Stephen de Tarczynski

MELBOURNE, Jan 22 2009 (IPS) – Australian scientists appear to have made a potentially major breakthrough in the battle to combat dengue fever, the mosquito-borne infection which leads to more than 20,000 fatalities worldwide each year.
In a best-case scenario, I think it could go a long way to eradicating dengue in certain locations and contexts, but we won t really know that until we get further down the track with our experiments and know how well they translate from the lab into the field, says Prof. Scott O Neill, head of the team of researchers at the University of Queensland s school of biological sciences which made the breakthrough.

The Australia-based scientists are part of a wider group working on dengue control from ten institutions in Australia, Vietnam, Thailand, the United States and Japan.

O Neill s team has successfully cut the lifespan of the main dengue-transmitting mosquito, Aedes aegypti a secondary dengue vector, Aedes albopictus, has spread recently from Asia to areas of the Americas, Europe and Africa by introducing Wolbachia bacterium into their laboratory s population.

They found that Wolbachia found naturally in fruit flies and which is apparently harmless to humans and other animals reduced the mosquitoes lifespan, which can be about 30 days in the field, by half. This is significant because Aedes aegypti are unable to transmit the dengue virus until they are around 12 to 15 days old, thereby dramatically reducing the potential for transmission to humans.

O Neill told IPS that the attempt to limit the insects lifespan was a first for efforts to combat dengue.
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Shortening lifespan is an inadvertent effect of some of the ways that insecticides are used for malaria control. Also, there has been research going on in using fungal pathogens as a way to limit the lifespan of malaria vectors, but nothing like this for dengue, he says.

An assistant of O Neill s at the university, Conor McMeniman, manually injected 10,000 mosquito embryos with Wolbachia using super-fine needles. The virus then spread through the population, passed by female mosquitoes to their offspring.

The key to the breakthrough was combining two sets of previously acquired knowledge. O Neill s team, which he says has been working with Wolbachia for many years , understood that the bacteria had modifying effects on insects, in this case halving mosquitoes lifespan.

But due to their related interest in insect-transmitted diseases, the scientists were also aware of the link between mosquito age and disease transmission.

Putting those two pieces of information together was what was critical, says O Neill.

There has been a dramatic rise in dengue infections in recent decades. In 1970, only nine countries had experienced dengue haemorrhagic fever (DHF) a potentially lethal complication of dengue fever found in hundreds of thousands of dengue cases annually but by 1995 that number had multiplied by more than four times.

Children are particularly susceptible to DHF. First recognised in the 1950s in the Philippines and Thailand, DHF is now a leading cause of hospitalisation and death among youngsters in Asia.

But while DHF has a fatality rate of around five percent, dengue fever itself is rarely fatal, although there is no specific treatment or vaccine to protect against the disease.

The World Health Organisation (WHO) estimates that as many as 50 million new infections occur around the world annually, with about 2.5 billion people some two-fifths of the world s population now at risk from dengue.

Found in tropical and sub-tropical locales, the WHO says that dengue is most-prevalent in Southeast Asia and the Western Pacific, but is also endemic in parts of Africa, the Americas and the Eastern Mediterranean.

O Neill believes that the simplicity of his team s strategy to tackle dengue he describes it as quite simple yet quite effective could be a major factor in determining its ultimate success.

I think in the developing world it s quite clear that we need technologies that are easy to implement and that are quite inexpensive. I think that it meets those requirements, he says.

According to O Neill, this strategy is also more environmentally friendly than other efforts to combat the mosquitoes, such as the spraying of insecticides.

The next stage of the project will involve controlled field experiments. Large cages covered by a fine mesh have been constructed in Cairns a town on Australia s northeast coast which has seen an outbreak of dengue in recent weeks with more than 160 cases reported to house the mosquitoes.

We can study the dynamics of the bacteria within the mosquito population to make sure that what it has done in the laboratory population it will do in a more natural setting, O Neill told IPS.

The trials are due to begin in February and are planned to run for 18 months. The successful completion of the trials, in combination with ongoing safety-related laboratory experiments focused on making sure the bacteria can t jump into unintended hosts and so forth, says O Neill would result in a pilot open release.

This would occur in a small geographic area to see how well it works in a real world setting. Then if that was to work we would hope to do a widespread open release, O Neill explains.

The scientist has recently returned from Vietnam, where he met with colleagues also working on the project it is being backed by the Bill and Melinda Gates Foundation, a philanthropic organisation which funds poverty reduction and healthcare projects around the world to discuss the breakthrough and in order to prepare a new grant proposal focusing on community engagement strategies.

O Neill says that the results have justified a sense of optimism among the teams working to minimise the impact of dengue. It s a large team of people working on this project and I think we re all quite excited about it at the moment.

The data, currently, is looking very strong. It looks very promising and if that holds together and we re keeping our fingers crossed that it does then I think it could be very exciting, he says.