By Afira Zulkifli – Code Green Subcommittee
Human health and climate change is not a common association to the average person. Rising temperatures and recycling might come to mind… but health?
However, the most immediate and directly detrimental effect of climate change is in fact its impact on human health. Increasing temperatures are a large component of climate change, and while this it in itself is concerning, what is more troubling are the environmental consequences of this increase. To give just one example, climate change may create a more suitable environment for certain pathogens.
Malaria is an infectious disease that causes fevers and headaches in its victims, in which severe cases can even cause death. It is caused by Plasmodium parasites. The most common species of this parasite are P. vivax and P. falciparum, with the latter being the most deadly. They are usually found in temperate climate zones, such as in the tropic and sub-tropic regions.
A female mosquito infected with the malaria parasite becomes its transmitter. When the mosquito consumes blood from another organism, the parasite is introduced into that organism’s bloodstream through the mosquito’s saliva. It only takes the parasite 30 minutes to get to the human liver, at which point an infection begins to develop in the red blood cells and spreads throughout the body. Thus, the population of mosquitoes directly influences the rate of malaria infections.
Climate conditions including rainfall patterns and temperature affect the amount and the survival of mosquitoes. Sustained rainfall is a key factor to the survival of mosquito populations, as they usually breed in freshwater pools or marshes instead of in flowing water. Hence, the peak of transmission often occurs during and just after the rain seasons. If global rainfall levels increase as predicted by climate change models, then the number of suitable breeding habitats for the mosquitoes will increase, thus increasing their population and the number of infected mosquitoes.
The time taken for the parasite to develop inside the mosquito is exponentially related to temperature, meaning that even a slight rise in temperature can greatly speed the parasite’s development rate. However, this rate plateaus and begins to decrease at temperatures beyond 32-34°C.
Higher temperatures also increase the rate at which mosquitoes can digest human blood. This results in the mosquitoes having a greater capacity to consume blood, consequently increasing the number of humans they bite and infect.
A recent study found that with an approximately 3°C increase in temperature, the estimated total population at risk of contracting malaria in 2050 is 3.2 billion – almost half of the global population. Furthermore, some areas in South America, Sub-Saharan Africa and China would be exposed to a 50 per cent higher malaria transmission probability rate.
The impact of climate change on the prevalence of malaria is not geographically even. It is expected that Africa will be affected most severely, with areas bordering those where malaria is currently prevalent being at most risk of outbreaks of malaria. Mosquitoes are already present in Northern Europe and North America, but the temperature is currently too low for the parasite to develop. However, with an increase in temperature, the climate conditions may become more suitable for parasite development and induce epidemics.
Australia’s northern neighbours Papua New Guinea and Indonesia both have malaria, and under the threat of climate change, it is even possible for an epidemic to develop in Australia. Though outbreaks of malaria are rare, it has occurred before in Far North Queensland in 2002.
It is possible for populations to develop a partial immunity to malaria over years of exposure, which can reduce the risk of the disease becoming severe. This is why most malaria deaths in Africa occur in young children. However, with outbreaks spreading to areas in which there is rarely malaria, the populations in those areas often have little or no immunity. This puts them at risk of not only higher infection rates of malaria, but also a high death count resulting from malaria.
Nevertheless, malaria is far from an invincible disease and it is both preventable and curable. The impact of malaria transmission can be minimised somewhat if protection measures, such as mosquito nets and insecticide, are taken up. However, this also largely depends on the resources at the disposal of the population. For example, Singapore and Burma are both tropical countries within the malaria belt, but urbanised Singapore has largely reduced the number of malaria infections within their population, whereas the disease is still common in Burma, a developing nation.
Malaria is just one factor in the long list of the likely impacts of climate change on human health. Others include increases in respiratory and diarrheal infections and mental health trauma resulting from displacement due to resource competition or extreme weather events. We need to realise we have the ability to prevent these looming disasters. Taking them seriously is the first step.
References
Béguin, A, Hales, S, Rocklöv, J, Åström, C, Louis, VR & Sauerborn, R 2011, ‘The opposing effects of climate change and socio-economic development on the global distribution of malaria’, Global Environmental Change, vol. 21, no. 4, pp. 1209–1214.
Githeko, AK 2009, Malaria and Climate Change, Commonwealth Health Ministers’ Update, Available from: http://www.thecommonwealth.org/files/190385/FileName/Githeko_2009.pdf
Hanna, JN, Ritchie SA, Brookes, DL, Montgomery BL, Eisen DP & Cooper, RD 2004, ‘An outbreak of Plasmodium vivax malaria in Far North Queensland, 2002’, The Medical Journal of Australia, vol. 180, no. 1, pp. 24-28.
The World Bank 2012, Turn Down the Heat: Why a 4C Warmer World Must Be Avoided, The World Bank, Available from: http://climatechange.worldbank.org
World Health Organisation 2013, Malaria Fact Sheet. Available from: http://www.who.int/mediacentre/factsheets/fs094/en/index.html
Image: ‘Progress against Malaria’ by Gates Foundation available at http://www.flickr.com/photos/gatesfoundation/5451415346/ under a Creative Commons Attribution 2.0. Full terms at http://creativecommons.org/licenses/by-nc-sa/2.0/