Get the science straight on climate change and disease

Governments need solid scientific evidence of the links between climate change and insect-borne disease Copyright: CDC

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Climate change’s complex links with insect-borne disease need solid research — not alarmism that distracts from other crucial factors.

To get the most from science for development, research agendas must both respond to social needs and offer good science.

Researching the relationship between insect-borne disease and climate change clearly meets a social need.

Diseases such as malaria, dengue fever and Rift Valley fever — transmitted by insect vectors — are endemic in many parts of the developing world and kill millions of people each year. So any research that provides better options for tackling them, or better understanding of the likely changes because of climate change, will be valuable.

But fulfilling the second condition is more tricky.

There is clearly a link between insect-borne diseases and climate. Variables such as temperature and rainfall influence vector and parasite development and lifecycles, as well as feeding rates — and therefore disease transmission rates.

But a whole host of non-climate factors also influence disease transmission, from living conditions and irrigation practices to drug resistance, health infrastructure and urbanisation.

So we mustn’t go overboard, reading too much into the role of climate change at the expense of research into other triggers of these major diseases.

Myths, models — and more evidence

This week we put these issues under the spotlight in a series of articles. These explore the evidence for (and against) the notion that climate change will worsen the burden of insect-borne disease, highlights gaps in our knowledge, and provides advice to policymakers.

A background article summarises the key issues, including how changing rainfall and temperature may affect vectors and pathogens; strategic priorities for tackling a potential crisis; and how far climate change has been scientifically proven to affect the spread of disease (see Climate change and insect-borne disease: Facts and figures).

How well models can predict these effects is a particularly thorny issue in the debate, given both the myriad ways that weather can influence disease transmission and the uncertainty attached to climate models themselves (see Climate complexities stoke disease controversies).

The solution, according to Jonathan Cox, from the London School of Hygiene and Tropical Medicine, is to forget predictive modelling for the moment and focus on research with a better chance of improving disease control — investigating how to strengthen national surveillance systems to detect outbreaks as early as possible (see Better surveillance key to malaria early warning systems).

This need for better surveillance is echoed by Ulisses Confalonieri from the Oswaldo Cruz Foundation in Brazil. He also calls for measures to make people less vulnerable to infection through, for example, better sanitation, housing and education. Regardless of climate change, these measures are crucial to tackling insect-borne disease in the developing world, he says (see Tackling insect-borne disease whatever the weather).

Meanwhile, Jai P. Narain, from the WHO Regional Office for South-East Asia, argues more research is the need of the hour. He warns that climate change is already affecting the spread of insect-borne diseases, such as malaria, in South-East Asia — through an increase in natural disasters such as cyclones and floods. But the relationship between climate change, disasters and disease remains little understood. If policymakers are to respond wisely, they need more information, he urges (see Climate change brings natural disasters and disease).

Paul Reiter, a medical entomologist from the Institut Pasteur in France, contests whether climate change is causing a rise in malaria at all. He sets out to dispel three common ‘malaria myths’: that climate change is spreading the disease to higher latitudes; letting it climb to higher altitudes; and spreading it at alarming speed across Sub-Saharan Africa. These myths, he says, have arisen through the alarmism of climate change activists, rather than from historical or scientific fact (see The malaria myths of climate change).

Certainly, we need responsible communication in this area. Asefaw Getachew, senior technical advisor to the Malaria Control and Evaluation Partnership in Africa, offers tips to journalists struggling to make sense of the complexity and uncertainty in the scientific literature (see The challenge of reporting on climate change and health).

No short-cuts

It is clear that the scientific jury considering climate change’s impact on insect-borne disease is still out. But good science is crucial for good policy, so researchers must strive to get the science straight.

The task is urgent — but this must not lead to short-cuts. There is a delicate balance to be struck. If we don’t research and confirm climate change effects on insect-borne disease we risk missing a strong argument for politicians to tackle global warming.

But there is equal danger in over-emphasising climate change as the driving factor — for example, if it channels funds away from research into other key factors that help spread diseases.

The bottom line is clear. For health sectors to justify the large sums of money they will need if climate change does accelerate insect-borne disease, they must be able to convince governments that it is a high priority. To do that they will need solid scientific evidence of the links between the two.

Sian Lewis
Commissioning editor, SciDev.Net