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.
The viscerotropic pathotype of Newcastle disease virus.
SUMMARY The viscerotropic form of Newcastle disease is defined and the history of the present panzootic of this disease is reviewed. Evidence is presented to support the concept that the viscerotropic form is genetically different from established enzootic forms of Newcastle disease. Ways of differentiating the pathologic forms are described. Transmission of the virus is discussed so as to identify problems of controlling its spread and preventing further introductions.
Further Observations on the Response of Birds to One Intranasal Vaccination with the B-1 Strain of Newcastle Disease Vaccine
APREVIOUS paper by the authors8 reported that 2month-old birds vaccinated once intranasally with the B-1 strain of Newcastle disease virus (NDV) resisted challenge for 8 months. These same birds responded early with high hemagglutination inhibition (HI) titers, and were later resistant to an intramuscular challenge with NDV even though serum neutralization (SN) titers were insignificant in some of the birds. The duration of resistance to challenge and the rapid and high HI responses to the B-1 vaccine prompted further investigation of the duration of immunity in birds vaccinated once with a commercially available B-1 strain of Newcastle disease (ND) vaccine. Also an objective of the present study was the correlation between HI and SN titers and the response of birds to ND intramuscular challenge.