Showing papers on "Tick published in 2017"

Tick-Pathogen Interactions and Vector Competence: Identification of Molecular Drivers for Tick-Borne Diseases

Abstract: Ticks and the pathogens they transmit constitute a growing burden for human and animal health worldwide. Vector competence is a component of vectorial capacity and depends on genetic determinants affecting the ability of a vector to transmit a pathogen. These determinants affect traits such as tick-host-pathogen and susceptibility to pathogen infection. Therefore, the elucidation of the mechanisms involved in tick-pathogen interactions that affect vector competence is essential for the identification of molecular drivers for tick-borne diseases. In this review, we provide a comprehensive overview of tick-pathogen molecular interactions for bacteria, viruses, and protozoa affecting human and animal health. Additionally, the impact of tick microbiome on these interactions was considered. Results show that different pathogens evolved similar strategies such as manipulation of the immune response to infect vectors and facilitate multiplication and transmission. Furthermore, some of these strategies may be used by pathogens to infect both tick and mammalian hosts. Identification of interactions that promote tick survival, spread, and pathogen transmission provides the opportunity to disrupt these interactions and lead to a reduction in tick burden and the prevalence of tick-borne diseases. Targeting some of the similar mechanisms used by the pathogens for infection and transmission by ticks may assist in development of preventative strategies against multiple tick-borne diseases.

The Tick Microbiome: Why Non-pathogenic Microorganisms Matter in Tick Biology and Pathogen Transmission.

Abstract: Ticks are among the most important vectors of pathogens affecting humans and other animals worldwide. They do not only carry pathogens however, as a diverse group of commensal and symbiotic microorganisms are also present in ticks. Unlike pathogens, their biology and their effect on ticks remain largely unexplored, and are in fact often neglected. Nonetheless, they can confer multiple detrimental, neutral, or beneficial effects to their tick hosts, and can play various roles in fitness, nutritional adaptation, development, reproduction, defense against environmental stress, and immunity. Non-pathogenic microorganisms may also play a role in driving transmission of tick-borne pathogens (TBP), with many potential implications for both human and animal health. In addition, the genetic proximity of some pathogens to mutualistic symbionts hosted by ticks is evident when studying phylogenies of several bacterial genera. The best examples are found within members of the Rickettsia, Francisella, and Coxiella genera: while in medical and veterinary research these bacteria are traditionally recognized as highly virulent vertebrate pathogens, it is now clear to evolutionary ecologists that many (if not most) Coxiella, Francisella, and Rickettsia bacteria are actually non-pathogenic microorganisms exhibiting alternative lifestyles as mutualistic ticks symbionts. Consequently, ticks represent a compelling yet challenging system in which to study microbiomes and microbial interactions, and to investigate the composition, functional, and ecological implications of bacterial communities. Ultimately, deciphering the relationships between tick microorganisms as well as tick symbiont interactions will garner invaluable information, which may aid in the future development of arthropod pest and vector-borne pathogen transmission control strategies.

The Essential Role of Tick Salivary Glands and Saliva in Tick Feeding and Pathogen Transmission

Abstract: As long-term pool feeders, ticks have developed myriad strategies to remain discreetly but solidly attached to their hosts for the duration of their blood meal. The critical biological material that dampens host defences and facilitates the flow of blood—thus assuring adequate feeding—is tick saliva. Saliva exhibits cytolytic, vasodilator, anticoagulant, anti-inflammatory and immunosuppressive activity. This essential fluid is secreted by the salivary glands, which also mediate several other biological functions, including secretion of cement and hygroscopic components, as well as the watery component of blood as regards hard ticks. When salivary glands are invaded by tick-borne pathogens, pathogens may be transmitted via saliva, which is injected alternately with blood uptake during the tick bite. Both salivary glands and saliva thus play a key role in transmission of pathogenic microorganisms to vertebrate hosts. During their long co-evolution with ticks and vertebrate hosts, microorganisms have indeed developed various strategies to exploit tick salivary molecules to ensure both acquisition by ticks and transmission, local infection and systemic dissemination within the vertebrate host.

Tick-Borne Zoonoses in the United States: Persistent and Emerging Threats to Human Health.

Abstract: In the United States, ticks transmit the greatest diversity of arthropod-borne pathogens and are responsible for the most cases of all vector-borne diseases. In recent decades, the number of reported cases of notifiable tick-borne diseases has steadily increased, geographic distributions of many ticks and tick-borne diseases have expanded, and new tick-borne disease agents have been recognized. In this review, we (1) describe the known disease agents associated with the most commonly human-biting ixodid ticks, (2) review the natural histories of these ticks and their associated pathogens, (3) highlight spatial and temporal changes in vector tick distributions and tick-borne disease occurrence in recent decades, and (4) identify knowledge gaps and barriers to more effective prevention of tick-borne diseases. We describe 12 major tick-borne diseases caused by 15 distinct disease agents that are transmitted by the 8 most commonly human-biting ixodid ticks in the United States. Notably, 40% of these pathogens were described within the last two decades. Our assessment highlights the importance of animal studies to elucidate how tick-borne pathogens are maintained in nature, as well as advances in molecular detection of pathogens which has led to the discovery of several new tick-borne disease agents.

Evolutionary changes in symbiont community structure in ticks.

Abstract: Ecological specialization to restricted diet niches is driven by obligate, and often maternally inherited, symbionts in many arthropod lineages. These heritable symbionts typically form evolutionarily stable associations with arthropods that can last for millions of years. Ticks were recently found to harbour such an obligate symbiont, Coxiella-LE, that synthesizes B vitamins and cofactors not obtained in sufficient quantities from blood diet. In this study, the examination of 81 tick species shows that some Coxiella-LE symbioses are evolutionarily stable with an ancient acquisition followed by codiversification as observed in ticks belonging to the Rhipicephalus genus. However, many other Coxiella-LE symbioses are characterized by low evolutionary stability with frequent host shifts and extinction events. Further examination revealed the presence of nine other genera of maternally inherited bacteria in ticks. Although these nine symbionts were primarily thought to be facultative, their distribution among tick species rather suggests that at least four may have independently replaced Coxiella-LE and likely represent alternative obligate symbionts. Phylogenetic evidence otherwise indicates that cocladogenesis is globally rare in these symbioses as most originate via horizontal transfer of an existing symbiont between unrelated tick species. As a result, the structure of these symbiont communities is not fixed and stable across the tick phylogeny. Most importantly, the symbiont communities commonly reach high levels of diversity with up to six unrelated maternally inherited bacteria coexisting within host species. We further conjecture that interactions among coexisting symbionts are pivotal drivers of community structure both among and within tick species.

A study of ticks and tick-borne livestock pathogens in Pakistan.

Abstract: Background As obligate blood-feeding arthropods, ticks transmit pathogens to humans and domestic animals more often than other arthropod vectors. Livestock farming plays a vital role in the rural economy of Pakistan, and tick infestation causes serious problems with it. However, research on tick species diversity and tick-borne pathogens has rarely been conducted in Pakistan. In this study, a systematic investigation of the tick species infesting livestock in different ecological regions of Pakistan was conducted to determine the microbiome and pathobiome diversity in the indigenous ticks. Methodology/Principal findings A total of 3,866 tick specimens were morphologically identified as 19 different tick species representing three important hard ticks, Rhipicephalus, Haemaphysalis and Hyalomma, and two soft ticks, Ornithodorus and Argas. The bacterial diversity across these tick species was assessed by bacterial 16S rRNA gene sequencing using a 454-sequencing platform on 10 of the different tick species infesting livestock. The notable genera detected include Ralstonia, Clostridium, Staphylococcus, Rickettsia, Lactococcus, Lactobacillus, Corynebacterium, Enterobacter, and Enterococcus. A survey of Spotted fever group rickettsia from 514 samples from the 13 different tick species generated rickettsial-specific amplicons in 10% (54) of total ticks tested. Only three tick species Rhipicephalus microplus, Hyalomma anatolicum, and H. dromedarii had evidence of infection with “Candidatus Rickettsia amblyommii” a result further verified using a rompB gene-specific quantitative PCR (qPCR) assay. The Hyalomma ticks also tested positive for the piroplasm, Theileria annulata, using a qPCR assay. Conclusions/Significance This study provides information about tick diversity in Pakistan, and pathogenic bacteria in different tick species. Our results showed evidence for Candidatus R. amblyommii infection in Rhipicephalus microplus, H. anatolicum, and H. dromedarii ticks, which also carried T. annulata.

Tick microbiome and pathogen acquisition altered by host blood meal.

Abstract: Lyme disease, a zoonotic disease, is the most prevalent vector-borne disease in the Northern Hemisphere. Diversity of the vector (tick) microbiome can impact pathogen transmission, yet the biotic and abiotic factors that drive microbiome diversity are largely unresolved, especially under natural, field conditions. We describe the microbiome of Ixodes pacificus ticks, the vector for Lyme disease in the western United States, and show a strong impact of host blood meal identity on tick microbiome species richness and composition. Western fence lizards, a host that is refractory to the Lyme disease pathogen, significantly reduces microbiome diversity in ticks relative to ticks that feed on a mammalian reservoir host. Host blood meal-driven reduction of tick microbiome diversity may have lifelong repercussions on I. pacificus vector competency and ultimately disease dynamics.

Autochthonous Crimean-Congo Hemorrhagic Fever in Spain.

Abstract: Crimean–Congo hemorrhagic fever (CCHF) is a widely distributed, viral, tickborne disease. In Europe, cases have been reported only in the southeastern part of the continent. We report two autochthonous cases in Spain. The index patient acquired the disease through a tick bite in the province of Avila — 300 km away from the province of Caceres, where viral RNA from ticks was amplified in 2010. The second patient was a nurse who became infected while caring for the index patient. Both were infected with the African 3 lineage of this virus. (Funded by Red de Investigacion Cooperativa en Enfermedades Tropicales [RICET] and Efficient Response to Highly Dangerous and Emerging Pathogens at EU [European Union] Level [EMERGE].)

Europe-Wide Meta-Analysis of Borrelia burgdorferi Sensu Lato Prevalence in Questing Ixodes ricinus Ticks.

Abstract: Lyme borreliosis is the most common zoonotic disease transmitted by ticks in Europe and North America. Despite having multiple tick vectors, the causative agent Borrelia burgdorferi sensu lato, is vectored mainly by Ixodes ricinus in Europe. In the present study, we aimed to review and summarize the existing data published from 2010 to 2016 concerning the prevalence of B. burgdorferi s.l. spirochetes in questing I. ricinus . The primary focus was to evaluate the infection rate of these bacteria in ticks, accounting for tick stage, adult tick gender, region and detection method, as well as to investigate any changes in prevalence over time. The obtained data was compared to findings of a previous meta-study. The literature search identified data from 24 countries with 115,028 ticks in total inspected for infection with B. burgdorferi s.l. We showed that the infection rate was significantly higher in adults than in nymphs and in females than in males. We found significant differences between European regions, with the highest infection rates in Central Europe. The most common genospecies were B. afzelii and B. garinii , despite a negative correlation of their prevalence rates. There were no statistically significant differences found among the prevalence rates determined by conventional polymerase chain reaction (PCR), nested PCR or real-time PCR. IMPORTANCE Borrelia burgdorferi sensu lato is a pathogenic bacterium whose clinical manifestations are associated with Lyme borreliosis. This vector-borne disease is a major public health concern in Europe and North America and may lead to severe arthritic, cardiovascular and neurological complications if left untreated. Although pathogen prevalence is considered an important predictor of infection risk, solitary isolated data have only limited value. Here, we provide summarized information about the prevalence of the B. burgdorferi s.l. spirochetes in the host-seeking Ixodes ricinus ticks, its principal tick vector in Europe. We compare the new results with previously published data in order to evaluate any changing trends in tick infection.

Distribution of ticks infesting ruminants and risk factors associated with high tick prevalence in livestock farms in the semi-arid and arid agro-ecological zones of Pakistan

Abstract: Tick infestation is the major problem for animal health that causes substantial economic losses, particularly in tropical and subtropical countries. To better understand the spatial distribution of tick species and risk factors associated with tick prevalence in livestock in Pakistan, ticks were counted and collected from 471 animals, including 179 cattle, 194 buffaloes, 80 goats and 18 sheep, on 108 livestock farms in nine districts, covering both semi-arid and arid agro-ecological zones. In total, 3,807 ticks representing four species were collected: Hyalomma anatolicum (n = 3,021), Rhipicephalus microplus (n = 715), Hyalomma dromedarii (n = 41) and Rhipicephalus turanicus (n = 30). The latter species is reported for the first time from the study area. Rhipicephalus microplus was the predominant species in the semi-arid zone, whereas H. anatolicum was the most abundant species in the arid zone. The overall proportion of tick-infested ruminants was 78.3% (369/471). It was highest in cattle (89.9%), followed by buffaloes (81.4%), goats (60.0%) and sheep (11.1%). The median tick burden significantly differed among animal species and was highest in cattle (median 58), followed by buffaloes (median 38), goats (median 19) and sheep (median 4.5). Female animals had significantly higher tick burdens than males and, in large ruminants, older animals carried more ticks than younger animals. The intensity of infestation was significantly lower in indigenous animals compared to exotic and crossbred cows. Analysis of questionnaire data revealed that the absence of rural poultry, not using any acaricides, traditional rural housing systems and grazing were potential risk factors associated with a higher tick prevalence in livestock farms. Absence of rural poultry, not performing acaricide treatments, traditional rural housing systems and grazing were important risk factors associated with higher tick prevalence in livestock farms. Age, gender, breed and animal species significantly affected the intensity of tick infestation. This report also describes the presence of R. turanicus in the Punjab Province of Pakistan for the first time. The outcomes of this study will be useful in the planning of integrated control strategies for ticks and tick-borne diseases in Pakistan.

Emerging Tick-Borne Viruses in the Twenty-First Century.

Abstract: Ticks, as a group, are second only to mosquitoes as vectors of pathogens to humans and are the primary vector for pathogens of livestock, companion animals, and wildlife. The role of ticks in the transmission of viruses has been known for over 100 years and yet new pathogenic viruses are still being detected and known viruses are continually spreading to new geographic locations. Partly as a result of their novelty, tick-virus interactions are at an early stage in understanding. For some viruses, even the principal tick-vector is not known. It is likely that tick-borne viruses will continue to emerge and challenge public and veterinary health long into the twenty-first century. However, studies focusing on tick saliva, a critical component of tick feeding, virus transmission, and a target for control of ticks and tick-borne diseases, point toward solutions to emerging viruses. The aim of this review is to describe some currently emerging tick-borne diseases, their causative viruses, and to discuss research on virus-tick interactions. Through focus on this area, future protein targets for intervention and vaccine development may be identified.

A Coxiella mutualist symbiont is essential to the development of Rhipicephalus microplus

Abstract: The cattle tick Rhipicephalus microplus is a hematophagous ectoparasite that causes important economic losses in livestock. Different species of ticks harbor a symbiont bacterium of the genus Coxiella. It was showed that a Coxiella endosymbiont from R. microplus (CERM) is a vertically transmitted mutualist symbiont, comprising 98% of the 16S rRNA sequences in both eggs and larvae. Sequencing of the bacterial genome revealed genes for biosynthetic pathways for several vitamins and key metabolic cofactors that may provide a nutritional complement to the tick host. The CERM was abundant in ovary and Malpighian tubule of fully engorged female. Tetracycline treatment of either the tick or the vertebrate host reduced levels of bacteria in progeny in 74% for eggs and 90% for larvae without major impact neither on the reproductive fitness of the adult female or on embryo development. However, CERM proved to be essential for the tick to reach the adult life stage, as under antibiotic treatment no tick was able to progress beyond the metanymph stage. Data presented here suggest that interference in the symbiotic CERM-R. microplus relationship may be useful to the development of alternative control methods, highlighting the interdependence between ticks and their endosymbionts.

Molecular and MALDI-TOF identification of ticks and tick-associated bacteria in Mali.

Abstract: Ticks are considered the second vector of human and animal diseases after mosquitoes. Therefore, identification of ticks and associated pathogens is an important step in the management of these vectors. In recent years, Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) has been reported as a promising method for the identification of arthropods including ticks. The objective of this study was to improve the conditions for the preparation of tick samples for their identification by MALDI-TOF MS from field-collected ethanol-stored Malian samples and to evaluate the capacity of this technology to distinguish infected and uninfected ticks. A total of 1,333 ticks were collected from mammals in three distinct sites from Mali. Morphological identification allowed classification of ticks into 6 species including Amblyomma variegatum, Hyalomma truncatum, Hyalomma marginatum rufipes, Rhipicephalus (Boophilus) microplus, Rhipicephalus evertsi evertsi and Rhipicephalus sanguineus sl. Among those, 471 ticks were randomly selected for molecular and proteomic analyses. Tick legs submitted to MALDI-TOF MS revealed a concordant morpho/molecular identification of 99.6%. The inclusion in our MALDI-TOF MS arthropod database of MS reference spectra from ethanol-preserved tick leg specimens was required to obtain reliable identification. When tested by molecular tools, 76.6%, 37.6%, 20.8% and 1.1% of the specimens tested were positive for Rickettsia spp., Coxiella burnetii, Anaplasmataceae and Borrelia spp., respectively. These results support the fact that MALDI-TOF is a reliable tool for the identification of ticks conserved in alcohol and enhances knowledge about the diversity of tick species and pathogens transmitted by ticks circulating in Mali.

Cattle Tick Rhipicephalus microplus-Host Interface: A Review of Resistant and Susceptible Host Responses

Abstract: Ticks are able to transmit tick-borne infectious agents to vertebrate hosts which cause major constraints to public and livestock health. The costs associated with mortality, relapse, treatments, and decreased production yields are economically significant. Ticks adapted to a hematophagous existence after the vertebrate hemostatic system evolved into a multi-layered defense system against foreign invasion (pathogens and ectoparasites), blood loss, and immune responses. Subsequently, ticks evolved by developing an ability to suppress the vertebrate host immune system with a devastating impact particularly for exotic and crossbred cattle. Host genetics defines the immune responsiveness against ticks and tick-borne pathogens. To gain an insight into the naturally acquired resistant and susceptible cattle breed against ticks, studies have been conducted comparing the incidence of tick infestation on bovine hosts from divergent genetic backgrounds. It is well-documented that purebred and crossbred Bos taurus indicus cattle are more resistant to ticks and tick-borne pathogens compared to purebred European Bos taurus taurus cattle. Genetic studies identifying Quantitative Trait Loci markers using microsatellites and SNPs have been inconsistent with very low percentages relating phenotypic variation with tick infestation. Several skin gene expression and immunological studies have been undertaken using different breeds, different samples (peripheral blood, skin with tick feeding), infestation protocols and geographic environments. Susceptible breeds were commonly found to be associated with the increased expression of toll like receptors, MHC Class II, calcium binding proteins, and complement factors with an increased presence of neutrophils in the skin following tick feeding. Resistant breeds had higher levels of T cells present in the skin prior to tick infestation and thus seem to respond to ticks more efficiently. The skin of resistant breeds also contained higher numbers of eosinophils, mast cells and basophils with up-regulated proteases, cathepsins, keratins, collagens and extracellular matrix proteins in response to feeding ticks. Here we review immunological and molecular determinants that explore the cattle tick Rhipicephalus microplus-host resistance phenomenon as well as contemplating new insights and future directions to study tick resistance and susceptibility, in order to facilitate interventions for tick control.

parasitised feathered dinosaurs as revealed by Cretaceous amber assemblages.

Abstract: Ticks are currently among the most prevalent blood-feeding ectoparasites, but their feeding habits and hosts in deep time have long remained speculative. Here, we report direct and indirect evidence in 99 million-year-old Cretaceous amber showing that hard ticks and ticks of the extinct new family Deinocrotonidae fed on blood from feathered dinosaurs, non-avialan or avialan excluding crown-group birds. A †Cornupalpatum burmanicum hard tick is entangled in a pennaceous feather. Two deinocrotonids described as †Deinocroton draculi gen. et sp. nov. have specialised setae from dermestid beetle larvae (hastisetae) attached to their bodies, likely indicating cohabitation in a feathered dinosaur nest. A third conspecific specimen is blood-engorged, its anatomical features suggesting that deinocrotonids fed rapidly to engorgement and had multiple gonotrophic cycles. These findings provide insight into early tick evolution and ecology, and shed light on poorly known arthropod–vertebrate interactions and potential disease transmission during the Mesozoic.

Characterizing the virome of Ixodes ricinus ticks from northern Europe.

Abstract: RNA viruses are abundant infectious agents and present in all domains of life. Arthropods, including ticks, are well known as vectors of many viruses of concern for human and animal health. Despite their obvious importance, the extent and structure of viral diversity in ticks is still poorly understood, particularly in Europe. Using a bulk RNA-sequencing approach that captures the complete transcriptome, we analysed the virome of the most common tick in Europe – Ixodes ricinus. In total, RNA sequencing was performed on six libraries consisting of 33 I. ricinus nymphs and adults sampled in Norway. Despite the small number of animals surveyed, our virus identification pipeline revealed nine diverse and novel viral species, phylogenetically positioned within four different viral groups – bunyaviruses, luteoviruses, mononegavirales and partitiviruses – and sometimes characterized by extensive genetic diversity including a potentially novel genus of bunyaviruses. This work sheds new light on the virus diversity in I. ricinus, expands our knowledge of potential host/vector-associations and tick-transmitted viruses within several viral groups, and pushes the latitudinal limit where it is likely to find tick-associated viruses. Notably, our phylogenetic analysis revealed the presence of tick-specific virus clades that span multiple continents, highlighting the role of ticks as important virus reservoirs.

Tick-Borne Viruses and Biological Processes at the Tick-Host-Virus Interface

Abstract: Ticks are efficient vectors of arboviruses, although less than 10% of tick species are known to be virus vectors. Most tick-borne viruses (TBV) are RNA viruses some of which cause serious diseases in humans and animals world-wide. Several TBV impacting human or domesticated animal health have been found to emerge or re-emerge recently. In order to survive in nature, TBV must infect and replicate in both vertebrate and tick cells, representing very different physiological environments. Information on molecular mechanisms that allow TBV to switch between infecting and replicating in tick and vertebrate cells is scarce. In general, ticks succeed in completing their blood meal thanks to a plethora of biologically active molecules in their saliva that counteract and modulate different arms of the host defense responses (haemostasis, inflammation, innate and acquired immunity, and wound healing). The transmission of TBV occurs primarily during tick feeding and is a complex process, known to be promoted by tick saliva constituents. However, the underlying molecular mechanisms of TBV transmission are poorly understood. Immunomodulatory properties of tick saliva helping overcome the first line of defense to injury and early interactions at the tick-host skin interface appear to be essential in successful TBV transmission and infection of susceptible vertebrate hosts. The local host skin site of tick attachment, modulated by tick saliva, is an important focus of virus replication. Immunomodulation of the tick attachment site also promotes co-feeding transmission of viruses from infected to non-infected ticks in the absence of host viraemia (non-viraemic transmission). Future research should be aimed at identification of the key tick salivary molecules promoting virus transmission, and a molecular description of tick-host-virus interactions and of tick-mediated skin immunomodulation. Such insights will enable the rationale design of anti-tick vaccines that protect against disease caused by tick-borne viruses.

Modulation of the tick gut milieu by a secreted tick protein favors Borrelia burgdorferi colonization.

Abstract: The Lyme disease agent, Borrelia burgdorferi, colonizes the gut of the tick Ixodes scapularis, which transmits the pathogen to vertebrate hosts including humans. Here we show that B. burgdorferi colonization increases the expression of several tick gut genes including pixr, encoding a secreted gut protein with a Reeler domain. RNA interference-mediated silencing of pixr, or immunity against PIXR in mice, impairs the ability of B. burgdorferi to colonize the tick gut. PIXR inhibits bacterial biofilm formation in vitro and in vivo. Abrogation of PIXR function in vivo results in alterations in the gut microbiome, metabolome and immune responses. These alterations influence the spirochete entering the tick gut in multiple ways. PIXR abrogation also impairs larval molting, indicative of its role in tick biology. This study highlights the role of the tick gut in actively managing its microbiome, and how this impacts B. burgdorferi colonization of its arthropod vector. Borrelia burgdorferi, the causative agent of Lyme disease, is transmitted by the tick Ixodes scapularis. Here, the authors show that a tick secreted protein (PIXR) modulates the tick gut microbiota and facilitates B. burgdorferi colonization.

Borrelia Diversity and Co-infection with Other Tick Borne Pathogens in Ticks.

Abstract: Identifying Borrelia burgdorferi as the causative agent of Lyme disease in 1981 was a watershed moment in understanding the major impact that tick-borne zoonoses can have on public health worldwide, particularly in Europe and the USA. The medical importance of tick-borne diseases has long since been acknowledged, yet little is known regarding the occurrence of emerging tick-borne pathogens such as Borrelia spp., Anaplasma phagocytophilum, Rickettsia spp., Bartonella spp., “Candidatus Neoehrlichia mikurensis”, and tick-borne encephalitis virus in questing ticks in Romania, a gateway into Europe. The objective of our study was to identify the infection and co-infection rates of different Borrelia genospecies along with other tick-borne pathogens in questing ticks collected from three geographically distinct areas in eastern Romania. We collected 557 questing adult and nymph ticks of three different species (534 Ixodes ricinus, 19 Haemaphysalis punctata, and 4 Dermacentor reticulatus) from three areas in Romania. We analyzed ticks individually for the presence of eight different Borrelia genospecies with high-throughput real-time PCR. Ticks with Borrelia were then tested for possible co-infections with Anaplasma phagocytophilum, Rickettsia spp., Bartonella spp., “Candidatus Neoehrlichia mikurensis”, and tick-borne encephalitis virus. Borrelia spp. was detected in I. ricinus ticks from all sampling areas, with global prevalence rates of 25.8%. All eight Borrelia genospecies were detected in I. ricinus ticks: Borrelia garinii (14.8%), B. afzelii (8.8%), B. valaisiana (5.1%), B. lusitaniae (4.9%), B. miyamotoi (0.9%), B. burgdorferi s.s (0.4%), and B. bissettii (0.2%). Regarding pathogen co-infection 64.5% of infected I. ricinus were positive for more than one pathogen. Associations between different Borrelia genospecies were detected in 9.7% of ticks, and 6.9% of I. ricinus ticks tested positive for co-infection of Borrelia spp. with other tick-borne pathogens. The most common association was between B. garinii and B. afzelii (4.3%), followed by B. garinii and B. lusitaniae (3.0%). The most frequent dual co-infections were between Borrelia spp. and Rickettsia spp., (1.3%), and between Borrelia spp. and “Candidatus Neoehrlichia mikurensis” (1.3%). The diversity of tick-borne pathogens detected in this study and the frequency of co-infections should influence all infection risk evaluations following a tick bite.

Integrated Pest Management in Controlling Ticks and Tick-Associated Diseases

Abstract: The increasing prevalence of Lyme disease and the emergence of other tick-associated human diseases in the United States have become a major public health concern. A wide variety of personal protection measures and tick control strategies have been used or investigated to reduce contact between ticks and humans, reduce tick abundance, or lower the prevalence of tick-borne agents in the ticks. These methods have generally been applied or evaluated as single interventions and other than some early computer model simulations, studies applying integrated tick management approaches are few. In this paper, we review surveyed human behaviors and risks for exposure to ticks, concepts pertinent to integrated pest management for ticks, simulation models, various tick control strategies, integrated tick management studies, and highlight what is needed going forward. Increased education and communication between physicians and veterinarians is essential to address tick-associated diseases in a ‘one health’ approach and unify the animal and human branches of medicine to identify, treat, and implement preventive measures. Novel simulation models using more recent empirical data on tick population dynamics, hosts, efficacy of various combinations of interventions, human exposure elements, and utilization of personal and environmental measures will help us better understand the interactions of integrated strategies for tick population management. Many questions remain related to the ecology of ticks and tick-borne pathogens, observed and modeled efficacy of various integrated interventions, human behavior and exposure to tick bite and disease risk, comparative cost of interventions, and the acceptance and use of prevention and tick control tools.

Crowdsourcing-based nationwide tick collection reveals the distribution of Ixodes ricinus and I. persulcatus and associated pathogens in Finland

Abstract: A national crowdsourcing-based tick collection campaign was organized in 2015 with the objective of producing novel data on tick distribution and tick-borne pathogens in Finland. Nearly 20 000 Ixod...

Deer presence rather than abundance determines the population density of the sheep tick, Ixodes ricinus, in Dutch forests.

Abstract: Understanding which factors drive population densities of disease vectors is an important step in assessing disease risk. We tested the hypothesis that the density of ticks from the Ixodes ricinus complex, which are important vectors for tick-borne diseases, is determined by the density of deer, as adults of these ticks mainly feed on deer. We performed a cross-sectional study to investigate I. ricinus density across 20 forest plots in the Netherlands that ranged widely in deer availability to ticks, and performed a deer-exclosure experiment in four pairs of 1 ha forest plots in a separate site. Ixodes ricinus from all stages were more abundant in plots with deer (n = 17) than in plots without deer (n = 3). Where deer were present, the density of ticks did not increase with the abundance of deer. Experimental exclosure of deer reduced nymph density by 66% and adult density by 32% within a timeframe of two years. In this study, deer presence rather than abundance explained the density of I. ricinus. This is in contrast to previous studies and might be related to the relatively high host-species richness in Dutch forests. This means that reduction of the risk of acquiring a tick bite would require the complete elimination of deer in species rich forests. The fact that small exclosures (< 1 ha) substantially reduced I. ricinus densities suggests that fencing can be used to reduce tick-borne disease risk in areas with high recreational pressure.

Cascading effects of predator activity on tick-borne disease risk.

Abstract: Predators and competitors of vertebrates can in theory reduce the density of infected nymphs (DIN)-an often-used measure of tick-borne disease risk-by lowering the density of reservoir-competent hosts and/or the tick burden on reservoir-competent hosts. We investigated this possible indirect effect of predators by comparing data from 20 forest plots across the Netherlands that varied in predator abundance. In each plot, we measured the density of questing Ixodes ricinus nymphs (DON), DIN for three pathogens, rodent density, the tick burden on rodents and the activity of mammalian predators. We analysed whether rodent density and tick burden on rodents were correlated with predator activity, and how rodent density and tick burden predicted DON and DIN for the three pathogens. We found that larval burden on two rodent species decreased with activity of two predator species, while DON and DIN for all three pathogens increased with larval burden on rodents, as predicted. Path analyses supported an indirect negative correlation of activity of both predator species with DON and DIN. Our results suggest that predators can indeed lower the number of ticks feeding on reservoir-competent hosts, which implies that changes in predator abundance may have cascading effects on tick-borne disease risk.

Prevalence of tick-borne pathogens in questing Ixodes ricinus ticks in urban and suburban areas of Switzerland

Abstract: Throughout Europe, Ixodes ricinus transmits numerous pathogens. Its widespread distribution is not limited to rural but also includes urbanized areas. To date, comprehensive data on pathogen carrier rates of I. ricinus ticks in urban areas of Switzerland is lacking. Ixodes ricinus ticks sampled at 18 (sub-) urban collection sites throughout Switzerland showed carrier rates of 0% for tick-borne encephalitis virus, 18.0% for Borrelia burgdorferi (sensu lato), 2.5% for Borrelia miyamotoi, 13.5% for Rickettsia spp., 1.4% for Anaplasma phagocytophilum, 6.2% for "Candidatus Neoehrlichia mikurensis", and 0.8% for Babesia venatorum (Babesia sp., EU1). Site-specific prevalence at collection sites with n > 45 ticks (n = 9) significantly differed for B. burgdorferi (s.l.), Rickettsia spp., and "Ca. N. mikurensis", but were not related to the habitat type. Three hundred fifty eight out of 1078 I. ricinus ticks (33.2%) tested positive for at least one pathogen. Thereof, about 20% (71/358) were carrying two or three different potentially disease-causing agents. Using next generation sequencing, we could detect true pathogens, tick symbionts and organisms of environmental or human origin in ten selected samples. Our data document the presence of pathogens in the (sub-) urban I. ricinus tick population in Switzerland, with carrier rates as high as those in rural regions. Carriage of multiple pathogens was repeatedly observed, demonstrating the risk of acquiring multiple infections as a consequence of a tick bite.

The Distinct Transcriptional Response of the Midgut of Amblyomma sculptum and Amblyomma aureolatum Ticks to Rickettsia rickettsii Correlates to Their Differences in Susceptibility to Infection.

Abstract: Rickettsia rickettsii is a tick-borne obligate intracellular bacterium that causes Rocky Mountain Spotted Fever (RMSF). In Brazil, two species of ticks in the genus Amblyomma, A. sculptum and A. aureolatum, are incriminated as vectors of this bacterium. Importantly, these two species present remarkable differences in susceptibility to R. rickettsii infection, where A. aureolatum is more susceptible than A. sculptum. In the current study, A. aureolatum and A. sculptum ticks were fed on suitable hosts previously inoculated with R. rickettsii, mimicking a natural infection. As control, ticks were fed on non-infected animals. Both midgut and salivary glands of all positively infected ticks were colonized by R. rickettsii. We did not observe ticks with infection restricted to midgut, suggesting that important factors for controlling rickettsial colonization were produced in this organ. In order to identify such factors, the total RNA extracted from the midgut was submitted to new generation RNA sequencing (RNA-seq). The majority of the coding sequences (CDSs) of A. sculptum differentially expressed by infection were upregulated, whereas most of modulated CDSs of A. aureolatum were downregulated. The functional categories that comprise upregulated CDSs of A. sculptum, for instance, metabolism, signal transduction, protein modification, extracellular matrix, and immunity also include genes of A. aureolatum that were downregulated by infection. This is the first study that reports the effects of an experimental infection with the highly virulent R. rickettsii on the gene expression of two natural tick vectors. The distinct transcriptional profiles of the midgut of A. sculptum and A. aureolatum upon infection stimulus strongly suggest that molecular factors in this organ are responsible for delineating the susceptibility to R. rickettsii. Functional studies to determine the role played by proteins encoded by differentially expressed CDSs in the acquisition of R. rickettsii are warranted and may be considered as targets for the development of strategies to control the tick-borne pathogens as well as to control the tick vectors.

Ticks and the city - are there any differences between city parks and natural forests in terms of tick abundance and prevalence of spirochaetes?

Abstract: Ixodes ricinus ticks are commonly encountered in either natural or urban areas, contributing to Lyme disease agents Borreliella [(Borrelia burgdorferi (sensu lato)] spp. and Borrelia miyamotoi enzootic cycles in cities. It is an actual problem whether urbanization affects pathogen circulation and therefore risk of infection. The aim of the study was to evaluate main tick-borne disease risk factors in natural, endemic areas of north-east (NE) Poland (Bialowieza) and urban areas of central Poland (Warsaw), measuring tick abundance/density, prevalence of infection with spirochaetes and diversity of these pathogens in spring-early summer and late summer-autumn periods between 2012 and 2015. Questing I. ricinus ticks were collected from three urban sites in Warsaw, central Poland and three natural sites in Bialowieza, NE Poland. A total of 2993 ticks were analyzed for the presence of Borreliella spp. and/or Borrelia miyamotoi DNA by PCR. Tick abundance was analyzed by General Linear Models (GLM). Prevalence and distribution of spirochaetes was analyzed by Maximum Likelihood techniques based on log-linear analysis of contingency tables (HILOGLINEAR). Species typing and molecular phylogenetic analysis based on the sequenced flaB marker were carried out. Overall 4617 I. ricinus ticks were collected (2258 nymphs and 2359 adults). We report well established population of ticks in urban areas (10.1 ± 0.9 ticks/100 m2), as in endemic natural areas with higher mean tick abundance (16.5 ± 1.5 ticks/100 m2). Tick densities were the highest in spring-early summer in both types of areas. We observed no effect of the type of area on Borreliella spp. and B. miyamotoi presence in ticks, resulting in similar prevalence of spirochaetes in urban and natural areas [10.9% (95% CI: 9.7–12.2%) vs 12.4% (95% CI: 10.1–15.1%), respectively]. Prevalence of spirochaetes was significantly higher in the summer-autumn period than in the spring-early summer [15.0% (95% CI: 12.8–17.5%) vs 10.4% (95% CI: 9.2–11.6%), respectively]. We have detected six species of bacteria present in both types of areas, with different frequencies: dominance of B. afzelii (69.3%) in urban and B. garinii (48.1%) in natural areas. Although we observed higher tick densities in forests than in maintained parks, the prevalence of spirochaetes was significantly higher in the latter [9.8% (95% CI: 8.6–11.0%) vs 17.5% (95% CI: 14.4–20.5%)]. Surprisingly, a similar risk of infection with Borreliella spp. and/or B. miyamotoi was discovered in highly- and low-transformed areas. We suggest that the awareness of presence of these disease agents in cities should be raised.

Crimean-Congo Hemorrhagic Fever: Tick-Host-Virus Interactions.

Abstract: Crimean-Congo hemorrhagic fever virus (CCHFV) is transmitted to humans by bite of infected ticks or by direct contact with blood or tissues of viremic patients or animals It causes to humans a severe disease with fatality up to 30% The current knowledge about the vector-host-CCHFV interactions is very limited due to the high-level containment required for CCHFV studies Among ticks, Hyalomma spp are considered the most competent virus vectors CCHFV evades the tick immune response, and following its replication in the lining of the tick's midgut, it is disseminated by the hemolymph in the salivary glands and reproductive organs The introduction of salivary gland secretions into the host cells is the major route via which CCHFV enters the host Following an initial amplification at the site of inoculation, the virus is spread to the target organs Apoptosis is induced via both intrinsic and extrinsic pathways Genetic factors and immune status of the host may affect the release of cytokines which play a major role in disease progression and outcome It is expected that the use of new technology of metabolomics, transcriptomics and proteomics will lead to improved understanding of CCHFV-host interactions and identify potential targets for blocking the CCHFV transmission

Vertical vs. horizontal transmission of the microbiome in a key disease vector, Ixodes pacificus.

Abstract: Vector-borne pathogens are increasingly found to interact with the vector's microbiome, influencing disease transmission dynamics. However, the processes that regulate the formation and development of the microbiome are largely unexplored for most tick species, an emerging group of disease vectors. It is not known how much of the tick microbiome is acquired through vertical transmission vs. horizontally from the environment or interactions with bloodmeal sources. Using 16S rRNA sequencing, we examined the microbiome of Ixodes pacificus, the vector of Lyme disease in the western USA, across life stages and infection status. We also characterized microbiome diversity in field and laboratory-collected nymphal ticks to determine how the surrounding environment affects microbiome diversity. We found a decrease in both species richness and evenness as the tick matures from larva to adult. When the dominant Rickettsial endosymbiont was computationally removed from the tick microbial community, we found that infected nymphs had lower species evenness than uninfected ticks, suggesting that lower microbiome diversity is associated with pathogen transmission in wild-type ticks. Furthermore, laboratory-reared nymph microbiome diversity was found to be compositionally distinct and significantly depauperate relative to field-collected nymphs. These results highlight unique patterns in the microbial community of I. pacificus that is distinct from other tick species. We provide strong evidence that ticks acquire a significant portion of their microbiome through exposure to their environment despite a loss of overall diversity through life stages. We provide evidence that loss of microbial diversity is at least in part due to elimination of microbial diversity with bloodmeal feeding but other factors may also play a role.