Tackling growing issue of mosquitoes at Sevington Inland Border Facility

To mark World Mosquito Day, we get an insight into the emerging issue of mosquitoes with this illuminating blog looking at how the team at Sevington Inland Border Facility are tackling this growing problem, likely to become only more prevalent with the impact of climate change and rising temperatures.

Background

Aedes albopictus, or the Asian tiger mosquito, is an invasive species posing a significant public health risk as a vector for diseases such as dengue, chikungunya, and Zika virus. Originally from Southeast Asia, its global spread is driven by climate change, trade, and travel. It has expanded across Europe and is responsible for local outbreaks of disease, including in Italy and France.

These mosquitoes have been detected by the UK Health Security Agency (UKHSA) and its predecessors in England on seven occasions since 2010, the first being in 2016. The last detection was in 2024 adjacent to the M20 motorway not far from the Inland Border Facility in Sevington, further evidencing the need for consistent and effective monitoring at a site where upwards of 1,500 food consignments a day and 2,500 vehicles a day could harbour them.

The impact of mosquito populations spreading north as a result of climate change and hotter temperatures can be shown by the spread, for example, of Chikungunya, a mosquito-borne infection, already prevalent in Italy where some of the freight be checked at Sevington in Ashford will have come from.

Historical context

Back in August 2017 action was taken in the Ashford borough area to eradicate eggs and larvae of an invasive species of mosquito, Aedes albopictus (Asian tiger).

Though the mosquito poses no immediate risk to public health, the decision was to treat the area and prevent it becoming established in the UK. Public Health England (PHE) and Ashford Borough Council ensured residents and businesses in the area were kept fully informed of all treatment taking place with both agencies working closely with Kent County Council.

The eggs and larvae were discovered through PHE’s mosquito surveillance programme which monitored 30 UK ports and airports, at a motorway truck stop. Since invasive mosquitoes became more widespread in France, surveillance had been conducted by PHE at motorway service stations in south east England on the main routes from the south coast ferry ports and Eurotunnel. This work has been continued by the UKSHA.

This was the second time this species had been found in the UK and is likely to have resulted from the importation of one adult female across the Channel via vehicular traffic. A similar discovery was made by PHE in Folkestone in September 2016, the first in the UK. The presence of a mosquito does not mean that it is carrying any diseases as they first need to bite an infected person and then move on to infect a second individual.

What we do

As outlined in the National Contingency Plan for Invasive Mosquitoes, the Medical Entomology and Zoonoses Ecology (MEZE) team at UKHSA works in partnership with local authorities, including teams based at Ashford Borough Council and the Ashford Port Health Border Control Post at Sevington. Together they coordinate surveillance efforts aimed at detecting and preventing the establishment of invasive mosquito species.

Local authorities play a key role in this response, with responsibility for carrying out surveillance and implementing control measures in their area. At Sevington, Ashford Port Health conduct the monitoring, liaising closely with colleagues at Ashford Borough Council who have reactive plans in place supported by the council’s pest control contractors Bounty.

Surveillance in practice

Surveillance focuses on high-risk areas and points of entry, including the port area at Sevington. Traps are concentrated in areas deemed higher risk by virtue of standing water, vegetation, or concentrated vehicle movements. Early detection reduces control costs and prevents mosquito colonies being establishing, minimising public health and economic impact.

The team use Ovitraps. These are water-filled traps used to attract egg-laying female mosquitoes. They are checked biweekly by Ashford Port Health from June to October. They send the samples of anything found to MEZE at Porton Down for analysis.

Extensive mosquito monitoring takes place between June and October with checks of around 40 traps left at key points around the Inland Border facility at Sevington.

They have not yet found Aedes albopictus, a disease-carrying mosquito, but have encountered other non-disease carrying native species.

The UK’s invasive mosquito surveillance began in 2010. Surveillance is primarily conducted by local health and port health authorities, focusing on high-risk locations such as ports, airports, service stations, and urban centres.

Insights from the frontline

Stephen Petri, Port Health Officer, Ashford Port Health, said: “My colleague Jack Styles of the food team at Ashford Borough Council (who would lead on any response) and I recently attended the National Contingency planning workshop for invasive species in Maidstone.

“As soon as we mentioned that we were from Ashford Port Health and that we covered the truck stop and the Inland Border Facility with parking together for over for 2,500 vehicles, a lot of the attendees turned and looked at us as if to say: yes, it’s going to be you isn’t it!?

“What we do Is relatively simple. It’s just that we do it on a much bigger scale than pretty much anywhere else as the site is huge. With our scale, climate change and the volume of traffic coming through, it’s really a question of when, not if, and that is why we are so conscientious and exacting in our role.

“There was a recent and well-documented dengue fever outbreak in Paris. It means the species is right on our border. Just as climate change encourages French growers of champagne to buy plots of land in Kent and Sussex to grow their vines, the same could apply to the Aedes mosquito spreading here and establishing itself. We are a vital line of defence and remain vigilant.

“We set out around 40 traps baited with polystyrene blocks that we then check between the months of June and October. These dates can change, as guided by UKHSA and dependent on the weather.

“Once baited, it gives any mosquitoes a protected, clean place to breed and lay eggs. Tiger Mosquitoes are attracted to small pockets of standing water, and litter. They are also highly attracted to vegetated areas.

“We’re careful when we plan out the trap layout to consider these factors knowing that should mosquitoes exit any vehicles on site, they’re most likely to head towards these types of area. They’re far too small to spot readily, when vehicle inspections take place. It would be the definition of a needle in the haystack. What we seek to do instead is encourage the mosquito to make its presence known to us – and that’s where the traps come in.

“Every two weeks we check traps, bag up the blocks and send them on to Porton Down and the UKHSA for analysis. They’ll take a look and determine a) whether there are mosquito eggs present and b) if they are the invasive species that we’re looking for present. If any Tiger Mosquito eggs are found, then the reaction plan kicks in, what we would refer to as Risk Level 1. Here the monitoring is led by us at Ashford Port Health, but any response would be led by the food team at Ashford Borough Council, along with guidance from MEZE and the UKHSA regional Health Protection Team.

“In reality, of course we would all lend support. A 300-metre radius control zone around the discovery site would be determined and we would be taking several steps to eliminate the risk.

“We hold a data list of all potential commercial and private residential properties and would alert those people in person, both with information and to initiate the response.

“We’d conduct an intense litter clear, incinerating the rubbish, removing any small areas of standing water and larvicide drains holding water. We would also engage intensified control through an enhanced trap system, introduce adult traps and conduct a habitat survey to discover any larvae or larval sources. This would be done under the guidance and supervision of the UKHSA MEZE zoonotic team from Porton Down, who would likely be on the scene within hours of detection, and who would monitor these traps every two days.

“These mosquitoes aren’t likely to cover great distance and don’t fly at height. So, unless they get carried favourably by the wind, the distance they will travel is relatively small. This makes it easier to control. However, we’re not complacent. If it is deemed necessary, we could also escalate the response by larvicide or applying a silicone monofilament layer to larger bodies of water, which prevents the larvae breathing. However, given the impact on other species that is a secondary control response.

“We know that our mosquito traps are effective and ensure that we follow guidance by UKHSA to the letter with the support of our pest control contractor. We know that is it effective because we regularly have mosquito eggs laid on the traps, these to date, however, have been native species, not Aedes albopictus which is positive news.”