With avian flu having now spread from Asia to Europe, U.S. health officials say they expect the disease to reach North America perhaps as early as this spring, possibly reaching the western continental U.S. this fall. In preparation, the departments of Agriculture and Interior, along with the U.S. Fish and Wildlife Service, will test up to 100,000 migratory birds starting this April. Some scientist, however, contend that the flu is unlikely to be spread through wild birds, but rather through the pet or poultry trade.