Epizootiology of Newcastle disease in waterfowl.

Antibodies to Newcastle disease virus (NDV) as measured by hemagglutination-inhibition and virus-neutralization tests were detected in 40/236 Canada geese captured while in their southward migration or in their wintering grounds. Antibodies were also found in 37/267 wild ducks and in 20/31 domestic geese. Adult geese were readily infected by several routes. Inapparent disease usually resulted, and only 1/13 cases were fatal. Goose embryos responded differently to inoculation with selected NDV strains than did chicken embryos of comparative developmental stages. Some goslings that hatched from inoculated embryos died and were found to have virus, whereas others survived and developed active antibodies. Four strains of virus isolated from migratory ducks of the Pacific flyway were characterized. All 4 strains were lentogenic but differed from lentogenic strains prevalent in chickens by being thermostable. It is proposed that wild waterfowl neither receive their ND infection from domestic poultry nor pass their disease to poultry. The virus reservoir probably exists in nature.