ZKEA

Biological Warfare : Biological Terrorism : Emerging Diseases

Environmental Impacts

The threat of catastrophic diseases is fundamentally intertwined with our impact on the environment. Disease and environment cannot be decoupled, for the problem of infectious disease is a systemic one. All pathogenic microorganisms arise, mutate and spread within an ecological context. As environments change and degrade due to human influence, new diseases arise and old diseases increase in lethality. This problem is further exaggerated by mankind's increase in population, mobility, and by the degradation of the urban environment, all of which are further engines for viral exploitation. Already, as we read in the newspapers every day, new diseases are attacking the world. So far none of these have been 100% fatal for Homo sapiens, but in statistical terms, such an outcome is inevitable. The genetic roulette wheel is remorseless.

Let's look at a few ongoing examples. Many diseases rely on insects as vectors in their life cycle. As insect ranges alter - due to global warming or habitat alteration, for instance - the range of disease can alter as well. We see this dynamic with certain species of mosquitoes. Over the past few decades the range of virus-carrying mosquitoes has expanded all over the world. Thus people in temperate climates are beginning to see a range of diseases that were historically confined to tropical climates. Malaria has spread to new regions of the globe, while also increasing its virulence and resistance to treatment. Likewise, dengue fever has reached Texas via Mexico (after spreading from its ancestral home in Southeast Asia). Dengue fever is at best a miserable experience, and is increasingly a fatal one as well.

Another example is lyme disease, spread by a species of deer tick which harbors the bacterium Borrelia burgdorferi. Deer populations have soared in the United States due to the elimination of their natural predators. This has led to an explosion in the number of ticks, which in turn has led to an explosion of Lyme cases. Lyme often leads to permanent neurological damage and disability.

The deadly disease AIDS also came about due to ecological disruption. The original ancestral HIV, known as SIV, inhabits certain African primates. In them the virus is apparently benign. Local human populations had no problems with this virus. But then massive deforestation and mankind's increasing numbers put him into increased contact with these primates. There was a mutation and a virus jumped from primate to man. HIV - and AIDS - was born.

Such mutations happen all the time; they are one of the prime engines of evolutionary biology and are usually inconspicuous against the broader fabric of life. Most such mutations are negative. They either grant no advantage or are actually detrimental to the organism. Such mutations are therefore not selected for and never gain a foothold in a populaton. Such was not the case with HIV. Facilitated by widespread poverty and lack of healthy services in Africa, plus increasing population and mobility, the new virus established itself deeply in the population. And then in a few decades, made its transition into the world population, with devastating results.

Another case is that of the West Nile virus. The recent introduction of the this virus into the United States could be catastrophic for parts of the environment. Endemic to parts of Africa it had never established itself in the temperate world. But, with climates warming and mosquitoes spreading, West Nile suddenly found a home in the United States. Finding virgin territory and biologically naive populations, it continues to spread unchecked. While rarely killing people, it is a broad-based and fearsome virus for many other creatures; it infects hundreds of different species and kills many of them extremely quickly. "I've never seen anything like it," says one biologist. "Crows, eagles, birds of all sorts are susceptible to it. It seems to be extremely deadly - crows are literally dying while in flight." West Nile looks set to destroy a large part of the ecosystem of North America.

Of course, people aren't crows. Although crows in North America may be in for a rough time, West Nile is rarely fatal to human beings. But will we be so lucky next time?

Other disease outbreaks are the direct result of overpopulation, lack of sanitation and the pollution of agricultural lands. A case in point here is hepatitis. The hepatitis virus comes in a variety of types. All these types infect the liver, and some types are particularly virulent and lethal. Fortunately, hepatitis is not very infectious under normal conditions. Unfortunately, conditions are increasingly abnormal. In particular, sewage contamination of crops can easily spread the virus into agricultural produce. In fact, it is just such contamination that has been responsible for a series of hepatitis outbreaks in Russia and the United States. As cities increasingly encroach upon agricultural lands, such outbreaks grow more likely.

And the examples continue: spreading water-borne diseases in China, new forms of cholera in South America, mysterious and deadly ebola outbreaks in Africa. The pace continues to quicken, as a world out of ecological balance spins off new viruses and new epidemics.

Unfortunately, environmental issues are often politicized around the world, especially in the United States. "Environmentalism", to some people, means preferring trees and animals over human beings. But, as we can see, Homo sapiens is deeply reliant on this planet, whether we acknowledge it or not. Environmental trends have a deep and direct impact on our species as well.