Dengue fever may be more of a worry to Australians than swine flu

May 6 2009

For the last week or so much of the world's media has been gripped by the new influenza A H1N1 (swine flu) virus which has dominated the headlines everywhere.

The latest figures from the World Health Organisation (WHO) states that 21 countries have now officially reported 1,490 cases of the new flu virus.

Meanwhile in Australia, Queensland health authorities continue to struggle with another threat which also causes flu-like symptoms and makes some victims so ill they need to be hospitalised.

Health officials say the outbreak of dengue fever in the state's north is the worst in 50 years and since last December more than 900 cases of the current type-3 outbreak have been reported including one death - the outbreak is notorious for the speed of the spread of the dengue virus.

The Tropical Population Health Service unit in Cairns has been at the forefront of the fight against dengue fever in the area and some working there have been directly affected and have contracted the mosquito bourne disease.

Queensland Health medical entomologist Brian Montgomery says north Queensland has been in the grip of the worst dengue epidemic in decades with 901 cases which is in excess of the previous large outbreak in 1992-1993 in Townsville and Charters Towers - this is the most significant outbreak since the mid-1950s.

Since the current dengue outbreak was declared in December, Queensland Health has been waging war against mosquitoes with officials in the state's north, visiting tens of thousands of properties and clearing more than 100,000 mosquito breeding sites.

Experts say globally dengue is becoming more and more of a problem and the result is that north Queensland, where dengue mosquitoes are present all year round, will remain at risk each year.

New research by Dr Nigel Beebe from the University of Queensland suggests that the threat from dengue is not just confined to tropical north Queensland and he warns that installing rainwater tanks in urban backyards could see the dengue virus spreading to cities throughout Australia by 2050.

Dr Beebe says they found that the installation of water tanks in major capital cities as a tool against drought is producing a risk of aedes aegypti, the dengue mosquito, getting back into some of these regions and actually moving further south - this would produce transmission risks for dengue in the summer months.

Queensland Health Senior Medical Entomologist, Brian Montgomery says the need to have rainwater storage devices in homes must be balanced with the realisation that they will need to be monitored and repaired to ensure that the dengue mosquito, which was previously more widely distributed outside of Queensland, does not re-establish itself and start to move southward again.

The new study challenges the common assumption that climate change will drive the spread of this mosquito, and suggests instead that the real driver is human behaviour.

The study involved the team from the University of Queensland, CSIRO Entomology, the Australian Army Malaria Institute, and the Communicable Diseases Branch of Queensland Health, Brisbane and used combined current and forecasted climate change conditions with historical epidemics to reveal the risk of dengue infections in all capital cities around Australia by 2050.

The researchers developed and critically assessed their models to project the distribution of the mosquito in 2030 and 2050.

Currently, dengue fever occurs in Queensland only, but the implementation of new water tanks, combined with already warm summer temperatures, could enable the mosquito to re-emerge and further its current reach.

Dr Beebe says Australian summers already provide ideal conditions for dengue transmission around the country, but the introduction of government-subsidized water storage devices now adds the ideal breeding ground for the dengue mosquito to re-emerge.

Dr Beebe says dengue risks will not be driven directly by warmer temperatures or changes in rainfall patterns and while research is properly focused on the impact of anthropogenic climate change, this study highlights the need to look also at our responses to those changes and the outcomes they generate.

The current dengue fever epidemic in far north Queensland is fast approaching 1,000 reported cases over the summer of 2008-2009 and health authorities found more than 50,000 potential mosquito breeding sites in Cairns alone.

Though the outbreak in and around Cairns does now appear to be receding, health authorities continue to urge residents to remain vigilant as active transmission can re-emerge.

Containers such as old tyres, pot plants, buckets and toys are among the main culprits cultivating dengue mosquito breeding grounds in the home, and must be removed or emptied out every two or three days.

Queensland Health says research into the outbreak has shown people who were around the home during the day have been more at risk of contracting the disease.

Beebe and colleagues are continuing this research under the auspices of the CSIRO Climate Change Adaption National Research Flagship.

This work was supported by a jointly funded position at the University of Queensland and the CSIRO Climate Adaptation Flagship and the funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.