A recent study showing climate change is unlikely to cause an increase in the spread of malaria has been criticised by one of Australia's leading tropical disease experts.
Appearing in the latest issue of Nature, the study casts doubt on the widely held view that climate change will see a surge in the tropical disease around the world, including northern parts of Australia.
The researchers from the University of Oxford-led Malaria Atlas Project (MAP) found that since 1900, the incidence of malaria has been on the decline, despite a warming of the planet during that time.
Lead author Dr Pete Gething, from the Department of Zoology at the University of Oxford, says the recession in malaria since 1900 is of little comfort to the billions of people still at risk, but it is important when thinking about the effects of climate on the future of the disease.
"We know that warming can boost malaria transmission, but the major declines we've measured have happened during a century of rising temperatures, so clearly a changing climate doesn't tell the whole story."
Dr Simon Hay, who leads the MAP group in Oxford, says the decrease in malaria is due to better prevention strategies.
"When we looked at studies measuring the possible impact of bed nets or drugs, it was clear that they could massively reduce transmission and counteract the much smaller effects of rising temperatures," Hay says.
But Professor Tony McMichael, of the Australian National University's National Centre for Epidemiology and Population Health, disagrees.
"It would be naïve if anyone concluded from this paper we are on a long-term and inexorable downturn in malaria, I don't think that's happening," McMichael says.
McMichael, who chaired the team that assessed the health risks of climate change for the UN's Intergovernmental Panel on Climate Change, says while the new study has a valid argument there are many variables the modelling does not take into account.
He says the model only looks at the geography of the disease and not the seasonality.
McMichael points to recent modelling in Zimbabwe that showed an increase of malaria incidence in the highlands, where the major city of Harare is based.
He says the study also shows the length of the malaria season will double by 2030, and treble by 2050.
According to McMichael, this will have a major impact on public health expenditure and whether countries can afford to maintain prevention programs.
"The other thing to ask ourselves is what type of world will we be living in 2030?" McMichael says.
He says with increased population displacement and the potential for increased disorder and geopolitical instability, "we can't assume we are going to have orderly health programs and budgetary policies to control these public health issues".
McMichael says the efficacy of malarial drugs is another variable the researchers overlooked.
"Hope springs eternal with malaria," he says. "We've been talking about a malaria vaccine being around the corner for the past 40 years and we still don't have it."
"[We are] now seeing ominous signs that malaria is developing resistance to the latest of drugs, Artemisinin, which has been the flag-bearer of new anti-malarial drugs for the past decade."