Immunogenicity and safety of a live Pasteurella anatipestifer vaccine in White Pekin ducklings: laboratory and field trials.

Oral or aerosol administration of a live trivalent Pasteurella anatipestifer (PA) vaccine (sero-types 1, 2 and 5) gave significant protection against homologous challenges in White Pekin ducklings. Vaccination of one-day-old ducklings by either method provided protection for at least 42 days of age (last challenge). The vaccine did not cause any untoward signs or mortality in one-day-old ducklings exposed to ten times the recommended dose. The vaccine strains did not revert to virulence on 10 back-passages. However, they were reisolated from tracheas and sinuses of the contact-exposed ducklings which were also resistant to challenge with homologous serotype. Feeding of chlortetracycline (0.044%) or sulphadime-thoxine-ormetoprim (0.02%) for first 2 weeks of age had no adverse effect on efficacy of the vaccine. The vaccine was found to be both safe and efficacious in field trials in which one-day-old ducklings were exposed by aerosol in the hatcher.