Posted: May 31st, 2009 - 10:02am
Source: Link

To most of us, animals are harmless companions. But what happens when a disease jumps across species from animals to humans?
This process – known as zoonosis – is more common than you may think. Many of the infectious diseases that have caused major sickness and deaths in humans worldwide originated from animals.
They include HIV, Ebola, bubonic plague, yellow fever, Lyme disease, rabies and mad cow disease. More recently there’s been bird flu, SARS, monkey malaria and, of course, A(H1N1), or swine flu.
About 60 to 75 per cent of infectious diseases that are known to affect humans are shared by animals. And unfortunately, it’s likely there will be worse to come – zoonosis is on the rise.
Professor Robert Booy, co-director of the National Centre for Immunisation Research and Surveillance at the University of Sydney, believes that it’s a matter of when rather than if a pandemic strikes. But he says we shouldn’t panic because medical advances should prevent the mass deaths of past disasters.
Cracking the code
“The virus has to evolve and mutate into a form where it can fit the lock and key of human mechanism,” he says.
Until the animal form of the disease finds the right “key” to enter humans, it is unable to infect us. It’s a process of trial and error, but the more opportunities the disease gets to try out different combinations through contact with humans, the more likely it is to eventually strike lucky.