for National Geographic News
Unlike the events depicted in tonight's made-for-TV movie about a bird-flu pandemic, so far avian influenza can't easily be transmitted from person to person.
But humans may still be responsible for much of the disease's spread.
"The most common way that avian influenza is spread is by the movement of poultry and poultry productsboth legal and illegal," said William Karesh, director of the New York-based Wildlife Conservation Society's (WCS) field veterinary program.
In the battle against bird flu, international health authorities must handle a thriving legal trade in live birds and chicks.
Illicit dealers also move poultry products, from meats to more unusual items, such as a large cargo of Chinese duck feathers recently seized at a North Carolina port.
Estimates place the market value of such illegal international trade well into the billions of U.S. dollars.
H5N1, the deadly bird flu strain responsible for 114 known human deaths since 2003, is tough enough to survive even in frozen products.
Bird flu can be spread through physical contact with foodstuffs or if those products are used as stock food or fertilizer for other animals.
The disease cannot be acquired by consuming properly cooked poultry even if that poultry is infected. (Read more bird flu facts.)
Africa's Open Borders
Migratory birds have been in the spotlight for their role in spreading H5N1 among wild birds and possibly introducing the virus into domestic flocks.
Karesh is among those tracking the flu in wild birds in hopes of short-circuiting its spread (related photos: tracking bird flu).
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