Just how big a threat is avian influenza to humans? It's still a matter of speculation, though scientists say a mutant variety capable of being passed from person to person could trigger a deadly global pandemic. Though no massive outbreaks have occurred, humans cases of bird flu -- from contact with infected poultry -- have resulted in more than 200 deaths worldwide since the disease was first reported in in South-east Asia in 2003. The scary truth is that over half the people who catch the disease die.

As the H5N1 virus has spread across Asia to Africa and Europe, on the wing of migratory birds, the flu threat has stirred debate on drug patents for possible vaccines for humans, poultry farming techniques, international trade and travel, wildlife conservation, and the role of governments in preparing for potential health and economic disasters.