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.
Response of congenitally immune chicks to viscerotropic velogenic Newcastle disease virus.
Separate groups of chicks of hen hyperimmune to viscerotropic velogenic Newcastle disease virus (VVNDV) were challenge-exposed to VVNDV by intraocular route at 1 day and 34 days old. Their response was evaluated by clinical symptoms, hemagglutination-inhibition (HI) titers, and virus isolations. Chicks exposed at 1 day old excreted VVNDV from the vent for up to 60 days; their active mean HI titers remained low (10-40); and deaths from VVNDV occurred early (5-16 days) and late (28-55 days). Chicks challenge-exposed at 34 days old excreted virus from the vent for 10 days; active HI titers developed quickly and remained high (891-1177); and deaths and signs of VVNDV occurred early (5-13 days).
A Modified Live Newcastle Disease Virus Vaccine.∗
Summary 1) Newcastle disease virus was modified by serial passage of the California 11914 strain through tissue cultures using minced chicken embryos suspended in Simm-Sanders medium. 2) The modified virus was administered intramuscularly to over 20,000 chickens of all ages without producing any nervous or respiratory symptoms, but produced an immunity as demonstrated serologically and by intramuscular challenge with a virulent strain of ND virus. One dose of the vaccine given to susceptible chicks at 5 days of age or over induced an immunity lasting at least 12 weeks. Two doses from 7 to 9 weeks apart have resulted in a high degree of immunity which was still evident 33 weeks later. 3) When administered to 2 flocks of chickens, one in acute stage of infectious bronchitis and the other with chronic respiratory disease, the virus apparently did not increase the severity of the respiratory disease condition. 4) Repeated trials showed that vaccinated chickens did not transmit the infection to unvaccinated susceptible birds within the same pen during 33 weeks. 5) The modified virus can be propagated on HeLa cells to produce a vaccine for poultry, thus avoiding the introduction of egg-borne infections to poultry flocks through vaccines produced in chicken embryonated eggs.