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SummaryViruses transmitted byAedesmosquitoes constitute an increasingly important global health burden. Defining common determinants of host susceptibility to this large group of heterogenous pathogens are key for informing the rational design of new pan-viral medicines. Infection of the vertebrate host with these viruses is enhanced by the presence of mosquito saliva, a complex mixture of salivary gland-derived factors and microbiota. We show that enhancement of infection by saliva was dependent on vascular function and was independent of most anti-saliva immune responses, including to salivary microbiota. Instead, theAedesgene product sialokinin mediated enhancement of virus infection through a rapid reduction in endothelial barrier integrity. Sialokinin is unique within the insect world as having vertebrate-like tachykinin sequence and is absent from non-vector competentAnophelesmosquitoes, whose saliva was not pro-viral and did not induce similar vascular permeability. Therapeutic strategies targeting sialokinin have potential to limit disease severity following infection withAedesmosquito-borne viruses.

Some free fatty acids derived from milk and vegetable oils are known to have potent antiviral and antibacterial properties. However, therapeutic applications of short- to medium-chain fatty acids are limited by physical characteristics such as immiscibility in aqueous solutions. We evaluated a novel proprietary formulation based on an emulsion of short-chain caprylic acid, ViroSAL, for its ability to inhibit a range of viral infections in vitro and in vivo. In vitro, ViroSAL inhibited the enveloped viruses Epstein–Barr, measles, herpes simplex, Zika and orf parapoxvirus, together with Ebola, Lassa, vesicular stomatitis and severe acute respiratory syndrome coronavirus 1 (SARS-CoV-1) pseudoviruses, in a concentration- and time-dependent manner. Evaluation of the components of ViroSAL revealed that caprylic acid was the main antiviral component; however, the ViroSAL formulation significantly inhibited viral entry compared with caprylic acid alone. In vivo, ViroSAL significantly inhibited Zika and Semliki Forest virus replication in mice following the inoculation of these viruses into mosquito bite sites. In agreement with studies investigating other free fatty acids, ViroSAL had no effect on norovirus, a non-enveloped virus, indicating that its mechanism of action may be surfactant disruption of the viral envelope. We have identified a novel antiviral formulation that is of great interest for the prevention and/or treatment of a broad range of enveloped viruses, particularly those of the skin and mucosal surfaces.

Mosquitoes can pass disease to humans when they bite, which includes infections caused by viruses, known as arboviruses. These viruses infect many millions of people each year and include viruses that cause diseases such as Zika, dengue and chikungunya. Most such infections are usually found in the tropics, but a changing climate and globalization means their range has spread at an alarming rate. Cumulatively these viruses are highly diverse at the genetic level and include up to 90 known human pathogens. It is hard to predict the nature, timing and location of these outbreaks. Furthermore, these viruses replicate to exceptionally high levels in the blood of infected patients. Thus, arbovirus infection constitutes an increasing concern for blood transfusion services. We suggest that it is important to identify common aspects of these infections to aid diagnosis, patient stratification and develop medicines that are applicable to multiple arbovirus infections. An important stage, common to all such infections, is the inoculation of virus at mosquito bites. We have recently shown that mosquito bite inflammation, which is common to all such infections, inadvertently enhances infection. In this study, we identified key aspects of mosquito bite inflammation that are important determinants of the subsequent systemic course and clinical outcome of infection. As such, host responses to mosquito saliva may prove to be a predictor of subsequent disease severity and consequently could also be useful in risk-stratifying blood products.

Arthropod-borne viruses (arboviruses) are important human pathogens for which there are no specific antiviral medicines. The abundance of genetically distinct arbovirus species, coupled with the unpredictable nature of their outbreaks, has made the development of virus-specific treatments challenging. Instead, we have defined and targeted a key aspect of the host innate immune response to virus at the arthropod bite that is common to all arbovirus infections, potentially circumventing the need for virus-specific therapies. Using mouse models and human skin explants, we identify innate immune responses by dermal macrophages in the skin as a key determinant of disease severity. Post-exposure treatment of the inoculation site by a topical TLR7 agonist suppressed both the local and subsequent systemic course of infection with a variety of arboviruses from the Alphavirus, Flavivirus, and Orthobunyavirus genera. Clinical outcome was improved in mice after infection with a model alphavirus. In the absence of treatment, antiviral interferon expression to virus in the skin was restricted to dermal dendritic cells. In contrast, stimulating the more populous skin-resident macrophages with a TLR7 agonist elicited protective responses in key cellular targets of virus that otherwise proficiently replicated virus. By defining and targeting a key aspect of the innate immune response to virus at the mosquito bite site, we have identified a putative new strategy for limiting disease after infection with a variety of genetically distinct arboviruses.

Arthropod-borne viruses (arboviruses) are important human pathogens for which there are no specific antiviral medicines. The large number of genetically-distinct arbovirus species, coupled with the unpredictable nature of their outbreaks, has made developing virus-specific anti-viral medicines challenging. Instead, we have defined and targeted a key aspect of the host innate immune response to virus at the arthropod bite that is common to all arbovirus infections, potentially circumventing the need for virus-specific therapies at this site. Using mouse models and human skin explants, we identify innate immune responses by dermal macrophages in the skin as a key determinant of disease severity. Post-exposure treatment of the inoculation site by a topical innate immune agonist significantly suppressed both the local and subsequent systemic course of infection and improved clinical outcome in mice to infection with a variety of arboviruses from the Alphavirus, Flavivirus and Orthobunyavirus genuses. In the absence of treatment, anti-viral interferon expression to virus in the skin was restricted to dermal dendritic cells. In contrast, targeting the more populous skin-resident macrophages with an immune agonist elicited protective responses in key cellular targets of virus that otherwise replicated virus to high levels. By defining and targeting a key aspect of the innate immune response to virus at the mosquito bite site, we have shown that it is possible to improve outcome to infection by targeting pathways activated at the site of inoculation, and thereby identified a putative new strategy for limiting disease following infection with a variety of genetically-distinct arboviruses.One-sentence summaryWe demonstrate that activation of innate immune responses to arbovirus at the mosquito bite is a limiting factor for preventing efficient systemic dissemination of virus and that therapeutic targeting of skin-resident macrophages can have defining inhibitory effects on the later systemic course.

Aedes aegypti mosquitoes are responsible for transmitting\ud many medically important viruses such as\ud those that cause Zika and dengue. The inoculation\ud of viruses into mosquito bite sites is an important\ud and common stage of all mosquito-borne virus infections.\ud We show, using Semliki Forest virus and\ud Bunyamwera virus, that these viruses use this inflammatory\ud niche to aid their replication and dissemination\ud in vivo. Mosquito bites were characterized by\ud an edema that retained virus at the inoculation site\ud and an inflammatory influx of neutrophils that coordinated\ud a localized innate immune program that inadvertently\ud facilitated virus infection by encouraging\ud the entry and infection of virus-permissive myeloid\ud cells. Neutrophil depletion and therapeutic blockade\ud of inflammasome activity suppressed inflammation\ud and abrogated the ability of the bite to promote infection.\ud This study identifies facets of mosquito bite\ud inflammation that are important determinants of the\ud subsequent systemic course and clinical outcome\ud of virus infection.