The climate change - malaria link

Madeleine Gordon | Climate Change and Energy Security Fellow

You’ve heard it before—in Australia, we’re spoilt. People don’t usually say this with reference to infectious diseases, but they should. The last case of malaria on the Australian mainland was in 1962. The rest of the world hasn’t been so lucky. Malaria is endemic in over 90 countries. There is no commercially available vaccine although it is possible to inherit or develop immunity through exposure.

There has been some progress. Between 2000 and 2015, malaria deaths worldwide decreased by 48 per cent. Now climate change threatens these advancements. Warming temperatures are shifting the land habitable for mosquitos, protecting some communities while exposing new ones. Climate migration undermines containment efforts. Since mosquitos breed in water, the effect of floods and droughts is also a concern. So, how are these transmission channels likely to impact the spread of malaria in the coming decades?

Let’s firstly look at temperature changes. Each year, Australia watches pods of humpback whales migrate north in search of warmer waters. The propensity for animals to follow a habitable climate is nothing new. The same is true for disease vectors such as mosquitos and bats. As our climate warms, environments previously too cold for these vectors warm, rendering their populations vulnerable to malaria. At the same time, warmer climates become too hot, reducing the spread.

Malaria transmission is possible between 18 and 34 degrees although it peaks between 26 and 29 degrees, as these temperatures are most conducive to mosquito fertility, larvae survival and a longer lifespan.

So, are warming temperatures increasing or decreasing the number of people vulnerable to malaria? There is no scientific consensus. Estimates range from an increase of 731 million people to a decrease of 25 million. This wide range is due to the multiple factors that complicate predictions. Scientists must not only estimate the rate of warming but also that of economic development, medical and technological progress, and population growth and density, all of which influence the spread of the disease.

However, even if shifting climates decrease the number of people exposed to malaria, it’s likely the disease will still become more deadly, as newly exposed communities have no immunity. This means that infection and mortality rates will be higher in these regions than they had been in the areas that become too hot for malaria. Put another way, even if the number of people involved isn’t large, the impact will be.

Secondly, malaria is particularly dangerous in areas with low GDP per capita.We don’t know exactly why but it is likely due to the unavailability of medical resources. Areas most likely to become more susceptible to malaria due to rising temperatures are Zambia and Central India, although concerns are also held for other parts of Central and Southern Africa, Central America, the Madagascar plateaux and the Indian-Nepalese border. These regions all fall within the bottom 55 per cent of GDP per capita rankings. This suggests that their ability to deal with a malaria epidemic is limited.

Climate migrants are another transmission channel of concern. Climate change-induced natural disasters and resource shortages are displacing communities at unprecedented rates. The movement of large populations catalyses the spread of diseases by moving infected people into unaffected areas or by pushing vulnerable people into infected areas. This was demonstrated in Brazil in the 1970s when almost one million people moved into the malaria-prone Amazon area in search of new mining opportunities and farmland. In the following two decades, malaria cases increased sixfold.

Finally, climate change can exacerbate malaria by creating more severe droughts and floods. Droughts worsen malaria by lowering water levels to the point where usually flowing water, such as rivers, become stagnant. Stagnant water creates ideal breeding grounds for mosquitos. Droughts are considered one of the drivers of malaria outbreaks in Sri Lanka between 1900 and 1940.

Ironically, floods can also be damaging. Malaria epidemics usually follow six to eight weeks after severe flooding. Initially, flooding can be beneficial as it flushes out established breeding grounds and creates more running water. However, as the situation settles, the impacted area is left with more stagnant pools of water, causing malaria outbreaks. This was exemplified in Costa Rica in 1991 and the Dominican Republic in 2004. Both severe flooding and droughts are considered conducive to malaria transmission.

A lot is still unknown about the relationship between malaria and climate change. However, three transmission channels; temperature change, climate migrants, and floods and droughts; give reasons for concern. Evidence today tells us that malaria is a dangerous disease. History bears this concern out. Policymakers and health care providers would be well advised to heed on the side of caution and implement the preventative policies necessary to combat climate change and prepare for potential new outbreaks.

Madeleine Gordon is the Climate Change and Energy Security Fellow for Young Australians in International Affairs.