Avian Flu

This year at Thanksgiving dinner, there is an added ingredient to the usual turkey entree, the thought of a potential pall of avian flu shrouding the world in years to come. Roasted turkeys don't make you sick; neither do farm-reared ones, for the moment, at least, but recent findings of the bird flu virus in North American fowl makes one sit up and take notice.

The virus itself is not new; it has probably been around for thousands of years. No doubt there have been a number of pandemics from it across the face of the globe through history, but none, as far as we know, that has affected humans or other mammals. The latest mutant strain shows that it's capable of doing just that.

It's hard to accept the popular notion of "intelligent design" unless, perhaps, we apply it to the first virus ever created. Given the power of our present-day understanding of molecular biology, genomes, and medical diagnostics, we are able to see viruses transform from one form to another before our very eyes. If this isn't evolution, in the Darwinian sense, what is?

Similarly, those proto-proteins called prions that cause mad cow disease, scrapie, and wasting disease in a variety of hoofed animals are found in a plethora of forms, some more harmful than others. They are always mutating and remutating, never static, always dynamic.

As we go further we will find more and more examples of such evolution from benign forms of microbes and submicrobes that have been here all along into virulent, lethal ones. The old idea that such agents are species-specific, i.e., are confined to this or that animal population, has been shattered. As they change their forms, they are able to spread from species to species, genus to genus, family to family, as in the H.I.V. virus, presumably starting out in monkeys, or from class to class, as in the avian flu virus.

The old idea that parasites start out as hostile forms, then evolve into nonthreatening, even helpful forms, is no longer the standard paradigm. Modern parasitological studies tell us that a symbiotic form resident in a species and causing no harm to it can mutate into one causing great harm overnight. There is no eternally safe or beneficent symbiont. The E. coli in our guts might aid us in digestion, but let a few get into our bladders and watch out!

It was thought that when a parasite killed a host it meant curtains for the parasite. On the other hand, the parasite that merely used the host, say, the way the Lyme disease spirochete bacterium uses the white-footed mouse to reproduce without harming it, was going to exist for a long time.

Now we know that a parasite can be benign in one animal, disease-causing in another. Malarial plasmodia don't hurt the mosquito that carry them, but they can be fatal to humans bitten by that mosquito.

As long as those parasitic agents that kill their hosts can get to another host before the first one succumbs, they can remain harmful throughout their evolution. Thus, the rabies virus, first discovered by the French microbiologist Louis Pasteur 150 years ago, is no less virulent today than it was then.

As long as the rabid mammal bites another mammal before it dies, the rabies virus will continue to thrive, spread geographically, and pass up through subsequent generations. The mammal that eats the flesh, especially the brains, of the one with a form of Creutzfeldt- Jakob disease, will perpetuate the mad cow prion in its lethal form, on and on and on.

The West Nile encephalitis virus is another case in point. Introduced into New York City mosquitoes in 1999, it spread rapidly from bird to bird, and from bird to human via mosquito bites, then took off across the country carried by bird vectors. Within a few years, every state in the Union had a human case or two of West Nile disease. While the disease is often fatal to the birds that carry it, and, to a lesser degree, to afflicted humans, in most hosts it is benign or merely causes a sickness that the host will recover from.

Diseases such as avian flu carried by birds are particularly scary because birds migrate and some cover thousands of miles in migration. Waterfowl, in particular, are great long-distance fliers. Eurasian ducks and geese often wind up in America, and vice versa. The fact that the avian flu virus has been found in North American waterfowl gives cause for worry. The flu virus can be devastating to birds, and, if it's the right strain, devastating to humans.

Knowing what we know now, and didn't then, the history of some of the great die-offs of bird species in the world might be attributable more to diseases such as bird flu, not as much to humans. Take the passenger pigeon's demise in America at the end of the 19th century. Was it the market gunners and "eggers" that did them in or was it a virus, perhaps an avian flu virus?

The mammalian species at this moment in the New World that is showing the most astronomical population growth is not the garbage rat, the feral cat, the coyote, or gray squirrel, it is the white-tailed deer. Wildlife biologists will tell you that in the absence of predators - the coyote, wolf, mountain lion, bobcat, and so on - the white-tail has the capability of reproducing until it covers every square inch of America the Beautiful.

Ah, but what about disease? It is only within the last several years that we have discovered large numbers of deer being taken by a wasting disease that affects only members of the deer family, that is, deer, elk, and moose. This prion-caused malady has been epidemic to deer in Wisconsin and Michigan, and it may become the very agent that limits deer here, having been discovered in a few upstate deer in 2004.

And what about the American turkey? Sure, it was shot by every Tom, Dick, and Harry indiscriminately for 250 years, but it's hard to imagine how a bird so widely distributed and in such great numbers as that species, when the colonists first settled America, could become reduced to a mere handful of native birds in the mountainous areas of northern Pennsylvania and southern New York by the beginning of the 20th century. Overhunting might not have been the only factor contributing to its near-extinction; disease could have played a role.

In nature and humankind too many of one thing is often a curse, not a blessing. Chickens, turkeys, ducks, and other fowl were not farmed by the millions prior to the Civil War in America, but now they are turned out like automobiles and computers at the end of mass production facilities called "ranches."

The same is true throughout the world. Millions upon millions of poultry have already been put to the sword in order to slow down the spread of avian flu disease among them. The grim reaper in the form of lethal strains of this virus knows no constraint. The big question is, will he stop at birds, or cross over into humans or other mammals? As we speak, he appears to be doing exactly that.