The battle between humans and mosquitoes has been raging for centuries. For as long as humans have existed, mosquitos have been there, right alongside us, making us sick.
Dengue alone causes 390 million infections a year, and as much as 40 per cent of the world’s population lives in a place where dengue is a risk.
As our world’s climate changes, even more people will be exposed to these mosquitoes, and the diseases they bring with them.
When it comes to mosquito control, the traditional methods don’t appear to be standing up to the sheer scale of this challenge.
Take mosquito breeding site destruction as a strategy, for example.
“You have to only spend a short amount of time in any growing, tropical, large city and imagine that you’re going to have to find all the pools of water where mosquitoes are breeding, and you can understand the enormity of it and how impossible it is to try to remove them all,” explains Professor Scott O’Neill, a microbiologist and the director of the World Mosquito Programme (WMP), a non-profit organisation dedicated to the eradication of mosquito-borne diseases.
And as far as chemical spraying goes, O’Neill is no less pessimistic.
“What we know is that the mosquitoes that transmit dengue are progressively getting more and more resistant to the chemicals used for control. Eventually very few of those chemicals are going to work very well anymore.”
The approach taken by O’Neill’s programme is different.
The WMP’s strategy relies on the Wolbachia bacteria found naturally in 60 per cent of insect species – but not Aedes aegypti, the primary mosquito that transmits dengue.
Scientists have found that when this particular bacteria is introduced into that particular mosquito, it prevents the dengue virus from being able to replicate and grow, reducing the likelihood that that mosquito can pass the virus to a human.
The WMP seeds a local area by releasing lab-raised mosquitoes that have been given the Wolbachia bacteria.
And everything is done with the active consent of local communities.
“We don’t operate under the assumption that just because scientists think the intervention is good that communities should just accept it,” O’Neill said.
“And if communities are not wanting, even if the government has approved it, then we don’t deploy.”
The initial results are incredibly promising.
In northern Australia, where the group began releasing Wolbachiainfected mosquitoes in 2011, they have seen a lasting reduction in the transmission of dengue by around 98 per cent.
WMP has several projects across Asia – in Sri Lanka as well as in Vietnam – but none of these projects is as big as the one in Yogyakarta, Indonesia, a city of around half a million people.
“It’s probably the largest mosquito-based clinical trial for dengue that’s ever been done,” O’Neill said.
The WMP, in collaboration with Gadjah Mada University, has divided the city into 24 sq km clusters.
Twelve of the clusters have received the Wolbachia-treated mosquitoes and 12 have not.
When the people in the area of study report to clinics and hospitals with a fever, they’re tested for dengue and enrolled in the study.
If patients test negative for dengue, they’re placed into the control group.
If dengue is detected, they get placed in the intervention group and are tracked according to their location to see if they live in a treated or untreated area of the city.
The results of this blind study aren’t expected until the end of next year.
But results are already coming in on another Yogyakarta study.
A simple comparison of one area of the city with Wolbachia mosquitoes with another area without them suggests the intervention has led to an 80 per cent reduction in dengue transmission.
Data from the WMP’s Vietnam site has yielded similarly sucessful results.
In studying the impact of Wolbachia on dengue transmission, scientists in Vietnam have found that the bacteria is actually even more effective at stopping the growth and transmission of dengue in the wild than it is in laboratories.
At this point, the WMP estimates that their intervention costs about $10 per person protected.
“We believe over the next three or four years we’ll pull that number down to around $2 per person protected,” O’Neill said.
And, according to cost-benefit projections created in collaboration with the US’ Brandeis University and the London School of Tropical Medicine and Hygiene, as well as the Oxford University Clinical Research Unit in Vietnam, fully scaled-up Wolbachia releases may end up being cost-saving for governments in the long term.
The study expects that this intervention can save governments around $50 million per year, which would offset the total cost of such a programme in a large city within around a decade.
The WMP has big plans for Wolbachia mosquitoes.
“We have put the intervention to over three million people, and our goal in the next five years is to expand that to be over a 100 million people,” O’Neill said.
Quinn Libson/Asia News Network