Abstract
Newcastle disease (ND) leading to heavy economic losses to the poultry industry worldwide is caused by Newcastle disease virus (NDV). Even though intensive vaccination programs have been implemented in many countries, virulent NDV can still be frequently isolated in well-vaccinated flocks. We compared the protection efficiency of LaSota and two sub-genotype VIId vaccines, NDV/AI4 and NDV O/AI4, in which NDV O/AI4 was constructed by replacing the hemagglutinin–neuraminidase (HN) gene of the vaccine strain NDV/AI4 with that from the variant NDV strain JS-14-12-Ch by the cross hemagglutination inhibition test and immune protection test. The number of birds shedding the virus and the titer of the shedding virus from the challenged birds were tested to evaluate the protection efficiency in the immune protection test. The cross hemagglutination inhibition and neutralization tests between JS-14-12-Ch and the three vaccines displayed a significant antigenic difference between JS-14-12-Ch and LaSota or NDV/AI4, but not between JS-14-12-Ch and NDV O/AI4. The results of the immune protection test showed that NDV O/AI4 could provide improved protection as determined by a significant decrease in both the number of birds shedding the virus and the titer of the shedding virus from the challenged birds. The results in this study indicated that the antigenic similarity between the vaccine strain and the challenge strain is important in reducing the shedding of virulent virus in which the congruence of the NDV HN protein may play a critical role.
Highlights
Newcastle disease (ND), which leads to heavy economic losses to the poultry industry, is caused by virulent Newcastle disease virus (NDV) [1]
Virulent virulent be still isolated from ND-vaccinated poultrywhich flocks,raised which raised the of concern of NDV could becould still isolated from ND-vaccinated poultry flocks, the concern whether whether the vaccines current vaccines are still effective, for the protection from disease clinical disease the current are still effective, not onlynot for only the protection from clinical but alsobut for for the reduction of virulent virus shedding and transmission
The genetic difference between the two in China is characterized as VIId [10,26,27]
Summary
Newcastle disease (ND), which leads to heavy economic losses to the poultry industry, is caused by virulent Newcastle disease virus (NDV) [1]. Intensive vaccination programs have been implemented in most poultry farms in China and the vaccine strain LaSota, which belongs to genotype II, has been the most extensively used since the 1970s. Infections of genotype VII NDVs have been frequently reported in China and other Asian countries in more recent years [2,3,4,5,6,7]. The isolation rate of the sub-genotype VIId NDV strains with the E347K variation in the hemagglutinin–neuraminidase (HN) protein has increased in China over the years [6]. Researchers have reported that the HN protein would intensify the antigenic difference [8].
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