolocate tick samples and ensure their work can be used to its full potential.

Influence of ecological and climatic conditions on the spread of Borrelia burgdorferi in domestic dogs in Ukraine

Lyme-borreliosis is a zoonotic, infectious disease that has a complex chain of transmission of the pathogen Borrelia burgdorferi sensu lato and includes the relationship between ixodid ticks, vertebrate hosts, humans and companion animals in the environment. The article shows general trends in the prevalence of canine Lyme-borreliosis in Ukraine depending on environmental, climatic and physiographic factors. The results of a comparative cartographic analysis of the prevalence of Lyme borreliosis among domestic dogs in Ukraine are presented by systematizing, mathematical and statistical processing of the data obtained by surveying veterinarians engaged in clinical veterinary practice. The paper includes generalized data on the clinical manifestations, methods of diagnosis and treatment of Lyme borreliosis in dogs. We determined the dependence of the prevalence of Lyme borreliosis in dogs on the types of physical and geographical territories – natural zones of Ukraine. Each of the natural zones differs in types of relief, climatic conditions, soil types, composition of fauna and flora, which affect the epizootic chain of Lyme disease. There is a clear correlation between the incidence of Lyme borreliosis in dogs and the types of natural areas. The highest incidence of Lyme borreliosis in dogs was observed in the forest-steppe zone and the zone of broad-leaved forests. A sharp decrease in the incidence of dogs was recorded in areas of mixed forests, the Ukrainian Carpathians and in the South of Ukraine in the steppe zone. The study also confirmed that the prevalence of Lyme disease among domestic dogs was influenced by the climatic factors, in particular: gross moisture of territories, average annual air temperature and soil temperature. In Ukraine, veterinarians in the vast majority of cases use serological diagnostic methods: immunochromatographic analysis, immunoenzymatic assay, and western blot, which are insufficient, since the presence of antibodies to the Lyme borreliosis pathogen is only a confirmation of the animal's contact with the antigen and may not indicate the presence of the disease in the clinical form. The generalized data on the use of antimicrobial drugs in the treatment of Lyme borreliosis in dogs indicate the predominant use of tetracycline antibiotics and cephalosporins. The majority of veterinarians reported symptoms of Lyme arthritis, somewhat fewer reported Lyme nephritis, neuroborreliosis, Lyme carditis and in rare cases, veterinarians observed erythema at the site of tick bite. About half of the veterinarians in Ukraine observed an increase in the incidence of Lyme disease in dogs, indicating a probable deterioration of the epizootic and epidemiological situation regarding Lyme borreliosis, especially in areas with favourable conditions for the circulation of Lyme borreliosis pathogens in natural and urban ecotopes. The results substantiate the need for the further study of the circulation of Borrelia burgdorferi sensu lato and their ability to cause disease in humans and animals, as well as the need to implement the principles of the One Health concept for the control and management of Lyme borreliosis.

Anaplasma phagocytophilum infection rates in questing and host-attached ticks: a global systematic review and meta-analysis

Anaplasma phagocytophilum causes a multi-organ non-specific febrile illness referred to as human granulocytic anaplasmosis. The epidemiologic risk of the pathogen is underestimated despite human encroachment into the natural habitats of ticks. In this study, we performed a systematic review and meta-analysis to determine the global infection rates and distribution of A. phagocytophilum in tick vectors. We pooled data using the random-effects model, assessed individual study quality using the Joanna Briggs Institute critical appraisal instrument for prevalence studies and determined heterogeneity and across study bias using Cochran's Q-test and Egger's regression test respectively. A total of 126 studies from 33 countries across 4 continents reported A. phagocytophilum estimated infection rate of 4.76% (9453/174,967; 95% CI: 3.96, 5.71). Estimated IRs across sub-groups varied significantly (p <0.05) with a range of 1.95 (95% CI: 0.63, 5.86) to 7.15% (95% CI: 5.31, 9.56). Country-based IRs ranged between 0.42 (95% CI: 0.22, 0.80) in Belgium and 37.54% (95% CI: 0.72, 98.03) in Norway. The highest number of studies on A. phagocytophilum were in Europe (82/126) by continent and the USA (33/126) by country. The risk of transmitting this pathogens from ticks to animals and humans exist and therefore, we recommend the use of chemical and biological control measures as well as repellents and protective clothing by occupationally exposed individuals to curtail further transmission of the pathogen to humans and animals.

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

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

International Rickettsia Disease Surveillance: An Example of Cooperative Research to Increase Laboratory Capability and Capacity for Risk Assessment of Rickettsial Outbreaks Worldwide

Cooperative research that addresses infectious disease surveillance and outbreak investigations relies heavily on availability and effective use of appropriate diagnostic tools, including serological and molecular assays, as exemplified by the current COVID-19 pandemic. In this paper, we stress the importance of using these assays to support collaborative epidemiological studies to assess risk of rickettsial disease outbreaks among international partner countries. Workforce development, mentorship, and training are important components in building laboratory capability and capacity to assess risk of and mitigate emerging disease outbreaks. International partnerships that fund cooperative research through mentoring and on-the-job training are successful examples for enhancing infectious disease surveillance. Cooperative research studies between the Naval Medical Research Center's Rickettsial Diseases Research Program (RDRP) and 17 institutes from nine countries among five continents were conducted to address the presence of and the risk for endemic rickettsial diseases. To establish serological and molecular assays in the collaborative institutes, initial training and continued material, and technical support were provided by RDRP. The laboratory methods used in the research studies to detect and identify the rickettsial infections included (1) group-specific IgM and IgG serological assays and (2) molecular assays. Twenty-six cooperative research projects performed between 2008 and 2020 enhanced the capability and capacity of 17 research institutes to estimate risk of rickettsial diseases. These international collaborative studies have led to the recognition and/or confirmation of rickettsial diseases within each of the partner countries. In addition, with the identification of specific pathogen and non-pathogen Rickettsia species, a more accurate risk assessment could be made in surveillance studies using environmental samples. The discoveries from these projects reinforced international cooperation benefiting not only the partner countries but also the scientific community at large through presentations (n = 40) at international scientific meetings and peer-reviewed publications (n = 18). The cooperative research studies conducted in multiple international institutes led to the incorporation of new SOPs and trainings for laboratory procedures; biosafety, biosurety, and biosecurity methods; performance of rickettsia-specific assays; and the identification of known and unknown rickettsial agents through the introduction of new serologic and molecular assays that complemented traditional microbiology methods.

Prevalence of Borrelia burgdorferi and Anaplasma phagocytophilum in Ixodid Ticks from Southeastern Ukraine

Objectives: Tick-borne diseases have emerged as an increasing medical problem in the world. Being the most prevalent ixodid ticks in Europe, Ixodes ricinus and Dermacentor reticulatus are responsible for transmission of numerous zoonotic pathogens (e.g., human granulocytic anaplasmosis and Lyme borreliosis). Despite their public health significance, studies on the prevalence of tick-borne agents are scare for Eastern Europe. The objective of this study was to examine the prevalence of Anaplasma phagocytophilum, Ehrlichia chaffeensis, and Borrelia burgdorferi sensu lato (B. burgdorferi s. l.) in ixodid ticks from Southeastern Ukraine. Methods: Over a 5-year period (2014-2018), 358 questing and 389 engorged ixodid ticks were collected from Southeastern Ukraine (Zaporizhzhya region). The ticks were identified as Dermacentor marginatus, D. reticulatus, I. ricinus, and Rhipicephalus rossicus. Nucleic acid samples extracted from tick pools were subjected to RT-PCR analyses for A. phagocytophilum, E. chaffeensis, and B. burgdorferi s. l. Results: The examined ixodid ticks tested negative for the aforementioned pathogens with the exception of I. ricinus ticks. For questing I. ricinus ticks, minimum infection rates of A. phagocytophilum and B. burgdorferi s. l. were, respectively, 4.2-7.7% and 8.6-12.7%. Conclusions: These findings will be valuable for medical and veterinary practitioners when risks associated with tick-borne diseases are assessed for southeastern regions of Ukraine.

Detection of pathogens in ixodid ticks collected from animals and vegetation in five regions of Ukraine

The distribution and prevalence of zoonotic pathogens infecting ixodid ticks in Western Europe have been extensively examined. However, data on ticks and tick-borne pathogens in Eastern Europe, particularly Ukraine are scarce. The objective of the current study was, therefore, to investigate the prevalence of Anaplasma phagocytophilum, Anaplasmataceae, Rickettsia spp., Babesia spp., Bartonella spp., and Borrelia burgdorferi sensu lato in engorged and questing ixodid ticks collected from five administrative regions (oblasts) of Ukraine, namely Chernivtsi, Khmelnytskyi, Kyiv, Ternopil, and Vinnytsia. The ticks were collected from both wild and domestic animals and from vegetation. Of 524 ixodid ticks collected, 3, 99, and 422 ticks were identified as Ixodes hexagonus, Ixodes ricinus, and Dermacentor reticulatus, respectively. DNA samples individually extracted from 168 questing and 354 engorged adult ticks were subjected to pathogen-specific PCR analyses. The mean prevalence in I. ricinus and D. reticulatus were, respectively: 10 % (10/97) and 3 % (12/422) for A. phagocytophilum; 69 % (67/97) and 52 % (220/422) for members of the Anaplasmataceae family; 25 % (24/97) and 28 % (117/422) for Rickettsia spp.; 3 % (3/97) and 1 % (6/422) for Babesia spp.; and 9 % (9/97) and 5 % (20/422) for Bartonella spp. Overall, between the five cities, there was no significant difference in the prevalence of any of the pathogens for the respective ticks (p > 0.05). The prevalence of B. burgdorferi s. l. in the questing and engorged I. ricinus varied from 0 to 27 % and 14-44%, respectively, with no statistical significance identified between the five cities (p > 0.05). In addition to reporting the updated data for Kyiv and Ternopil, this study is the first to provide the prevalences of the tick-borne pathogens for Chernivtsi, Khmelnytskyi, and Vinnytsia. This investigation is also the first to detect Neoehrlichia mikurensis in ixodid ticks from Ukraine. These new data will be useful for medical and veterinary practitioners as well as public health officials when diagnosing infections and when implementing measures to combat tick-borne diseases in Ukraine.