New millennium diseases
A glance at recent news headlines shows our species apparently threatened from every direction by microscopic enemies. In December 2003, the spectre of mad cow disease re-emerged, when the discovery of the disease in American cattle raised fresh fears over human safety. In China, the start of 2004 brought new cases of SARS - the respiratory infection that killed 774 people in various parts of the world during the previous winter. Several people in East Asia have recently died of 'bird flu', a virus that is currently a threat only to those who handle live poultry, but could potentially evolve into something much nastier. And West Nile Virus, a mosquito-borne African disease that was accidentally introduced to the USA in 1999, has now spread across half the country. This, too, is primarily a bird disease, but it can also infect humans: the virus killed 284 Americans in 2002.
However, although the death of a few hundred people is a tragedy for those involved, it is hardly a serious dent in the world's population. Despite the paranoia they can create, in their present forms the diseases mentioned above are never likely cause massive global epidemics, either because they are not terribly contagious, or because they are animal diseases that only occasionally affect humans. The real fear is that these diseases, or others like them, might evolve into something new that can threaten humanity on a large scale. It is certainly possible for animal infections to evolve into human ones - this is how most modern diseases originated. (The ancestry of HIV, for example, can be traced back to a virus found in chimpanzees.)
For up-and-coming new diseases, our species is a very tempting target. Population growth and long-distance travel have turned humanity into a vast herd of six billion individuals, just waiting to be infected. It is said that each of us is connected to every other person on the planet by a chain of no more than seven acquaintances, which has frightening implications for the spread of disease. It remains to be seen whether some deadly new infection will emerge to take advantage of this global opportunity.
It is in Africa that the evolutionary struggle between humans and their diseases has been longest and most vicious. As well as old scourges such as malaria and tuberculosis (which continue to kill millions in the developing world), the continent is home to scary new diseases such as Ebola and its relatives - the dreaded 'haemorrhagic fevers' that liquefy internal organs and cause bleeding from every orifice. Mercifully, these viruses have never spread beyond small, isolated areas (yet). However, there is one new disease that is already causing misery across the continent on an almost incomprehensible scale: HIV. In the time it takes you to read this article, this devastating virus will claim another ten African lives.
Although the possible emergence of new diseases is indeed a threat against which humanity should be vigilant, we should not forget that deadly epidemics are already rampant in many parts of the world. For the millions in Africa who are infected with HIV or malaria, I doubt that mad cows or flu-infected chickens are a major concern.
This article was written in 2004 for Hype, the Edinburgh University Students Association magazine.