Vector-borne diseases: what will be the impact of climate and other environmental changes?

9 Mar 2010

Paul Chinnock

Source: Journal of Experimental Biology (see original article or PDF)

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Citation: Tabachnick WJ (2010). Challenges in predicting climate and environmental effects on vector-borne disease episystems in a changing world. J Exp Biol; 213(Pt 6):946-954.

2010 The Company of Biologists

Aedes albopictus feeding on human blood. This mosquito has been shown to be able to transmit West Nile Virus, a vector-borne disease that has caused outbreaks in several parts of the world.

It has been estimated that vector-borne diseases account for 17% of the global disease burden due to all parasitic and infectious diseases. Every year, for example, there are around 300 million cases of malaria, 50–100 million dengue cases and 120 million filariasis cases. Vector-borne infections of livestock also have an indirect but significant impact on human health. As the author of a new review article points out, “Vector-borne diseases will continue to evolve in a changing world as they have done throughout history”, but what impact is climate change having on this evolutionary process?

Professor Walter Tabachnick is Director of the Florida Medical Entomology Laboratory, USA. He believes that climate is a major environmental driver influencing vector-borne disease epidemiology but he considers it important also to explore alternative explanations for changes in vector-borne disease epidemiology. For example, whilst climate change has been linked by some researchers to the changes observed in the epidemiology of malaria and dengue, others experts, who emphasize the complexity of vector-borne disease cycles, have proposed alternative explanations.

Tabachnick says there is a need for greater understanding of the ecology of vector-borne diseases in order to understand and predict the effects of changes in the environment. He makes use of the “episystem” concept. An episystem, he says, “encompasses all of the biological and environmental components and aspects of the entire epidemiological vector-borne disease system within specified geographical and/or temporal scales”. He states the aims of his review as being to:

"describe the complexity of vector-borne diseases
explore the influence of climate on these systems
explore our capability to assess the potential impact of changes in climate on these systems
set the issue of climate in the broader context of environmental change in general
outline the kinds of information that will be necessary for accurately predicting future climatic or environmental effects on vector-borne disease systems".

In order to do so he focuses on two new vector-borne disease episystems – blue tongue virus (an animal infection) in Europe and West Nile virus in North America.

Tabachnick’s conclusion is that there is still much that is not yet understood about the genetic systems controlling vector competence, the environmental factors influencing genotypes and as to how environmental factors interact with one another within any vector-borne disease episystem. As a result, scientists have little ability to predict the future behaviour of episystems under changing environmental conditions. In his view, “The consequences of climate change are not predictable with assurance, only that there will be likely changes”. Other environmental changes will also have an impact.

Nevertheless, despite our current lack of understanding, Tabachnick argues that there is much that can be done now to reduce the impact of vector-borne diseases. Priorities that he identifies include improved disease surveillance, better health care in developing countries, and the elimination of poverty in these countries.