2.5 Mink challenge assay
The SVV-CH-09-2018 strain was used for the challenge test. Mink (n=6) weaned for approximately 60 days were observed for 1 week to ensure they were asymptomatic. SVV, FMDV, SVDV, VSV, and pseudorabies virus were not detected by the corresponding ELISA and RT-PCR or PCR(Luis Gabriel Gimenez-Lirola et al., 2016). The mink were divided into two groups, the 3 minks were in each group. The first group was injected intraperitoneally with a 5 mL volume of strain SVV-CH-09-2018 (1×109 median cell culture infective dose [TCID50]/mL). The second group was inoculated with DMEM as a negative control (NC). Both groups were fed under the same conditions and in separate rooms. Strict biosafety protocols were followed to avoid crossover contamination. Clinical symptoms were monitored daily for 28 days. At 0, 3, 7, 14, 21, or 28 days post-challenge (dpc), serum was collected from each animal, and the anti-SVV neutralizing antibody titer was determined(Joshi, Fernandes, et al., 2016). TaqMan real-time RT-PCR was used to detect viral load(Dall Agnol et al., 2017) (J. Zhang et al., 2019). A standard curve was generated by plotting the threshold values against serially diluted plasmid DNA encoding the SVV VP1 gene fragment. At 28 dpc, the mice were euthanized for pathological examination. The heart, spleen, liver, kidney, lung, inguinal lymph nodes, and other organs were collected for histopathological observation. TaqMan real-time RT-PCR was used to detect mRNA viral titers in these organs.