Author
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King, Daniel |
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Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 6/22/1999 Publication Date: N/A Citation: N/A Interpretive Summary: Newcastle disease vaccines were developed in the 1940s and their use in poultry has been effective in preventing mortality from lethal forms of the disease as well as those forms that are similar to the common cold. The different forms of the disease are caused by different strains of the virus although the viruses are similar enough to be recognized as members of the same family. The most widely used vaccines are live viruses that can themselves cause mild disease. A new commercial vaccine was developed by methods in biotechnology and incorporates only the two parts of the virus that are most important in stimulating the protective response. It was not known whether the new vaccine could provide protection against the viruses that are the greatest threat to poultry, those similar to the cause of the Newcastle disease outbreak in California in 1971. The new vaccine was found to be equally effective as the most widely used vaccine in preventing the symptoms and mortality of Newcastle disease. Use of the new vaccine can prevent loss to the severe forms of disease and would reduce the potential of production losses associated with the mild disease that often follows use of the current vaccines. Technical Abstract: Four-week-old specific-pathogen-free White Rock chickens were immunized subcutaneously (SC) with a commercial recombinant fowlpox virus vectored Newcastle disease vaccine (FP-N) expressing the hemagglutinin-neuraminidase and fusion protein genes of Newcastle disease virus (NDV) strain B1. Vaccinates were challenged by eye drop and intranasally (E/I) with a viscerotropic velogenic NDV. Virus clearance was complete by day 14 postchallenge and was similar in seropositive chickens whether they received a low or high dose of vaccine 14 days before challenge. Clinical signs and high tissue virus titers were observed only in low dose vaccinates that were seronegative. Chickens vaccinated with FP-N SC, B1 SC, or B1 E/I at 6 or 10 days before challenge were all protected against clinical disease. However, only birds vaccinated with B1 E/I 10 days before challenge were also protected against infection by the NDV challenge. Vaccination at 3 days before challenge with B1 E/I provided early protection, but severe nervous signs developed later. Disease in B1 SC and FP-N SC groups vaccinated 3 days before challenge was similar to that in challenge controls. |
