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Welcome to Vector-Borne RADAR

Vector-Borne RADAR is a multi-disciplinary, £1.15 million UKRI and Defra funded, One Health project, focused on understanding emergence and transmission pathways for zoonotic mosquito-borne viruses of wild birds in the United Kingdom. The project runs from 2023-2026. 

Mosquito-borne disease in the UK

Globally, mosquito-borne disease has a severe negative impact on both animal and public health.  Mosquitoes are a group of insects that are related to common flies. However, in female mosquitoes the mouth parts have been extended and adapted (to form a proboscis) for taking blood meals from vertebrates to provide protein. Indirectly, during this feeding interaction pathogens can be transmitted.  In recent decades, mosquito-borne diseases have undergone relatively rapid geographic expansion, including movements from tropic and sub-tropic environments into temperate regions, primarily driven by human-assisted movement and global climate change. Historically, the United Kingdom (UK) had been considered relatively free of such diseases. However, in the summer of 2020 Usutu virus (USUV), a mosquito-borne virus, was detected here for the first time in wild birds, following range expansion in recent decades across Europe.  

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Female Culex pipiens mosquito. Photo credit Arran Folly 2022

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Eurasian blackbird (Turdus merula). Photo credit Rob Robinson 2022

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Usutu virus phylogeny, UK detections in yellow. Image courtesy of Folly et al. 2022

This was a really important milestone in national biosecurity, as it is the first mosquito-borne viral zoonosis (a disease which can be transmitted from animals to humans) to emerge in animal hosts in the UK.  The initial USUV outbreak appeared to be geographically restricted to Greater London, and only a small number of birds were found dead that had been infected. There have been no reported human infections in the UK to date and the risk to human health is deemed very low.  However, USUV infection in blackbirds (a primary USUV host) can result in disease mediated population declines. Indeed, subsequent to the USUV outbreak, the 2022 Breeding bird survey identified a 39% decline in blackbirds in Greater London, which may be linked to USUV infection.

Since the original UK USUV detection in 2020, the virus has been detected in 2021 and 2022, again in blackbirds recovered in Greater London. Molecular analysis highlights that the UK detections are most closely related to each other when compared to other known USUV isolates from mainland Europe. This suggests that USUV is persisting in the UK (most likely in overwintering [hibernating] mosquitoes), which has obvious implications for native blackbird populations. Combined, this also indicates that the UK climate may be permissive for the establishment of other mosquito-borne viruses that have similar climatic requirements. 

Future threats and VB RADAR

West Nile virus (WNV) and USUV are both flaviviruses (a family of viruses which are primarily transmitted by arthropods), and as such have a close genetic relationship and share very similar ecological requirements (including environmental conditions, vector networks, and vertebrate hosts).  Both viruses have followed a relatively similar expansion pattern across Europe, and WNV has been detected as far north as The Netherlands in 2020. However, this virus has not been identified in animal hosts in the UK to date. This is important because West Nile fever is a notifiable disease of horses in the UK and is likely to have a greater impact on animal and public health, compared to USUV infection. With the ongoing expansion of WNV across Europe, combined with the persistence of USUV in the UK, it is becoming increasingly likely that WNV might emerge in the UK, and we need to ensure we can rapidly detect it and advise public and animal health organisations, should an outbreak occur. 

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Blackbird disease incident reports in 2020, showing a cluster around USUV index site. Image courtesy of Lawson et al. 2022

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Sampling for VB RADAR, green areas are higher risk of WNV incursion (map courtesy of Bessel et al. 2014.)

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The team behind VB RADAR is a pre-existing collaboration that unified to investigate the emergence, impact and persistence of USUV in the UK.  During this process we identified that there was scope to enhance surveillance for mosquito-borne zoonotic viruses, such as WNV and USUV, in the UK to further safeguard biosecurity.  WNV and USUV primarily cause disease in wild birds, which can 'spill-over' to humans and other animals, via mosquitoes (the insect vector) as they consume blood from a range of vertebrates. 

Currently it remains unclear how USUV emerged in the UK (most likely in an infected bird migrating from the near continent where related USUV isolates are circulating) and what its initial transmission network looked like.  Our project aims to enhance wild bird surveillance through  engagement with wildlife rehabilitators, zoos and other stakeholders while also sampling native and migrant birds at areas deemed of high risk of viral incursion to investigate how mosquito-borne diseases of wild birds are emerging and persisting in the UK, and what impact they might have. 

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Immunohistochemical analysis of USUV infected blackbird. Image courtesy of Folly et al. 2022

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