Human Ecology & Human Behavior: Climate change & health in perspective
by Prof. Paul Reiter
Human ecology and human behavior are the two key factors that determine the transmission of human infectious diseases. When the cycle of transmission includes mosquitoes, ticks, rodents or other intermediaries, their ecology and behavior are also critical. When multiple species are involved, the levels of complexity are even greater. Lastly, the virulence of the pathogen, the susceptibility of its vectors and hosts, the immunity of those hosts and the collective immunity of the host populations all contribute to the force of transmission. The significance of climate factors can only be assessed in the perspective of this daunting complexity.
Enteric infections: In the developing world, scarcity of basic needs such as shelter, food, clothing, electricity, clean water, education, and healthcare is the dominant factor in disease transmission. In wealthier countries, new and challenging problems have arisen as a result of economic success. Straightforward strategies are available to prevent infections in all these scenarios, given suitable economic resources. In nearly all cases, climate is at most a minor, often irrelevant parameter.
Mosquito-borne diseases: Mosquitoes are found throughout the world in all climates. Meteorological variables are of limited value as a guide to the population densities, behavior and geographic range of vector species. The same is true for the pathogens they transmit. Future changes in climate may result in minor changes in prevalence and incidence of mosquito-borne diseases, but the critical factors will remain human ecology and human behavior.
Tick-borne diseases: As with mosquito-borne diseases, the prevalence and incidence of tick-borne infections is affected by an incredible range of parameters. In northern temperate regions, for example, Tick-borne Encephalitis is influenced by agricultural practices, land-cover, populations of small mammals and their predators, small mammal immunology, population and behavior of large mammals, hunting, wild-life conservation, industrial activity, income levels, leisure activities, depth of winter snow, the micro timing of springtime temperatures, and summer rainfall and humidity. Moreover, the interaction of these variables is distributed over a two to three-year period. In the context of this complexity, it is ludicrous to claim a direct cause and effect relation between climate and infection.
In conclusion, it cannot be over-stressed that the ecology and natural history of disease transmission, particularly transmission by arthropods, involves the interplay of a daunting multitude of interacting factors that defy simplistic analysis. The rapid increase in the incidence of many diseases worldwide is a major cause for concern, but the principal determinants are politics, economics, human ecology and human behavior. A creative and organized application of resources to reverse this increase is urgently required, irrespective of any changes of climate.
Paul Reiter is a British scientist whose entire career has been devoted to the biology, ecology and behaviour of mosquitoes, the transmission dynamics and epidemiology of the diseases they transmit, and methods for their control. He worked for 22 years as a researcher in the Division of Vector-borne Infectious Diseases of the US Centers for Disease Control and Prevention (CDC). In 2003 he was appointed Professor at the Institut Pasteur, Paris, where he established a new unit of Insects and Infectious Disease.
He has led the entomological component of numerous field investigations of outbreaks of vector-borne disease on behalf of the US Government, the World Health Organization (WHO), and the Pan American Health Organization. He is a member of the WHO Expert Advisory Committee on Vector Biology and Control, and has served as a consultant to governments worldwide.
He has been actively involved in the international debate on climate change for more than a decade. He served as a lead author for the US National Assessment of Potential Consequences of Climate Variability and Change, and an Expert Reviewer for the Intergovernmental Panel on Climate Change Fourth Assessment Report. He is a frequent commentator in the news media on this and other issues that concern vector-borne disease.
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