Australian scientists’ new approach to controlling dengue vector

9 Jan 2009

Paul Chinnock

Source: University of Queensland (see original article)

Comments

In a paper published in Science 2nd January, researchers from The University of Queensland say they have proven the effectiveness of a new way of limiting the lifespan of the type of mosquito that spreads dengue fever.

They have done it by infecting the dengue mosquito, Aedes aegypti, with a bacterium that is harmless to humans and other animals but halves Aedes’ lifespan. This has the potential to greatly reduce dengue because only old mosquitoes are effective at transmitting the virus to humans.

Carried out in the laboratory of Professor Scott O’Neill, Head of the university’s School of Biological Sciences, the experiment’s focus was painstaking work with the Aedes mosquito and Wolbachia, a bacterium that occurs naturally in fruit flies.

PhD student Conor McMeniman used super-fine needles to manually inject 10,000 mosquito embryos with Wolbachia, and encouraged the surviving mosquitoes to feed on his own blood. “We ended up having to inject thousands of embryos to achieve success, but it was well and truly worth it in the end,” Mr McMeniman said.

The hypothesis the researchers set out to prove was that the bacterium would:

reduce the lifespan of mosquitoes, which must be approximately 12-15 days old before they can transmit the dengue virus.
be passed by females to their offspring and spread into mosquito populations.
not kill mosquitoes before they were old enough to breed and produce more bacterium-carrying insects.

The researchers have shown that Wolbachia halves mosquitoes’ lifespan, which can be up to 30 days in the field. This dramatically curtailed their potential to spread dengue fever, without preventing the hereditary transmission of the bacterium.

Professor O’Neill said the project’s next stage would be a contained field cage setting in northern Queensland: “If that proves successful we hope to deploy this new dengue control measure in other parts of Australia, as well as Thailand and Vietnam.”

Queensland’s own dengue burden

The work has been done in the northeastern Australian state of Queensland which (as already reported in TropIKA.net) has itself experienced rising rates of dengue fever. Now, according to the Courier Mail, hospitals are ‘struggling to cope’ with the latest outbreak in the north of the state, mostly around the city of Cairns. Current weather conditions are said to be ideal for Aedes.

Public health specialist Jeffrey Hanna described Cairns as ‘a mosquito-friendly city’. “We’re finding a lot of mosquito breeding in the properties we visit,” he said. “This outbreak clearly has a momentum about it. I expect it’s going to be several months before it’s overcome”. Fears have also been expressed that the disease will return to southeastern Australia for the first time in 60 years.

Dengue vaccine on the way?

Control of Aedes will always be an important part of the battle against dengue. However, an effective vaccine would also make a major contribution. An article on the Voice of America website features an interview with Lieutenant Colonel Stephen Thomas who heads the US Army’s Dengue Vaccine Development programme, in Bangkok. He says The US Army is testing a possible vaccine in the US and Thailand. He notes that, there being four types of dengue virus, designing a vaccine is not an easy task: “We’ve had vaccine candidates that we've given to US adults and we said this does not generate any immune response, so we have to throw them away”. Colonel Thomas thinks many questions about how the virus behaves and spreads globally will remain unanswered even with a vaccine.