Tick immunobiology

Local immune response to larvae of Rhipicephalus microplus in Santa Gertrudis cattle

This study investigated the local immune response at larval attachment sites in Santa Gertrudis cattle with low and high levels of tick resistance. Skin samples with tick larvae attached were collected from Santa Gertrudis cattle at the end of a period of 25 weekly infestations, when the animals manifested highly divergent tick-resistant phenotypes. There was a tendency for more CD3⁺ , CD4⁺ , CD8⁺ , CD25⁺ , γδ T cells and neutrophils to concentrate at larval tick attachment site in susceptible cattle than in resistant cattle but the differences were significant only for γδ T cells and CD4⁺ cells. Most of the cattle developed intra-epidermal vesicles at the larval attachment site but the predominant cell within or around the vesicles was the neutrophil in susceptible animals and eosinophil in the resistant animals. The monoclonal antibodies (mAbs) specific for CD45 and CD45 RO antigens reacted with skin leucocytes from a higher number of susceptible cattle than resistant cattle. Our data suggest that some of the cellular responses mounted at larval attachment site are not involved in tick protection. The mAbs specific for CD45 and CD45 RO directly, or a test for CD45 genotype might be developed as markers of tick susceptibility or resistance.

Immunomodulatory Effects of Amblyomma variegatum Saliva on Bovine Cells: Characterization of Cellular Responses and Identification of Molecular Determinants

The tropical bont tick, Amblyomma variegatum, is a tick species of veterinary importance and is considered as one of major pest of ruminants in Africa and in the Caribbean. It causes direct skin lesions, transmits heartwater, and reactivates bovine dermatophilosis. Tick saliva is reported to affect overall host responses through immunomodulatory and anti-inflammatory molecules, among other bioactive molecules. The general objective of this study was to better understand the role of saliva in interaction between the Amblyomma tick and the host using cellular biology approaches and proteomics, and to discuss its impact on disease transmission and/or activation. We first focused on the immuno-modulating effects of semi-fed A. variegatum female saliva on bovine peripheral blood mononuclear cells (PBMC) and monocyte-derived macrophages in vitro. We analyzed its immuno-suppressive properties by measuring the effect of saliva on PBMC proliferation, and observed a significant decrease in ConA-stimulated PBMC lymphoproliferation. We then studied the effect of saliva on bovine macrophages using flow cytometry to analyze the expression of MHC-II and co-stimulation molecules (CD40, CD80, and CD86) and by measuring the production of nitric oxide (NO) and pro- or anti-inflammatory cytokines. We observed a significant decrease in the expression of MHC-II, CD40, and CD80 molecules, associated with decreased levels of IL-12-p40 and TNF-α and increased level of IL-10, which could explain the saliva-induced modulation of NO. To elucidate these immunomodulatory effects, crude saliva proteins were analyzed using proteomics with an Orbitrap Elite mass spectrometer. Among the 336 proteins identified in A. variegatum saliva, we evidenced bioactive molecules exhibiting anti-inflammatory, immuno-modulatory, and anti-oxidant properties (e.g., serpins, phospholipases A2, heme lipoprotein). We also characterized an intriguing ubiquitination complex that could be involved in saliva-induced immune modulation of the host. We propose a model for the interaction between A. variegatum saliva and host immune cells that could have an effect during tick feeding by favoring pathogen dissemination or activation by reducing the efficiency of host immune response to the corresponding tick-borne diseases.

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

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 defenses 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.

Protease Inhibitors in Tick Saliva: The Role of Serpins and Cystatins in Tick-host-Pathogen Interaction

The publication of the first tick sialome (salivary gland transcriptome) heralded a new era of research of tick protease inhibitors, which represent important constituents of the proteins secreted via tick saliva into the host. Three major groups of protease inhibitors are secreted into saliva: Kunitz inhibitors, serpins, and cystatins. Kunitz inhibitors are anti-hemostatic agents and tens of proteins with one or more Kunitz domains are known to block host coagulation and/or platelet aggregation. Serpins and cystatins are also anti-hemostatic effectors, but intriguingly, from the translational perspective, also act as pluripotent modulators of the host immune system. Here we focus especially on this latter aspect of protease inhibition by ticks and describe the current knowledge and data on secreted salivary serpins and cystatins and their role in tick-host-pathogen interaction triad. We also discuss the potential therapeutic use of tick protease inhibitors.

Serine Protease Inhibitors in Ticks: An Overview of Their Role in Tick Biology and Tick-Borne Pathogen Transmission

New tick and tick-borne pathogen control approaches that are both environmentally sustainable and which provide broad protection are urgently needed. Their development, however, will rely on a greater understanding of tick biology, tick-pathogen, and tick-host interactions. The recent advances in new generation technologies to study genomes, transcriptomes, and proteomes has resulted in a plethora of tick biomacromolecular studies. Among these, many enzyme inhibitors have been described, notably serine protease inhibitors (SPIs), whose importance in various tick biological processes is only just beginning to be fully appreciated. Among the multiple active substances secreted during tick feeding, SPIs have been shown to be directly involved in regulation of inflammation, blood clotting, wound healing, vasoconstriction and the modulation of host defense mechanisms. In light of these activities, several SPIs were examined and were experimentally confirmed to facilitate tick pathogen transmission. In addition, to prevent coagulation of the ingested blood meal within the tick alimentary canal, SPIs are also involved in blood digestion and nutrient extraction from the meal. The presence of SPIs in tick hemocytes and their involvement in tick innate immune defenses have also been demonstrated, as well as their implication in hemolymph coagulation and egg development. Considering the involvement of SPIs in multiple crucial aspects of tick-host-pathogen interactions, as well as in various aspects of the tick parasitic lifestyle, these molecules represent highly suitable and attractive targets for the development of effective tick control strategies. Here we review the current knowledge regarding this class of inhibitors in tick biology and tick-borne pathogen transmission, and their potential as targets for future tick control trials.

A new method for in vitro feeding of Rhipicephalus australis (formerly Rhipicephalus microplus) larvae: a valuable tool for tick vaccine development

BACKGROUND

Rhipicephalus microplus is a hard tick that has a major impact on cattle health in tropical and subtropical regions because it feeds on cattle and is implicated in the transmission of pathogens that cause diseases such as bovine anaplasmosis and babesiosis. Presently, acaricides are used to control tick infestation but this is becoming increasingly less effective due to the emergence of tick strains that are resistant to one or more classes of acaricides. Anti-tick vaccines are a promising alternative to control tick infestation in cattle. The life-cycle and host preference of R. microplus, however, makes vaccine research in cattle costly and would therefore greatly benefit from an in vitro screening system.

METHODS

To this aim, a stacked 24-well in vitro feeding system was designed in which the blood meal was administered in a chamber on top of the compartment containing the ticks, exploiting their anti-gravitational tendency. Both compartments were separated by a special feeding membrane, which was made by applying a silicone mixture to a gold beater's skin (baudruche membrane) with a paint roller to create a slightly uneven surface of 17-40 μm variable thickness. To further stimulate feeding, the membrane was treated with bovine hair extract and the unit was placed at 37 °C with 90% RH and 5% CO2.

RESULTS

Using this set-up with Rhipicephalus australis (formerly Rhipicephalus microplus), a larval engorgement rate of up to 71% could be achieved. The larvae could successfully feed on blood, but also on serum. The latter allows easy screening of the effect of sera that are raised against tick proteins on feeding. As an example, serum from cattle that were vaccinated with the Bm86 midgut protein of R. microplus significantly reduced larval engorgement rates by 42%.

CONCLUSION

The in vitro feeding system's high throughput design and its ability to measure statistically significant anti-tick effects in sera from immunized cattle enables screening of multiple vaccine candidates in a cost-effective manner.

Ticks elicit variable fibrinogenolytic activities upon feeding on hosts with different immune backgrounds

Ticks secrete several anti-hemostatic factors in their saliva to suppress the host innate and acquired immune defenses against infestations. Using Ixodes scapularis ticks and age-matched mice purchased from two independent commercial vendors with two different immune backgrounds as a model, we show that ticks fed on immunodeficient animals demonstrate decreased fibrinogenolytic activity in comparison to ticks fed on immunocompetent animals. Reduced levels of D-dimer (fibrin degradation product) were evident in ticks fed on immunodeficient animals in comparison to ticks fed on immunocompetent animals. Increased engorgement weights were noted for ticks fed on immunodeficient animals in comparison to ticks fed on immunocompetent animals. Furthermore, the LC-MS/MS and quantitative real-time-PCR analysis followed by inhibitor and antibody-blocking assays revealed that the arthropod HSP70-like molecule contributes to differential fibrinogenolysis during tick feeding. Collectively, these results not only indicate that ticks elicit variable fibrinogenolysis upon feeding on hosts with different immune backgrounds but also provide insights for the novel role of arthropod HSP70-like molecule in fibrinogenolysis during blood feeding.

Diversity and distribution of tick species (Acari: Ixodidae) associated with human otoacariasis and socio-ecological risk factors of tick infestations in Sri Lanka

Tick infestation in humans is a major public health concern. The diversity and distribution of tick species associated with human otoacariasis was studied in five districts: Anuradhapura, Kandy, Kurunegala, Nuwara Eliya and Ratnapura in the main agro-climatic zones of Sri Lanka. Ticks from patients attending the ear, nose and throat clinics of the General Hospitals were collected during a 3 year period. In total 426 ticks were collected. Most human otoacariasis cases were reported from Kandy (33.8 %) and the fewest from Nuwara Eliya (8.2 %). Of the five tick species identified, nymphs of Dermacentor auratus constituted 90.6 % of the collection. Rhipicephalus sanguineus, Hyalomma isaaci, Haemaphysalis bispinosa and Otobius megnini were found rarely infesting humans possibly as an accidental host; H. bispinosa and O. megnini in the human ear canal were first time records in Sri Lanka. Females and children under 10 years were identified as risk groups of human otoacariasis. Subsequently, a field study was carried out to determine socio-ecological risk factors of human tick infestations in the five districts. Based on hospital data, eight villages with high prevalence of otoacariasis were selected from each district. A total 40 villages were visited and 1674 household members were interviewed. Involvement in outdoor activities, presence of wild animals around the house, location of the house in close proximity to a forest and occupation were identified as major risk factors.

Immunomodulatory effects of tick saliva on dermal cells exposed to Borrelia burgdorferi, the agent of Lyme disease

BACKGROUND

The prolonged feeding process of ixodid ticks, in combination with bacterial transmission, should lead to a robust inflammatory response at the blood-feeding site. Yet, factors present in tick saliva may down-regulate such responses, which may be beneficial to spirochete transmission. The primary goal of this study was to test the hypothesis that tick saliva, in the context of Borrelia burgdorferi, can have widespread effects on the production of immune mediators in skin.

METHODS

A cross-section of tick feeding on skin was examined histologically. Human THP-1 cells stimulated with B. burgdorferi and grown in the presence or absence of tick saliva were examined by human DNA microarray, cytokine bead array, sandwich ELISA, and qRT-PCR. Similar experiments were also conducted using dermal fibroblasts.

RESULTS

Tick feeding on skin showed dermal infiltration of histiocytes and granulocytes at the bite location. Changes in monocytic transcript levels during co-culture with B. burgdorferi and saliva indicated that tick saliva had a suppressive effect on the expression of certain pro-inflammatory mediators, such as IL-8 (CXCL8) and TLR2, but had a stimulatory effect on specific molecules such as the Interleukin 10 receptor, alpha subunit (IL-10RA), a known mediator of the immunosuppressive signal of IL-10. Stimulated cell culture supernatants were analyzed via antigen-capture ELISA and cytokine bead array for inflammatory mediator production. Treatment of monocytes with saliva significantly reduced the expression of several key mediators including IL-6, IL-8 and TNF-alpha. Tick saliva had an opposite effect on dermal fibroblasts. Rather than inhibiting, saliva enhanced production of pro-inflammatory mediators, including IL-8 and IL-6 from these sentinel skin cells.

CONCLUSIONS

The effects of ixodid tick saliva on resident skin cells is cell type-dependent. The response to both tick and pathogen at the site of feeding favors pathogen transmission, but may not be wholly suppressed by tick saliva.

Larvae of Ixodes ricinus transmit Borrelia afzelii and B. miyamotoi to vertebrate hosts

Background

Lyme borreliosis is the most common tick-borne human disease and is caused by Borrelia burgdorferi sensu lato (s.l.). Borrelia miyamotoi, a relapsing fever spirochaete, is transmitted transovarially, whereas this has not been shown for B. burgdorferi (s.l). Therefore, B. burgdorferi (s.l) is considered to cycle from nymphs to larvae through vertebrates. Larvae of Ixodes ricinus are occasionally B. burgdorferi (s.l) infected, but their vector competence has never been studied.

Methods

We challenged 20 laboratory mice with field-collected larvae of I. ricinus. A subset of these larvae was analysed for infections with B. burgdorferi (s.l) and B. miyamotoi. After three to four challenges, mice were sacrificed and skin and spleen samples were analysed for infection by PCR and culture.

Results

Field-collected larvae were naturally infected with B. burgdorferi (s.l) (0.62 %) and B. miyamotoi (2.0 %). Two mice acquired a B. afzelii infection and four mice acquired a B. miyamotoi infection during the larval challenges.

Conclusion

We showed that larvae of I. ricinus transmit B. afzelii and B. miyamotoi to rodents and calculated that rodents have a considerable chance of acquiring infections from larvae compared to nymphs. As a result, B. afzelii can cycle between larvae through rodents. Our findings further imply that larval bites on humans, which easily go unnoticed, can cause Lyme borreliosis and Borrelia miyamotoi disease.

Effect of O. porcinus Tick Salivary Gland Extract on the African Swine Fever Virus Infection in Domestic Pig

African swine fever is a haemorrhagic disease in pig production that can have disastrous financial consequences for farming. No vaccines are currently available and animal slaughtering or area zoning to restrict risk-related movements are the only effective measures to prevent the spread of the disease. Ornithodoros soft ticks are known to transmit the African swine fever virus (ASFV) to pigs in farms, following the natural epidemiologic cycle of the virus. Tick saliva has been shown to modulate the host physiological and immunological responses during feeding on skin, thus affecting viral infection. To better understand the interaction between soft tick, ASFV and pig at the bite location and the possible influence of tick saliva on pig infection by ASFV, salivary gland extract (SGE) of Ornithodoros porcinus, co-inoculated or not with ASFV, was used for intradermal auricular inoculation. Our results showed that, after the virus triggered the disease, pigs inoculated with virus and SGE presented greater hyperthermia than pigs inoculated with virus alone. The density of Langerhans cells was modulated at the tick bite or inoculation site, either through recruitment by ASFV or inhibition by SGE. Additionally, SGE and virus induced macrophage recruitment each. This effect was enhanced when they were co-inoculated. Finally, the co-inoculation of SGE and virus delayed the early local spread of virus to the first lymph node on the inoculation side. This study has shown that the effect of SGE was powerful enough to be quantified in pig both on the systemic and local immune response. We believe this model should be developed with infected tick and could improve knowledge of both tick vector competence and tick saliva immunomodulation.

Amblyomma sculptum tick saliva: α-Gal identification, antibody response and possible association with red meat allergy in Brazil

The anaphylaxis response is frequently associated with food allergies, representing a significant public health hazard. Recently, exposure to tick bites and production of specific IgE against α-galactosyl (α-Gal)-containing epitopes has been correlated to red meat allergy. However, this association and the source of terminal, non-reducing α-Gal-containing epitopes have not previously been established in Brazil. Here, we employed the α-1,3-galactosyltransferase knockout mouse (α1,3-GalT-KO) model and bacteriophage Qβ-virus like particles (Qβ-VLPs) displaying Galα1,3Galβ1,4GlcNAc (Galα3LN) epitopes to investigate the presence of α-Gal-containing epitopes in the saliva of Amblyomma sculptum, a species of the Amblyomma cajennense complex, which represents the main tick that infests humans in Brazil. We confirmed that the α-1,3-galactosyltransferase knockout animals produce significant levels of anti-α-Gal antibodies against the Galα1,3Galβ1,4GlcNAc epitopes displayed on Qβ-virus like particles. The injection of A. sculptum saliva or exposure to feeding ticks was also found to induce both IgG and IgE anti-α-Gal antibodies in α-1,3-galactosyltransferase knockout mice, thus indicating the presence of α-Gal-containing epitopes in the tick saliva. The presence of α-Gal-containing epitopes was confirmed by ELISA and immunoblotting following removal of terminal α-Gal epitopes by α-galactosidase treatment. These results suggest for the first known time that bites from the A. sculptum tick may be associated with the unknown etiology of allergic reactions to red meat in Brazil.

The vector tick Ixodes ricinus feeding on an arboreal rodent-the edible dormouse Glis glis

The reservoir competence and long life expectancy of edible dormice, Glis glis, suggest that they serve as efficient reservoir hosts for Lyme disease (LD) spirochetes. Their arboreality, however, may reduce the probability to encounter sufficient questing Ixodes ricinus ticks to acquire and perpetuate LD spirochetes. To define the potential role of this small arboreal hibernator in the transmission cycle of LD spirochetes, we examined their rate and density of infestation with subadult ticks throughout the season of activity. Of the 1081 edible dormice that we captured at five study sites in Southern Germany and inspected for ticks at 2946 capture occasions, 26 % were infested with at least one and as many as 26 subadult ticks on their ear pinnae. The distribution of ticks feeding on edible dormice was highly aggregated. Although only few individuals harbored nymphal ticks soon after their emergence from hibernation, the rate of nymphal infestation increased steadily throughout the season and reached about 35 % in September. Dormice inhabiting a site with few conspecifics seemed more likely to be infested by numerous ticks, particularly nymphs, than those individuals living in densely populated sites. Male dormice were more likely to be parasitized by numerous nymphs than were females, independent of their age and body mass. Our observation that season, population density, and sex affect the rates of ticks feeding on edible dormice suggests that the contribution of edible dormice to the transmission cycle of LD spirochetes depends mainly on their ranging behavior and level of activity.

Modulation of host immunity by tick saliva

Next generation sequencing and proteomics have helped to comprehensively characterize gene expression in tick salivary glands at both the transcriptome and the proteome level. Functional data are, however, lacking. Given that tick salivary secretions are critical to the success of the tick transmission lifecycle and, as a consequence, for host colonization by the pathogens they spread, we thoroughly review here the literature on the known interactions between tick saliva (or tick salivary gland extracts) and the innate and adaptive vertebrate immune system. The information is intended to serve as a reference for functional characterization of the numerous genes and proteins expressed in tick salivary glands with an ultimate goal to develop novel vector and pathogen control strategies.

SIGNIFICANCE

We overview all the known interactions of tick saliva with the vertebrate immune system. The provided information is important, given the recent developments in high-throughput transcriptomic and proteomic analysis of gene expression in tick salivary glands, since it may serve as a guideline for the functional characterization of the numerous newly-discovered genes expressed in tick salivary glands.

Transgene expression in tick cells using Agrobacterium tumefaciens

Ticks transmit infectious agents to humans and other animals. Genetic manipulation of vectors like ticks could enhance the development of alternative disease control strategies. Transgene expression using the phytopathogen Agrobacterium tumefaciens has been shown to promote the genetic modification of non-plant cells. In the present work we developed T-DNA constructs for A. tumefaciens to mediate transgene expression in HeLa cells as well as Rhipicephalus microplus tick cells. Translational fusions eGfp:eGfp or Salp15:eGfp, including the enhanced-green fluorescent protein and the Ixodes scapularis salivary factor SALP15 genes, were constructed using the CaMV 35S (cauliflower mosaic virus) promoter, "PBm" tick promoter (R. microplus pyrethroid metabolizing esterase gene) or the Simian Virus SV40 promoter. Confocal microscopy, RT-PCR and Western-blot assays demonstrated transgene(s) expression in both cell lines. Transgene expression was also achieved in vivo, in both R. microplus and I. scapularis larvae utilizing a soaking method including the A. tumefaciens donor cells and confirmed by nested-RT-PCR showing eGfp or Salp15 poly-A-mRNA(s). This strategy opens up a new avenue to express exogenous genes in ticks and represents a potential breakthrough for the study of tick-host pathophysiology.

Molecular identification and bioinformatics analysis of a potential anti-vector vaccine candidate, 15-kDa salivary gland protein (Salp15), from Ixodes affinis ticks

Salp15, a 15-kDa salivary gland protein plays an important role in tick blood-feeding and transmission of Borrelia burgdorferi, the causative agent of Lyme borreliosis. The comparative studies reveal that Salp15 is a genetically conserved protein across various Ixodes species. In this study, we have identified a Salp15 homolog, designated as Iaff15, from Ixodes affinis ticks that are the principal enzootic vectors of B. burgdorferi sensu stricto in the southeastern part of the United States. Comparison of the annotated amino acid sequences showed that Iaff15 share 81% homology with I. sinensis Salp15 homolog and 64% homology with I. scapularis Salp15. Phylogenetic analysis revealed that Iaff15 come within the same clade with I. sinensis, I. scapularis, and I. pacificus Salp15 homologs. The bioinformatics analysis of the posttranslational modifications prediction revealed that all the Salp15 family members contain glycosylation sites. In addition, Iaff15 carried a higher number of Casein Kinase II phosphorylation sites in comparison to the other Salp15 family members. Collectively, high sequence conservation distributed over the entire amino acids sequence not only suggests an important role for Iaff15 in I. affinis blood feeding and vector-pathogen interactions but may also lead to the development of an anti-vector vaccine against this group of ticks.

Application of M13 phage display for identifying immunogenic proteins from tick (Ixodes scapularis) saliva

Background

Ticks act as vectors for a large number of different pathogens, perhaps most notably Borrelia burgdorferi, the causative agent of Lyme disease. The most prominent tick vector in the United States is the blacklegged tick, Ixodes scapularis. Tick bites are of special public health concern since there are no vaccines available against most tick-transmitted pathogens. Based on the observation that certain non-natural host animals such as guinea pigs or humans can develop adaptive immune responses to tick bites, anti-tick vaccination is a potential approach to tackle health risks associated with tick bites.

Results

The aim of this study was to use an oligopeptide phage display strategy to identify immunogenic salivary gland proteins from I. scapularis that are recognized by human immune sera. Oligopeptide libraries were generated from salivary gland mRNA of 18 h fed nymphal I. scapularis. Eight immunogenic oligopeptides were selected using human immune sera. Three selected immunogenic oligopeptides were cloned and produced as recombinant proteins. The immunogenic character of an identified metalloprotease (MP1) was validated with human sera. This enzyme has been described previously and was hypothesized as immunogenic which was confirmed in this study. Interestingly, it also has close homologs in other Ixodes species.

Conclusion

An immunogenic protein of I. scapularis was identified by oligopeptide phage display. MP1 is a potential candidate for vaccine development.

Tick Saliva Enhances Powassan Virus Transmission to the Host, Influencing Its Dissemination and the Course of Disease

Powassan virus (POWV) is an encephalitic tick-borne flavivirus which can result in serious neuroinvasive disease with up to a 10% case fatality rate. The study objective was to determine whether the salivary gland extract (SGE) from Ixodes scapularis ticks facilitates the transmission and dissemination of POWV in a process known as saliva-activated transmission. Groups of BALB/c mice were footpad inoculated with either a high dose of POWV with and without SGE or a low dose of POWV with and without SGE. Mice from each group were sacrificed daily. Organ viral loads and gene expression profiles were evaluated by quantitative real-time PCR. Both groups of mice infected with high-dose POWV showed severe neurological signs of disease preceding death. The presence of SGE did not affect POWV transmission or disease outcome for mice infected with the high dose of POWV. Neuroinvasion, paralysis, and death occurred for all mice infected with the low dose of POWV plus SGE; however, for mice infected with the low dose of POWV in the absence of SGE, there were no clinical signs of infection and no mice succumbed to disease. Although this group displayed low-level viremias, all mice were completely healthy, and it was the only group in which POWV was cleared from the lymph nodes. We conclude that saliva-activated transmission occurs in mice infected with a low dose of POWV. Our study is the first to demonstrate virus dose-dependent saliva-activated transmission, warranting further investigation of the specific salivary factors responsible for enhancing POWV transmission.

IMPORTANCE

Powassan virus (POWV) is a tick-borne flavivirus that continues to emerge in the United States, as is evident by the surge in number and expanding geographic range of confirmed cases in the past decade. This neuroinvasive virus is transmitted to humans by infected tick bites. Successful tick feeding is facilitated by a collection of pharmacologically active factors in tick saliva. In a process known as saliva-activated transmission, tick bioactive salivary molecules are thought to modulate the host environment, making it more favorable for the transmission and establishment of a pathogen. This phenomenon has been demonstrated for several tick-borne pathogens; however, a systematic investigation of the role of tick saliva on dissemination and pathogenesis of a tick-borne viral disease has never been attempted before. This study will fill that gap by systematically examining whether the presence of tick saliva contributes to the transmission and dissemination of POWV in mice.

Morpho-histochemical characterization of the salivary glands of semi-engorged Amblyomma triste (Koch, 1844) (Acari: Ixodidae) female ticks

This study presents the morphological and physiological characterization of the salivary glands of semi-engorged Amblyomma triste females. Unfed individuals were placed on New Zealand White rabbits for feeding and the females, after 4 days, were collected, dissected and the salivary glands were submitted to the application of histological (hematoxylin–eosin technique) and histochemical tests for the detection of protein (bromophenol blue technique, polysaccharides (periodic acid–Schiff technique), lipid (Nile blue technique) and calcium (von Kossa technique). The histological results show that the glandular tissue is composed by a system of ducts and three types of acini (I, II and III). The acini I are formed by a large central cell surrounded by several smaller agranular peripheral cells. Acini II are formed by cells a, c1, c2, c3 and c5, which are full of secretion granules. Acini III are constituted by cells d, e and f; the former two contain secretion granules, the latter is agranular. The glandular histochemical composition was also verified. Data obtained here will certainly help in the understanding of the cellular morphology and of the general physiology of these organs in this specie, providing important information for the creation of scientific bases which will contribute for the development of more specific and efficient methods of control.

Tick saliva increases production of three chemokines including monocyte chemoattractant protein-1, a histamine-releasing cytokine

The effect of Ixodes ricinus tick saliva on the production of various cytokines and chemokines by mouse splenocytes was tested by a cytokine array. We demonstrated a strong upregulation of three chemokines, monocyte chemoattractant protein-1 (MCP-1), thymus-derived chemotactic agent 3 (TCA-3) and macrophage inflammatory protein 2 (MIP-2). MCP-1 could be induced by tick saliva itself. While TCA-3 and MIP-2 are engaged in Th2 polarization of the host immune response associated with tick feeding, MCP-1 may act as a histamine release factor, increasing blood flow into the feeding lesion thus facilitating tick engorgement in the late, rapid feeding phase.

Seasonal variation in infestations by ixodids on Siberian chipmunks: effects of host age, sex, and birth season

In mammalian hosts, macroparasite aggregation is highly heterogeneous over space and time and among individuals. While the exact causes of this heterogeneity remain unclear, it has mainly been attributed to individual differences in exposure and susceptibility. Although some extrinsic (e.g., parasite availability) and intrinsic (e.g., sex or age) factors are well known to affect infestation patterns, the joint and possibly interacting effects of these factors are poorly understood. Here, we study the infestation of hard ticks (mainly Ixodes ricinus) in a small rodent, the Siberian chipmunk (Tamias sibiricus), introduced to an oak-hornbeam forest in France. We investigate the seasonal variation in infestation according to the sex, age, birth season (spring-born or summer-born), and body weight of individual hosts while controlling for interannual variability. During the 10-year study period, 3421 tick count events were recorded involving 1017 chipmunks monitored by the capture-mark-recapture procedure. Our results reveal a male-biased parasitism in the Siberian chipmunk, which is not consistent among individuals born in different seasons. This sex bias is observed among spring-born juveniles from July to the beginning of hibernation. For adults, this difference becomes apparent along the reproduction period (May-September) for summer-born adults only. These complex interactions between sex, age, and birth season suggest overall that the seasonal variation of tick load is critically linked to the reproductive behavior of this small ground sciurid.

Complex interactions within the ectoparasite community of the eastern rock sengi (Elephantulus myurus)

•

We monitored and manipulated the ectoparasite community of rock sengis over 3 years.

•

We found a number of facilitating interactions between tick species.

•

Inter-taxon interactions were mostly antagonistic.

•

Experimental manipulation had long-term effects on the ectoparasite community.

Concomitant infection with more than one parasite species is the rule in nature. Since co-infecting parasites are exploiting the same host, interspecific interactions at the infracommunity level are likely. The nature of such interactions can be expected to affect the distribution of parasites within host populations. Intraspecific interactions within the infracommunity are not easily discernible from cross-sectional studies and the focus of most of these studies lies on relationships between endoparasitic micro- and macroparasites. In the current study of the ectoparasite community of wild eastern rock sengis (Elephantulus myurus) we experimentally reduced tick and flea infestations and monitored ectoparasite burdens over the course of three years. We found a number of within-taxon facilitating interactions between tick species that might be the result of decreasing immune responses with increasing tick burden. In contrast, inter-taxon relationships appeared to be dominated by antagonistic relationships likely to be linked to competition over feeding sites. Only one of the observed interspecific interactions was reciprocal. Our experimental manipulation revealed additional antagonistic relationships that cross-sectional studies would not have captured. In addition, we found substantial long-term changes in the sengi ectoparasite community as a result of our experimental manipulation suggesting carry-over effects of our treatment. This study is the first that evaluates interspecific interactions within the entire ectoparasite community exploiting a mammalian host in Africa and highlights the complexity of interspecific interactions within an ectoparasite community.

Soluble cysteine-rich tick saliva proteins Salp15 and Iric-1 from E. coli

•

Tick saliva proteins Salp15 and Iric-1 promote tick feeding and pathogen transmission.

•

We established the first bacterial expression system for soluble Salp15 and Iric-1.

•

Using this system we mapped monoclonal antibody epitopes on Salp15 and Iric-1.

•

We defined the interaction sites with Borrelia outer surface protein C (OspC).

•

We elucidated first secondary structure features in Iric-1 by NMR.

Ticks transmit numerous pathogens, including borreliae, which cause Lyme disease. Tick saliva contains a complex mix of anti-host defense factors, including the immunosuppressive cysteine-rich secretory glycoprotein Salp15 from Ixodes scapularis ticks and orthologs like Iric-1 from Ixodesricinus. All tick-borne microbes benefit from the immunosuppression at the tick bite site; in addition, borreliae exploit the binding of Salp15 to their outer surface protein C (OspC) for enhanced transmission. Hence, Salp15 proteins are attractive targets for anti-tick vaccines that also target borreliae. However, recombinant Salp proteins are not accessible in sufficient quantity for either vaccine manufacturing or for structural characterization. As an alternative to low-yield eukaryotic systems, we investigated cytoplasmic expression in Escherichia coli, even though this would not result in glycosylation. His-tagged Salp15 was efficiently expressed but insoluble. Among the various solubility-enhancing protein tags tested, DsbA was superior, yielding milligram amounts of soluble, monomeric Salp15 and Iric-1 fusions. Easily accessible mutants enabled epitope mapping of two monoclonal antibodies that, importantly, cross-react with glycosylated Salp15, and revealed interaction sites with OspC. Free Salp15 and Iric-1 from protease-cleavable fusions, despite limited solubility, allowed the recording of ¹H–¹⁵N 2D NMR spectra, suggesting partial folding of the wild-type proteins but not of Cys-free variants. Fusion to the NMR-compatible GB1 domain sufficiently enhanced solubility to reveal first secondary structure elements in ¹³C/¹⁵N double-labeled Iric-1. Together, E. coli expression of appropriately fused Salp15 proteins may be highly valuable for the molecular characterization of the function and eventually the 3D structure of these medically relevant tick proteins.

Co-feeding transmission in Lyme disease pathogens

This review examines the phenomenon of co-feeding transmission in tick-borne pathogens. This mode of transmission is critical for the epidemiology of several tick-borne viruses but its importance for Borrelia burgdorferi sensu lato, the causative agents of Lyme borreliosis, is still controversial. The molecular mechanisms and ecological factors that facilitate co-feeding transmission are therefore examined with particular emphasis on Borrelia pathogens. Comparison of climate, tick ecology and experimental infection work suggests that co-feeding transmission is more important in European than North American systems of Lyme borreliosis, which potentially explains why this topic has gained more traction in the former continent than the latter. While new theory shows that co-feeding transmission makes a modest contribution to Borrelia fitness, recent experimental work has revealed new ecological contexts where natural selection might favour co-feeding transmission. In particular, co-feeding transmission might confer a fitness advantage in the Darwinian competition among strains in mixed infections. Future studies should investigate the ecological conditions that favour the evolution of this fascinating mode of transmission in tick-borne pathogens.

The sialotranscriptome of Amblyomma triste, Amblyomma parvum and Amblyomma cajennense ticks, uncovered by 454-based RNA-seq

Background

Tick salivary constituents antagonize inflammatory, immune and hemostatic host responses, favoring tick blood feeding and the establishment of tick-borne pathogens in hosts during hematophagy. Amblyomma triste, A. cajennense and A. parvum ticks are very important in veterinary and human health because they are vectors of the etiological agents for several diseases. Insights into the tick salivary components involved in blood feeding are essential to understanding vector-pathogen-host interactions, and transcriptional profiling of salivary glands is a powerful tool to do so. Here, we functionally annotated the sialotranscriptomes of these three Amblyomma species, which allowed comparisons between these and other hematophagous arthropod species.

Methods

mRNA from the salivary glands of A. triste, A. cajennense and A. parvum ticks fed on different host species were pyrosequenced on a 454-Roche platform to generate four A. triste (nymphs fed on guinea pigs and females fed on dogs) libraries, one A. cajennense (females fed on rabbits) library and one was A. parvum (females fed on dogs) library. Bioinformatic analyses used in-house programs with a customized pipeline employing standard assembly and alignment algorithms, protein databases and protein servers.

Results

Each library yielded an average of 100,000 reads, which were assembled to obtain contigs of coding sequences (CDSs). The sialotranscriptome analyses of A. triste, A. cajennense and A. parvum ticks produced 11,240, 4,604 and 3,796 CDSs, respectively. These CDSs were classified into over 100 distinct protein families with a wide range of putative functions involved in physiological and blood feeding processes and were catalogued in annotated, hyperlinked spreadsheets. We highlighted the putative transcripts encoding saliva components with critical roles during parasitism, such as anticoagulants, immunosuppressants and anti-inflammatory molecules. The salivary content underwent changes in the abundance and repertoire of many transcripts, which depended on the tick and host species.

Conclusions

The annotated sialotranscriptomes described herein richly expand the biological knowledge of these three Amblyomma species. These comprehensive databases will be useful for the characterization of salivary proteins and can be applied to control ticks and tick-borne diseases.

Electronic supplementary material

The online version of this article (doi:10.1186/1756-3305-7-430) contains supplementary material, which is available to authorized users.

An immunological marker of tolerance to infection in wild rodents

Hosts are likely to respond to parasitic infections by a combination of resistance (expulsion of pathogens) and tolerance (active mitigation of pathology). Of these strategies, the basis of tolerance in animal hosts is relatively poorly understood, with especially little known about how tolerance is manifested in natural populations. We monitored a natural population of field voles using longitudinal and cross-sectional sampling modes and taking measurements on body condition, infection, immune gene expression, and survival. Using analyses stratified by life history stage, we demonstrate a pattern of tolerance to macroparasites in mature compared to immature males. In comparison to immature males, mature males resisted infection less and instead increased investment in body condition in response to accumulating burdens, but at the expense of reduced reproductive effort. We identified expression of the transcription factor Gata3 (a mediator of Th2 immunity) as an immunological biomarker of this tolerance response. Time series data for individual animals suggested that macroparasite infections gave rise to increased expression of Gata3, which gave rise to improved body condition and enhanced survival as hosts aged. These findings provide a clear and unexpected insight into tolerance responses (and their life history sequelae) in a natural vertebrate population. The demonstration that such responses (potentially promoting parasite transmission) can move from resistance to tolerance through the course of an individual's lifetime emphasises the need to incorporate them into our understanding of the dynamics and risk of infection in the natural environment. Moreover, the identification of Gata3 as a marker of tolerance to macroparasites raises important new questions regarding the role of Th2 immunity and the mechanistic nature of the tolerance response itself. A more manipulative, experimental approach is likely to be valuable in elaborating this further.

Factors determining immunological response to vaccination against tick-borne encephalitis virus in older individuals

We performed a cross-sectional study including 533 individuals (median age 61) from the highly TBE endemic Åland Islands in the archipelago between Sweden and Finland. Blood samples, questionnaires and vaccination records were obtained from all study participants. The aim was to investigate if there was any association between TBEV antibody titer and 12 health-related factors. Measurement of TBEV IgG antibodies was performed using two commercial ELISA assays (Enzygnost and Immunozym), and a third in-house rapid fluorescent focus inhibition test was used to measure TBEV neutralizing antibodies. The age of the individual and the number of vaccine doses were the two most important factors determining the immunological response to vaccination. The response to each vaccine dose declined linearly with increased age. A 35 year age difference corresponds to a vaccine dose increment from 3 to 4 to achieve the same immunological response. Participants previously vaccinated against other flaviviruses had lower odds of being seropositive for neutralizing TBEV antibodies on average, while participants with self-reported asthma had higher odds of being seropositive. By comparing the 3 serological assays we show that the Enzygnost and Immunozym assay differ due to choice of cutoffs, but not in overall accuracy.

Can antibodies against flies alter malaria transmission in birds by changing vector behavior?

Transmission of insect-borne diseases is shaped by the interactions among parasites, vectors, and hosts. Any factor that alters movement of infected vectors from infected to uninfeced hosts will in turn alter pathogen spread. In this paper, we study one such pathogen-vector-host system, avian malaria in pigeons transmitted by fly ectoparasites, where both two-way and three-way interactions play a key role in shaping disease spread. Bird immune defenses against flies can decrease malaria prevalence by reducing fly residence time on infected birds or increase disease prevalence by enhancing fly movement and thus infection transmission. We develop a mathematical model that illustrates how these changes in vector behavior influence pathogen transmission and show that malaria prevalence is maximized at an intermediate level of defense avoidance by the flies. Understanding how host immune defenses indirectly alter disease transmission by influencing vector behavior has implications for reducing the transmission of human malaria and other vectored pathogens.

Identification and partial characterization of a Salp15 homolog from Ixodes ricinus

The immunomodulatory molecule Salp15 is originally described in Ixodes scapularis and has been shown to inhibit CD4 T cell activation. Many Salp15 homologs have been described from Ixodes species, and all were well conserved at C-terminal residues that seem to be essential for the function of the protein. In this study, a gene sequence was amplified from cDNA isolated from engorged female I. ricinus ticks, which was predicted to generate a protein of 12.3 kDa. The protein displayed distinct amino acid differences from previously described I. ricinus Salp15 homologs, with amino acid identity ranging between 46.6% and 93.9%. It was referred to as I. ricinus Salp15-like protein. The protein showed 48.1% sequence identity to I. scapularis Salp15. We analyzed the effect of the recombinant I. ricinus Salp15-like protein on the production of cytokines from human peripheral blood mononuclear cells stimulated with LPS. The recombinant protein exerted no effect on the production of TNF-α and IL-6, but the production of IL-10 was dose-dependently reduced. It can be concluded that I. ricinus Salp15-like protein exerts an immunomodulatory effect on the host. The inhibition of IL-10 production may possibly lead to a retardation of B cell activity.

Cellular responses to Rhipicephalus microplus infestations in pre-sensitised cattle with differing phenotypes of infestation

The blue tick, Rhipicephalus microplus, threatens cattle production in most tropical and subtropical areas of the world. Delayed skin hypersensitivity reactions are thought to cause Nguni cattle to be more resistant to R. microplus than Bonsmara cattle yet the cellular mechanisms responsible for these differences have not been classified. Tick counts and inflammatory cell infiltrates in skin biopsies from feeding sites of adult R. microplus ticks were determined in 9-month-old Nguni and Bonsmara heifers to determine the cellular mechanisms responsible for tick immunity. Nguni heifers (1.7 ± 0.03) had lower (P < 0.05) tick counts than the Bonsmaras (2.0 ± 0.03). Parasitized sites in Nguni heifers had higher counts of basophils, mast and mononuclear cells than those in the Bonsmara heifers. Conversely, parasitized sites in Nguni heifers had lower neutrophil and eosinophil counts than those in the Bonsmara heifers. Tick count was negatively correlated with basophil and mast cell counts and positively correlated with eosinophil counts in both breeds. In the Bonsmara breed, tick count was positively correlated with mononuclear cell counts. Cellular responses to adult R. microplus infestations were different and correlated with differences in tick resistance in Nguni and Bonsmara cattle breeds. It is essential to further characterise the molecular composition of the inflammatory infiltrate elicited by adult R. microplus infestation to fully comprehend immunity to ticks in cattle.

Hard tick factors implicated in pathogen transmission

Ticks are the most common arthropod vector, after mosquitoes, and are capable of transmitting the greatest variety of pathogens. For both humans and animals, the worldwide emergence or re-emergence of tick-borne disease is becoming increasingly problematic. Despite being such an important issue, our knowledge of pathogen transmission by ticks is incomplete. Several recent studies, reviewed here, have reported that the expression of some tick factors can be modulated in response to pathogen infection, and that some of these factors can impact on the pathogenic life cycle. Delineating the specific tick factors required for tick-borne pathogen transmission should lead to new strategies in the disruption of pathogen life cycles to combat emerging tick-borne disease.

An experimental test of host specialization in a ubiquitous polar ectoparasite: a role for adaptation?

The evolution of host specificity is considered to be an essential mechanism driving parasite diversity. It may be governed by adaptive constraints that lead to host-dependent fitness trade-offs. Alternatively, specificity may arise via transmission constraints that isolate parasite populations, without necessarily involving adaptation per se. Here, we ask whether the repeated observation of host-associated genetic races across the worldwide distribution of the seabird ectoparasite Ixodes uriae is associated with host adaptation. We conducted a field-based experiment to test for adaptive specialisation in host races of I. uriae. We transferred unengorged ticks of two life stages (nymphs and adults) originating from three host species (black-legged kittiwake, common guillemot and Atlantic puffin) onto young kittiwake nestlings and followed attraction and attachment rates, engorgement times and feeding success of the transplanted ticks. All ticks were also typed genetically to match exploitation patterns with genetic differences among races. Ticks from atypical hosts were significantly less attracted to nestlings than ticks from the typical host, and showed lower feeding success and higher mortality. The degree of host specificity matched patterns of neutral genetic variation among races, with puffin ticks being more specific than guillemot ticks. Differences in specificity were also apparent among tick life stages, suggesting that nymphal ticks may be less discriminating of host type than adult ticks. Our results indicate that the genetic divergence previously observed among sympatric I. uriae host races is at least partially linked to adaptive specialisation to the host species and not simply to host-mediated transmission. They also suggest that the adaptation process may evolve differently in different life stages based on trade-offs with physiological constraints. The identification of the selective forces acting in host specialization will now be necessary to better characterize these patterns and to understand how transmission interacts with the adaptation process to generate parasite biodiversity.

Effect of host lizard anemia on host choice and feeding rate of larval western black-legged ticks (Ixodes pacificus)

Although ticks are known to exhibit preferences among host species, there is little evidence that ticks select hosts within a species based on physiological condition. It may be beneficial for ticks to choose hosts that are easier to feed upon if the ticks can perceive indicative chemical or other signals from the host. For example, if ticks can detect host hematocrit they may choose hosts with high hematocrit, facilitating a faster blood meal. It may similarly be adaptive for ticks to avoid anemic hosts because it may be difficult for them to obtain an adequate meal and feeding duration may be extended. We tested the hypothesis that larval western black-legged ticks (Ixodes pacificus) detect host hematocrit using external cues and choose healthy over anemic hosts, allowing them to feed more quickly. We presented groups of larval ticks with pairs of healthy and anemic male western fence lizards (Sceloporus occidentalis), allowed them to select a host, and measured the feeding duration of the ticks. We found that the ticks did not exhibit a statistically significant preference for healthy over anemic lizards, but that the ticks fed to repletion significantly faster on healthy hosts than on anemic hosts. Larval ticks may not be able to detect external cues indicating the health of the host, at least not in terms of their hematocrit. The extended feeding duration likely reflects the extra time needed for the ticks to concentrate the blood meal of their anemic hosts.

Host specialization in ticks and transmission of tick-borne diseases: a review

Determining patterns of host use, and the frequency at which these patterns change, are of key importance if we are to understand tick population dynamics, the evolution of tick biodiversity, and the circulation and evolution of associated pathogens. The question of whether ticks are typically host specialists or host generalists has been subject to much debate over the last half-century. Indeed, early research proposed that morphological diversity in ticks was linked to host specific adaptations and that most ticks were specialists. Later work disputed this idea and suggested that ticks are largely limited by biogeographic conditions and tend to use all locally available host species. The work presented in this review suggests that the actual answer likely lies somewhere between these two extremes. Although recent observational studies support the view that phylogenetically diverse host species share ticks when found on similar ecological ranges, theory on host range evolution predicts that host specialization should evolve in ticks given their life history characteristics. Contemporary work employing population genetic tools to examine host-associated population structure in several tick systems support this prediction and show that simple species records are not enough to determine whether a parasite is a true host generalist; host specialization does evolve in ticks at local scales, but may not always lead to speciation. Ticks therefore seem to follow a pattern of being global generalists, local specialists. Given this, the notion of host range needs to be modified from an evolutionary perspective, where one simply counts the number of hosts used across the geographic distribution, to a more ecological view, where one considers host use at a local scale, if we are to better understand the circulation of tick-borne pathogens and exposure risks for humans and livestock.

Cutaneous hypersensitivity responses to Rhipicephalus tick larval antigens in pre-sensitized cattle

Nguni cattle are known to be more resistant to ticks than Bonsmara cattle, even if the immunological mechanisms responsible for this phenomenon are not fully understood. Cutaneous hypersensitivity responses to unfed larval extracts (ULE) of the ticks Rhipicephalus decoloratus and Rhipicephalus microplus were investigated in Nguni and Bonsmara cattle to improve knowledge on the immunity to ticks. Hypersensitivity reactions were induced by intradermal inoculation of 0.1ml of ULE of R. decoloratus and R. microplus ticks (50μg protein) in the right and left ear, respectively, of 8-9-month-old Nguni (n=11) and Bonsmara (n=9) heifers. Ear thickness was measured using callipers before and 0.5, 1, 6, 24, 48, and 72h post inoculation (PI). Bonsmara cattle showed a more intense immediate reaction with maximum response at 1h PI and no delayed hypersensitivity reaction. Nguni heifers, conversely, presented a less intense immediate reaction with maximum response at 1h PI, and a delayed hypersensitivity reaction at 72h PI. Reactions to R. decoloratus ULE produced a more intense skin response than to R. microplus in both breeds at all time intervals. Nguni cattle showed lower tick infestation indicating higher tick resistance than Bonsmara cattle. Delayed hypersensitivity reaction could be associated with superior tick resistance in the Nguni breed, while immediate hypersensitivity reaction could be associated with increased tick susceptibility in the Bonsmara breed. This study indicates the need for further investigations on the correlation of tick resistance and cellular immune responses to tick infestation in Nguni cattle.

Tick infestation patterns in free ranging African buffalo (Syncercus caffer): Effects of host innate immunity and niche segregation among tick species

Ticks are of vast importance to livestock health, and contribute to conflicts between wildlife conservation and agricultural interests; but factors driving tick infestation patterns on wild hosts are not well understood. We studied tick infestation patterns on free-ranging African buffalo (Syncercus caffer), asking (i) is there evidence for niche segregation among tick species?; and (ii) how do host characteristics affect variation in tick abundance among hosts? We identified ticks and estimated tick burdens on 134 adult female buffalo from two herds at Kruger National Park, South Africa. To assess niche segregation, we evaluated attachment site preferences and tested for correlations between abundances of different tick species. To investigate which host factors may drive variability in tick abundance, we measured age, body condition, reproductive and immune status in all hosts, and examined their effects on tick burdens.

Two tick species were abundant on buffalo, Amblyomma hebraeum and Rhipicephalus evertsi evertsi. A. hebraeum were found primarily in the inguinal and axillary regions; R. e. evertsi attached exclusively in the perianal area. Abundances of A. hebraeum and R. e. evertsi on the host were unrelated. These results suggest spatial niche segregation between A. hebraeum and R. e. evertsi on the buffalo. Buffalo with stronger innate immunity, and younger buffalo, had fewer ticks. Buffalo with low body condition scores, and pregnant buffalo, had higher tick burdens, but these effects varied between the two herds we sampled.

This study is one of the first to link ectoparasite abundance patterns and immunity in a free-ranging mammalian host population. Based on independent abundances of A. hebraeum and R. e. evertsi on individual buffalo, we would expect no association between the diseases these ticks transmit. Longitudinal studies linking environmental variability with host immunity are needed to understand tick infestation patterns and the dynamics of tick-borne diseases in wildlife.

Evidence for competition between Ixodes scapularis and Dermacentor albipictus feeding concurrently on white-tailed deer

Competition among ticks, and among ectoparasites generally, has rarely been demonstrated. Ixodes scapularis and Dermacentor albipictus are both hard ticks commonly found feeding on deer harvested at Letterkenny Army Depot, in south central Pennsylvania, USA. The two species have contrasting life histories resulting in D. albipictus spending notably more time on the shared host. We hypothesized that this would give D. albipictus an advantage in locating and occupying optimal attachment sites (highly vascularized areas like the head and ears). Ticks were collected from 224 hunter-killed deer in December 2005 and November 2006 to determine if there is evidence of competition for attachment sites when these two species concurrently infest deer. A timed sample (3 min per region) of representative ticks was collected from the head (ears, face and neck regions) and body (axillae regions). Ixodes scapularis was more abundant and prevalent overall than D. albipictus. Dermacentor albipictus was found almost exclusively on the head, whereas I. scapularis was more evenly distributed, but somewhat more abundant on the body than on the head. The proportion of I. scapularis on the head was reduced at high D. albipictus abundances, but I. scapularis abundance did not alter the distribution of D. albipictus. This study supports the hypothesis of competition for preferred attachment sites between these two species of ticks, and suggests that D. albipictus may be competitively dominant over I. scapularis on the head region of concurrently infested white-tailed deer.

Ixodes scapularis saliva mitigates inflammatory cytokine secretion during Anaplasma phagocytophilum stimulation of immune cells

Background

Ixodes scapularis saliva enables the transmission of infectious agents to the mammalian host due to its immunomodulatory, anesthetic and anti-coagulant properties. However, how I. scapularis saliva influences host cytokine secretion in the presence of the obligate intracellular rickettsial pathogen Anaplasma phagocytophilum remains elusive.

Methods

Bone marrow derived macrophages (BMDMs) were stimulated with pathogen associated molecular patterns (PAMPs) and A. phagocytophilum. Cytokine secretion was measured in the presence and absence of I. scapularis saliva. Human peripheral blood mononuclear cells (PBMCs) were also stimulated with Tumor Necrosis Factor (TNF)-α in the presence and absence of I. scapularis saliva and interleukin (IL)-8 was measured.

Results

I. scapularis saliva inhibits inflammatory cytokine secretion by macrophages during stimulation of Toll-like (TLR) and Nod-like receptor (NLR) signaling pathways. The effect of I. scapularis saliva on immune cells is not restricted to murine macrophages because decreasing levels of interleukin (IL)-8 were observed after TNF-α stimulation of human peripheral blood mononuclear cells. I. scapularis saliva also mitigates pro-inflammatory cytokine response by murine macrophages during challenge with A. phagocytophilum.

Conclusions

These findings suggest that I. scapularis may inhibit inflammatory cytokine secretion during rickettsial transmission at the vector-host interface.