Increased movement of people making dengue outbreaks more common, says mosquito expert

RNZ News

09-06-2025

The Lautoka City Council carried out anti mosquito spraying soon after a Dengue Clean Up campaign over the weekend.
Photo:
Ministry of Health & Medical Services - Fiji
Dengue fever outbreaks have been surging in recent decades but new initiatives like infecting mosquitos with bacteria or genetic modification could dramatically slow the spread.
According to the World Health Organization there was just over 500,0000 reported cases in 2000 - ballooning to 5.2 million in 2019.
Last year, there were
14 million dengue cases
- a record number dwarfing the previous 2023 high of 6.5 million.
This year, there's been 2.5 million.
Samoa, Fiji, Tonga and the Cook Islands have all
declared dengue outbreaks
. Samoa, Fiji and Tonga have each had at least one death from the viral infection.
Greg Devine from the World Mosquito Program said increased globalisation is making outbreaks more common.
Devine said mosquitos that carry the virus "hitchhike around the world" and the increased movement of people is increasing those infected by dengue.
Devine said a lot of people also don't have immunity.
"They don't have any protection against it because they've never been exposed to it before," he said.
"Dengue comes in four different serotypes, so just because you've had one doesn't mean you can't get another."
Photo:
123RF
He said
climate change was having an increasing impact
.
"We are hotter and wetter than we've ever been before and that's great for mosquitoes. It also means that the virus in mosquitoes is replicating more rapidly."
The aedes aegypti mosquito - which carries dengue - is considered a tropical or subtropical mosquito, but Devine said warmer weather would also increase the mosquitoes' range of where it inhabits.
In the Pacific, health ministries are trying to stamp out mosquito breeding grounds and are spraying insecticides outside.
But Devine said doing so has had limited success in reducing the spread.
He said the aedes aegypti mosquito is "completely reliant upon humans for its blood meals" which meant it liked to stay indoors, not outdoors where the majority of the spraying happens.
"Outdoor use of insecticides, it's perhaps better than nothing and the truth is that the community wants to see something happening.
"That's a very visible intervention but the reality is, there's a very limited evidence base for its impact."
Mosquitoes continually exposed to insecticides would also evolve resistance, Devine said.
The World Mosquito Programme infects mosquitos with a naturally occurring bacteria called Wolbachia, which stops viruses like dengue growing in the mosquitoes' bodies.
Photo:
123RF
"It's been
trialled in New Caledonia
, where it's been extremely successful," Devine said.
"In the years since, the mosquito releases have been made by the World Mosquito Program, there's been no dengue epidemics where once they were extremely common."
He said genetically modified mosquitoes were also being looked at as a solution.
"That's a different kind of strategy, where you release large numbers of mosquitoes which have been modified in a way which means when those males interact with the local mosquito female population, the resulting offspring are not viable, and so that can crash the entire population."
When asked if that could collapse the entire aedes aegypti mosquito population, Devine said he wouldn't be "particularly worried about decimating numbers".
"People often refer to it as the kind of cockroach of the mosquito world.
"It's very, very closely adapted to the human population in most parts of its range. The species evolved in Africa and has since, spread throughout the world. It's not a particularly important mosquito for many ecosystems."