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Mark Walters

The new diseases of our own making

From swine flu to mad cow to HIV-AIDS, the Age of Ecodemics has arrived. Now our attention is focused on swine flu as we count the number of confirmed cases and deaths, close and then reopen schools and cancel then reschedule sporting events. But we should remember how we are creating many of these diseases in the first place.

You can't get swine flu from eating pork, but you can get it from live pigs. When pigs get the flu — and they often do — they cough and sneeze. Nearly half of commercially raised swine in the United States have at some point been infected with some kind of flu. Up to one-quarter of pig farmers and about 10 percent of veterinarians may have been exposed to one type or another, according to the Centers for Disease Control and Prevention. Human cases are almost always mild, and it's extremely rare for swine flu to spread from one person to the next. The current outbreak is one such rare strain.

Swine flu is one of several notable human diseases arising of late from agriculture or food production. Mad cow was born when farmers fed rendered parts of sheep infected with scrapie to their cows in an effort to turn every scrap of meat, sinew and bone into profit. HIV probably jumped to humans through the African bush meat trade in which infected chimpanzees or mangabeys with a similar virus were slaughtered and sold in large markets where contaminated blood or bodily fluids infected hunters, butchers, market workers or buyers. Some drug-resistant strains of salmonella have been traced to agriculture in which antibiotics were regularly used to make animals grow faster instead of to treat them for illness. Bird flu jumped from wild aquatic birds to domesticated poultry and then to people. The list goes on.

It is not surprising that livestock agriculture has given rise to so many human diseases new and old. One of the first great waves of human epidemics may have occurred during the Neolithic Revolution millennia ago, when humans began domesticating animals. Smallpox came from cattle and the common cold apparently from horses. Now, through modern livestock agriculture, along with ecological disruptions such as global climate change, humans are creating a new wave of epidemics or spreading old diseases into new areas. Increased global trade and travel have accelerated the spread.

These new diseases include viruses (novel influenzas, HIV), bacteria (drug-resistant food poisoning and Lyme disease) as well as rare prion diseases (mad cow), to name a few. Influenza is of paramount concern because agricultural practices permit a regular influx of genes from their natural home in wild aquatic birds into human- and swine-flu strains. These genetic exchanges are games of chance whose gravity can range from Friday night poker to the Russian roulette of a severe pandemic.

So many diseases are coming at us that new ones seem to become old almost overnight. SARS (unrelated to influenza) emerged in southern China in late 2002. Bird flu, which has been all but forgotten, claimed its first human victim the following year. So far in 2009, 26 people have caught it from poultry. Seven have died. Fortunately, bird flu does not spread person to person.

Each of the two novel influenzas around now separately carries a key trait of a severe pandemic. Swine flu is contagious but mild (so far), while bird flu is lethal but unable to spread (so far). That doesn't mean the two will ever meet — or, even if they did, fiendishly combine into a dangerous pandemic. But two new types circulating at once reminds us that, far from closing the book on infectious disease, as the surgeon general in the late 1960s suggested we would do, we are quickly adding new chapters.

From novel influenzas to mad cow to HIV-AIDS, the Age of Ecodemics has arrived. As our attention now understandably turns to creating a swine flu vaccine if one is needed, we would do well to consider how we are creating many of these diseases in the first place and begin to find ways to mitigate their emergence.

Whatever the future of swine flu — and there are indications it is not as severe as first feared — it is still a warning. And it will not be our last.

Mark Walters is a veterinarian, the author of Six Modern Plagues and How We Are Causing Them, and a professor at the University of South Florida St. Petersburg.

The new diseases of our own making 05/06/09 [Last modified: Thursday, May 7, 2009 6:58pm]

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