Published by Australian Academy of Science
Warmer and sicker? Global warming and human health Box 1 | Mosquito-borne disease

Malaria kills between one and two million people every year, mainly in tropical Africa, and debilitates up to 400 million others. This disease is caused by protozoans from the genus Plasmodium, which are transmitted from person to person by mosquitoes from the Anopheles genus. Scientists believe that climate is the major determinant of malaria distribution in Africa – both the vector and the protozoa prefer warm, humid conditions. Mosquito control measures are largely responsible for limiting its distribution in other regions.

Malaria was once endemic in parts of northern Australia, but was eradicated by control measures and changes to water supply practices. Only a dozen or so locally acquired cases have been reported since 1962. Modelling suggests that climatic conditions are currently suitable for the survival of both the protozoa and its mosquito vector in the very north of the continent. Under a warmer and wetter climate-change scenario, the malaria-receptive zone could spread down the coast to southern Queensland by 2050 – including to towns such as Rockhampton, Gladstone and Bundaberg – and into the coastal hinterland. Under a warmer and drier scenario, the disease could still be transmitted in southern Queensland, but would be more limited to the coastal zone and islands. A report published by the Australian Australian Government Department of Health and Ageing in 2003 concluded that malaria is unlikely to constitute a major direct threat to human health in Australia under climate change 'as long as a high priority is placed on prevention via the maintenance and extension of public health and local government infrastructure'.

The authors predict a similar increase in the potential distribution of dengue fever in Australia, although dengue would probably be a greater threat to public health. This is because dengue's mosquito vector is a morning and evening biter and can breed in urban environments, increasing the risk of exposure, and because no treatments are available to reduce the period in which victims are infectious.

Related site

• Human health and climate change in Oceania: a risk assessment 2002 (Australian Government Department of Health and Ageing, Australia)