ZKEA

Emerging Diseases : Biological Terrorism : Biological Warfare

Historical Background

In ecological terms, mankind is a herd animal. Like many species of fish, mammals and birds, we are highly social and tend to congregate into large units. Such congregations provide ideal environments for the spread of herd diseases, that is, microorganisms which rely on such high-density populations in order to spread. These pathogens rely on the mathematical fact that, once they've infected one organism, there will be a sufficient set of others nearby to infect as well. In this fashion the pathogen can spread and not die out with its host. From the viewpoint of the virus or bacteria, it's a statistical issue. Such situations can be very precisely modeled. For example, computer simulations indicate that measles requires a population of at least 10,000 people living within a few square miles, in order to be viable. A population less than that would be insufficient, resulting in the eventual extinction of the virus.

Therefore, before the dawn of civilization humans suffered relatively little from epidemic disease. Since our population was low and dispersed, there was insufficient environmental kindling in which to start the fires of an epidemic. Further, given Homo sapiens was a relatively rare animal, few pathogens had yet bothered to adapt themselves to our species. So not only did our lack of population prevent large-scale infectious disease, but there were few candidate pathogens that could even make the attempt. From the standpoint of epidemic disease, we simply weren't worth it yet.

This is not to say that prehistoric man had an easy life, or was never exposed to illness. Certainly insect-born diseases often afflicted some individuals. And it was always possible to get a one-off infection from an animal source. For example, rabies contracted via animal bite has certainly been with humanity from the beginning, given that rabies is a very ancient virus linked to a variety of mammals. But the specific herd diseases, those that relied on the proximity of larger populations, did not yet exist for mankind. Thus virtually all the diseases we take as given, ranging from the common cold to measles to smallpox did not exist until fairly recent times.

Given these diseases did not exist until recently, what is their origin? Most of these pathogens already existed in some form in other species. As mankind progressively urbanized in close proximity to other domesticated herd creatures (such as pigs, horses, cattle, fowl etc) the pathogens in these animals eventually adapted and made the leap to our own species. Thus, most of our illnesses can be traced to similar (or identical) illnesses in our domesticated animals. These diseases are called zoonotic. Measles, for example, originated from pigs. Influenza, from fowl. As these pathogens grew better adapted to Homo sapiens, they eventually gained the ability to be transmitted directly from one human to another. In this fashion, herd diseases jumped from other herd animals to mankind.

The mechanism for this jump is evolution. Evolution is the core unifying principle of modern biology, explaining all facets of organism structure and behavior. Very simply put, what happens in the case of a new human viral disease is this: a virus, happily living in its usual host, suffers a mutation. (I say "suffer" since mutations are almost invariably detrimental to the organism. Given the random nature of mutations, it's likely that any change will cause more damage to the organism than improvement). But in this case the mutation is beneficial - it allows the virus to infect a Homo sapien. Normally such a mutation would not be selected for, given the chance of a Homo sapien being around in the lifetime of the mutated virus is vanishing small. But given enough viruses, and enough mutations, and given enough Homo sapiens in close proximity, eventually the inevitable happens. A single virus makes the jump. Finding the new home to its liking, it quickly spreads. Eventually the virus may evolve further improvements to its new home, becoming a disease quite specific to our species. In this fashion mankind has slowly gathered an increasing burden of infectious diseases.

The origin of some pathogens is obscure, even though we understand the general mechanism. Smallpox is a good example. The world is filled with a swarm of pox species. There are camel poxes, there are monkey poxes and mouse poxes, and a multitude of insect poxes. Poxes are very effective in keeping a species population under control and are found everywhere. But for most of its existence humanity did not have a pox to call its own.

This happy state of affairs continued until the first urban centers were created. The evidence is inconclusive, but it's believed that smallpox might have first jumped to our species sometime in the Old Egyptian period. Mummies have been found with smallpox scars, and certainly after the Old Egyptian period smallpox was already an ancient disease. Presumably a very unfortunate Egyptian peasant had a close encounter with an animal diseased with a pox, one which through mutation was sufficiently capable of jumping to the human. What was the animal? No one knows, although it is interesting to note that recent sequencing data indicates camelpox is an extremely close relative. Whatever the ancestral virus, smallpox has evolved since then and become highly tuned to our species. In fact, smallpox can only infect Homo sapiens and would itself become extinct upon our demise as a species.

In addition to just pure population growth, a prime engine for the increase of human pathogens was ecological disruption. As environments was shifted or changed by human activity, new ecological opportunities arose for pathogenic exploitation. For example, the destruction of Central Asian grasslands facilitated the spread of the bubonic plague, while the conversion of North African marshlands to irrigated zones created the ecology for blood diseases and river blindness. Through the dynamic of increasing population, urbanization and environmental change, humanity slowly accumulated its share of diseases.

These diseases played a critical role in our population history and migrations. In fact, no other element has so determined human destiny as that of epidemic disease.

Epidemic disease repeatedly ravaged ancient Chinese populations, leading to mass migrations, famine and the collapse of dynasties. Epidemics played a key role in Roman history, cutting down populations and leading to political turmoil. In fact, much of the decline of the Roman Empire was due to the role of increasing epidemics and their fatal effect on the Roman population structure. Similarly, the Black Death had an epic effect on European society, wiping out over a third of the population and leading to widespread economic and political fallout that echoed for centuries thereafter.

As mankind spread around the globe, pathogens that had been localized to one area became worldwide - often with apocalyptic results. For example, it's generally believed that syphilis originated in the New World. Unknown to Europe, it suddenly appeared upon return of Columbus' expeditions, with horrific results. Millions perished and many more millions suffered debilitating effects and shortened life spans. The social and cultural dislocations resulting from these sexually-transmitted diseases continues to this day. But then the Old World more than returned the favor, introducing a number of novel pathogens to Native American populations, including malaria, smallpox and measles. These diseases ravaged the New World, killing up to 90% of the population and completely annihilating entire cultures.

It is indeed a historic pattern than novel diseases - no matter what their origin - usually had dramatic and often fatal consequences to the culture to which they were introduced. With little in the way of natural immunity or traditions to protect them, societies that suffered new diseases have often been fatally battered by such epidemics.

Even so, the human population continued to slowly rise. This growth was driven by slowly-improving technology plus the opening up of new habitats. The growth was fitful - there were centuries where populations crashed quite spectacularly - but on average mankind's numbers increased. And then, a few centuries ago, an exponential growth phase was reached, the so-called "population explosion". The explosive metaphor is apt. For plotted on a chart, this growth is absolutely stunning and unique. It is also non-maintainable.

Driven by a historic upsurge in technology, improved food sources and a basic scientific understanding on how to deal with disease, human populations swelled. From just 1 billion in 1800, populations grew to 2 billion in 1940, to 3 billion by 1970, to 6 billion by 2000. Much of this growth was in ecological areas ill-suited for maintaining large populations. And throughout the world the environmental degradation increased at a similar exponential rate. Forests vanished, deserts spread, agricultural land grew increasingly impoverished and fisheries collapsed. Mankind kept ahead of this negative curve through increasing inputs of technology and capital. Like the tuna fish - which is warm blooded so that it can swim faster, and swims faster so that it get enough oxygen to keep it warm blooded - Homo sapiens found itself on a technological treadmill, just one step ahead of contracting environmental constraints.

Even so, among most people there was, and is, great confidence. After all, we've come this far, haven't we? Hasn't technology always saved us? Isn't the direction of the future ever-upward? Such people are not aware of history. Nor are they aware of how deeply embedded and dependent mankind is on the environment. Already the warning signs are apparent. As in the past, ecological dislocation and population growth are the two great engines of epidemic illness. Thus as mankind's herd increases and as the environment deteriorates, pathogens increase in novelty and virulence. Already, public health is going backwards for large proportions of the world's population, as infectious diseases reassert their historic dominance. Already, new epidemics, such as AIDS, are making their mark on our ever-upward future. Already, old diseases thought defeated, such as smallpox, are casting dark shadows on daily headlines.

And then, for the ultimate irony, man's technology itself is being turned against him in the form of genetically engineered pathogens specifically designed to cause his extinction. One way or another, new and extraordinarily lethal plagues are heading in mankind's direction. This is what history teaches.

This new century will be indeed by pivotal and historic for humanity. But not in the way most people envision.