Nearly 12 million birds had to be destroyed. In Seal's lab, analyses of gene sequences within the last few years helped confirm scientists' long-suspected connection between this outbreak and infected imported parrots. Virulent Newcastle strains have been detected in U.S. pet bird populations in all but 3 years since 1974. In addition, virulent Newcastle virus periodically flares up in other countries. In 1998, Australia began battling a virulent strain that apparently evolved from a weak virus indigenous to Australian poultry for at least 30 years.
Wild birds can also carry strains deadly to poultry.
Cormorants were the suspected source. Hundreds had died from the disease at a lake near where the turkeys were being reared on range. Seal confirmed this suspicion when he compared the genomes of turkey and cormorant isolates. Besides directly threatening U.S. poultry, Newcastle can damage our export markets. In 1998, several dead and dying game chickens from a backyard flock in California's Central Valley were delivered by the owner to the California Veterinary Diagnostic Laboratory in Fresno.