How worried should we be about the invasive mosquitoes in the UK? 

Aedes aegypti mosquitoes and larvae – which can transmit infections like dengue, chikungunya and Zika virus – have been found breeding in the UK.

The UK Health Security Agency (UKHSA) announced on 3 September that the species has been detected at residential properties in east London. This marks the fourth time it has been detected in the UK in recent years, and the first time its been found breeding.

The mosquitoes are usually found in more tropical climates. So, is this a result of climate change? How concerned should we be? Here’s what you need to know.

What do we know about Aedes aegypti?

Aedes aegypti mosquitoes are native to North Africa but can be found in tropical and temperate regions around the world, including parts of Europe. Although the species has been found in the UK before, this is the first time these mosquitoes have been found breeding in the country.

This species can transmit many different pathogens, inlcuding dengue, yellow fever, chikungunya and Zika virus. It commonly feeds at dusk and dawn, and indoors and in shady areas.

Where were the mosquitoes found?

According to the UKHSA, the mosquitoes and larvae were found breeding in residential properties in East London. They were spotted and reported under the government’s Mosquito Watch scheme, which aims to detect the presence of invasive mosquitoes.

The UKHSA said the larvae have been destroyed and promised the area will be monitored closely to eradicate any further mosquitoes and larvae that might emerge.

What’s the threat to public health?

The UKHSA insists the threat to public health remains very low. There is no evidence the Aedes aegypti mosquitoes found in London have transmitted any infections to people, and so far there have not been any more mosquitoes or larvae being found in nearby public areas.

César López-Camacho at the University of Oxford said in a statement to the Science Media Centre that the discovery of their presence should be seen as an “early warning rather than an immediate public health threat”.

It is worth noting the UK is home to many species of native mosquitoes, but these generally don’t carry serious infections, and are largely an annoyance rather than a public health threat.

How did they get to the UK?

Jolyon Medlock at the UKHSA said in a statement that the mosquitoes were likely to be “accidental importations”, having “hitchhiked” in vehicles, suitcases or via imported plants.

Are these mosquitoes here to stay?

The UK has just had its hottest summer on record. London has seen some of the highest temperatures in the country, as heatwaves are usually amplified in cities due to the urban heat island affect.

That may mean the mosquitoes have been able to successfully breed over the summer months this year. But Medlock said the UK’s climate is still too cold overall to enable the mosquitoes to breed over the long-term – for now.

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Is this a sign of climate change?

Mosquitoes are expanding their range north as the climate warms. Warmer weather also increases the rate at which viruses replicate in an insect’s body.

That means mosquito-borne viruses are rapidly becoming more common in Europe as the continent warms. In late August, French authorities reported cases of locally transmitted dengue, west Nile and chikungunya virus across the country, including Paris.

And a study published earlier this year found that the Asian tiger mosquito, another invasive mosquito species in Europe, can transmit chikungunya over several months of the year on the continent. The study authors said Europe’s rapid rate of warming was enabling virus transmission to become more widespread across the continent.

Over time, the threat of mosquito-borne disease to the British public is also expected to rise. Last year, West Nile virus was detected in the UK for the first time in mosquitoes in Nottinghamshire. For now, authorities hope to keep invasive mosquitoes out of the country for as long as possible to prevent disease transmission.

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What should I do if I am stung by a mosquito?

For most people in the UK, a mosquito bite is an annoyance but nothing to worry about. It will usually produce a red, itchy swelling that will subside within a few days. If you develop a fever or become unwell, and have recently travelled to a location where dengue, chikungunya or Zika is circulating, you should seek medical attention.

How can I prevent mosquitoes breeding in my home?

Scientist say it is important to minimise the chance of mosquitoes breeding in the UK, to try to prevent invasive species gaining a foothold on UK shores. Aedes aegypti mosquitoes are well adapted to human environments and can breed in small quantities of standing water, so the most important action people can take is to eliminate, as far as possible, any standing water around the home. That could include emptying water trays under houseplants, clearing rainfall from containers, keeping lids on waterbutts, washing out pet bowls and flower vases regularly, and keeping shower areas as clean and dry as possible between use.

If you spot a mosquito in the UK, you can report it to the Mosquito Watch scheme.