How did scientists think that highly pathogenic avian influenza (HPAI) reached North America in spring 2015?

• A. Contaminated poultry products imported from China
• B. Infected migratory waterfowl migrating on the East Asia/Australia flyway
• C. Illegal exotic bird smuggling past USDA ports of entry
• D. All of the above

Answer: (B)

Spread through infected wild waterfowl traveling along the East Asia/Australia flyway. Genetic analyses showed North American isolates were closely related to Asian strains, pointing to introduction from Asia rather than local spread from poultry or illegal import routes. Detections in wild birds occurred before poultry outbreaks and followed the timing of spring migration, when birds move from Asia toward North America via Alaska and the Bering Strait region. While contaminated poultry or smuggling can cause outbreaks in other contexts, the available evidence for spring 2015 supports wild-bird movement as the primary mechanism.