Corporate report

UKHSA Advisory Board: Preparedness for Environmental Hazards

Updated 4 July 2025

1. Purpose of the paper

The purpose of this paper is to provide an update to the March 2024 paper describing environmental threats and hazards to health, including climatic and natural hazards, as well as environmental threats associated with vector-borne diseases (VBD). This paper highlights changes to environmental hazards, the specific threat of West Nile virus, and the specialist public health and scientific functions and capabilities of the UK Health Security Agency (UKHSA) to prepare and respond to these hazards.

The previous update reported no change in environmental hazards. In contrast, this paper does update on changing hazards, focusing specifically on changing risks posed by vector-borne diseases.

This paper also highlights incremental but persistent increasing environmental risks and the trade-offs in allocating resources across changing risks.

2. Recommendations

The Advisory Board is asked to:

• note continued progress at the UKHSA to maintain and build capacity to protect health from environmental hazards
• note the current work UKHSA is doing to respond to the threat of West Nile virus
• comment on the work that UKHSA is doing to maintain capabilities to ensure preparedness to protect health from environmental hazards

3. Summary and conclusions

Risks due to environmental hazards are growing. Impacts on health and health equity are expected to increase, particularly as the climate warms and given an ageing population and housing stock.

Risks due to vector-borne diseases are a particular concern, highlighted by the recent detection of West Nile virus in the UK for the first time, alongside the movement of new mosquito vectors (specifically Aedes albopictus) and pathogens northwards through Europe (e.g. Dengue outbreak in Paris).

Dynamic Risk Assessment of West Nile virus risk indicates that current severity and risk are low and response and the WNV detection has been treated as a routine incident. It is thus not response to the current incident that is highlighted here, but rather implications for preparedness for growing VBD, including but not limited to WNV.

Keeping Aedes albopictus (the mosquito vector of Dengue and other pathogens of public health importance) from becoming established in the UK is possible, as highlighted by successes elsewhere (e.g. Netherlands), but would require substantial investment, particularly in vector and vector borne pathogen surveillance and control.

Within UKHSA’s portfolio of environmental hazards to health, increased investment in VBD capabilities comes with the trade-offs of capacity to respond to other environmental risks, including preparedness and response to the risks of extreme heat, indoor health safety (overheating, air quality, mould, radon), and outdoor health risks (water quality and contamination).

4. Update on changing vector-borne disease (VBD) risks

Hazards associated with VBD risk in the UK are growing, largely due to climate and environmental change, which affect both the vector and pathogen species. Warming temperatures mean that areas previously unsuitable for insect vector survival are increasingly warm enough to support invasive species or expanded/improved habitat for existing vector species (usually mosquitoes or ticks).

There are also increasing threats posed by northward expansion in Europe of sand-fly transmitted infections, as well as new epidemics of emerging Culicoides midge-transmitted Oropouche virus in the Americas, threatening Europe.

In addition, the extrinsic incubation periods of pathogens transmitted by insect vectors can also be temperature-sensitive, meaning some pathogens may become transmissible for the first time as the UK warms, which is a particular concern if infected travellers return to newly suitable areas, and animal movements (migratory birds and imported pets) shift in intensity or location).

The most recent evidence of changing VBD risk is detection of West Nile virus (WNV) for the first time in the UK. WNV was detected in samples of Aedes vexans mosquitoes collected by UKHSA from wetlands near the River Idle in Nottinghamshire in July 2023. Mosquitoes were collected as part of grant-funded research in 2023, with virus testing occurring in 2025. This is an area of significant biting risk, associated with extreme summer rainfall events, where environmental change strategies offer solutions for control.

Aedes vexans mosquitoes are endemic to the UK, albeit localised to extreme summer flood events, which will increase in intensity with climate change. Another thermophilic mosquito vector species able to transmit WNV is Culex modestus, which has only been detected in the UK in the last 15 years and appears to be spreading.

Thus, while there have been competent mosquito vectors in the UK for some time, there has been no presence of the pathogen (WNV) in any sampled mosquito to date. Early warning systems for virus testing of mosquitoes and birds provide an opportunity to detect and intervene before human outbreaks occur.

Detection of WNV is not unexpected given widespread prevalence of the virus in European birds and other host species, and its emergence in neighbouring European countries. Risk of WNV transmission to humans is currently low, and there have been no cases of locally acquired WNV detected in humans to date in the UK. There is no evidence to suggest there has been ongoing circulation of the virus in mosquitoes or birds in the UK.

Evidence of WNV spread and transition into human incidence once established in local mosquito populations has ranged from rapid (North America) to gradual (Europe). The virus is currently endemic in many parts of Europe. High resourcing of extensive and enhanced mosquito surveillance, vector control and rapid response to virus detection has been successful elsewhere in preventing virus establishment and human transmission.

Detection of WNV, however, highlights continued and growing risk associated with emerging VBD’s. The last update paper highlighted accelerated spread in the distribution of key arbovirus mosquito vectors throughout many countries in Europe, notably in France where two thirds of French departments now report the invasive mosquito Aedes albopictus present, including its widespread establishment in Paris. This has resulted in an increasing number of locally acquired dengue cases in France, with increases also documented in Italy. Both locally acquired dengue and chikungunya virus cases have been reported in Paris.

Early indications of emergence of vector species and new pathogens are already apparent: localised detection of invasive Aedes albopictus and now WNV in the UK in recent years and increasing reports of small outbreaks of dengue, chikungunya and Zika in Europe are examples of early indicators of rising risk.

Hazard to UK health posed by VBD’s is increasing with a warming climate. Areas where the climate has historically been unsuitable for vector survival or pathogen viability will become increasingly able to support transmission. UKHSA’s Health Effects of Climate Change in the UK: state of the evidence 2023 assessed the risk of VBD’s due to climate change and highlighted a number of climate-sensitive pathogens that are likely to increase in extent or incidence or become established in the UK.

Ticks remain the main disease vector in the UK, with increasing cases of Lyme disease being reported, as well as the first detection of Tick-borne encephalitis virus in 2019. Ticks are responsive to weather patterns, showing earlier activity in spring, but are also driven by changes in land use that promote woodland creation, scrub development, and reduced grazing promoted by agri-environment schemes. The role of deer is critical and their spread has been linked to the expansion of ticks, with particular concern for increases in urban Lyme incidence.

5. Update on UKHSA capabilities to respond to increasing VBD hazard

UKHSA is increasing preparedness and response capabilities to keep pace with growing VBD risks. UKHSA has expanded its VBD capabilities since 2022 and requires further expansion to keep pace as new vectors and pathogens are detected.

UKHSA has a lead role in coordinating the response in the event of detection of invasive mosquitoes or associated locally acquired infections. Regional UKHSA Health Protection Teams (HPTs) lead the local investigation and coordinate the local response to an incident. If required, UKHSA would chair a national Incident Management Team to bring together national and local partners to take the necessary decisions and coordinate actions.

UKHSA’s coordinates surveillance of mosquitoes and human cases of disease related to these; monitors the changing epidemiology of vector-borne diseases (VBDs) nationally and internationally; provides technical support and advice to support vector surveillance and control; assesses risk to public health, communicates risk to the public and other government departments, contributes to travel health advice, alerts NHS Blood and Transplant (NHSBT) of any infection related risks for substances of human origin, advises on risk mitigation and vaccination, and provides reference diagnostic services and expert clinical advice on cases of imported and/or undiagnosed fever.

UKHSA work with public health colleagues in Public Health Wales, Public Health Scotland and Public Health Agency Northern Ireland to share knowledge and approached to managing vector threats including invasive mosquitoes.

Local authorities are responsible for reducing the risk of establishment of invasive mosquitoes in high-risk areas (i.e. litter management), trapping to detect mosquitoes at high-risk sites (coordinated and supported by UKHSA), preparing contingency plans, leading the local response to incidents that present a risk to public health, and responding to an outbreak.

A significant portion of UKHSA VBD capabilities related to vector surveillance, control, and epidemiology. These capabilities are located within the Medical Entomology and Vector Ecology (MEZE) team. Prior to 2022, the MEZE team had 5.6 FTE staff. This was increased to 12 FTE, though the team’s work is supported by additional grant funding from UK Research & Innovation, Foreign Commonwealth & Development Officer, and the European Centre for Disease Prevention and Control.

UKHSA established an Incident Management Team in response to initial WNV detection and to manage ongoing needs in terms of preparedness and response to emergent WVN risk.

UKHSA has finalised an updated National Contingency Plan for Invasive Aedes Mosquitoes in England (publication planned for later this year). The plan outlines key risk levels and the actions, roles, and responsibilities that will be undertaken if/as Aedes mosquitoes progress from initial detection to establishment and transmission of new pathogens. This plan is developed in close collaboration with partners at the Department for Environment, Food and Rural Affairs, Ministry of Housing, Communities and Local Government, NHS Blood and Transplant, NHS England, and UKHSA Regional Leads for Zoonoses and Emerging Infections.

Within this plan there are committed demands on UKHSA to deliver expanded and additional functions, with enhanced vector surveillance being the immediate priority for controlling mosquito incursions.

UKHSA has established a VBD Taskforce to coordinate capabilities and governance across the Agency. The Taskforce is assessing capabilities, functions, data flows, and responsibilities to ensure effective and robust coordination of preparedness and response functions. The Taskforce will produce actions recommendations for improved coordination, and highlight residual capability gaps.

Resources will need to be diverted from existing projects and tasks to support the extension of key VBD capabilities. These include VBD modeling and enhanced mosquito surveillance and arbovirus testing capabilities. The latter, which was responsible for the work that detected WNV, was funded through external research funding that has now ended. The National Contingency Plan for Invasive Aedes Mosquitoes in England provisions will mean these capabilities will need to be extended and maintained.

UKHSA is currently confirming temporary extension of both areas of capability until the end of the fiscal year to cover the summer 2025 mosquito season and proceeding diagnostics.

Local authorities have a range of statutory powers and duties related to vector and VBD surveillance, monitoring, and response. There is, however, very limited capacity among local authorities in terms of both capacity and capabilities to undertake these responsibilities. UKHSA provides support and training to Local Authorities to improve local capabilities.

Experience and assessment from other countries have shown that the most effective, and cost effective, approach to protecting health from vector-borne disease threats is early action to prevent and control vector establishment and/or establishment of pathogens in existing vectors populations. This means ensuring a strong vector-borne disease surveillance and response capability.

Once a vector species is established in the UK, it is nearly impossible to eliminate; suppression and control (e.g. of mosquitoes) across large areas of the country are continuous and costly. Similarly, once a pathogen is established in a vector population, and particularly once transmission to humans has occurred, prevention, control, and response are resource intensive and very costly.

To date, acting swiftly in response to invasive mosquito detection has successfully delayed and prevented establishment of new species in the UK, notably Aedes albopictus. The longer establishment can be prevented, the more time we will have to develop new tools for control, particularly leveraging learning from Europe where invasive mosquitoes and the pathogens they carry typically arrive first. Europe is thus an important early warning system for UK risk.

Within Europe, the Netherlands has so far managed to successfully respond to introductions of Aedes albopictus and prevent establishment and the key aspect of their strategy is to delay establishment for as long as possible. The extent to which the UK can delay and prevent Aedes albopictus establishment depends on the scale of resources invested, learning from other countries, and development of new technologies such as sterile insect release.

UKHSA has developed robust capabilities to prepare for and respond to VBD risks, and to-date has successfully prevented establishment of key invasive species. This includes leading on the development of contingency planning for invasive mosquitoes/dengue and West Nile virus, which key roles and responsibilities for UKHSA to be mandated to deliver a number of activities including vector surveillance. To secure existing and enhanced capabilities will require further allocation of resources.

Failing to secure and maintain capabilities, learning from European partners both successful and unsuccessful, will incur substantially greater costs if key vector species endemic and human transmission cycles are established. To develop capabilities comparable to the Netherlands will require approximate doubling of current resources. This is consistent with the upcoming recommendations of the National Contingency Plan for Invasive Aedes Mosquitoes in England. This will primarily cover the need for enhanced entomological surveillance across the country, but also VBD modeling and arbovirus testing.

6. Update on broader capacity to respond to environmental hazards to health

In parallel with growing VBD risks, other threats to human health posed by environmental hazards are growing as well. These include for example risks associated with extreme heat, flooding, air pollution, poor water quality, noise and impacts of warming weather on antimicrobial resistance and other climate-sensitive pathogens. Local Authorities and other partners are increasingly calling for greater support to prepare for environmental health risks.

The greatest climate-related risks in the short term are a severe or catastrophic heatwave, flood, or emergence of a new vector-borne disease into the UK. Wildfires will become a growing hazard. These risks will accelerate progressively until at least mid-century, regardless of decarbonisation. The UK can expect climate and environmental hazards to health, and to broader public health security, to grow.

Chronic and incremental risks associated with environmental hazards are particularly acute in the case of growing risks to health from indoor environments, including the combination of overheating, poor indoor air quality, and mould. In outdoor environments, water quality is an increasing priority and will be affected by climate change as increasing frequency and severity of heavy rainfall events will affect risk of wastewater contamination.

UKHSA plays a key role in national preparedness and response to the risks of overheating. UKHSA leads, in partnership with the Met Office, the Weather-Health Alerting system, and manages the Adverse Weather and Health Plan . These programmes are recognised around the world as leaders in weather-health preparedness. As the climate warms, however, demand for increased guidance, support, and resources are growing.

The Climate Change Committee, an arms-length public body tasked with assessing the government’s progress in adapting to climate change, recently commended UKHSA’s heat planning but rated progress in the health sector as insufficient as progress is persistently failing to meet the rising health risks from overheating.

Water quality is a rising health priority. The UKHSA coordinates a Water Advisory group which has primarily focussed on public health risks from drinking water but is extending its scope to include bathing water and recreational water, including consideration of wastewater.

People in the UK spend a considerable proportion of their time in indoor environments and are exposed to the impact of environmental factors and pathogens. Indoor environmental quality (IEQ) includes factors as diverse as indoor air quality (chemical, particle, mould and bioaerosols as well as radon), thermal comfort, sound and noise, lighting (including UV), as well as transmission of infectious disease. Exposure to many of these attributes are often interlinked through ventilation provision and occupant behaviours. Thus, IEQ has a strong impact on the building occupants’ physical and mental health and wellbeing. Equity and inequality considerations arise due to variations in exposure and vulnerability.

Furthermore, there is growing evidence that climate change has the potential to significantly affect public health, due to mitigation and adaptation policies in the building sector. A better understanding is needed of how IEQ factors interact and how current and emerging building infrastructure design, construction, and materials used, with an aim to address Net Zero polices, may affect IEQ and hence our health and wellbeing.  The evidence base is developing rapidly in this area and UKHSA is collaborating with academia and other partners to assess potential public health impacts and protect health.

Risks to health from environmental hazards are compounded by an ageing UK population and infrastructure, including UK’s ageing housing stock. Environmental hazards associated with poor infrastructure include over-heating, mould, cold exposure, poor air or water quality and exposures to radon or chemicals indoors.

Climate and environmental hazards pose substantial risk for exacerbation of existing health inequalities, particularly for those over 65 years and people living in poor housing conditions, though more broadly to inequities across CORE20PLUS groups.

While UKHSA has legislative responsibilities to protect health from environmental hazards, the interventions and levers to reduce risk are often outside of the health sector. This means that UKHSA often plays the role of producing guidance, ensuring a health perspective in policy development in other sectors, and advocating for health protection across government. For example, risks to health associated with environmental hazards in homes (overheating, mould, poor air quality) require intervention in housing and building design. In the case of VBD risk, changing risks are closely linked to agriculture (deer populations, land cover), urban landscape design, and landscape restoration or greening, which determine the ecology of vector habitat suitability. Management of land planning, urban design, and agriculture are outside of the remit of UKHSA and the health sector. UKHSA thus plays a role in generating evidence and advocating for consideration of health implications in across sectors.

UKHSA has been working with DHSC colleagues on an air quality dashboard for local authorities to provide localised data. This will include currently existing data such as on pollution concentrations, the public health outcomes framework indicator, costs to the NHS and social care from air pollution and a vulnerability indicator. The air pollution vulnerability indicator will show which areas are most at risk from exposure to air pollution and will help identify areas where interventions are needed most and assist in helping to address health inequalities.

Growing VBD capacity implies trade-offs to other environmental risks to health. For example, the resources required for enhanced mosquito surveillance are equivalent to roughly the size of the team available to respond to extreme heat and adverse weather.