Will climate change promote the spread of malaria?
By transmitting a wide variety of diseases, including malaria, yellow fever, dengue fever and various forms of encephalitis, mosquitoes may have been responsible for more human deaths than any other single organism.
Mosquitoes have evolved to fill a particular environmental niche and form part of a complex web of interactions with other organisms – an ecosystem. What’s more, the mosquito has several distinct stages in its life cycle – egg, larva, pupa and adult – each of which has its own environmental niche.
Several climate factors could affect these stages, such as:
- timing of seasons.
Yet the climate-related causes of mosquito-borne illnesses, such as increased temperature and increased rainfall, are so complex and so interrelated with other factors that scientists find it very challenging to pinpoint their precise effects.
The World Health Organization estimates that malaria kills over 600,000 people a year. It exists only where particular species of mosquito live, so if climate change alters the distribution of mosquitoes, malaria will move too.
Changing land use and human activities such as insecticide spraying and bednet use will also have an impact.
Up in the highlands
One controversy has centred on the possible role of climate change in the recent resurgence of malaria in the highlands of Kenya. Although initial studies found little evidence of a local rise in temperatures, a reanalysis including more recent data found a clear increase. Moreover, a model of mosquito biology in the area suggested that every 1°C increase in temperature led to at least a ten-fold increase in mosquito numbers.
Such findings emphasise that even small changes in climate variables, such as temperature, can be amplified by biological processes into far larger impacts.
Some areas may be lucky and become unsuitable habitats for mosquitoes. Recent reports suggest it is more likely that cases of malaria will shift geographically rather than increase overall.Lead image:
AusAID, Department of Foreign Affairs and Trade/Flickr CC BY