Usutu virus risk to the UK: Determining local vector competence and modelling climate suitability

Usutu virus is an immediate and direct threat to the UK's wild birds, urban ecology and public health. It is present in London, but we do not whether it will become more significant in future as British summer temperatures increase. The mosquito Culex pipiens (s.l.) is believed to be the major European vector among birds. Colonised forms of UK Cx. pipiens kept at 25oC developed transmissible infections. It is not known if wild-caught Cx. pipiens can develop transmissible infections, or whether this is possible at temperatures more typical of the UK summer. In WP1, we will test wild-caught Cx. pipiens, at 19 and 23 degree Celsius, for their ability to develop transmissible infections with USUV. Zoonotic transmission requires a mosquito to feed on a bird to become infected, and then to a person; such a species is called a 'bridge vector'. The UK has a number of potential bridge vectors (e.g. Cx. modestus, Ochlerotatus detritus, Aedes vexans) which we have shown are capable of transmitting several flaviviruses. In WP2, we will investigate the ability of these bridge vector species to develop transmissible infections of USUV, at a range of temperatures, and thereby identify lower temperature thresholds and develop temperature-based risk maps. During WPs1&2, we will also collect adult females from the areas. These will be RT-PCR screened for USUV to confirm field virus acquisition. As added-value, we will also screen these mosquitoes for other arboviruses to identify any unknown viral circulation. In WP3, we will collect and screen wild adult mosquitoes for USUV and other arboviruses. In WP4, we will combine these newly gained data from WPs1-3 to assess the risk of USUV circulation in the UK. We will use the temperature-transmission data from WPs1&2 to inform temperature-driven models of USUV transmission in the UK, and use these models to determine the potential distribution and optimal seasons for transmission now, and in the future climate change scenarios