Malaria: biting into the climate change debate

This article was written by a student in the Science Communication program at the University of Western Australia. In the unit, Introduction to Scientific Practices, students learn how to effectively present scientific information for different audiences. As part of the process of learning to distil complex science into simple, engaging formats, structured tutorials are given on how to use The Debunking Handbook. This article was submitted as part of an assignment on writing an engaging article for a non-specialist audience.

With modern drugs, insecticides and the prospects for vaccination, malaria should be a thing of the past. However, our ability to keep malaria at bay is now facing a new challenge - climate change.

Malaria is an infectious disease which results in the infection of red blood cells, and reduces the blood’s oxygen-carrying capacity. The parasite Plasmodium that causes malaria can be divided into four different species. The most common species of malaria is P. vivax, and is found in temperate climate zones, as well as in the tropics. Within the tropic and sub-tropic regions, where malaria is a large problem, P. falciparum is also a very common species of malaria. Female mosquitoes are the transmitters of the malaria parasite, and therefore the infection rate of malaria relies heavily on the survival of female mosquito populations.

Mosquitoes transfer the parasite when consuming blood from another organism. In humans, the malaria parasite only takes 30 minutes to enter the liver once it has entered the bloodstream. From here an infection develops within the red blood cells, which eventually burst and infect other red blood cells. The malaria parasite can also be transferred from humans to mosquitoes.

Predicting the effect of climate change on malaria prevalence is a complex exercise. Several models of global climate change have been used to make predictions based on a variety of possible climate change scenarios. These studies concluded that climate change will have a definite impact on the prevalence of malaria, but will affect different regions to different extents.

A major component of the threat climate has on humanity is that average global temperatures have been rising over the past century, and are predicted to continue rising.

The time in which it takes the parasite to develop whilst in the female mosquito is exponentially related to temperature, meaning that only a slight increase in temperature can result in a several-fold greater increase in the development rate of the parasite. However this rapid increase is only present for a restricted range of temperatures, after which the proportion of surviving parasites rapidly decreases, as the accelerated development of the parasite can no longer outweigh the decreased life expectancy of the mosquito.

For P. vivax, the minimum temperature at which it can develop is between 14.5 and 15°C, and between 16 and 19°C for P. falciparum. At temperatures beyond 32-34°C, the development rates of both P. vivax and P. falciparum begin to decrease.

With increasing environmental temperature, the rate at which mosquitoes can digest human blood also increases. This means that with increasing temperature, mosquitoes will be able to consume more blood, and therefore bite and consequently infect, more humans.

Another scenario which these climate change models predict is an increase in global rainfall levels. Sustained rainfall is a key factor for the survival of mosquito populations. This is because mosquitoes usually breed in freshwater pools or marshes, rather than in flowing water. If rainfall does increase as predicted, we will see an increase in the number of suitable breeding habitats for mosquitoes, which will in turn lead to mosquito populations increasing, and therefore the total population of infected mosquitoes is also set to increase.

The effect climate change has on malaria prevalence is expected to affect different regions of the world in different ways. In the temperate climates of Asia, Northern Europe and North America, the mosquito vector is already present, but it is too cold for the parasite to develop. An increase in temperature in these geographical regions will result in the climate becoming more suitable for parasite development, leading to the possibility of an epidemic.

Highland regions, such as those in Eastern Africa and the Andes region in South America, will also experience an increase in the prevalence of malaria due to this same increase in temperature. However the areas that are most at risk of an outbreak of malaria are those regions bordering areas where malaria is currently prevalent.

The predicted effects of climate change on malaria prevalence could have devastating effects on global health, as well as the economy, as the cost of curing and preventing this often deadly disease is large. In order to prevent the disease from becoming more widespread, action must be taken now, before mosquito populations and malaria infested regions become too large for us to combat.


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Posted by Sarah Finlay-Jones on Tuesday, 23 April, 2013

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