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October 20, 2005

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Fighting the battle against epidemic disease

There are four conditions that through the ages have always been harbingers of viral or bacterial evolution and their incursion into our lives.
BY TOM KOCH

We are all double agents in the war against epidemic disease. On the one hand, we promote the conditions that assure the evolution and spread of bacteria and viruses that will be deadly to us. On the other, we struggle mightily to control the diseases that result.
At the start of the influenza season, as we totter on the brink of a range of new conditions - Avian flu and SARS are harbingers of that future - it is important to remember where infectious disease originates and what encourages its spread.

Viruses and bacteria have only two goals, fine-tuned by millions of years of evolution: propagation and diffusion.

Nor are we very different. Indeed, the first order of business for every species is to find a niche in a habitat where continuance is assured, permitting the species a future. The second order of business - for us all - is to find new locations where successive generations (diffusion) will flourish.

It is called evolution and our microbial friends are very good at it indeed. They change in response to the world we create and then we wonder how it happened.

My recently published, three-year study of the ecology of epidemic disease Cartographies of Disease: Maps, Mapping and Medicine, finds three, perhaps four conditions that through the ages have always been harbingers of viral or bacterial evolution and their incursion into our lives. These include increasing trade (global and regional), increasing urbanization, increasing income inequality and war.

Travel
Viruses and bacteria are not natural travelers. Most live in narrow niches of specialized habitats within stable environments. Humans are what typically make them mobile. They travel on our persons or with the cargo we ship from one place to another. Where we are not the solitary carriers we enable the disease vectors - rats, insects, ticks - that transmit a disease pathogen from one place to another.

Human agency explains much of the passage of bubonic plague in the Middle Ages and later, of yellow fever in the eighteenth century and cholera in the nineteenth. We spread influenza year after year and it was humans who took poliomyelitis from one country to another in the twentieth century pandemics.

Urbanization
Increasing urbanization means a changed landscape as forest is cleared for settlements and farmland. It has been an engine of viral change since the Chinese domesticated poultry in 1600 B.C. to feed a then-developing urban population, providing the impetus for the virus to evolve in first poultry and then human beings.

It is not simply the city and its density that are culpable. Historically it has always been density combined with income inequalities that assures the evolution of pathogens that find humankind an inviting host. Poverty means crowded, substandard living conditions and a lack of appropriate health care that together assure communities ripe for microbial colonization.

Inequalities
This was the 19th century argument of reformers - Edmund Chadwick, John Snow, etc. - who saw consistently higher rates of disease among the poorest working classes. They saw, too, that diseases spread from pockets of poverty - in the cities and in the mines - to society at large.

Diseases among the poor become diseases, therefore, among the well to do. Viruses and bacteria are thoroughly democratic in this regard.

War
Finally, war is a terrific engine for microbial dispersion. It is not simply the poverty that war causes in the homes and lives of those whose land is embattled, or the displacement and subsequent ghettoization of millions of persons displaced by war. It is also the enormous movements of troops and goods between areas that assure pathways of dispersal for developing diseases.

This was true in the 14th century's Black Death and spectacularly true of the 1918 influenza epidemic. As John Barry makes clear in his recent history of The Great Influenza, the Spanish flu began in the United States and moved with U.S. troops to the European front and from there around the world in troop carriers.

Today
Are these conditions present today? Indeed, they are. Increasing international (and regional) trade has joined in recent decades with increasing urbanization at a time of ever greater social disparity.

A series of small-to-mid-sized wars around the globe has assured large communities of displaced persons and soldiers going to and from the front will serve as incubators for viral and bacterial evolution.

It is therefore no surprise that a host of new diseases has evolved in recent decades. These include, in a partial list, AIDS, Ebola, Legionnaire's disease, Marburg virus, new influenza and tuberculosis strains, and SARS. Others are on their way.

Think of them as nature's response pathogens perfectly suited to the environment we have crafted. Think of them as nature's judgment on the society and culture we have made.

Yes, another pandemic is inevitable. It's nature's way.

Are we prepared? No. We have neither the social policies nor the health infrastructure to assure a robust response to epidemic disease.

In recent years the government has cut hospital service capacity by between 12-18 per cent and reduced emergency response capacity through the closure of some hospital emergency rooms.

At the best of times many B.C. emergency rooms are hard pressed to see those waiting for service on a timely basis or to find beds for those who need them. Multiply the number of persons seeking emergency care by 10-15 per cent -- the epidemic scenario - and disaster will be the result.


Tom Koch has appointments at both Simon Fraser University (gerontology) and the University of British Columbia (medical geography).
















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