Why Brazil has built the world's largest mosquito factory
It sounds odd. Why would anyone breed more mosquitoes. Aren't there enough already buzzing around the globe, leaving in their wake a path of itchy bites and debilitating, sometimes fatal, fevers?
Yet on Saturday, an team of scientists unveiled the world's largest mosquito factory in Curitiba, a city in southern Brazil.
'Nowhere in the world can produce the number of mosquitoes that will be produced here with this technology,' Alexandre Padilha, the country's health minister, said at the inauguration. '[The factory] represents an exercise in national sovereignty and innovation.'
At its peak, the 5,000 square metre 'bio-factory' is set to churn out roughly 100 million mosquito eggs every week – more than five billion a year. These eggs, which carry a disease-blocking bacteria, will then be hatched in cities across the country, in the latest stage of an ambitious initiative to curb the spread of dengue.
Colloquially known as 'breakbone fever', the mosquito-borne virus has wrought havoc across Latin America, with more than 13 million cases reported in the region last year – by far the worst epidemic on record.
In Brazil alone, some 6.5 million people were infected, pushing the healthcare system to the brink, while 5,700 people died.
'You could see dengue everywhere – you'd go to the supermarket and there would be very few employees, because people were sick,' said Dr Luciano Moreira, a vector biologist and chief executive of Wolbito Brazil, one of the organisations behind the factory. 'So many friends and relatives were really ill… it was really a huge thing that affected everyone, rich and poor.'
Now, after a year of construction, the factory in southern Brazil will start providing crucial reinforcements for Brazil's battle against the debilitating disease.
That's because the Aedes aegypti mosquito eggs bred here carry a bacteria called Wolbachia, which blocks the mosquito's ability to transmit dengue.
The Wolbachia bacteria is naturally found in a range of insects, though not the Aedes aegypti mosquito. When the insect is infected with the bacteria, it inhibits the dengue virus's ability to replicate inside it. In effect, the bacteria and the virus are competing for resources – and Wolbachia bacteria comes out on top.
This has major ramifications for disease control, because it means the mosquito's bite no longer transmits the virus to people. The bacteria, which doesn't spread into humans, can also block Zika, yellow fever and chikungunya.
'We have seen that insecticides alone are not enough [to control dengue],' said Dr Moreira. 'You pay a lot, you have to damage the environment, and then the mosquitoes become resistant. So we really need to bring something else to the fight, and Wolbachia is one of these interventions.
'The advantage of Wolbachia is it's sustainable,' he added. 'It's biologically sound, it's not a chemical, and it doesn't interfere with the health of people or the environment or animals. So it holds a lot of promise.'
It's not just Brazil that's in need of additional tools to fight dengue. In 1970, the virus had been detected in just seven countries; now roughly half the world's population are at risk of infection, with cases jumping to as many as 400 million a year. The increase – which is also occurring in Europe – has been driven by rising temperatures, rapid urbanisation and international travel.
Experts hope that, alongside new vaccinations, Wolbachia could help turn the tide.
There are two main ways the bacteria is deployed for disease control: either to suppress or replace mosquitoes.
In Singapore, for instance, only male Wolbachia-infected mosquitoes are released. When they mate with wild, Wolbachia-free females, their eggs become infertile and do not hatch, causing the overall insect population to gradually get smaller over time. However, to be effective a constant stream of Wolbachia-carrying males have to be released.
Brazil uses a different technique, reliant on both male and female Wolbachia-infected mosquitoes. When these bacteria-carrying insects mate, they pass the Wolbachia onto their offspring. The aim is that, after several generations, the majority of insects in any given area carry the bacteria, which then helps to suppress the spread of disease.
'In our case we want to have the replacement of the [mosquito] population, so that this becomes sustainable over time,' said Dr Moreira. 'We did a set of releases in 2014 and 2015. In those areas, Wolbachia is still in the mosquitoes. We don't need to do new releases again and again.'
Since scientists at Monash University in Australia first identified the dengue-blocking capacity of Wolbachia some 15 years ago, multiple real-world studies have confirmed that this concept works – and it's safe.
In 2020, a major randomised control trial in Indonesia found dengue cases dropped by 77 per cent in areas of Yogyakarta city where Wolbachia mosquitoes were released, while results in 2023 showed incidence fell by at least 94 per cent in three Colombian cities.
But Dr Moreira warned the intervention is not an overnight fix.
'Wolbachia is a very powerful tool, especially when it is integrated with other measures,' he said. 'But it takes time for Wolbachia mosquitoes to establish.
'Politicians call in the middle of an epidemic and say they want us to come next month. We are clear and transparent that this won't help next month, it might take a year or two.'
There are other limitations too, said Professor Eng Eong Ooi, a researcher at Duke-NUS Medical School's Emerging Infectious Diseases programme in Singapore.
'I think Wolbachia has shown great success but not universally. The environment, particularly how warm the place is, affects how well Wolbachia works,' he said.
Mosquitoes were first released in the Brazilian capital Rio de Janeiro in a pilot in 2014. Studies have since shown drops in dengue of 38 per cent to 90 per cent in different areas of the city.
The innovation has now become a central plank of the country's dengue control strategy, with Wolbachia mosquitoes so far released in 11 sites across Brazil.
Until now, scientists were breeding roughly 15 million Wolbachia-carrying mosquito eggs every week, at a facility within the Fiocruz health institute in Rio. The biofactory in Curitiba will turbocharge the availability of disease-blocking insects, with scientists aiming to breed some 100 million mosquito eggs a week.
'The way we reared mosquitoes in the facilities for instance at Fiocrux, was a simple way: in trays and with lots of labour and hand processes,' said Dr Moreira. 'With the creation of our big factory now, we are bringing new equipment. We have machines to hatch the eggs… and we feed mosquitoes with automated devices.'
He added that the facility also has a highly-controlled environment, to optimise conditions for the eggs, larvae and mosquitoes. Temperatures range from 27C to 29C depending on the stage of the life cycle, with humidity at 70 to 80 per cent, while insects are fed sugar, fish food and horse blood (a replacement for biting live animals, including humans).
But only a small proportion of the eggs actually hatch in the factory. The vast majority will be shipped by car, plane and boat across the vast country as eggs, before local health officials add water and rear the larvae.
'We dry the eggs, and they don't hatch until they [come] into contact with the water,' said Dr Moreira. 'We put the eggs in capsules, or we can ship in filter paper. They can be [stored] for two or three months, they will still survive.'
He added that the government has earmarked 40 cities, each home to more than 100,000 people, where they would like these eggs to be sent. Six cities have already been selected, where the first Curitiba-bred mosquitoes will be released as early as August.
'It will be exciting to get to that moment,' said Dr Moreira, who was working in the lab in Australia in 2009, when scientists first identified Wolbachia's disease-blocking potential.
'It's been a long time coming, slowly going through the scientific evidence and expanding into a robust programme in Brazil,' he added. 'Wolbachia is only one element of the solution for dengue, but I think it will be a very significant one for the country.'
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