Etiological analysis of 2 strains of genotype XII Newcastle disease viruses originated from geese in Guangxi

【Objective】To understand etiological characteristics of 2 strains of genotype XII Newcastle disease virus (NDV) originated from geese in Guangxi, so as to provide reference for systematic monitoring of NDV distribution and scientific prevention and control of ND.【Method】Two strains of genotype XII NDV(Goose/China/GX02/2018 and Goose/China/GX17/2018) from geese in Guangxi were purified by viral plaques. The pathogenicity of NDV was determined by mean time to death(MDT) of lethal chicken embryos and intracorporeal inoculation index(ICPI) test. The amino acid difference sites of F and HN proteins and reference strains were analyzed, and genetic evolution analysis was performed based on the full length of F gene.【Result】After 4 passages of plaque purification of DF-1 cells, two purified strains were obtained, corresponding to MDT of 54 h and 48 h, ICPI of 1.65 and 1.65, respectively. The genome length of the 2 isolates was 15192 nt, the 3'-end guide sequence was 55 nt, and the 5'-end trailing sequence was 114 nt. The phylogenetic tree of NDV genotype XII constructed based on the full length of F gene showed that the 2 isolates(Goose/China/GX02/2018 and Goose/China/GX17/2018) belonged to the XIIb subtype, the same subtype as the Guangdong strains. In addition, Chinese isolates in 2010, 2011 and 2017 formed 3 small branches respectively. The F protein cleavage site of the 2 isolates was ¹¹²RRQKRF¹¹⁷. Compared with the South American isolates(XIIa subtype) and the Vietnamese isolates(XIId subtype), there were 14 different amino acid sites in the signal peptide region, fusion peptide region, hepta-peptide repeat region and transmembrane region. Two amino acid differential sites(¹⁹I→V and ²⁹⁴N→S) were unique Guangxi isolates. The amino acid sequences of the transmembrane region and antigenic neutralization region of the HN protein of the 2 isolates were consistent with those of the Guangdong isolates, and there were seven amino acid differences(²⁷V→I, ²⁸A→S, ³⁴V→I, ⁴¹A→T, ⁴²V→A, ²⁶³K→R and ³⁴⁷E→D) compared with the South American isolates(subtype XIIa).【Conclusion】The amino acid differences in F protein and HN protein between Chinese isolates(subtype XIIb) and South American isolates(subtype XIIa) and Vietnamese isolates(subtype XIId) may be related to the differences in pathogenicity to chickens. In addition, NDV genotype XII is under constant evolution, and the epidemic distribution of NDV genotype XII needs to be continuously monitored.