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).

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.

Viscerotropic velogenic Newcastle disease in Turkeys: virus shedding and persistence of infection in susceptible and vaccinated poults.

Susceptible turkeys and turkeys vaccinated with live lentogenic B1 strain Newcastle disease virus (NDV) were inoculated intracularly with viscerotropic velogenic (VV) Fontana strain NDV and studied for virus shedding and persistence of infection. Susceptible poults that survived infection (15%) continued to shed NDV from the intestinal tract up to 46 days postinoculation. Turkeys that were vaccinated with B1 strain NDV did not develop clinical signs when their immunity was challenged with VV Fontana strain virus. Virus was covered up to 53 days postchallenge (PC) from the cloaca of poults that were vaccinated once at 4 days of age and challenged at 1 month of age. Older turkeys that had been vaccinated one to three times did not generally shed virus after 4 days PC. Newcastle disease virus was recovered later in convalescence by the organ-culture method when swabs of trachea and cloaca were negative for virus. Persistent infection was detected as long as 88 days PC in organ cultures of cecal tonsil. Five of seven NDV isolants from organ cultures or from swabs caused fatal disease in chickens.

Viscerotropic velogenic Newcastle disease in turkeys: isolation of Newcastle disease virus from tracheal and cecal tonsil organ cultures.

Tracheal and cecal-tonsil organ cultures were made from vaccinated turkeys that had survived challenge of immunity with viscerotropic velogenic strain of Newcastle disease virus (NDV). Culture fluids were tested to show that latent infections did exist in the vaccinated and challenged turkeys, thus indicating a possible carrier state. NDV was recovered from 6 of 159 turkeys examined. Preliminary tests indicate that 4 isolants are velogenic and 2 are lentogenic.

Viscerotropic velogenic Newcastle disease in turkeys: vaccination against loss of egg production.

Live B1 Newcastle disease virus was administered to young turkeys either intraocularly or by driniking water, or by both methods. Protection against egg production loss was evaluated by challenge-exposure to viscerotropic velogenic Newcastle disease virus in drinking water. During 22 days postchallenge (PC), none of the vaccinated hens had morbidity, whereas 44% of the unvaccinated controls died 6-13 days PC. Percent egg production (PEP) of all groups 1-5 and 6-22 days PC were compared with their levels 1-5 days before challenge. For days 1-5 PC, changes were not significant. For days 6-22 PC, changes for all groups were siginficant lower. The controls had 0 production. Hens vaccinated only at 4 days or at 4 days and again at 4 weeks averaged one-third or less of prechallenge levels but were recovering. Those revaccinated at 4 months maintained 84-91% of their prechallenge levels and were considered satisfactory. Broodiness was a detracting factor in one group of hens vaccinated at 4 days, 4 weeks, and 51/2 months. They averaged two-thirds of prechallenge levels but were in decline.