Such mutations happen when two distinct virus strains shuffle their eight-part genetic instructions, combining bits of each to create a new strain. A worldwide outbreak, or pandemic, arises. The earliest recorded influenza pandemic struck in 1580. But just how these hybrid strains evolve is up for debate. Influenza can make its home in several species, depending on its genetic makeup.
Some strains prefer birds, others favor pigs, still others flourish with a human host.
In a new environment, this intruder encounters and mixes with unfamiliar strains to create a totally original virus. He also traveled to Hong Kong in 1997 after 18 people became infected with influenza that had previously infected only birds. Six people died from it. The Wisconsin professor combed through Hong Kong's live poultry markets, searching for the source of the bug and helped find it. Since 1997, his lab has been studying the bug he helped locate, looking for clues to its evolution, hoping for a cue or tip on what strain may next make the leap from fowl to humans.