3.5 Amino acid polymorphism analysis
To further explore the characteristics of both newly identified NDRV strains, amino acid polymorphism of the σC proteins was compared with reference strains. The results showed that most of the amino acid mutations in both newly identified NDRV isolates located in the σC protein head domain (Table 1), such as P233S, V253A, and A298V, indicating both isolates were closely related to each other. Meanwhile, some mutations were only found in HNXX-1/2021 & HNJZ-2/2021 (P233S in σC protein head domain), HeNXX-1/2021 (E305G, A328R, and T329Q in σC protein head domain) and HNJZ-2/2021 (A328R and T329Q in the σC protein head domain). Moreover, there was a unique amino acid mutation site (Q158H) in the σC protein shaft domain of both newly identified NDRV strains.