A mosquito species capable of transmitting potentially lethal tropical diseases such as dengue and the Zika virus has been found breeding in the United Kingdom for the first time.
The UK Health Security Agency (UKHSA), the government body responsible for protecting public health from infectious diseases, announced that the insects were discovered at residential properties in east London.
Health officials believe the mosquitoes, known as Aedes aegypti, arrived in Britain accidentally. They suggested the insects may have hitchhiked from overseas in imported plants, luggage, or vehicles.
The Aedes aegypti mosquito is native to Africa but has expanded its range into warmer climates globally in recent times, establishing populations across the Americas, Australia, and South East Asia. The species is a known vector for several serious illnesses. Dengue, a viral infection, causes more than 12,000 deaths globally each year, while yellow fever is responsible for up to 82,000 annual fatalities worldwide. The insect can also spread the Zika virus and chikungunya.
Larvae destroyed in London
The discovery marks the fourth time the species has been detected in the UK, but it is the first time there is evidence of it breeding in the country.
The UKHSA said measures have been put in place to destroy the mosquito larvae discovered at the London properties, and officials will continue to monitor the area.
Dr Jolyon Medlock, head of medical entomology at the UKHSA, said the risk to the public remains "very low," noting there is no evidence that the mosquitoes have infected anyone. The insects have also not been found in public areas.
"We believe these mosquitoes are accidental importations," Dr Medlock said. "Invasive mosquitoes can hitchhike in vehicles, baggage and imported plants, and if they find a suitable climate, can survive."
Impact of rising temperatures
Despite the discovery of breeding mosquitoes in the local area and recent heatwaves, Dr Medlock said the species is not established in the UK and cannot survive long-term in the typical British climate, which is too cold overall. UKHSA chiefs noted that the species has not managed to survive the winter anywhere in northern Europe.
However, officials cautioned that mosquitoes can adapt quickly. The warning follows a recent announcement by the Met Office that Britain experienced its hottest summer on record this year. As annual temperatures rise, invasive species may become increasingly capable of surviving in the UK.
"However, it is expected that in a warming climate, we will continue to see incursions of invasive mosquitoes, and increased reports of them being able to survive in the UK," Dr Medlock said.
He advised east London residents to take steps to reduce the risk of mosquitoes breeding in their gardens by removing standing water from outdoor spaces, including from plant pots, paddling pools, containers, and buckets.
Risk of tropical disease
Other experts emphasised that a mosquito bite in London does not mean a person has been exposed to dengue, chikungunya, or the Zika virus.
"The current risk remains very low and there is no evidence of local transmission associated with this detection," said Dr Cesar Lopez-Camacho of the Nuffield Department of Medicine at the University of Oxford. "For most people, a mosquito bite in the UK will simply result in the usual reaction such as itching, redness or mild swelling."
Dr Lopez-Camacho said the situation is different for individuals who develop a fever or become unwell after recently travelling to an area where Zika, chikungunya, or dengue are circulating. Those individuals should seek medical advice and ensure they mention their travel history.
The arrival of the species should be viewed as "an early warning rather than an immediate public-health threat," Dr Lopez-Camacho added. "We therefore should not be alarmist, but neither should we regard mosquito-borne viruses as exclusively tropical diseases. The epidemiology of arboviruses in Europe is changing."
Changing geographical spread
The changing spread of these diseases is becoming evident across the continent. Last week, health officials in France revealed they had seen 33 cases of chikungunya this summer driven by tiger mosquitoes, which were previously only established in the forests of South East Asia.
Professor Trudie Lang, a professor of global health research at the University of Oxford, described the arrival of the mosquitoes in London as concerning.
"We have seen an increasing number of locally acquired mosquito-borne infections across parts of Europe, including locally acquired chikungunya cases in France this summer," Professor Lang said. "These diseases are usually limited to and associated with significant health impacts in tropical and subtropical regions, but that geographical distinction is becoming less clear."
