At just six millimetres long, the Asian tiger mosquito might not sound like much of a threat to Britain’s public health. Not only is it minute but, as its name suggests, its natural habitat is thousands of miles away in the warmer climes of the southern hemisphere.
So why is this tiny creature, which gets its name from its exotically striped back and legs, now regarded by some leading experts as one of the biggest threats to the nation’s health in decades?
Thanks to climate change, this bug has travelled so far north that it is now flourishing in parts of South East England.
Colonies of the Asian Tiger mosquito, pictured here, has established colonies in the south of England although small numbers of the potentially dangerous bug have been found as far north as Merseyside
Small numbers have even been discovered in Merseyside.
Last summer was the joint hottest on record for the UK as a whole, and the hottest ever for England, with temperatures climbing above 35C. And if trends continue, some experts fear the Asian tiger – also known as Aedes albopictus – will eventually populate much of the country. Alarm bells are ringing because a bite from an infected mosquito like this can transmit deadly tropical diseases such as Zika virus, dengue fever and an illness called chikungunya, which can cause joint pain, headaches and nose bleeds.
Last month, Professor Chris Whitty, a chief scientific adviser on public health issues for the Department of Health, warned MPs that the presence of the tiny insect here is strong evidence that we face a potential outbreak of Zika.
The virus is a huge concern, causing flu-like symptoms in most adults but triggering severe birth defects if a pregnant woman is infected.
The Asian tiger, it must be said, has a lower capacity for transmitting disease than its close cousin Aedes aegypti, the yellow fever mosquito, which was responsible for the recent Zika outbreak in South America.
Nevertheless, the World Health Organisation has said there is strong scientific consensus that Zika can also cause Guillain- Barre, a rare neurological syndrome that leads to temporary paralysis in adults.
The only hope, warned Prof Whitty, is that scientists can create a vaccine before an epidemic strikes the UK.
Europe has it… and trucks bring it here
Last month, a study from scientists at Liverpool University warned that almost all of England and Wales could be populated by the disease-carrying Asian tiger mosquito in the next few decades if global warming continues at its current rate.
The species is already well established in parts of Europe, and the WHO warns that ‘the likelihood that Zika virus will spread in countries where Aedes mosquitoes are present is high or moderate’.
It’s possible that travellers infected in countries where Zika is more common – the Pacific region, South and Central America, the Caribbean, Africa and parts of South East Asia – could return and be bitten by an Asian tiger. That insect could then transmit the Zika virus to others.
The Tiger mosquito, pictured, is rapidly spreading disease across Europe
Currently France, Italy, Spain and Switzerland are considered a moderate risk for Zika.
Cases of flu-like dengue, also spread by mosquitoes, were reported in France and Spain last year. Similarly, outbreaks of chikungunya – with symptoms including fever, joint pain and bleeding gums – have been reported in several European nations, including more than 600 cases in Italy.
So what of Britain?
In recent years the Asian tiger has been discovered at truck stops and service stations along motorways such as the M20 from Dover to London – imported from Europe on lorries and settling along motorway arteries.
Because they thrive in stagnant water, the insects are being accidentally brought into the UK in cargoes of used tyres, potted plants and anything else that allows water to ‘pool’ easily.
What’s more, the eggs they lay are not just drought-resistant but can undergo a process called diapause, where their development is suspended if weather conditions are unfavourable for survival.
This means they can survive Britain’s cold winters until the increasingly warm summer months, when they can hatch.
Researcher Soren Metelmann, from Liverpool’s Institute of Infection and Global Health, warned: ‘For now, only some small areas in South East England seem to be suitable [for Asian tiger mosquitoes], but future scenarios suggest that it could become established over almost all of England and Wales.’
The return of some deadly enemies
it’s not just the Asian tiger mosquito that threatens to wreak havoc on Britain’s health with dangerous tropical diseases.
In Kent, another invasive mosquito is threatening to bring further unpleasant surprises.
Culex modestus largely disappeared from Britain in the 1940s. Now it is reappearing in large numbers in the Thames Marshes in Kent and Essex, according to an investigation last year by Public Health England.
This is a worry because Culex modestus is known to transmit West Nile disease, an infection that, in severe cases, can cause coma, seizures and paralysis. While no human infections have so far occurred in the UK, West Nile virus has already been discovered in the corpses of British wild birds and, most worryingly, in farm chickens.
Biologists warn that it is a comparatively small step for a Culex modestus mosquito to feed on a virus-carrying farm chicken and then bite and infect a farmworker.
Malaria was once common in the UK but the last recorded case of someone contracting it in this country was in 1950, when infected soldiers returning to the UK from malaria-hit zones were bitten by local species capable of transmitting the bug. These mosquitoes then passed it on to other people when they bit them.
Potentially deadly mosquitoes have been found as far north as Merseyside, pictured
But there are still about 1,600 cases a year of ‘imported’ malaria in UK travellers returning from infected areas of the world.
In the battle against rising sea levels, some local authorities are promoting the reintroduction of wetlands by allowing the sea walls to collapse. The idea is that the wetlands can absorb batterings by coastal storms more resiliently than man-made sea walls. But, says Matthew Baylis, professor of veterinary epidemiology at Liverpool University, this policy could pave the way for the return of malaria – a disease that kills more than 400,000 people globally every year.
Prof Baylis says: ‘Reintroducing wetlands creates the right environment for mosquito species that spread malaria.’
There are believed to be at least five species of mosquito still in the UK that are capable of spreading the infection. Higher temperatures, coupled with marshland habitat, allow the mosquitoes to thrive. The malaria parasites, which grow inside the mosquitoes, also need high temperatures to multiply.
‘At the moment, our summers are probably too cool for significant transmission to take place,’ Prof Baylis told The Mail on Sunday. ‘But in an exceptionally warm summer, we could definitely see that happening in future.’
Epidemic could be ‘overwhelming’
Grim warnings from experts are finally prompting Government action. In March, Health Minister Nicola Blackwood announced up to £56 million funding for research into the biggest challenges facing public health: climate change, air pollution, antimicrobial resistance and new pandemics, with the projects due to start in 2020.
Dr Nick Watts, executive director of Lancet Countdown, a research collaboration between 24 international institutions that monitors relationships between health and climate change, warns: ‘It’s crucial to talk about new infectious diseases now. If we are not prepared, with the right treatments to hand and with the right people trained, then any of these new infections can very quickly go from just a couple of cases to something that spreads very rapidly and overwhelms us.’
The big question… How long do we have?
The presence of disease-carrying mosquitoes in Britain is not in itself enough for tropical infections to thrive. It depends on many other factors, such as the viruses’ and parasites’ ability to replicate and survive in their new environment.
Some experts say it could take 30 to 40 years for those conditions to materialise. But others warn that it could be much sooner. One factor that could speed their arrival is the rate at which viruses such as Zika become more virulent in response to climate change.
This healthcare worker in Malawi is preparing a malaria vaccine for a child in the Mitundu Community Hospital in Lilongwe
A report last year in the journal Nature Climate Change warned that warmer weather is encouraging viruses to evolve rapidly, enabling them to become significantly more infectious and more able to resist drug therapies.
For example, for more than 50 years Zika was a mild disease that caused only sporadic outbreaks – until it suddenly affected tens of thousands of people across South and Central America with severe symptoms not seen before.
One alarming theory is that Zika – like West Nile virus and chikungunya – has undergone genetic mutations that are allowing it to spread far and wide.
Perhaps even as far as the UK.
The terrifying diseases carried by mosquitoes… and how they could affect you
For most people the infection is mild, causing a rash and itching, high temperature and headache. For pregnant women it can cause serious birth defects – in particular, abnormally small heads (microcephaly). There is currently no treatment.
Symptoms include a high temperature, feeling hot and shivery, headaches, vomiting and muscle pains. If the symptoms are not treated promptly, malaria can be fatal. Treatment involves taking antimalarial drugs.
Causes severe flu-like symptoms, which can be life-threatening, especially to younger children and frail or immune-compromised adults. There is no cure for dengue. Treatment includes paracetamol to relieve pain, and drinking plenty of fluids.
Symptoms include fever, joint pain, muscle pain, headache, and nose- and gum- bleeding. Joint pain can last for years. The virus can also cause heart disease, hepatitis and neurological disorders. There is no specific medication to tackle the virus.
Symptoms may include fever, headache, body aches, skin rash and swollen lymph nodes. More serious infections may cause tremors, convulsions and paralysis. However, about 80 per cent of cases are mild. There are no vaccines or antiviral drugs for West Nile virus.