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Building capability against vector-borne diseases - Core Funded - SE4116

Arthropod-borne viruses are the cause of some of the greatest burdens to human and animal health worldwide. Due to a combination of anthropogenic change, including the effects of global climate, wildlife migration and increased surveillance, there is strong evidence that temperate regions are undergoing repeated introduction of mosquito-borne viruses and the re-emergence of viruses that previously were not detected by surveillance. In Europe, the repeated introductions of West Nile virus (WNV) and Usutu virus (USUV) have been associated with bird migration from Africa and led to the establishment of these viruses in southern and eastern Europe. Subsequent short distance spread of these viruses has occurred into new areas in western Europe. There have also been repeated reports of autochthonous transmission of chikungunya (CHIKV) and dengue (DENV) viruses caused by rapid transcontinental travel by infected humans and transmission by human-biting mosquitoes. Improved surveillance has also detected the presence of emerging pathogens such as Sindbis virus (SINV) and Batai virus (BATV) in Germany. Other arthropod-borne viruses are emerging across Europe or on the fringes of the continent including bluetongue virus (BTV), lumpy skin disease virus (LSDV), bovine ephemeral fever (BEFV) and Rift Valley fever virus (RVFV). As a consequence the UK, currently free of mosquito-borne viral diseases, is at risk from the introduction of these viruses. Of particular note has been the upsurge in human and equine cases of WNV across Europe in 2018, especially its emergence in northern areas of Germany. Based on previous years, WNV is likely to establish and spread in these regions, increasing the risk that it will be introduced into the UK through either bird migration or human mediated activities. Further horizon scanning and knowledge acquisition is needed to identify and assess emerging arthropod-borne virus threats in order to support Defra policy as it evolves in response to new threats.
A critical component of the UK capability to respond to incursions of disease is the ability to detect and characterise both zoonotic and non-zoonotic viral pathogens responsible for notifiable livestock diseases. This also includes those that could present a severe future threat to UK human and animal health. A key activity within APHA has been to identify those viruses where there is no capacity and introduce new detection assays. Currently, APHA does not offer a test for Japanese encephalitis virus (JEV), a zoonotic virus that is particularly pathogenic in pigs, but is also known to infect cattle and horses (Mansfield et al., 2017). Infection can lead to spontaneous abortion and congenital deformities, resulting in economic losses within the pig production industry. In Asia the virus is transmitted by mosquitoes in a bird-mosquito cycle, similar to that observed for the related WNV. The principal vector in Asia is Culex tritaeniorhynchus, a species present in south east Europe, although other species are capable of transmitting JEV.
The UK has over 30 species of indigenous mosquitoes, many of which feed on livestock and humans. APHA has been instrumental in defining the feeding preference of the UK mosquito fauna, identifying those that target livestock and thus require further investigation (Brugman et al., 2017; Hernández-Triana et al., 2018). Ongoing research by APHA and the University of Liverpool has demonstrated that some UK mosquito species are capable of transmitting viruses such as WNV and RVFV, pathogens of equids and ruminants, respectively. However, these preliminary studies have suggested that climatic factors, particularly temperature, are highly influential to the efficiency of transmission and the interval between mosquito infection and transmission (the extrinsic incubation period – EIP). Further research is required to define the conditions under which UK mosquitoes will transmit emerging livestock viruses and establish the minimum EIP for key mosquito species. In addition to native mosquitoes, Europe has been colonized by a series of invasive aedine mosquitoes. The initial introduction of each, and subsequent spread have all resulted from human translocation of desiccated eggs, for example in used tyres, or movement of adult mosquitoes in cars. Despite the natural barrier provided by the English Channel, there have been three reports of the introduction of the Asian tiger mosquito (Aedes albopictus) into the UK in recent years (Medlock et al., 2017). This trend is likely to continue and would increase the risk of transmission of mosquito-borne viruses as the species feeds preferentially on mammals, as shown by the recent report of the establishment of the invasive species Aedes japonicus in Spain ( The ability to predict the role of invasive mosquito species in virus transmission is essential to assess the future risks that the UK will face. Studies conducted jointly between APHA and the University of Liverpool has indicated that the UK mosquito species, Aedes detritus is capable of transmitting JEV at temperatures above 23oC (Mackenzie-Impoinvil et al., 2015). A key question is whether the WNV vector, Culex pipiens, a species abundant in the UK, is able to transmit JEV and other emerging viral pathogens under the climatic conditions found in the UK.
Objective 1. Develop knowledge of new and emerging vector-borne virus diseases of livestock through horizon scanning activities including regular review of the vector-borne disease scientific literature and reports, maintenance of expertise in notifiable vector–borne diseases and developing collaborations with international partners (EU reference laboratories, OIE experts). This objective will address the prevention and control of notifiable and emerging vector-borne viruses through identification of gaps in the UK capability to respond to emerging viruses and adapting the testing capacity of APHA to respond to vector-borne diseases. Collaborative links will be maintained with Public Health England to continue monitoring UK mosquito and tick populations and to provide a source of arthropod samples. This will enable APHA to maintain capability to respond to tick-borne diseases. Examples of tick-borne viruses causing disease in livestock include endemic louping ill virus and exotic viruses such as Spanish goat encephaltitis virus and Nairobi sheep disease virus. The impact of climatic changes will also be assessed and how they influence vector-borne disease transmission.

Objective 2. Development of rapid detection of mosquito-borne livestock diseases. This objective will develop knowledge and support prevention and control of notifiable and emerging vector-borne diseases. It will also increase APHA’s diagnostic capability through the development of rapid screening methods for detection of Japanese encephalitis in livestock. Tests developed in Objective 2 will be used to detect virus infection in experiments in Objective 3.

Objective 3. Investigate the vectorial capacity of British mosquitoes for emerging livestock viruses and investigate the impact of climate change on the ability of mosquitoes to be infected with and transmit viruses. This objective will increase our existing knowledge base and provide data to improve future options of prevention and control for notifiable and emerging vector-borne diseases. Key parameters, such as the minimum extrinsic incubation period, associated with the ability of UK mosquitoes to transmit arthropod derived viruses will be vital in developing future control strategies. Infected samples generated in Objective 3 will be used to assist in the validation of tests developed in Objective 2.
Time-Scale and Cost
From: 2019

To: 2023

Contractor / Funded Organisations
APHA (Animal and Plant Health Agency)
Fields of Study
Animal Health