RCG Culex distribution, vector competence and threat of transmission of arboviruses to humans and animals in the UK

The people and animals of the UK are threatened by mosquito-borne diseases for the first time in several decades. In the last 10-15 years we have witnessed two species of mosquito invade the UK. Parts of northern Europe with climates similar to our own are experiencing mosquito-borne disease which may imminently spread to the UK. And research has shown that some of our native mosquito species may be able to spread diseases, if provided the opportunity. The rapidly changing situation is likely due to a combination of factors including climate change (enabling mosquitoes to occupy new areas and transmit diseases in them) and ever greater volumes of travel and trade, facilitating their spread.

While most people are familiar with mosquitoes as transmitters of malaria parasites to humans, mosquitoes are also important as transmitters of many different viruses to both humans and animals. The threat from mosquito-borne viruses is the focus of this proposal. In particular, we focus on two African viruses that have spread to, and caused disease in humans and animals, in northern Europe in the last few years: West Nile virus and Usutu virus. Both viruses are transmitted by types of Culex mosquito - these include the common house mosquito, a native species found across the UK, and also certain invasive species.

To prepare for future disease outbreaks - in people and/or animals - of West Nile or Usutu, we want to develop an understanding of the risk of virus transmission and how it may vary across England and Wales. Understanding this risk will enable us to identify years or areas of higher or lower risk and may enable the targeting of control measures.

To achieve this we will undertake the first national surveys for Culex mosquitoes across England and Wales. Their distributions are, in large part, determined by the nature of the water bodies in which they breed and we will characterise these. The establishment of the viruses in the UK requires mosquitoes that feed on birds (which are the natural hosts of the viruses); and threat to humans/livestock/companion animals arises from mosquitoes that become infected from a bird and then feed on mammals. We will measure the feeding preferences of the different Culex mosquitoes by using molecular methods to identify the sources of their last bloodmeal. Virus transmission risk also requires mosquitoes that are capable of being infected with virus, and then transmitting it in saliva; we will quantify this (termed vector competence) at temperature regimes typical of the UK summer and some more extreme conditions. Finally, we will integrate these different datasets into an innovative modelling framework that will enable us to map the different levels of risk across England and Wales and show how this may vary over time.

Once achieved, this project will put the UK in a much stronger position for addressing the threat of mosquito-borne viruses and tackling disease outbreaks if - and more likely 'when' - they occur in the future.

The UK has so far not faced significant threats from mosquito-borne viruses. This situation is rapidly changing for three reasons: (i) mosquito species that are important vectors of disease elsewhere in the world are successfully invading the UK; (ii) some mosquito-borne viruses, such as West Nile and Usutu, have recently spread through northern Europe, including recent incursions into the UK; and (iii) it is increasingly clear that some native mosquito species present a greater risk of disease transmission than they did in the past. The overarching aim of this proposal is to assess the risk from the UK's most widespread native vector species, the Culex pipiens complex and closely related Cx torrentium for transmission of the most immediate threats, West Nile virus and Usutu virus. We will identify information needed to effect mitigation strategies to minimise future outbreaks of both human and animal disease.

We will achieve this by collecting geographic location and larval habitat data for Culex species/forms across the UK - enabling us to construct detailed vector probability maps. Further, we will assess the host feeding preference and vector competence of each of the species/forms; together, these data will enable us to build virus transmission simulation models across the UK. Finally, with these data collected and analysed, we will be in a unique position to identify which vectors present the most risk, where, and for which viruses. Hence, our project will produce the information needed to design mitigation strategies based on targeting individual vectors and/or larval rearing habitats for specific regions of the UK, and enable modelling of the effectiveness of such mitigation strategies.

Importantly, the data collection and experimental work will be performed within the consortium to focus on UK applicability and readiness, and our modelling will be performed under 'typical UK summer', 'UK heatwave', and 'future climate' conditions