Viscerotropic velogenic Newcastle disease in turkeys: immune response following vaccination with either viable B1 strain or inactivated vaccine.
When used as a vaccine, live letogenic B1 Newcastle disease virus (NDV) protects turkeys against challenge-exposure to viscerotropic velogenic NDV (VVNDV). Low-level passively-immune poults were vaccinated one, two, or three times at various intervals and their immunity challenged at various times from 1 to 10 months of age. Newcastle disease virus was isolated readily from either the blood, trachea, or vent of turkeys in all challenge groups (through 5 months of age) on the 3rd to 6th days postchallenge (PC) but after 14 days PC was isolated rarely. Virus was isolated from turkeys that had high titers of serum hemagglutination-inhibition antibodies at the time of challenge. The anamnestic antibody response appeared to be stronger in poults that had low antibody titers prior to challenge-exposure to VVNDV. In a small-scale study with an inactivated VVNDV vaccine, vaccinated poults were protected against challenge with the homologous viscerotropic virus. Parallel control studies on the infectivity of viscerotropic NDV for turkeys indicated that resistance to VVNDV increased with age.
Field vaccination of turkeys against exotic viscerotropic Newcastle disease virus.
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Newcastle disease in Paraguay.
A serious outbreak of a velogenic strain of Newcastle disease occurred in Paraguay in August, 1970. Deaths of domestic poultry were very high in affected flocks. Vaccination against Newcastle disease had been prevented by law. This was rescinded, however, and voluntary vaccination was started. The incidence of new outbreaks dropped sharply thereafter. This is the first report of isolation and identification of Newcastle disease in Paraguay. Evidence is presented, however, suggesting that Newcastle was present in Paraguay between 1957 and 1959. At that time, diagnostic facilities were not available, so no attempt was made to differentiate between Newcastle disease and fowl plague by those doing the diagnostic and regulatory work.