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.

More than 25% of human infectious diseases are vector-borne diseases (VBDs). These diseases, caused by pathogens shared between animals and humans, are a growing threat to global health with more than 2.5 million annual deaths. Mosquitoes and ticks are the main vectors of arboviruses including flaviviruses, which greatly affect humans. However, all tick or mosquito species are not able to transmit all viruses, suggesting important molecular mechanisms regulating viral infection, dissemination, and transmission by vectors. Despite the large distribution of arthropods (mosquitoes and ticks) and arboviruses, only a few pairings of arthropods (family, genus, and population) and viruses (family, genus, and genotype) successfully transmit. Here, we review the factors that might limit pathogen transmission: internal (vector genetics, immune responses, microbiome including insect-specific viruses, and coinfections) and external, either biotic (adult and larvae nutrition) or abiotic (temperature, chemicals, and altitude). This review will demonstrate the dynamic nature and complexity of virus–vector interactions to help in designing appropriate practices in surveillance and prevention to reduce VBD threats.

Ticks are the most important vectors of pathogens affecting both domestic and wild animals worldwide. Hard tick feeding is a slow process—taking up to several days—and necessitates extended control over the host response. The success of the feeding process depends upon injection of tick saliva, which not only controls host hemostasis and wound healing, but also subverts the host immune response to avoid tick rejection that creates a favorable niche for the survival and propagation of diverse tick-borne pathogens. Here, we report on the molecular and biochemical features and functions of an Ixodes ricinus serine protease inhibitor (IrSPI). We characterize IrSPI as a Kunitz elastase inhibitor that is overexpressed in several tick organs—especially salivary glands—during blood-feeding. We also demonstrated that when IrSPI is injected into the host through saliva, it had no impact on tissue factor pathway-induced coagulation, fibrinolysis, endothelial cell angiogenesis or apoptosis, but the protein exhibits immunomodulatory activity. In particular, IrSPI represses proliferation of CD4+ T lymphocytes and proinflammatory cytokine secretion from both splenocytes and macrophages. Our study contributes valuable knowledge to tick-host interactions and provides insights that could be further exploited to design anti-tick vaccines targeting this immunomodulator implicated in I. ricinus feeding.

Mosquito-borne diseases caused by viruses and parasites are responsible for more than 700 million infections each year. Anopheles and Aedes are the two major vectors for, respectively, malaria and arboviruses. Anopheles mosquitoes are the primary vector of just one known arbovirus, the alphavirus o’nyong-nyong virus (ONNV), which is closely related to the chikungunya virus (CHIKV), vectored by Aedes mosquitoes. However, Anopheles harbor a complex natural virome of RNA viruses, and a number of pathogenic arboviruses have been isolated from Anopheles mosquitoes in nature. CHIKV and ONNV are in the same antigenic group, the Semliki Forest virus complex, are difficult to distinguish via immunodiagnostic assay, and symptomatically cause essentially the same human disease. The major difference between the arboviruses appears to be their differential use of mosquito vectors. The mechanisms governing this vector specificity are poorly understood. Here, we summarize intrinsic and extrinsic factors that could be associated with vector specificity by these viruses. We highlight the complexity and multifactorial aspect of vectorial specificity of the two alphaviruses, and evaluate the level of risk of vector shift by ONNV or CHIKV.

The effect of climate on the evolution of tick populations remains difficult to disentangle from other possible causes and undoubtedly varies depending on the region concerned and local tick species. Large-scale, long-term monitoring is, therefore, necessary to accurately assess climatic impact on tick populations. Climate change can alter tick populations, either indirectly by affecting vertebrate host populations or directly by increasing or decreasing their numbers. These ectoparasites, and in particular hard ticks, spend almost their entire life cycle in the external environment, thus climatic conditions influence their activity, viability and distribution. This expert opinion aims to illustrate the impact of climate change, and its association with other variables, on the distribution and abundance of tick populations in Europe using Ixodes ricinus and Hyalomma marginatum as typical examples of endemic and invasive species, respectively.

30Ticks are strict hematophagous arthropods and are the most important vectors of pathogens 31 affecting both domestic and wild animals worldwide. Moreover, they are second only to mosquitoes as 32 vectors of human pathogens. Hard tick feeding is a slow process-taking up to several days for repletion 33 prior to detachment-and necessitates extended control over the host response. The success of the 34 feeding process depends upon injection of saliva by tick, which not only controls host haemostasis and 35 wound healing, but also subverts the host immune response to avoid tick rejection during this long-36 lasting process. In turn, the manipulation of the host immune response creates a favourable niche for the 37 survival and propagation of diverse tick-borne pathogens transmitted during feeding. Here, we report 38 on the molecular and biochemical features and functions of IrSPI, an Ixodes ricinus salivary serine 39 protease inhibitor involved in blood meal acquisition. Our results show that IrSPI harbours the typical 40 conformational fold of Kunitz type I serine protease inhibitors and that it functionally inhibits the 41 elastase and, to a lesser extent, chymotrypsin. We also show that IrSPI is injected into the host during 42 feeding. Crucially, we found that IrSPI has no impact on tissue factor pathway-induced coagulation, 43 fibrinolysis, apoptosis, or angiogenesis, but a strong effect on immune cells. IrSPI affects antigen-44 presenting macrophages by hampering IL-5 production. In addition, IrSPI represses proliferation of 45 mitogen-stimulated CD4 + cells. The inhibition of T cell proliferation was associated with marked 46 reductions in pro-inflammatory cytokine secretion. Our study contributes valuable knowledge to tick-47 host interactions and provides insights that could be further exploited to design anti-tick vaccines 48 targeting this immunomodulator implicated in successful I. ricinus tick feeding. 50Author summary 51 Ticks are the most important vector influencing both human and animal health in Europe, where 52 Ixodes ricinus is the most abundant tick species. Ticks feed on animal or human blood for an extended 53 period, during which their saliva allows both feeding and pathogen transmission by interfering with 54 native host responses. A better understanding of tick-host-pathogen interactions is central to the 55 discovery of improved control methods. Within this context, we previously identified IrSPI as an I.3 56 ricinus salivary molecule implicated in both tick feeding and bacterial transmission. This serine protease 57 inhibitor was almost characterised as an elastase inhibitor, and here, we show IrSPI overexpression in 58 several tick organs-especially salivary glands-during blood feeding. We demonstrate that IrSPI is 59 injected into the host through saliva, and despite having no impact on endothelial cell angiogenesis or 60 apoptosis during blood feeding, we report an immunomodulatory role, whereby CD4 + T lymphocyte 61 proliferation is repressed and where the cytokine secretion pattern ...

The G3BP proteins in vertebrates and Aedes mosquito ortholog, Rasputin, are essential for alphavirus infection, but the underlying mechanism of Rasputin/G3BP proviral activity is poorly understood. It has been suggested that G3BP could influence host immune signaling, but this has not been functionally demonstrated. Here, we find that depletion of Rasputin activity in Anopheles mosquitoes, the primary vectors of the alphavirus o-nyong-nyong (ONNV), provokes dysregulation of the antiviral Imd, JAK/STAT and RNAi pathways, indicating that Rasputin is required for expression of normal basal immunity in uninfected mosquitoes. Depletion of Rasputin during ONNV bloodmeal infection causes increased transcript abundance of genes in the Imd pathway including positive regulator Rel2, and decreases ONNV infection in mosquitoes. Loss of Rasputin is complemented by co-depletion of Imd pathway positive regulator, Rel2, which restores normal ONNV infection levels. Thus, the presence of Rasputin is required for ONNV inhibition of Imd activity, and viral inhibition of Imd explains much of the Rasputin proviral activity. The viral non-structural protein 3 (nsP3) binds to Rasputin and alters the profile of cellular proteins binding to Rasputin. In the presence of nsP3, 48 Rasputin-binding proteins are unchanged but seven binding proteins are excluded and eight new proteins bind Rasputin. The Rasputin binding partners altered by nsP3 are candidate factors for ONNV immune manipulation and subversion through Rasputin. Overall, these results are consistent with and strongly suggest a mechanism in which ONNV, probably nsP3, co-opts the normal Rasputin function assuring basal cellular immune activity in order to inhibit antiviral immunity and promote infection. These observations may be generalizable for Rasputin function during alphavirus infection of other mosquitoes, as well as for G3BP function in the mammalian host, and could offer a target for vector-based control of arbovirus transmission.