Vector competence of British mosquitoes to flaviviruses

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Are British mosquitoes capable of transmitting viruses to livestock and people? There is great uncertainty whether British mosquitoes are capable of transmitting arthropod-borne viruses ("arboviruses"). On one hand, the UK has some mosquito species that are implicated in the transmission of arboviruses in mainland Europe, and the climate and environment in some of these locations are similar to those in the UK. On the other hand, mosquito-borne viruses are not known to have been transmitted in the UK (apart from a small number that are 'mechanically' transmitted on the insects' mouthparts). Furthermore, regional differences in competence of mosquitoes to different viruses have been reported. Therefore, it is not clear whether the UK has the right mosquitoes but the wrong conditions for virus transmission; whether our mosquitoes simply cannot transmit viruses; or whether our mosquitoes are capable of transmitting viruses, but the opportunity has not yet arisen. Given the impact of global change on the emergence of infectious diseases, it is paramount that UK vectors are assessed for their potential to transmit arboviruses, in order to mount informed mitigation procedures in advance of, or in the event of, an outbreak. Furthermore, the ability of mosquitoes to spread arboviruses is sensitive to temperature, making such viruses likely to be affected by climate change; it is important to understand the effects of temperature in order to assess future risks.Our main aim here is to determine whether native British mosquitoes and invasive mosquito species present in the UK can be infected and transmit viruses that affect livestock and humans, and how this ability, if present, is affected by temperature. Ten mosquito-borne arboviruses have been reported in Europe with some at similar latitude to the UK. Field observations have shown potential native vectors, particularly West Nile virus (WNV) vectors, to be present in the UK. In 2011, Culex modestus, a major vector of WNV, was found actively propagating in the UK, representing the first known introduction and establishment of an invasive mosquito species. While the mere presence of these mosquitoes suggests a risk for arbovirus transmission, further support for the potential of these mosquitoes to serve as vectors must be demonstrated in detailed laboratory experiments since there is genetic and environmental variation in the ability of these mosquitoes to transmit these viruses. While the emergence(s) of several mosquito-borne viruses is plausible, we have chosen Japanese encephalitis virus (JEV) and WNV for evaluation in UK mosquitoes. JEV was selected for this study because we have already infected Ochlerotatus detritus, a mosquito from the UK, and found this mosquito able to transmit JEV. Though JEV occurs mostly on the Asian continent inter-continental introductions of arboviruses do occur, and with increased human mobility, may become more common. In fact, evidence for JEV has recently been reported in European mosquitoes. WNV was selected for this study because it arguably poses the most imminent threat to UK. WNV is widely distributed across the globe, being found in Africa, West Central Asia, the Middle East, Europe and recently North America. The virus infects a wide range of mosquitoes and vertebrate hosts. Due to its spread in North America and in Europe, particularly southern France, and its occurrence in similar latitudes to the UK elsewhere in Europe, this virus is of major interest to the UK. We will use an infection model where mosquitoes from the field will be directly infected with recently isolated strains of viruses. Mosquitoes will be assessed for: their ability to transmit virus; the viral dosage required to achieve infection; and the effect of temperature on their vector competence.