Dengue down 77% in 'groundbreaking' study due to 'miraculous' hack

·3-min read
Aedes aegypti Mosquito. Close up a Mosquito sucking human blood.
Aedes aegypti – the mosquito species that transmits the dengue virus – is expected to have spread from its native tropical and subtropical regions to 159 countries by 2080. (Stock, Getty Images)

Dengue cases were cut by 77% in a "groundbreaking" study.

Spread by mosquitoes, the viral infection is usually mild. More than 20,000 people die from its complications every year, however, with the virus set to become more prevalent worldwide.

With dengue having no set treatment or widely-available vaccine, scientists from the World Mosquito Programme at Monash University infected the insects with "miraculous" bacteria that reduce their ability to spread the virus.

Known as Wolbachia, the bacteria do not harm the mosquito but camp in the same part of its body that the dengue virus inhabits, making it more difficult for the infection to replicate.

Read more: Genetically-modified mosquitoes released in Florida to combat dengue

Five million Wolbachia-riddled mosquito eggs were placed around the city of Yogyakarta in Indonesia every two weeks, building up the population of infected insects over nine months.

Just over two years later, dengue cases had dropped by 77%, while the number of people requiring hospital care was down 86%.

Bacteria flowing with depth of field. Can also be used as plant cells.
Mosquito eggs were infected with bacteria that reduce their ability to carry the dengue virus. (Stock, Getty Images)

"This result is groundbreaking," study author Dr Katie Anders told the BBC.

"We think it can have an even greater impact when it is deployed at scale in large cities around the world, where dengue is a huge public health problem."

Around 105 million dengue infections are thought to occur every year across 120 countries, three quarters (75%) of which arise in South-East Asia and the Western Pacific region. 

Symptoms typically include a fever, severe headache, eye pain, muscle and joint discomfort, nausea, vomiting, rashes, abdominal pain and a loss of appetite.

Most people fight off the infection naturally within a week. 

Read more: Social distancing leading to surge in dengue in Thailand

In serious cases, a patient may endure severe abdominal pain, bleeding beneath the skin or breathlessness. Repeatedly vomiting blood, developing a weak but fast pulse, losing consciousness and even death can also occur.

Dengue infections are said to have increased 30-fold over the past 50 years due to rising temperatures, travel and urban sprawl. 

By 2080, Aedes aegypti – the mosquito species that transmits the virus – is expected to have spread from its native tropical and subtropical regions to 159 countries.

Watch: Genetically-modified mosquitoes released in Florida

The Wolbachia-eggs were placed in buckets of water around Yogyakarta. The eggs hatch in water into larvae, known as "wrigglers". 

The city was divided into 24 zones, with the buckets only left in half of them.

Read more: Pesticide raises risk of an early death

Results – published in the New England Journal of Medicine – reveal the zones with the buckets had significantly fewer dengue cases and subsequent hospitalisations.

"It's better than we could have hoped for to be honest," said Dr Anders.

The approach has now been introduced across the city, with plans to also plant the infected eggs in Yogyakarta's surrounding area.

Dr Anders has described Wolbachia as "naturally miraculous".

The bacteria reportedly alter the mosquitoes' fertility, causing Wolbachia to be passed down to the insects' future generations. Once Wolbachia-infected eggs are established, the bacteria should therefore stick around.

This is preferred over insecticides, which have to be continually applied and runs the risk of mosquitoes developing resistance.

The release of sterile male insects, another approach, also has to be carried out over and over again.

Modelling studies suggest Wolbachia could completely suppress dengue if the approach becomes established. It may also have potential for other mosquito-spread infections, like Zika and yellow fever.

Watch: Anaemia may accelerate dengue's spread

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