Emergent Diseases and Urbanized Environments

Prof. Lea Berrang Ford’s seminar at the Institute for Health and Social Policy looked at the effects of climate change, present and predicted, on human health, in particular on the emergence of infectious diseases. Prof. Berrang Ford began her seminar by discussing McMichael’s four major historical transitions in human population dispersal which led to periods of high rates of emergence of new diseases. I found this to be a particularly interesting way to frame the problem of emergence diseases, because it places them firmly within the context of the environment. Often we only think about infectious diseases after their emergence, when our concerns are regarding cure and slowing of spread within a population. We forget the important relationship these diseases have with the environment, especially in their original emergence. The first of these historical phases was during the advent of local agrarian ecology, which coincided with a settling phase, leading to a concentration of people, their animals and their wastes. The second phase was characterized by an increase in multiregional overland trade and warfare (e.g., interactions between the ancient Greek and Roman empires). The third coincided with European transcontinental travel and colonial exploitation. McMichael hypothesizes that we are now into the fourth phase, which is characterized by air travel. This has changed the dynamics of the spread of disease, from continuous overland spread to “hopping” between cities, which act as “hubs” for further spread. This is due to an increase in human travel, but also in animal travel and “globalization” of food production. The importance of the movement of animals is of particular importance when we consider that more than 50% of emergent infectious diseases are zoonoses (i.e. diseases originating in domestic animals and wildlife).

This year marked a significant global demographic shift: for the first time more people are living in cities than in rural areas. From what we know about the environmental impacts of cities (e.g., they are heat islands, they are large concentrated sources of waste, and they require the burning of large amounts of fossil fuels to bring in sufficient supplies, etc.), this should already signal a necessary shift in how cities are planned and managed. From the perspective of emergent infectious diseases, we should be even more concerned. High density centres, paired with high travel between these centres, sets up super-highways along which diseases can spread. Paradoxically, it seems that now more than ever, when more and more people are living “away from nature,” we need to consider the place of cities within the environment when we are planning them.

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