Countries in the developing world have been left reeling from a surge in dengue fever outbreaks, as the hottest year on record combined with a destructive El Nino weather pattern to create the perfect conditions for disease-carrying mosquitoes.
Experts are warning that the tropical disease is “taking off” and could become a serious threat to new parts of the world, including areas of Europe and the US, over the next decade.
This will put pressure on health systems as climate change progresses.
But dengue is a “controllable problem” that is still not getting the attention or resourcing needed, said Prof Scott O’Neill, chief executive of the World Mosquito Programme.
He travelled to Dubai last week to speak about his organisation’s pioneering solution for controlling mosquito-borne diseases, on the first day in the history of Cop summits dedicated to health.
“Despite the huge economic drag it puts on countries, despite all of the illness, the hospitalisation, the children not in school, it doesn't get talked about,” he told The National.
“The encouraging thing is there are new tools in the pipeline, including what we are doing, and I think if there was the desire, and the political will, those tools can be mobilised to fix problems.”
About half of the world’s population is now at risk of dengue, a viral infection transmitted by Aedes mosquitoes, with an estimated 100-400 million infections occurring each year.
More than five million cases and 5,500 deaths have been reported across the 20 worst-affected countries in 2023, according to data from Save The Children.
The heart of the crisis: Bangladesh
In Bangladesh more than 1,500 people have died this year, including 160 children, in the country’s worst dengue outbreak.
More than 300,000 cases have been reported since January, resulting in a death toll more than five times that of 2022.
This has put the country's healthcare system under a level of strain comparable to the Covid-19 pandemic, according to Dr Yasir Arafat, Save The Children’s senior regional health and nutrition adviser for Asia.
“I think this is a somewhat unprecedented event that Bangladesh is facing. Not only Bangladesh, but there are many countries in the world already facing this outbreak,” Dr Arafat, who is based in Bangladesh, told The National.
“It becomes an overwhelming issue for the healthcare system, which was not prepared for it at all.”
He said children were more vulnerable to the more intense form of the disease, known as severe dengue haemorrhagic fever, which can kill if urgent treatment is no provided.
Many parents had become too scared to send their children to school for fear of infection, Dr Arafat said.
“It disrupts people's life. When people are taking extra precautions to avoid mosquito bites, they can’t go out. They can’t go to school, or work," he said.
“A lot of families are living with so much anxiety about what could happen because they have already seen deaths within their community, they have seen so many fatal cases, severe cases. So people get mentally stressed.
“When a child loses his parents or caregiver to dengue, it has long-lasting emotional and social consequences on the child. More children are getting orphaned because they're losing their parents to dengue.”
In Bangladesh, the monsoon season has been getting longer, with hotter temperatures and heavy sporadic rain creating the perfect conditions for the rapid proliferation of Aedes Aegypti mosquitoes, the primary carrier of dengue fever.
“Usually in September, October we would start feeling the winter cold. Even a few years ago, we expected that, but the over the past decade we have seen the summer and monsoon are extending and the winter is shortening,” Dr Arafat said.
“This mosquito is shifting from one place to another and the seasonal distribution of the disease, all are changing. So it's really, really unpredictable.”
The new front line: Europe
On the other side of the world, Europe has become a new front line in the relentless advance of mosquitoes, with dozens of cases of locally acquired dengue reported across France, Italy and Spain this year.
The World Health Organisation’s chief scientist cautioned in October that dengue will “take off” and become a serious threat to southern parts of the US and Europe and new parts of Africa this decade, putting acute pressure on hospital systems.
Jeremy Farrar said in an interview with Reuters that there was a need to talk “much more proactively” about the disease and prepare countries for how they will deal with it.
Aedes albopictus, a cousin of Aedes aegypti popularly known as the Tiger mosquito, first appeared in the lemon-growing coastal town of Menton, close to the Italian border, about 20 years ago.
Since then the aggressive mosquito, known for feeding during the day, has spread north to almost every department of France, aided by warming temperatures and transportation networks.
This has created a menace for people doing outdoor activities and raised the prospect of more serious dengue outbreaks on European soil.
In Paris, authorities fumigated for Tiger mosquitoes for the first time in September, amid fears dengue could spread from infected returning travellers in two different suburbs.
“There have always been imported cases from people who were travelling to tropical countries,” Prof Arnaud Fontanet, head of the epidemiology of emerging diseases unit at the Institut Pasteur in Paris, told The National.
“But now we do see Aedes albopictus, tiger mosquitoes, picking up on feeding on people that were infected in tropical countries, and transmitting the virus locally in France.”
“This is much more than what we had seen before".
Italy this year reported outbreaks and local infections of dengue too, the French epidemiologist said.
“Transmission takes place in late summer for us, but we could imagine that with time we will see also the range of months during which autochthonous transmission can take place increase," he warned.
"And with increasing densities of mosquitoes by the end of the summer, the number of cases will also continue to increase.”
Rather than becoming endemic, Prof Fontanet said he believed it was more likely that imported cases would continue to cause seasonal spread in France, with the winter breaking the chain of transmission.
“My guess would be in the short to medium term, that it is going to be fed by imported cases, but the range and number of months during which transmission will take place will probably increase,” he said.
He said there was a need educate people on how to systematically clean around the home for anything containing water, to reduce breeding grounds for the mosquitoes.
“You can already do a lot by the mechanical removal of the places where the mosquito breeds.”
“We have to find the right ways to explain to people how you can get rid of mosquitoes because it's 80 per cent of the job. It's really a responsibility that we have for ourselves, but also for the collective.”
Bacteria and AI bring new hope
While the spread of mosquitoes may be inevitable in a warming world, two emerging scientific solutions hold promise for reducing the impact of dengue fever.
The fight against mosquito-borne diseases has traditionally relied on killing mosquitoes with pesticides, but one of the most effective solutions paradoxically involves releasing more of them into the environment.
The World Mosquito Programme has pioneered a method which involves introducing mosquitoes infected with a bacteria called Wolbachia into existing mosquito populations. The naturally occurring bacteria does not kill the mosquitoes, but prevents them from transmitting viruses including dengue, yellow fever, chikungunya and Zika.
The non-profit organisation has projects operating in 14 countries with a high rate of success and is now collaborating in the creation of a large factory in Brazil that will be capable of producing five million mosquito eggs a year to be used for Wolbachia releases.
Professor O’Neill said the big strengths of the method are that it usually only needs to be deployed once to establish the bacteria in a region and it can be used over large geographical areas, including entire cities.
“It's cost effectiveness is that you do it once, and then you don't have to repeat doing it. It's like building a bridge in a city … the benefit just accrues year after year after year from that infrastructure.”
Another promising solution on the horizon is a drug discovered with the help of Artificial Intelligence, which is expected to go to human trials in the second half of next year.
There are no specific drugs available for dengue and the main vaccine currently in use, Dengvaxia, is only recommended for children who have previously been infected with the disease and are at risk of contracting it again.
Scientists from the Drugs for Neglected Diseases Initiative (DNDi) have been working with AI-enabled drug discovery company BenevolentAI to rapidly identify a drug that can be repurposed to fight severe dengue.
Dr Peter Sjo, Head of Drug Discovery Programme at DNDi, said a candidate had been found and had shown promising results in preclinical trials.
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He is hopeful that the drug will start clinical trials in the second half of next year. If successful, the treatment could potentially be brought to market within three to four years.
DNDi has developed 12 treatments for six deadly neglected diseases since it was founded in 2003, but this is the first time it has used AI to aid the process.
“It is quite exciting, actually. It's worked much better than I, as a kind of born sceptic, expected,” Dr Sjo said.
DNDi’s main goal is to reduce the huge burden of dengue on hospital systems by developing an affordable treatment that can be widely distributed.
The World Mosquito Programme, on the other hand, aims to heavily suppress or even wipe out transmission of dengue altogether in its target regions. It may seem like an ambitious goal, but Prof O’Neill points out that dengue has been effectively eradicated in Australia since Wolbachia was deployed in 2011.
He said by some estimates showed dengue was creating a drag of about $12 billion a year on the world economy.
“For about that same amount of money, our method could be deployed globally,” he said.
“I definitely think dengue is a controllable problem with the new tools that are coming online. And that hasn't been achievable previously, but I think it now is.”
While noting that new solutions were looking promising in the long-term fight against dengue, Prof Fontanet cautioned against people waiting for a “magic bullet” before taking action against mosquitoes at home.
“There are also very simple things that we can do ourselves. There is a need for education about where those mosquitoes live and how we can each of us have an impact just by cleaning our backyard.”
