Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 12, 1998
Publication Date: N/A
Interpretive Summary: Two forms of Newcastle disease (ND) are a concern of the U.S. poultry industry. One is a respiratory disease that causes continued economic loss from reduced rate of gain, poor feed conversion, increased mortality and carcass condemnation at processing. The disease is caused by infections with ND virus (NDV) strains of low virulance and vaccination is widely used for control. The second form is a disease of high mortality from infection with virulent NDV strains, a form not seen in the U.S. but is a threat to enter via infected pet birds or poultry. International control measures are employed to prevent the spread of virulent ND. Proposed international ND standards include a test to differentiate high and low virulence NDV strains by intracerebral (IC) inoculation of chicks a procedure not routinely used in the U.S. Fifty-four NDV isolates from chickens and turkeys were characterized by IC inoculation and by other assays. All isolates from poultry were of low virulence by the IC test and would not result in restriction of export of U.S. poultry products by the proposed standards. The isolates were not identical and several had new properties that differentiated them from NDV reference and current vaccine strains. Continued evaluation of new NDV isolates is essential to completely understand viral origins and a means to control these infections to prevent problems that could impact international trade.
Technical Abstract: Fifty-seven Newcastle disease virus isolates from chickens, turkeys, a rhea, a parrot, and an anhinga were pathotyped and characterized by monoclonal antibody (mAb) inhibition profile, elution rate, and hemagglutinin thermostability. Selected isolates received further characterization by nucleotide sequencing portions of the fusion protein and matrix protein genes. Seven of the 43 chicken isolates were recovered from flocks in Canada. The remaining isolates including 11 from turkeys were isolated in the United States. All isolates except an anhinga isolate were of low virulence by mean death time in embryos, intracerebral pathogenicity index, and/or intravenous pathogenicity index procedures and were classified as lentogens. The anhinga isolate was more virulent than the other strains and was pathotyped as a mesogen. Nucleotide sequence analysis of the anhinga isolate revealed a homology with the virulent cormorant isolates of 1992 rather than classical United States mesogens characterized by the Roakin strain. Variability was evident among the lentogenic isolates. Two of the turkey isolates had mAb profiles that differed from B1 and La Sota reference and vaccine strains and 38% (21/56) of the isolates had more thermostable hemagglutinins than those reference strains. There was no evidence that any of the isolates from poultry were more virulent than the lentogenic pathotype.