Molecular characterization, pathogenicity, and protection efficacy analysis of 2 wild-type lentogenic class I Newcastle disease viruses from chickens in China.

In this study, 2 wild-type Newcastle disease viruses (NDVs), designated as CK/GX/65/15 and CK/GX/26/15, were isolated from asymptomatic chickens in Guangxi province, China. They were identified as lentogenic NDV with mean death time (MDT) above 90 and intracerebral pathogenicity index (ICPI) below 0.7. The results of complete genome sequence analysis show that the 2 NDV strains are members of class I genotype 3 with the length 15,198 nt, which followed the "rule of six" and the order 3'-NP-P-M-F-HN-L-5'. In addition, 8 amino acid substitutions were identified in the functional domains of fusion protein (F) of CK/GX/65/15 and 9 in CK/GX/26/15, whose amino acid sequences of F protein cleavage site are 112E-R-Q-E-R-L117. The isolates were found to be apathogenic in specific pathogen free (SPF) chickens and ducks without morbidity or mortality. Furthermore, the protection study shows that isolates can provide the same effective protection against a major NDV virulent strain in China (class II genotype VII) as the commercial vaccine LaSota. Moreover, vaccination with isolates reduced number of chickens shedding virus compared to those vaccinated with LaSota. In conclusion, 2 wild-type NDV strains exhibited fine protection efficacy against genotype VII NDV in poultry and can be considered as candidate vaccines against NDV.