As swine flu spreads globally, it's important to understand the short- and long-term causes and consequences.

Experts have been warning of a worldwide outbreak of a horrific influenza ever since 1997, when the first human cases of so-called H5N1 avian influenza were reported in Hong Kong. Two years ago the news was filled with a similar threat -- bird flu.

"We got lucky that time. That threat didn't ripen into a pandemic. But now we are watching and waiting to see what happens with another type of influenza -- swine flu," said Mark Jerome Walters, D.V.M., Associate Professor, University of South Florida St. Petersburg. Dr. Walters is a veterinarian and the author of "Six Modern Plagues and How We Are Causing Them" (Island Press, 2004).


"A spate of ominous mounting human cases has suddenly cast the threat of a pandemic into the headlines once again. If a severe pandemic does occur, nobody knows how many people will get sick or how many will die. The death toll could be in the millions," he cautioned.

Dr. Walters explained that nearly all infectious diseases are the result of the intersection of people and animals, with people disrupting natural processes and bringing on the trouble. He described the genesis of swine flu: "You have three different pools or families of influenza zooming around the globe," Dr. Walters told DOTmed News. "You have the birds migrating... carrying the virus from one pig farm to another. Then you have two billion people a year who fly. People migrate in their own way and so you now have these different pools colliding."

While people can contract a virus directly from livestock or birds, that is a contained or "dead end" jump because the virus spreads no further. This is what happened with the bird flu. The problem with today's swine flu is that it spreads directly from human to human.

"There have been a tremendous number of mild cases and one death in the U.S. and many more in Mexico but you cannot come up with a fatality rate. There are just not the numbers to do that. It may be extremely low. And it may stay that way. It may decrease or it could increase [in fatality]."

The time of year may come to our rescue here, at least for now. "It could be that -- because we are getting out of flu season--maybe this will just putter along until the next flu season when it will break out with a vengeance."

Because flu is transmitted from respiratory coughing and sneezing, it's associated with winter climates when people crowd together in confined places, increasing the likelihood of spreading.

"That doesn't mean that pandemic flus cannot spread outside of flu season. They can," Dr. Walters said.

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