Viscerotropic Velogenic Newcastle Disease in Turkeys: Virus Shedding and Persistence of Infection in Susceptible and Vaccinated Poults

Abstract

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.

Serological Methods in the Identification and Characterization of Viruses

“…The neutralization of viruses by homologous antibody in the body fluids sometimes hampers the detection of inapparent viral infections. This is the case with Newcastle disease virus in poultry, where inapparent infections in convalescent or vaccinated birds are believed to playa role in the dissemination of the disease (Gillette et al, 1975). The usual virus isolation procedures generally fail to detect these infections, and it is necessary, for efficient recovery of the virus, first to dissociate the virus-antibody complexes.…”

Reactivation of Newcastle Disease Virus Neutralized by Antibody

“…In this regard, one area of major concern is the paucity of data describing the epizoological significance of inapparent NDV infections. Such infections have been reported in convalescent birds (6,11), but the frequency of their occurrence and the role they play in viral dissemination are yet to be defined.…”

“…Collection of data on the significance of inapparent NDV infections has been hampered by the difficulty of identifying the infected, though clinically normnal, birds. Routine virus isolation procedures generally fail to detect these infections, but NDV has been isolated from tracheal tissues of convalescent birds by prolonged in vitro culture of tissue explants (6,11). This difficulty of virus isolation may be the result of neutralization of virus, either before or after sample collection, by homologous antibody in the body fluids.…”