Tick immunobiology

Responses of juvenile blacklegged ticks (Acari: Ixodidae) to hosts of varying quality

Blacklegged ticks (Ixodes scapularis) are the most medically and economically important vectors in North America. Each of their 3 life stages requires a blood meal from one of many potential host species, during which they can acquire or transmit pathogens. Host species, however, vary tremendously in their quality for ticks, as measured by differences in feeding and molting success. There should be clear fitness benefits for ticks that preferentially feed upon high-quality hosts (e.g., white-footed mice, Peromyscus leucopus), or at least avoid feeding on very low-quality hosts (e.g., Virginia opossums, Didelphis virginiana). Indeed, laboratory experiments have found some evidence of host preferences in I. scapularis; but these involve presenting ticks with hosts simultaneously and measuring movement towards hosts on a horizontal plane. In nature, however, host-seeking ticks encounter hosts sequentially and their movements are principally in a vertical plane. Here, we present the results of a study in which we measured the vertical movements of host-seeking juvenile blacklegged ticks before and after a host (P. leucopus, Tamias striatus, Sciurus carolinensis, or D. virginiana) was present, and whether the strength of their responses varies with host quality. We found ticks did not measurably alter the speed of their vertical movement in the presence of any hosts, regardless of host quality. Both larvae and nymphs quested slightly higher in the presence of hosts, but this did not vary by host species. These results call into question the existence of active host preferences, at least in this stage of the host-seeking process.

Hard Ticks as Vectors: The Emerging Threat of Tick-Borne Diseases in India

Hard ticks (Ixodidae) play a critical role in transmitting various tick-borne diseases (TBDs), posing significant global threats to human and animal health. Climatic factors influence the abundance, diversity, and vectorial capacity of tick vectors. It is imperative to have a comprehensive understanding of hard ticks, pathogens, eco-epidemiology, and the impact of climatic changes on the transmission dynamics of TBDs. The distribution and life cycle patterns of hard ticks are influenced by diverse ecological factors that, in turn, can be impacted by changes in climate, leading to the expansion of the tick vector's range and geographical distribution. Vector competence, a pivotal aspect of vectorial capacity, involves the tick's ability to acquire, maintain, and transmit pathogens. Hard ticks, by efficiently feeding on diverse hosts and manipulating their immunity through their saliva, emerge as competent vectors for various pathogens, such as viruses, parasites and bacteria. This ability significantly influences the success of pathogen transmission. Further exploration of genetic diversity, population structure, and hybrid tick vectors is crucial, as they play a substantial role in influencing vector competence and complicating the dynamics of TBDs. This comprehensive review deals with important TBDs in India and delves into a profound understanding of hard ticks as vectors, their biology, and the factors influencing their vector competence. Given that TBDs continue to pose a substantial threat to global health, the review emphasizes the urgency of investigating tick control strategies and advancing vaccine development. Special attention is given to the pivotal role of population genetics in comprehending the genetic diversity of tick populations and providing essential insights into their adaptability to environmental changes.

Co-infection patterns in the ectoparasitic community affecting the Iberian ibex Capra pyrenaica

BACKGROUND

Sarcoptic mange is one of the main parasitic diseases affecting the Iberian ibex Capra pyrenaica. Scabietic animals suffer a decline in body condition and reproductive fitness and in severe cases may die. Although several previous studies of the pathology of this disease and the physiological changes it produces in ibex have been carried out in recent years, our knowledge of the relationship between Sarcoptes scabiei and other ectoparasites of this host is still limited.

METHODS

We analysed 430 Iberian ibex skin samples. Ectoparasites were removed, counted and identified. Mite (S. scabiei) numbers were obtained after digesting the skin samples in a 5% KOH solution. We modelled mite numbers in terms of host sex and age, site, year, season and the presence of other ectoparasites such as ticks and lice using generalized linear mixed models (GLMMs) and ectoparasite co-occurrence patterns using two different models: the probabilistic model species co-occurrence and the generalized linear latent variable model (GLLVM).

RESULTS

The ectoparasite community was mainly composed of S. scabiei, six ticks (Haemaphysalis sulcata, Haemaphysalis punctata, Rhipicephalus bursa, Rhipicephalus turanicus, Dermacentor marginatus and Ixodes ricinus) and two lice (Bovicola crassipes and Linognathus stenopsis). Adult male ibex harboured more mites than females. Mite numbers varied greatly spatially and seasonally and increased with the presence of other parasites. Some positive co-occurrence relationships between pairs of different ectoparasites were observed, particularly between ticks. The presence of S. scabiei negatively affected lice and H. sulcata numbers.

CONCLUSIONS

Sarcoptic mange has spread above all in ibex populations in and around the Mediterranean Basin, where it is now found in almost a third of its host's range. Mite numbers varied seasonally and spatially and were higher in male hosts. The presence of S. scabiei had a negative effect on lice numbers but favoured the presence of ticks.

Molecular characterization of hexokinase (HK) in Haemaphysalis longicornis and evaluation of HK protein- and DNA-based vaccines against adult ticks

BACKGROUND

Haemaphysalis longicornis is an obligate hematophagous ectoparasite, which transmits various pathogens to humans, livestock and wild animals. Hexokinase (HK) is a key regulatory enzyme of the glycolytic pathway in the organisms. However, little is known about hexokinase and its functions in ticks.

RESULTS

The open reading frame of the H. longicornis HK (HlHK) gene was 1425 bp and encoded a protein of 474 amino acids, containing conserved domains for glucose, glucose 6-phosphate, and adenosine triphosphate. The expression of HlHK gene was detected at different developmental stages and in different tissues of unfed female ticks. Enzyme-linked immunosorbent assay revealed that both HK protein- and DNA-based vaccines increased the antibody levels of the immunized animals. A vaccination trail on rabbits against H. longicornis infestation indicated that the rHlHK protein and HlHK DNA vaccines reduced the number of attached female ticks by 9% and 12%, egg mass weight by 36% and 34%, and egg hatching rate by 41% and 17%, respectively. Overall, protein vaccination conferred 65.6% protection against adult female ticks, whereas the DNA vaccine conferred 51.8% protection.

CONCLUSION

This is the first report of the molecular characterization of the HK protein and sequencing of the HK gene from H. longicornis. Positive results from vaccination trials on rabbits of the recombinant HK protein and HK DNA suggest that these novel anti-tick vaccines potentially can be used as viable tick control tools for the management of the Asian longhorned tick. Additionally, inhibition of glucose metabolism may be a new strategy for tick control. © 2023 Society of Chemical Industry.

The Impact of Host Abundance on the Epidemiology of Tick-Borne Infection

Tick-borne diseases are an increasing global public health concern due to an expanding geographical range and increase in abundance of tick-borne infectious agents. A potential explanation for the rising impact of tick-borne diseases is an increase in tick abundance which may be linked to an increase in density of the hosts on which they feed. In this study, we develop a model framework to understand the link between host density, tick demography and tick-borne pathogen epidemiology. Our model links the development of specific tick stages to the specific hosts on which they feed. We show that host community composition and host density have an impact on tick population dynamics and that this has a consequent impact on host and tick epidemiological dynamics. A key result is that our model framework can exhibit variation in host infection prevalence for a fixed density of one host type due to changes in density of other host types that support different tick life stages. Our findings suggest that host community composition may play a crucial role in explaining the variation in prevalence of tick-borne infections in hosts observed in the field.

Identification of novel conserved Ixodes vaccine candidates; a promising role for non-secreted salivary gland proteins

Ixodes ricinus and Ixodes scapularis are the main vectors for the causative agents of Lyme borreliosis and a wide range of other pathogens. Repeated tick-bites are known to lead to tick rejection; a phenomenon designated as tick immunity. Tick immunity is mainly directed against tick salivary gland proteins (TSGPs) and has been shown to partially protect against experimental Lyme borreliosis. TSGPs recognized by antibodies from tick immune animals could therefore be interesting candidates for an anti-tick vaccine, which might also block pathogen transmission. To identify conserved Ixodes TSGPs that could serve as a universal anti-tick vaccine in both Europe and the US, a Yeast Surface Display containing salivary gland genes of nymphal I. ricinus expressed at 24, 48 and 72 h into tick feeding was probed with either sera from rabbits repeatedly exposed for 24 h to I. ricinus nymphal ticks and/or sera from rabbits immune to I. scapularis. Thus, we identified thirteen TSGP vaccine candidates, of which ten were secreted. For vaccination studies in rabbits, we selected six secreted TSGPs, five full length and one conserved peptide. None of these proteins hampered tick feeding. In contrast, vaccination of guinea pigs with four non-secreted TSGPs - two from the current and two from a previous human immunoscreening - did significantly reduce tick attachment and feeding. Therefore, non-secreted TSGPs appear to be involved in the development of tick immunity and are interesting candidates for an anti-tick vaccine.

Global genomic methylation related to the degree of parasitism in cattle

The objective of the present study was to characterize a herd of 72 ½ Angus × ½ Nellore heifers, identify the resistant, resilient and susceptible animals to parasites, relate the overall DNA methylation of these animals with the degree of parasitism, evaluated by the egg count per gram of feces (EPG), Haematobia irritans count (horn fly) and Rhipicephalus microplus count (bovine tick). The experiment was carried out in a completely randomized design, containing 72 treatments, with each animal considered a treatment, and 11 repetitions, with each collection within a year considered a repetition. The data obtained from the counts of the evaluated parasites were subjected to statistical analysis using the SISVAR program, to classify heifers according to the degree of parasitism in low (resistant), intermediary (resilient) and high (susceptible) parasite load for infection by nematodes, infestation by ticks and flies. Addition the animals in these three groups, by hierarchical grouping using the GENES program, heifers were classified as to the degree of parasitism by the three parasites along with the DNA methylation content of the animals in each group. A negative relationship was observed between resistance and methylated DNA content in both classifications, with the resistant, resilient, and susceptible animals showing the highest, intermediate, and lowest methylated DNA quantifications, respectively. Thus, the methodologies used herein enabled the classification of 72 heifers according to the degree of collective infection by gastrointestinal nematodes and infestation by ticks and horn flies, thereby establishing a link between the degree of parasitic resistance in cattle and the global methylated DNA quantification.

Evolutionary Origins of Metabolic Reprogramming in Cancer

Metabolic changes that facilitate tumor growth are one of the hallmarks of cancer. These changes are not specific to tumors but also take place during the physiological growth of tissues. Indeed, the cellular and tissue mechanisms present in the tumor have their physiological counterpart in the repair of tissue lesions and wound healing. These molecular mechanisms have been acquired during metazoan evolution, first to eliminate the infection of the tissue injury, then to enter an effective regenerative phase. Cancer itself could be considered a phenomenon of antagonistic pleiotropy of the genes involved in effective tissue repair. Cancer and tissue repair are complex traits that share many intermediate phenotypes at the molecular, cellular, and tissue levels, and all of these are integrated within a Systems Biology structure. Complex traits are influenced by a multitude of common genes, each with a weak effect. This polygenic component of complex traits is mainly unknown and so makes up part of the missing heritability. Here, we try to integrate these different perspectives from the point of view of the metabolic changes observed in cancer.

Recovery of Partially Engorged Haemaphysalis longicornis (Acari: Ixodidae) Ticks from Active Surveillance

The invasive Asian longhorned tick, Haemaphysalis longicornis, has rapidly spread across the northeastern United States and is associated with pathogens of public health and veterinary concern. Despite its importance in pathogen dynamics, H. longicornis blood-feeding behavior in nature, specifically the likelihood of interrupted feeding, remains poorly documented. Here, we report the recovery of partially engorged, questing H. longicornis from active tick surveillance in Pennsylvania. Significantly more engorged H. longicornis nymphs (1.54%) and adults (3.07%) were recovered compared to Ixodes scapularis nymphs (0.22%) and adults (zero). Mean Scutal Index difference between unengorged and engorged nymph specimens was 0.65 and 0.42 for I. scapularis and H. longicornis, respectively, suggesting the questing, engorged H. longicornis also engorged to a comparatively lesser extent. These data are among the first to document recovery of engorged, host-seeking H. longicornis ticks and provide initial evidence for interrupted feeding and repeated successful questing events bearing implications for pathogen transmission and warranting consideration in vector dynamics models.

Host Immune Responses to Salivary Components - A Critical Facet of Tick-Host Interactions

Tick sialome is comprised of a rich cocktail of bioactive molecules that function as a tool to disarm host immunity, assist blood-feeding, and play a vibrant role in pathogen transmission. The adaptation of the tick's blood-feeding behavior has lead to the evolution of bioactive molecules in its saliva to assist them to overwhelm hosts' defense mechanisms. During a blood meal, a tick secretes different salivary molecules including vasodilators, platelet aggregation inhibitors, anticoagulants, anti-inflammatory proteins, and inhibitors of complement activation; the salivary repertoire changes to meet various needs such as tick attachment, feeding, and modulation or impairment of the local dynamic and vigorous host responses. For instance, the tick's salivary immunomodulatory and cement proteins facilitate the tick's attachment to the host to enhance prolonged blood-feeding and to modulate the host's innate and adaptive immune responses. Recent advances implemented in the field of "omics" have substantially assisted our understanding of host immune modulation and immune inhibition against the molecular dynamics of tick salivary molecules in a crosstalk between the tick-host interface. A deep understanding of the tick salivary molecules, their substantial roles in multifactorial immunological cascades, variations in secretion, and host immune responses against these molecules is necessary to control these parasites. In this article, we reviewed updated knowledge about the molecular mechanisms underlying host responses to diverse elements in tick saliva throughout tick invasion, as well as host defense strategies. In conclusion, understanding the mechanisms involved in the complex interactions between the tick salivary components and host responses is essential to decipher the host defense mechanisms against the tick evasion strategies at tick-host interface which is promising in the development of effective anti-tick vaccines and drug therapeutics.

Apoptosis and Autophagy: Current Understanding in Tick–Pathogen Interactions

Tick-borne diseases are a significant threat to human and animal health throughout the world. How tick-borne pathogens successfully infect and disseminate in both their vertebrate and invertebrate hosts is only partially understood. Pathogens have evolved several mechanisms to combat host defense systems, and to avoid and modulate host immunity during infection, therefore benefitting their survival and replication. In the host, pathogens trigger responses from innate and adaptive immune systems that recognize and eliminate invaders. Two important innate defenses against pathogens are the programmed cell death pathways of apoptosis and autophagy. This Mini Review surveys the current knowledge of apoptosis and autophagy pathways in tick-pathogen interactions, as well as the strategies evolved by pathogens for their benefit. We then assess the limitations to studying both pathways and discuss their participation in the network of the tick immune system, before highlighting future perspectives in this field. The knowledge gained would significantly enhance our understanding of the defense responses in vector ticks that regulate pathogen infection and burden, and form the foundation for future research to identify novel approaches to the control of tick-borne diseases.

Challenges in Veterinary Vaccine Development

Animals provide food and clothing in addition to other value-added products. Changes in diet and lifestyle have increased the consumption and the use of animal products. Infectious diseases in animals are a major threat to global animal health and its welfare; their effective control is crucial for agronomic health, for safeguarding food security and also alleviating rural poverty. Development of vaccines has led to increased production of healthy poultry, livestock, and fish. Animal production increases have alleviated food insecurity. In addition, development of effective vaccines has led to healthier companion animals. However, challenges remain including climate change that has led to enhancement in vectors and pathogens that may lead to emergent diseases in animals. Preventing transmission of emerging infectious diseases at the animal-human interface is critically important for protecting the world population from epizootics and pandemics. Hence, there is a need to develop new vaccines to prevent diseases in animals. This review describes the broad challenges to be considered in the development of vaccines for animals.

Tick Saliva and Salivary Glands: What Do We Know So Far on Their Role in Arthropod Blood Feeding and Pathogen Transmission

Ticks are blood-sucking arthropods that have developed myriad of strategies to get a blood meal from the vertebrate host. They first attach to the host skin, select a bite site for a blood meal, create a feeding niche at the bite site, secrete plethora of molecules in its saliva and then starts feeding. On the other side, host defenses will try to counter-attack and stop tick feeding at the bite site. In this constant battle between ticks and the host, arthropods successfully pacify the host and completes a blood meal and then replete after full engorgement. In this review, we discuss some of the known and emerging roles for arthropod components such as cement, salivary proteins, lipocalins, HSP70s, OATPs, and extracellular vesicles/exosomes in facilitating successful blood feeding from ticks. In addition, we discuss how tick-borne pathogens modulate(s) these components to infect the vertebrate host. Understanding the biology of arthropod blood feeding and molecular interactions at the tick-host interface during pathogen transmission is very important. This information would eventually lead us in the identification of candidates for the development of transmission-blocking vaccines to prevent diseases caused by medically important vector-borne pathogens.

Phosphoproteomic Analysis of Haemaphysalis longicornis Saliva Reveals the Influential Contributions of Phosphoproteins to Blood-Feeding Success

Tick saliva, an essential chemical secretion of the tick salivary gland, is indispensable for tick survival owing to the physiological influence it exerts on the host defence mechanisms via the instrumentality of its cocktail of pharmacologically active molecules (proteins and peptides). Much research about tick salivary proteome has been performed, but how most of the individual salivary proteins are utilized by ticks to facilitate blood acquisition and pathogen transmission is not yet fully understood. In addition, the phosphorylation of some proteins plays a decisive role in their function. However, due to the low phosphorylation level of protein, especially for a small amount of protein, it is more difficult to study phosphorylation. Maybe, for this reason, the scarcity of works on the phosphorylated tick salivary proteomes still abound. Here, we performed a phosphoproteomic analysis of Haemaphysalis longicornis tick saliva via TiO₂ enrichment and the most advanced Thermo Fisher Orbitrap Exploris 480 mass spectrometer for identification. A total of 262 phosphorylated tick saliva proteins were identified and were subjected to functional annotation/enrichment analysis. Cellular and metabolic process terms accounted for the largest proportion of the saliva proteins, with the participation of these proteins in vital intracellular and extracellular transport-oriented processes such as vesicle-mediated transport, exocytic process, cell adhesion, and movement of cell/subcellular component. “Endocytosis”, “Protein processing in endoplasmic reticulum”, and “Purine metabolism” were the most significantly enriched pathways. The knockdown (RNAi) of Tudor domain-containing protein (TCP), actin-depolymerizing factors (ADF), programmed cell death protein (PD), and serine/threonine-protein kinase (SPK) resulted in the dissociation of collagen fibers and the pilosebaceous unit, increased inflammatory infiltrates/granulocytes (possibly heterophiles), and the depletion of the epithelium. Ticks injected with SPK dsRNA engorged normally but with a change in skin colour (possibly an autoimmune reaction) and the failure to produce eggs pointing to a possible role of SPK in reproduction and host immune modulation. Ticks injected with ADF dsRNA failed to acquire blood, underscoring the role of ADF in facilitating tick feeding. The results of this study showed the presence of phosphorylation in tick saliva and highlight the roles of salivary phosphoproteins in facilitating tick feeding.

Characterization of a single-domain von Willebrand factor type C protein (HaSVC) from the salivary gland of the tick Hyalomma asiaticum

As a widely distributed arthropod and vector for various pathogens, Hyalomma asiaticum presents great risk and potential losses in animal husbandry. Effective measures, including the use of vaccines, are necessary for controlling ticks and tick-borne diseases. A concise understanding of the tick-host interaction associated molecules and pathways is required for vaccine development. In the present study, a protein containing a single-domain von Willebrand factor type C (HaSVC) was isolated from H. asiaticum and was subjected to functional identification. As a result, the full-length sequence of the HaSVC (506 bp) gene was obtained, which putatively encodes 100 amino acids with a predicted molecular mass of 11 kDa, excluding the 23-amino acid signal peptide. HaSVC contains 8 cysteines to form 4 disulfide bonds. The native HaSVC protein was detected in multiple tick organs. HaSVC neither attenuated the anti-coagulation process nor directly affected the blood feeding of adult ticks. However, the purified recombinant protein HaSVC (rHaSVC/GST) significantly increased the proliferation of mice spleen cells. This might suggest a regulatory function for HaSVC on inflammation, thus providing new information that may explain the "crosstalk" between ticks and hosts.

Salivary gland extract from the deer tick, Ixodes scapularis, facilitates neuroinvasion by Powassan virus in BALB/c mice

Powassan virus (POWV) is a neuroinvasive flavivirus transmitted to mammals by the bite of ixodid ticks. In this study, we sought to investigate the impact of tick salivary gland extract (SGE) on POWV neuroinvasion. BALB/c mice were footpad inoculated with either a high dose or a low dose of POWV, with and without Ixodes scapularis salivary gland extract. Brain and spinal cord were extracted daily, and immunohistochemical techniques were used for temporal tracking of POWV antigen. The temporal pattern of POWV staining showed a caudal to rostral spread of POWV in the brains of mice from both high dose infection groups. For the high dose infection groups, the presence of tick SGE did not influence the spread of POWV in the brain. Mice infected with the low dose of virus alone did not present POWV staining in the brain; however, in the presence of SGE, low dose infected mice presented scattered foci of POWV-infected cells throughout the brain. This study shows that tick SGE facilitates POWV neuroinvasion when mice are infected with the lower dose of POWV. We also found two patterns of central nervous system invasion that were directly influenced by the dose of POWV administered.

From Bench to Field: A Guide to Formulating and Evaluating Anti-Tick Vaccines Delving beyond Efficacy to Effectiveness

Ticks are ubiquitous blood-sucking ectoparasites capable of transmitting a wide range of pathogens such as bacteria, viruses, protozoa, and fungi to animals and humans. Although the use of chemicals (acaricides) is the predominant method of tick-control, there are increasing incidents of acaricide tick resistance. Furthermore, there are concerns over accumulation of acaricide residues in meat, milk and in the environment. Therefore, alternative methods of tick-control have been proposed, of which anti-tick cattle vaccination is regarded as sustainable and user-friendly. Over the years, tremendous progress has been made in identifying and evaluating novel candidate tick vaccines, yet none of them have reached the global market. Until now, Bm86-based vaccines (Gavac™ in Cuba and TickGARD^PLUS™ Australia-ceased in 2010) are still the only globally commercialized anti-tick vaccines. In contrast to Bm86, often, the novel candidate anti-tick vaccines show a lower protection efficacy. Why is this so? In response, herein, the potential bottlenecks to formulating efficacious anti-tick vaccines are examined. Aside from Bm86, the effectiveness of other anti-tick vaccines is rarely assessed. So, how can the researchers assess anti-tick vaccine effectiveness before field application? The approaches that are currently used to determine anti-tick vaccine efficacy are re-examined in this review. In addition, a model is proposed to aid in assessing anti-tick vaccine effectiveness. Finally, based on the principles for the development of general veterinary vaccines, a pipeline is proposed to guide in the development of anti-tick vaccines.

Probing an Ixodes ricinus salivary gland yeast surface display with tick-exposed human sera to identify novel candidates for an anti-tick vaccine

In Europe, Ixodes ricinus is the most important vector of human infectious diseases, most notably Lyme borreliosis and tick-borne encephalitis virus. Multiple non-natural hosts of I. ricinus have shown to develop immunity after repeated tick bites. Tick immunity has also been shown to impair B. burgdorferi transmission. Most interestingly, multiple tick bites reduced the likelihood of contracting Lyme borreliosis in humans. A vaccine that mimics tick immunity could therefore potentially prevent Lyme borreliosis in humans. A yeast surface display library (YSD) of nymphal I. ricinus salivary gland genes expressed at 24, 48 and 72 h into tick feeding was constructed and probed with antibodies from humans repeatedly bitten by ticks, identifying twelve immunoreactive tick salivary gland proteins (TSGPs). From these, three proteins were selected for vaccination studies. An exploratory vaccination study in cattle showed an anti-tick effect when all three antigens were combined. However, immunization of rabbits did not provide equivalent levels of protection. Our results show that YSD is a powerful tool to identify immunodominant antigens in humans exposed to tick bites, yet vaccination with the three selected TSGPs did not provide protection in the present form. Future efforts will focus on exploring the biological functions of these proteins, consider alternative systems for recombinant protein generation and vaccination platforms and assess the potential of the other identified immunogenic TSGPs.

Sphingomyelinases in a journey to combat arthropod-borne pathogen transmission

Ixodes scapularis ticks feed on humans and other vertebrate hosts and transmit several pathogens of public health concern. Tick saliva is a complex mixture of bioactive proteins, lipids and immunomodulators, such as I. scapularis sphingomyelinase (IsSMase)-like protein, an ortholog of dermonecrotoxin SMase D found in the venom of Loxosceles spp. of spiders. IsSMase modulates the host immune response towards Th2, which suppresses Th1-mediated cytokines to facilitate pathogen transmission. Arboviruses utilize exosomes for their transmission from tick to the vertebrate host, and exosomes derived from tick saliva/salivary glands suppress C-X-C motif chemokine ligand 12 and interleukin-8 immune response(s) in human skin to delay wound healing and repair processes. IsSMase affects also viral replication and exosome biogenesis, thereby inhibiting tick-to-vertebrate host transmission of pathogenic exosomes. In this review, we elaborate on exosomes and their biogenesis as potential candidates for developing novel control measure(s) to combat tick-borne diseases. Such targets could help with the development of an efficient anti-tick vaccine for preventing the transmission of tick-borne pathogens.

The role of basophils in acquired protective immunity to tick infestation

Ticks are blood-feeding ectoparasites that transmit a variety of pathogens to host animals and humans, causing severe infectious diseases such as Lyme disease. In a certain combination of animal and tick species, tick infestation elicits acquired immunity against ticks in the host, which can reduce the ability of ticks to feed on blood and to transmit pathogens in the following tick infestations. Therefore, our understanding of the cellular and molecular mechanisms of acquired tick resistance (ATR) can advance the development of anti-tick vaccines to prevent tick infestation and tick-borne diseases. Basophils are a minor population of white blood cells circulating in the bloodstream and are rarely observed in peripheral tissues under steady-state conditions. Basophils have been reported to accumulate at tick-feeding sites during re-infestation in cattle, rabbits, guinea pigs and mice. Selective ablation of basophils resulted in a loss of ATR in guinea pigs and mice, illuminating the essential role of basophils in the manifestation of ATR. In this review, we discuss the recent advance in the elucidation of the cellular and molecular mechanisms underlying basophil recruitment to the tick-feeding site and basophil-mediated ATR.

Nested PCR assay for detection of Theileria annulata in Hyalomma anatolicum infesting cattle from coastal Odisha, India

Ticks are economically important obligatory blood feeding arthropods that have a pivotal role in transmission of infection. The present study was conducted in ixodid ticks collected from four districts of coastal Odisha, India to investigate the prevalence of Theileria annulata. Adult semi engorged Hyalomma anatolicum ticks (n = 178) were dissected, the salivary gland was isolated and DNA was extracted. A nested PCR targeting the Tams1 gene of T. annulata, utilizing two sets of primers (N516F, N517R, and Ta14136iF, Ta249R) was utilized for detection of the parasite. The PCR products were then sequenced and subjected to BLAST analysis, alignment, and phylogenetic study. Two sequences deposited in GenBank were assigned Accession No MH477290.1 and Accession No MH477291.1. The molecular investigation of T. annulata revealed an overall prevalence of 14.6% in tick vectors, and nested PCR was found to have significant (p < 0.05) higher results than primary PCR. A significant higher presence (p < 0.05) was recorded in female ticks compared with male ticks. This is the first report of detection of the parasite in tick vectors in the state of Odisha.

Rhipicephalus sanguineus salivary gland extract as a source of immunomodulatory molecules

Rhipicephalus sanguineus sensu lato (s.l.), popularly known as 'brown dog tick', is the primary vector of pathogens affecting dogs worldwide. To enter the host's organism, these pathogens utilise the anticoagulant, antiplatelet, anti-inflammatory and immunomodulatory actions of compounds present in the tick's saliva; such compounds are released by the ectoparasite in order to attach and feed on dogs. Nitric oxide (NO) is one of the regulatory factors in inflammation, apoptosis and immunomodulation. Here, we evaluated the in vitro activity of salivary gland extract of female dog ticks on the macrophage-derived J774 cell line, with and without lipopolysaccharide (LPS) stimulation. Cultures were evaluated for possible morphological alterations caused by exposure to the extract. There was no apparent in vitro cytotoxicity of the extract. Also, the NO secretory response in the non-LPS-stimulated cells was not inhibited. On the other hand, the extract presented modulatory action in the cultures of LPS-stimulated cells at a concentration of 0.1 μg/mL, possibly through macrophage activation, and induced a significant decrease in NO secretion. These results confirm the modulatory potential of bioactive molecules in the salivary glands of R. sanguineus ticks.

Changing the Recipe: Pathogen Directed Changes in Tick Saliva Components

Ticks are obligate hematophagous parasites and are important vectors of a wide variety of pathogens. These pathogens include spirochetes in the genus Borrelia that cause Lyme disease, rickettsial pathogens, and tick-borne encephalitis virus, among others. Due to their prolonged feeding period of up to two weeks, hard ticks must counteract vertebrate host defense reactions in order to survive and reproduce. To overcome host defense mechanisms, ticks have evolved a large number of pharmacologically active molecules that are secreted in their saliva, which inhibits or modulates host immune defenses and wound healing responses upon injection into the bite site. These bioactive molecules in tick saliva can create a privileged environment in the host’s skin that tick-borne pathogens take advantage of. In fact, evidence is accumulating that tick-transmitted pathogens manipulate tick saliva composition to enhance their own survival, transmission, and evasion of host defenses. We review what is known about specific and functionally characterized tick saliva molecules in the context of tick infection with the genus Borrelia, the intracellular pathogen Anaplasma phagocytophilum, and tick-borne encephalitis virus. Additionally, we review studies analyzing sialome-level responses to pathogen challenge.

What do we still need to know about Ixodes ricinus?

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

Tick hypersensitivity and human tick-borne diseases

Immune-mediated hypersensitivity reactions to ticks and other arthropods are well documented. Hypersensitivity to ixodid (hard bodied) ticks is especially important because they transmit infection to humans throughout the world and are responsible for most vector-borne diseases in the United States. The causative pathogens of these diseases are transmitted in tick saliva that is secreted into the host while taking a blood meal. Tick salivary proteins inhibit blood coagulation, block the local itch response and impair host anti-tick immune responses, which allows completion of the blood meal. Anti-tick host immune responses are heightened upon repeated tick exposure and have the potential to abrogate tick salivary protein function, interfere with the blood meal and prevent pathogen transmission. Although there have been relatively few tick bite hypersensitivity studies in humans compared with those in domestic animals and laboratory animal models, areas of human investigation have included local hypersensitivity reactions at the site of tick attachment and generalized hypersensitivity reactions. Progress in the development of anti-tick vaccines for humans has been slow due to the complexities of such vaccines but has recently accelerated. This approach holds great promise for future prevention of tick-borne diseases.

Tick saliva-induced programmed death-1 and PD-ligand 1 and its related host immunosuppression

The tick Rhipicephalus microplus is a harmful parasite of cattle that causes considerable economic losses to the cattle breeding industry. Although R. microplus saliva (Rm-saliva) contains several immunosuppressants, any association between Rm-saliva and the expression of immunoinhibitory molecules, such as programmed death (PD)-1 and PD-ligand 1 (PD-L1), has not been described. In this study, flow cytometric analyses revealed that Rm-saliva upregulated PD-1 expression in T cells and PD-L1 expression in CD14⁺ and CD11c⁺ cells in cattle. Additionally, Rm-saliva decreased CD69 expression in T cells and Th1 cytokine production from peripheral blood mononuclear cells. Furthermore, PD-L1 blockade increased IFN-γ production in the presence of Rm-saliva, suggesting that Rm-saliva suppresses Th1 responses via the PD-1/PD-L1 pathway. To reveal the upregulation mechanism of PD-1/PD-L1 by Rm-saliva, we analyzed the function of prostaglandin E₂ (PGE₂), which is known as an inducer of PD-L1 expression, in Rm-saliva. We found that Rm-saliva contained a high concentration of PGE₂, and PGE₂ treatment induced PD-L1 expression in CD14⁺ cells in vitro. Immunohistochemical analyses revealed that PGE₂ and PD-L1 expression was upregulated in tick-attached skin in cattle. These data suggest that PGE₂ in Rm-saliva has the potential to induce the expression of immunoinhibitory molecules in host immune cells.

Naturally Acquired Resistance to Ixodes scapularis Elicits Partial Immunity against Other Tick Vectors in a Laboratory Host

In many regions where ticks negatively impact public health or economic production, multiple medically important tick species may have overlapping geographic distribution, and in North America, this includes members of Ixodes, Dermacentor, and Amblyomma genera. Acquired tick resistance is the process by which some animals develop an immune response against feeding ticks after one or more exposures. This form of immunity can restrict the ability of ticks to feed and may inhibit transmission of pathogens. Likewise, many proteins present in tick saliva are conserved among tick species, and prior studies have reported cross-protective host immunity against certain combinations of ticks. In this study, we used a guinea pig model to assess whether host resistance against Ixodes scapularis could confer protection against two other medically important tick vectors, Dermacentor variabilis and Amblyomma americanum. Tick challenges using nymphs were used to induce host resistance against a primary species, followed by additional challenge using a secondary tick species. Tick attachment to hosts and engorgement weights were reduced significantly for D. variabilis and A. americanum feeding on I. scapularis-sensitized hosts. Reciprocally, I. scapularis engorgement weights were reduced to a lesser extent, and attachment was unaffected when feeding on hosts sensitized with either D. variabilis or A. americanum. These results indicate that immunity against I. scapularis could potentially be exploited for use in an anti-tick vaccine targeting multiple tick species and their associated pathogens.

Acquired tick resistance: The trail is hot

Acquired tick resistance is a phenomenon wherein the host elicits an immune response against tick salivary components upon repeated tick infestations. The immune responses, potentially directed against critical salivary components, thwart tick feeding, and the animal becomes resistant to subsequent tick infestations. The development of tick resistance is frequently observed when ticks feed on non-natural hosts, but not on natural hosts. The molecular mechanisms that lead to the development of tick resistance are not fully understood, and both host and tick factors are invoked in this phenomenon. Advances in molecular tools to address the host and the tick are beginning to reveal new insights into this phenomenon and to uncover a deeper understanding of the fundamental biology of tick-host interactions. This review will focus on the expanding understanding of acquired tick resistance and highlight the impact of this understanding on anti-tick vaccine development efforts.

The Central Role of Salivary Metalloproteases in Host Acquired Resistance to Tick Feeding

During feeding on vertebrate hosts, ticks secrete saliva composed of a rich cocktail of bioactive molecules modulating host immune responses. Although most of the proteinaceous fraction of tick saliva is of little immunogenicity, repeated feeding of ticks on mammalian hosts may lead to impairment of tick feeding, preventing full engorgement. Here, we challenged rabbits with repeated feeding of both Ixodes ricinus nymphs and adults and observed the formation of specific antibodies against several tick salivary proteins. Repeated feeding of both I. ricinus stages led to a gradual decrease in engorged weights. To identify the salivary antigens, isolated immunoglobulins from repeatedly infested rabbits were utilized for a protein pull-down from the saliva of pilocarpine-treated ticks. Eluted antigens were first identified by peptide mass fingerprinting with the aid of available I. ricinus salivary gland transcriptomes originating from early phases of tick feeding. To increase the authenticity of immunogens identified, we also performed, for the first time, de novo assembly of the sialome from I. ricinus females fed for six days, a timepoint used for pilocarpine-salivation. The most dominant I. ricinus salivary immunogens identified in our study were zinc-dependent metalloproteases of three different families. To corroborate the role of metalloproteases at the tick/host interface, we fed ticks micro-injected with a zinc metalloprotease inhibitor, phosphoramidon, on a rabbit. These ticks clearly failed to initiate feeding and to engorge. However, neither feeding to ticks immune blood of repeatedly infested rabbits, nor phosphoramidon injection into ticks, prevented their engorgement when fed in vitro on an artificial membrane system. These data show that Zn metalloproteases play a decisive role in the success of tick feeding, mediated by complex molecular interactions between the host immune, inflammatory, and hemostatic processes, which are absent in in vitro feeding. This basic concept warrants further investigation and reconsideration of the current strategies towards the development of an effective “anti-tick” vaccine.

Tick salivary gland transcriptomics and proteomics

'Omics' technologies have facilitated the identification of hundreds to thousands of tick molecules that mediate tick feeding and play a role in the transmission of tick-borne diseases. Deep sequencing methodologies have played a key role in this knowledge accumulation, profoundly facilitating the study of the biology of disease vectors lacking reference genomes. For example, the nucleotide sequences of the entire set of tick salivary effectors, the so-called tick 'sialome', now contain at least one order of magnitude more transcript sequences compared to similar projects based on Sanger sequencing. Tick feeding is a complex and dynamic process, and while the dynamic 'sialome' is thought to mediate tick feeding success, exactly how transcriptome dynamics relate to tick-host-pathogen interactions is still largely unknown. The identification and, importantly, the functional analysis of the tick 'sialome' is expected to shed light on this 'black box'. This information will be crucial for developing strategies to block pathogen transmission, not only for anti-tick vaccine development but also the discovery and development of new, pharmacologically active compounds for human diseases.

Comprehensive analysis of protein expression levels and phosphorylation levels in host skin in response to tick (Haemaphysalis longicornis) bite

Ticks are parasitic arthropods that suck blood from the surface of most vertebrates. They can transmit a variety of pathogens. The blood sucking of ticks causes varying degrees of damage to the skin of the host. Proteins related to immune regulation, vascular repair, and wound healing in mammalian skin respond to tick bites by regulating their expression and post-translational modifications to protect the skin from injury. Phosphorylation of proteins, as the most common post-translational modification of proteins, plays an important role in the rapid regulation of cell signal transduction, gene expression and cell cycle. To systematically explore the molecular regulatory mechanisms employed by mammalian skin to resist tick bites, larval, nymphal, and adult Haemaphysalis longicornis were used to bite the skin tissues of healthy rabbits in the present study. The quantitative proteomic technology data-independent acquisition was then carried out to investigate in depth the changes in protein expression and phosphorylation in rabbit skin after tick bite. The results showed that among the 4034 proteins and 1795 phosphorylated proteins identified, a total of 202 proteins and 435 phosphorylation sites were changed after H. longicornis bite. In order to provide convenience for sucking blood, active substances in the saliva of H. longicornis injected into the rabbit's skin can cause the expression level of trichohyalin and peptidyl arginine deiminase 3 in the skin of the host downregulate, which can make the host hair loss and regeneration disorders. At the same time, the active substances in saliva of the H. longicornis led to the phosphorylation of microtubule actin cross-linking factor 1 in the host's skin and further inactivation, so as to delay the healing of the host wound. In response to tick bites, the host skin promotes coagulation through high expression of fibrinogen and fibronectin, and vascular repair through high expression of integrin linked kinase and tenascin C, as well as accelerated phosphorylation of the phosphorylated protein Nck adaptor protein 1, and wound healing through high expression of ezrin and integrin. The upregulation of proteins such as coronin, NADPH oxidase, calnexin, and calreticulin and phosphorylation level of IL-4R in the host skin after the H. longicornis bite indicated that the immune response was playing an important defensive role in response to tick bites. Meanwhile, we found that the upregulated two lectins, mannose receptor C-type 1 and DC-SIGN, may serve as molecular makers to identify and monitor whether the skin is bitten by ticks. SIGNIFICANCE: Haemaphysalis longicornis are parasitic arthropods that suck blood from the surface of most vertebrates. They can transmit a variety of pathogens and are harmful to humans and livestock. The present study is the first quantitative proteomic study on protein expression levels in the rabbit skin after infection by H. longicornis. It is also the first quantitative phosphoproteomic study in the host skin infected by ticks. In this study, we found that tick bites cause the host hair loss and regeneration disorders. For resisting tick bite, the host activates the immune response and initiates vascular repair and wound-healing systems. In addition, some phosphorylated proteins promote host immunity and vascular repair. These results can help us further understand the defence mechanism of the host against tick bites, provide a basis for the development of an anti-tick vaccine, the development of anti-tick drugs, and the diagnosis of tick-borne diseases.

Discovery of Exosomes From Tick Saliva and Salivary Glands Reveals Therapeutic Roles for CXCL12 and IL-8 in Wound Healing at the Tick-Human Skin Interface

Ticks secrete various anti-coagulatory, anti-vasoconstrictory, anti-inflammatory, and anti-platelet aggregation factors in their saliva at the bite site during feeding to evade host immunological surveillance and responses. For the first time, we report successful isolation of exosomes (small membrane-bound extracellular signaling vesicles) from saliva and salivary glands of partially fed or unfed ixodid ticks. Our data showed a novel role of these in vivo exosomes in the inhibition of wound healing via downregulation of C-X-C motif chemokine ligand 12 (CXCL12) and upregulation of interleukin-8 (IL-8). Cryo-electron microscopy (cryo-EM) analysis revealed that tick saliva and salivary glands are composed of heterogeneous populations of in vivo exosomes with sizes ranging from 30 to 200 nm. Enriched amounts of tick CD63 ortholog protein and heat shock protein 70 (HSP70) were evident in these exosomes. Treatment of human skin keratinocytes (HaCaT cells) with exosomes derived from tick saliva/salivary glands or ISE6 cells dramatically delayed cell migration, wound healing, and repair process. Wound healing is a highly dynamic process with several individualized processes including secretion of cytokines. Cytokine array profiling followed by immunoblotting and quantitative-PCR analysis revealed that HaCaT cells treated with exosomes derived from tick saliva/salivary glands or ISE6 cells showed enhanced IL-8 levels and reduced CXCL12 loads. Inhibition of IL-8 or CXCL12 further delayed exosome-mediated cell migration, wound healing, and repair process, suggesting a skin barrier protection role for these chemokines at the tick bite site. In contrast, exogenous treatment of CXCL12 protein completely restored this delay and enhanced the repair process. Taken together, our study provides novel insights on how tick salivary exosomes secreted in saliva can delay wound healing at the bite site to facilitate successful blood feeding.

Interrupted Blood Feeding in Ticks: Causes and Consequences

Ticks are obligate hematophagous arthropods and act as vectors for a great variety of pathogens, including viruses, bacteria, protozoa, and helminths. Some tick-borne viruses, such as Powassan virus and tick-borne encephalitis virus, are transmissible within 15–60 min after tick attachment. However, a minimum of 3–24 h of tick attachment is necessary to effectively transmit bacterial agents such as Ehrlichia spp., Anaplasma spp., and Rickettsia spp. to a new host. Longer transmission periods were reported for Borrelia spp. and protozoans such as Babesia spp., which require a minimum duration of 24–48 h of tick attachment for maturation and migration of the pathogen. Laboratory observations indicate that the probability of transmission of tick-borne pathogens increases with the duration an infected tick is allowed to remain attached to the host. However, the transmission time may be shortened when partially fed infected ticks detach from their initial host and reattach to a new host, on which they complete their engorgement. For example, early transmission of tick-borne pathogens (e.g., Rickettsia rickettsii, Borrelia burgdorferi, and Babesia canis) and a significantly shorter transmission time were demonstrated in laboratory experiments by interrupted blood feeding. The relevance of such situations under field conditions remains poorly documented. In this review, we explore parameters of, and causes leading to, spontaneous interrupted feeding in nature, as well as the effects of this behavior on the minimum time required for transmission of tick-borne pathogens.

Humoral immune response of pigs, Sus scrofa domesticus, upon repeated exposure to blood-feeding by Ornithodoros turicata Duges (Ixodida: Argasidae)

BACKGROUND

Ornithodoros turicata is an important vector of both human and veterinary pathogens. One primary concern is the global spread of African swine fever virus and the risk of its re-emergence in the Americas through potential transmission by O. turicata to domestic pigs and feral swine. Moreover, in Texas, African warthogs were introduced into the state for hunting purposes and evidence exists that they are reproducing and have spread to three counties in the state. Consequently, it is imperative to develop strategies to evaluate exposure of feral pigs and African warthogs to O. turicata.

RESULTS

We report the development of an animal model to evaluate serological responses of pigs to O. turicata salivary proteins after three exposures to tick feeding. Serological responses were assessed for ~ 120 days by enzyme-linked immunosorbent assay and immunoblotting using salivary gland extracts from O. turicata.

CONCLUSIONS

Our findings indicate that domestic pigs seroconverted to O. turicata salivary antigens that is foundational toward the development of a diagnostic assay to improve soft tick surveillance efforts.

Ixodes scapularis saliva components that elicit responses associated with acquired tick-resistance

Ticks and tick-borne diseases are on the rise world-wide and vaccines to prevent transmission of tick-borne diseases is an urgent public health need. Tick transmission of pathogens to the mammalian host occurs during tick feeding. Therefore, it is reasoned that vaccine targeting of tick proteins essential for feeding would thwart tick feeding and consequently prevent pathogen transmission. The phenomenon of acquired tick-immunity, wherein, repeated tick infestations of non-natural hosts results in the development of host immune responses detrimental to tick feeding has served as a robust paradigm in the pursuit of tick salivary antigens that may be vaccine targeted. While several salivary antigens have been identified, immunity elicited against these antigens have only provided modest tick rejection. This has raised the possibility that acquired tick-immunity is directed against tick components other than tick salivary antigens. Using Ixodes scapularis, the blacklegged tick, that vectors several human pathogens, we demonstrate that immunity directed against tick salivary glycoproteins is indeed sufficient to recapitulate the phenomenon of tick-resistance. These observations emphasize the utility of tick salivary glycoproteins as viable vaccine targets to thwart tick feeding and direct our search for anti-tick vaccine candidates.

Immunosuppressive effects of sialostatin L1 and L2 isolated from the taiga tick Ixodes persulcatus Schulze

Tick saliva contains immunosuppressants which are important to obtain a blood meal and enhance the infectivity of tick-borne pathogens. In Japan, Ixodes persulcatus is a major vector for Lyme borreliosis pathogens, such as Borrelia garinii, as well as for those causing relapsing fever, such as B. miyamotoi. To date, little information is available on bioactive salivary molecules, produced by this tick. Thus, in this study, we identified two proteins, I. persulcatus derived sialostatin L1 (Ip-sL1) and sL2 (Ip-sL2), as orthologs of I. scapularis derived sL1 and sL2. cDNA clones of Ip-sL1 and Ip-sL2 shared a high identity with sequences of sL1 and sL2 isolated from the salivary glands of I. scapularis. Semi-quantitative PCR revealed that Ip-sL1 and Ip-sL2 were expressed in the salivary glands throughout the life of the tick. In addition, Ip-sL1 and Ip-sL2 were expressed even before the ticks started feeding, and their expression continued during blood feeding. Recombinant Ip-sL1 and Ip-sL2 were developed to characterize the proteins via biological and immunological analyses. These analyses revealed that both Ip-sL1 and Ip-sL2 had inhibitory effects on cathepsins L and S. Ip-sL1 and Ip-sL2 inhibited the production of IP-10, TNFα, and IL-6 by LPS-stimulated bone-marrow-derived dendritic cells (BMDCs). Additionally, Ip-sL1 significantly impaired BMDC maturation. Taken together, these results suggest that Ip-sL1 and Ip-sL2 confer immunosuppressive functions and appear to be involved in the transmission of pathogens by suppressing host immune responses, such as cytokine production and dendritic cell maturation. Therefore, further studies are warranted to investigate the immunosuppressive functions of Ip-sL1 and Ip-sL2 in detail to clarify their involvement in pathogen transmission via I. persulcatus.

Evasins: Tick Salivary Proteins that Inhibit Mammalian Chemokines

Ticks are hematophagous arachnids that parasitize mammals and other hosts, feeding on their blood. Ticks secrete numerous salivary factors that enhance host blood flow or suppress the host inflammatory response. The recruitment of leukocytes, a hallmark of inflammation, is regulated by chemokines, which activate chemokine receptors on the leukocytes. Ticks target this process by secreting glycoproteins called Evasins, which bind to chemokines and prevent leukocyte recruitment. This review describes the recent discovery of numerous Evasins produced by ticks, their classification into two structural and functional classes, and the efficacy of Evasins in animal models of inflammatory diseases. The review also proposes a standard nomenclature system for Evasins and discusses the potential of repurposing or engineering Evasins as therapeutic anti-inflammatory agents.

Immunomodulatory effects of Rhipicephalus haemaphysaloides serpin RHS2 on host immune responses

Background

Rhipicephalus haemaphysaloides is a widespread tick species in China and other South East Asian countries, where it is the vector of many pathogens. The objective of this study was to study the role of serpin (serine protease inhibitor) during the tick-host interaction.

Methods

The differentiation of bone marrow-derived dendritic cells (BMDC) was induced in vitro, and the effect of RHS2 on the maturation of DCs was evaluated. The effects of RHS2 on T cell activation and cytotoxic T lymphocytes’ (CTLs) activity were analyzed by flow cytometry. Antibody subtypes after immunization of mice with RHS2 and OVA were determined.

Results

RHS2 can inhibit the differentiation of bone marrow-derived cells into DCs and promote their differentiation into macrophages. RHS2 can inhibit the maturation of DCs and the expression of CD80, CD86 and MHCII. The number of CD3⁺CD4⁺ and CD3⁺CD8⁺ T cells secreting IFN-γ, IL-2 and TNF-α was decreased, and the number of CD3⁺CD4⁺ T cells secreting IL-4 was increased, indicating that RHS2 can inhibit the activation of CD4 T cells and CD8 T cells, leading to inhibition of Th1 immune response. RHS2 inhibits the elimination of target cells by cytotoxic T lymphocytes. After immunization of mice with RHS2 and OVA, serum IgG2b was significantly reduced and IgM was increased.

Conclusions

The results show that RHS2 has an inhibitory effect on the host immune response. Ticks have evolved various ways to circumvent adaptive immunity. Their serpin inhibits BMDC differentiation to reduce immune responses.

[Immunomodulatory effect of tick saliva in pathogen transmission]

Ticks are the most important vectors of pathogens in human and veterinary medicine. These strictly haematophagous acarines produce a saliva containing a variety of bioactive molecules affecting host pharmacology and immunity. This process is vital for hard ticks to prevent rejection by the host during the blood meal that lasts several days. All actors involved in the immunity interplay are impacted by this saliva, the innate immunity being represented by resident and migrating immune cells, as well as the T and B lymphocytes of the adaptive immune system. The skin plays a key role in vector-borne diseases. During the long co-evolution with the tick, the infectious agents benefit from this favorable environment to be transmitted efficiently into the skin and to multiply in the vertebrate host. Therefore, the saliva is an important virulence booster, which enhances substantially their pathogenicity.

How ticks keep ticking in the adversity of host immune reactions

Ixodid ticks are acknowledged as one of the most important hematophagous arthropods because of their ability in transmitting a variety of tick-borne diseases. Mathematical models have been developed, based on emerging knowledge about tick ecology, pathogen epidemiology and their interface, to understand tick population dynamics and tick-borne diseases spread patterns. However, no serious effort has been made to model and assess the impact of host immunity triggered by tick feeding on the distribution of the tick population according to tick stages and on tick population extinction and persistence. Here, we construct a novel mathematical model taking into account the effect of host immunity status on tick population dynamics, and analyze the long-term behaviours of the model solutions. Two threshold values, [Formula: see text] and [Formula: see text], are introduced to measure the reproduction ratios for the tick-host interaction in the absence and presence of host immunity. We then show that these two thresholds (sometimes under additional conditions) can be used to predict whether the tick population goes extinct ([Formula: see text]) and the tick population grows without bound ([Formula: see text]). We also prove tick permanence (persistence and boundedness of the tick population) and the existence of a tick persistence equilibrium if [Formula: see text]. As the host species adjust their immunity to tick infestation levels, they form for the tick population an environment with a carrying capacity very much like that in logistic growth. Numerical results show that the host immune reactions decrease the size of the tick population at equilibrium and apparently reduce the tick-borne infection risk.

An insight into the ecobiology, vector significance and control of Hyalomma ticks (Acari: Ixodidae): A review

Ticks (Acari:Ixodoidea) are important ectoparasites infesting livestock and human populations around the globe. Ticks can cause damage directly by affecting the site of infestation, or indirectly as vectors of a wide range of protozoa, bacteria and viruses which ultimately lead to lowered productivity of livestock populations. Hyalomma is a genus of hard ticks, having more than 30 species well-adapted to hot, humid and cold climates. Habitat diversity, vector ability, and emerging problem of acaricidal resistance in enzootic regions typify this genus in various countries around the world. This paper reviews the epidemiology, associated risk factors (temperature, climate, age, sex, breed etc.), vector role, vector-pathogen association, and reported control strategies of genus Hyalomma. The various proteins in saliva of Hyalomma secreted into the blood stream of host and the prolonged attachment are responsible for the successful engorgement of female ticks in spite of host immune defense system. The various immunological approaches that have been tried by researchers in order to cause tick rejection are also discussed. In addition, the novel biological control approaches involving the use of entomo-pathogenic nematodes and Bacillus thuringiensis (B. thuringiensis) serovar thuringiensis H14; an endotoxin, for their acaricidal effect on different species and life cycle stages of Hyalomma are also presented.

Morphological evaluation of the liver in Wistar rats inoculated with Rhipicephalus sanguineus (Latreille, 1806) (Acari: Ixodidae) salivary gland extracts

The Rhipicephalus sanguineus is considered a species of medical and veterinary importance. The feeding process of these animals occurs due to the combined action of their mouthparts and the saliva produced by the salivary glands, vital organs for the biological success of the ticks. In addition, these glands act as storage sites for the pathogens transmitted to the host through the inoculation of the saliva. In this sense, the present study had the objective to analyze the behavior of male Wistar rat hepatic cells submitted to in vivo application of the salivary gland extract (SGE) obtained from R. sanguineus female ticks. The study involved five groups (four male adults each): CG (non-inoculated individuals); PBS1 (one phosphate buffer saline injection); PBS2 (two PBS injections); SGE1 (one injection of SGE at 0.04 μg/μL) and SGE2 (two injections of SGE at 0.04 μg/μL). After the exposures, the livers were removed and submitted to the following histological and histochemical stains: HE, toluidine blue, Xylidine Ponceau, alcian blue/PAS, and osmium-imidazole. The results showed that both the PBS and the SGE caused hepatic moderate alterations, such as: (a) emergence of lipid plaques among the hepatic cords; (b) cytoplasmic vacuolation of the hepatic cells; (c) hepatocytes showing pyknotic nuclei; (d) presence of homogeneous or granular secretion in the cytoplasm of the hepatocytes. Despite the slight morphological alterations observed in the hepatic cells and tissue, the latter did not show signs of disorganization after the exposure to the extracts.

Mosquito and Tick-borne Illnesses in the United States. Guidelines for the Recognition and Empiric Treatment of Zoonotic Diseases in the Wilderness

BACKGROUND

In the United States, tick-borne illnesses account for a significant number of patients that have been seen and treated by health care facilities. This in turn, has resulted in a significant morbidity and mortality and economic costs to the country.

METHODS

The distribution of these illnesses is geographically variable and is related to the climate as well. Many of these illnesses can be diagnosed and treated successfully, if recognized and started on appropriate antimicrobial therapy early in the disease process. Patient with illnesses such as Lyme disease, Wet Nile illness can result in chronic debilitating diseases if not recognized early and treated.

CONCLUSION

This paper covers illnesses such as Lyme disease, West Nile illness, Rocky Mountain Spotted fever, Ehrlichia, Tularemia, typhus, mosquito borne illnesses such as enteroviruses, arboviruses as well as arthropod and rodent borne virus infections as well. It covers the epidemiology, clinical features and diagnostic tools needed to make the diagnosis and treat these patients as well.

Whole body transcriptomes and new insights into the biology of the tick Ixodes ricinus

BACKGROUND

Ixodes ricinus is the most important vector of tick-borne diseases in Europe. A better knowledge of its genome and transcriptome is important for developing control strategies. Previous transcriptomic studies of I. ricinus have focused on gene expression during the blood meal in specific tissues. To obtain a broader picture of changes in gene expression during the blood meal, our study analysed the transcriptome at the level of the whole body for both nymphal and adult ticks. Ixodes ricinus ticks from a highly inbred colony at the University of Neuchâtel were used. We also analysed previously published RNAseq studies to compare the genetic variation between three wild strains and three laboratory strains, including the strain from Neuchâtel.

RESULTS

RNA was extracted from whole tick bodies and the cDNA was sequenced, producing 162,872,698 paired-end reads. Our reference transcriptome contained 179,316 contigs, of which 31% were annotated using Trinotate. Gene expression was compared between ticks that differed by feeding status (unfed vs partially fed). We found that blood-feeding in nymphs and female adult ticks increased the expression of cuticle-associated genes. Using a set of 3866 single nucleotide polymorphisms to calculate the heterozygosity, we found that the wild tick populations of I. ricinus had much higher levels of heterozygosity than the three laboratory populations.

CONCLUSION

Using high throughput strand-oriented sequencing for whole ticks in different stages and feeding conditions, we obtained a de novo assembly that significantly increased the genomic resources available for I. ricinus. Our study illustrates the importance of analysing the transcriptome at the level of the whole body to gain additional insights into how gene expression changes over the life-cycle of an organism. Our comparison of several RNAseq datasets shows the power of transcriptomic data to accurately characterize genetic polymorphism and for comparing different populations or sources of sequencing material.

Ticks and Tick-Borne Infections: Complex Ecology, Agents, and Host Interactions

Ticks transmit the most diverse array of infectious agents of any arthropod vector. Both ticks and the microbes they transmit are recognized as significant threats to human and veterinary public health. This article examines the potential impacts of climate change on the distribution of ticks and the infections they transmit; the emergence of novel tick-borne pathogens, increasing geographic range and incidence of tick-borne infections; and advances in the characterization of tick saliva mediated modulation of host defenses and the implications of those interactions for transmission, establishment, and control of tick infestation and tick-borne infectious agents.

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.