ABSTRACT
The world is fi lled with the enormous potential for disease. Bacteria, protozoa and fungi have colonised the whole planet with amazing diversity and fl exibility. Every human body has (both in and on it) more ‘bugs’ than there are people in the whole world. However, very few of them cause any diseases and many, in fact, do us favours by providing us a type of protective skin care and helping our digestion. Most of our bacteria live in true symbiosis with us, whereas viruses are parasites and need to penetrate a living cell to survive and reproduce. One way to characterise viruses is to call them a piece of genetic material protected by a protein coat. Sir Peter Medawar described this as: ‘a piece of bad news wrapped up in protein’. However, many common infections (such as pneumonia or meningitis) can be caused by both bacteria and viruses and, therefore, people do not always pay full attention to the fundamentally different nature of the two. The essence of viruses is to invade living cells and try to turn them into factories for virus production. To succeed they need to circumvent the defences of the body. The disease is just a side-effect of successful virus production that often leads to a weakening or destruction of cells and whole organs. 1
In other words the human body is battleground, where the viruses are constantly attacking the immune system and where the immune system wins most of the time. The viruses do not have a brain or any grand strategy. Instead, they just co-evolve with their hosts. Some viruses have been around for a very long time: herpes viruses are the most widespread in nature and even primitive invertebrates like oysters have their own. Analysing the human herpes viruses allows us to compare how much or little we have changed since we left our African ape brothers to continue their own voyage. 2 Mammals have immune systems that have been shaped and passed on by the victors of evolutionary battles. However, viruses have a major advantage over their hosts as they can easily produce thousands of offspring every day and therefore can mutate more quickly. The adaption to viruses can often seem more like a simple case of mathematics. The Brazilian rabbits have the myxomatosis virus that does not cause them any harm, but which wiped out almost all European rabbits. In 1950 it was deliberately introduced into Australian rabbits (of European origin) to protect the local wildlife. In the fi rst
year it killed 99.8 percent of infected rabbits, but after three years rabbit numbers started to grow as the small number of virus-resistant rabbits multiplied freely and without competition. Now the Australian rabbit numbers are back to where they were in 1950 and the rabbits are now resistant to the Brazilian myxomatosis virus while the virus has also become less fatal. Part of the math is that the generation time of a rabbit is as low as six months.
