Severe Acute Respiratory Syndrome: the world can expect more of the same

The world has recently been convulsed by the threat of a "new" virus, which has evoked widespread scenes of panic, fear and hysteria. There is now talk of the new killer on the loose, Severe Acute Respiratory Syndrome (SARS) virus, one that threatens world health.

Travel has been restricted, quarantines erected and there have been scenes of unbridled fear as people rush for face masks, antibiotics and avoid people thought to be at risk. It is amazing how little part our historical memory plays when we are confronted by an epidemic crisis.

SARS is not the first "killer" virus to confront us over the past 30 or so years, and it won't be the last. It is not that long since the Asian flu pandemic of 1958-59 or the Hong Kong flu of 1968-69. The former probably killed at least a million people worldwide.

More to the point, the past few decades have seen many examples of emerging or re-emerging infectious diseases. SARS is but one in a long line of infections that include, Lassa fever, Ebola, Lyme disease, HIV/AIDS, Hantavirus pulmonary syndrome and Dengue hemorrhagic fever.

Interestingly, many of these so-called "new" infections are not really new but have probably been around for a very long time, often nurtured among animal species, but then somehow afforded an advantageous "leg up" by virtue of some human intervention and/or changed environmental circumstances.

This is what probably happened in the case of SARS. South China has served as an "incubation chamber" for a number of respiratory diseases, probably for centuries. Many of these infections have circulated naturally among a variety of water-bird and animal species. Only occasionally have they made the leap to affect human populations.

In the case of SARS, the common agricultural process of mixed pig-duck-chicken farming and the presence of other livestock in southern China have probably encouraged the exchange of genetic material between viruses and the emergence of a new "lethal" strain.

There would seem little doubt that human behaviour and demographics, environmental modification, global travel, the complacency (and in some cases breakdown) of public health systems, allied to a general disinterest in the role that the biophysical environment might play on our lives, has encouraged the emergence of a wide range of infections.

Not only have we over-used antibiotics and thus produced a large number of antibiotic-resistant diseases but our quest to eradicate or control infectious disease agents is probably utopian. They have never been a stationary target and, like all life forms, have been selected for survival. We have consistently underestimated the complexity of our environment and the capacity of species to adapt and evolve.

Human modification of the environment adds another factor. New agricultural practices, roads, mining ventures, forestry, and urbanisation have all brought human populations into contact with a variety of infectious diseases normally restricted to wildlife.

This has often resulted in the disruption of natural disease ecosystems with the result that often benign zoonotic infections have been transformed into more virulent human diseases. This is what probably happened in the case of Ebola and HIV/AIDS.

Global travel has added another dimension. Millions of people regularly cross international borders every year with a speed unknown in earlier years. This and the increasing desire to visit "exotic" remote locations, in essence means that a person could be in central Africa one day and walking around the streets of Sydney 24 hours later, possibly incubating a new infection. The implications of this for the control of infectious disease in an ever-more interconnected world are profound.

There are many other factors which have encouraged the emergence of infectious disease including the ageing of the world's population and increasing susceptibility to infection because of impaired immune systems, increasing rural-urban migration in the developing world which serves to redistribute "new" rural infections in urban areas and the general complacency of public health systems which see their mission largely in terms of catering for degenerative lifestyle and behavioural diseases, like cancer, stroke and heart disease.

The upshot of all of this is that the SARS experience is not new and that the world should realise that there may well be more such epidemic events over the next decade.