Wolbachia after the winter? - After a very dry Cairns winter, I have to admit to heaving a sigh of relief when it rained in October. Our first field trial held in Yorkeys Knob and Gordonvale earlier this year was successful and told us that Wolbachia based strategies can be deployed as a practical new approach to dengue suppression. Monitoring of mosquitoes showed that Wolbachia was present in over 90% of the dengue mosquito in these two locations – but the question was would Wolbachia still be present after the dry season? I can now report that yes it is.

Over 98% of Aedes aegypti mosquito eggs collected from the two suburbs in late September did have Wolbachia – which is as we had hoped but with all experiments it’s always good when the results match your expectations. Over the coming months we will continue to monitor Wolbachia levels in Yorkeys Knob and Gordonvale, and the neighbouring suburbs of Holloways Beach and Pyramid Estate and report those results to you.

Further trials in 2012 - We are now focusing on further trials for the coming wet season in Cairns. Our original thinking had been to take the Wolbachia mosquitoes from Yorkeys Knob and Gordonvale and release these into less contained areas in Cairns and monitor how

well the Wolbachia spreads. But now that we know Wolbachia will establish relatively easily it has allowed us to consider an alternative direction.

In our labs we have been working with a number of different strains of Wolbachia. Each strain has slightly different properties in relation to how well it should establish in mosquito populations and also how well it can block dengue.

Stronger dengue protection - The 2011 field trial was run with a Wolbachia strain called WMel that we believed would establish well and at the same time provide dengue protection. A second strain wMelPop gives the strongest dengue blockage we have encountered in laboratory tests. We chose not to release this strain initially as we felt it would have difficulty establishing in the wild mosquito population. However, given that the first field trial went so well we now feel more optimistic about its potential.

We plan this wet season to repeat the experiments we did in Yorkeys Knob and Gordonvale in Machans Beach and Babinda with this more powerful dengue blocking strain. If we can successfully introduce this strain, then it might prove to be an even better prospect for dengue control in the Cairns region.

Community Engagement - As we did with Yorkeys Knob and Gordonvale, before we release any mosquitoes, we are engaging with the community to listen to all questions and concerns and ensure they are addressed. We only release mosquitoes from properties with the permission of residents.

The results of this second trial will help determine what the best strategy should be for a future roll out of the strategy more generally in Cairns and in other countries where dengue is a major problem.

Dengue Field Trial UpdateBy Professor Scott O’Neill, Program Leader November 2011

E: eliminatedengue@uq.edu.au

www.eliminatedengue.comFree call from a landline in Australia

Ph: 1800 811 054

Flora Zigterman, pictured above with Machans Beach resident Russell King, has joined the Cairns project team in a Community Engagement role.

Please call Flora on 1800 811 054 or email flora.zigterman@monash.edu if you or your group would like to meet with the team or to register your support for the 2012 field trials.

The Eliminate Dengue program involves research institutions in Australia, Vietnam, Thailand, the USA and Brazil and is led by Professor Scott O’Neill, Monash University, Melbourne.

The Program is supported by the following organisations and programs:

• The Foundation for the National Institutes of Health through the Grand Challenges in Global Health Initiative of the Bill and Melinda Gates Foundation

• The National and International Research Alliances Program of the Queensland Government

• The National Health and Medical Research Council of Australia.

How we hope to control dengueOur aim is to stop the Aedes aegypti mosquito from passing dengue virus between humans and we hope to do this by introducing a naturally occurring bacterium called Wolbachia into the existing wild mosquito population.

We have found that when Wolbachia is introduced into the Aedes aegypti mosquito it acts like a ‘vaccine’ for the mosquito and reduces its ability to pass the dengue virus to people.

Wolbachia is already found in up to 70 per cent of the world’s insect species, including fruit flies, moths and butterflies found in Cairns, as well as mosquitoes that bite but don’t harm people. Our laboratory trials and independent analysis has concluded that Wolbachia is not harmful to humans, animals or the environment.

Professor Scott Ritchie and his team (pictured above) at James Cook University will rear Wolbachia Aedes aegypti mosquitoes in the Mosquito Research Facility at Smithfield, to release in a second field trial in Cairns.

When mosquitoes carrying Wolbachia are introduced into the environment, they mate with wild mosquitoes, and pass Wolbachia to their offspring until all Aedes aegypti mosquitoes have Wolbachia. If they have Wolbachia, dengue virus transmission will be reduced. It is hoped the releases will begin in early January for approximately 12 weeks in Machans Beach and Babinda.

Visit the Cairns project office at: Suite 11/36 Grafton St, Cairns. Open Monday - Friday 8.30am – 5.00pm. Visit the program website www.eliminatedengue.com for progress updates

Bites dengue infected person

1

Mosquito ingests blood with dengue virus. Takes 8-10 days for dengue virus to incubate.

2

Dengue infected mosquito bites another person

3

That person gets dengue 4-13 days later

4

WildAedes aegypti

WolbachiaAedes aegypti

That person doesn’t get dengue

4

Bites dengue infected person

1

Mosquito ingests blood with dengue virus - Wolbachia blocks the dengue virus

2

Dengue infected mosquito with Wolbachia bites another person

3

A. How dengue is transmitted

Left to right: Jessica Dickie, Scott Ritchie, Clare Omodei and Chris Paton

B. Wolbachia blocks dengue virus

Mosquitoes reared at JCU