Development of a Recombinant O/CATHAY Topotype Foot-and-Mouth Disease Virus as a Resource for Vaccine Matching and Efficacy Evaluation

Figures

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  Figure 1. Phylogenetic analysis based on the VP1 nucleotide sequences of foot-and-mouth disease virus serotype O. Phylogenetic relationships were inferred by the maximum-likelihood method under the Tamura–Nei model. Node support was assessed using 1000 bootstrap replicates, with the resulting values shown at the corresponding branches. Branch lengths reflect nucleotide substitutions per site across the 633 positions included in the final dataset (scale, 0.05 substitutions/site). The analysis included O/CATHAY topotype viruses isolated from Hong Kong, Vietnam, and China, as well as the O/ME-SA/Ind-2001 and O/SEA/Mya-98 topotype viruses that have emerged in the Republic of Korea. This analysis was conducted using MEGA11. The O/VIT/18-5490/2018 strain, which was used as the donor of the P1 region for constructing the recombinant virus, is indicated by a filled circle (●).

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  Figure 2. Characterization of the recombinant O/CATHAY virus, O/CATH/APQA-V18. (A) Schematic diagram of the recombinant viral genome comprising the O1 Manisa backbone, including the region upstream of P1, and the P1 (VP4–VP2–VP3–VP1) region derived from O/VIT/18-5490/2018. (B) Antigen-detection strip test results of the produced virus. (C) Transmission electron micrograph (TEM) of purified recombinant O/CATH/APQA-V18 virus particles. The left panel shows an overview of the purified viral particles, and the right panel represents an enlarged view of the red-boxed area. Scale bar = 100 nm. (D) Reverse transcription-polymerase chain reaction (RT-PCR) amplification of the structural protein-coding regions VP4–VP2, VP2–VP3, and VP3–VP1. Mock, RNA extracted from the culture supernatant of uninfected cells was used as a negative control.

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  Figure 3. Evaluation of vaccine efficacy against the challenge virus in pigs. (A) Schematic timeline of the animal experiment, detailing vaccination at 0 dpv, challenge with porcine O/CATH/APQA-V18 at 28 dpv (0 dpc), daily clinical monitoring, serum and oral swab sampling, and euthanasia at 7 dpc. The ellipsis indicates the omitted time interval between 0 and 28 dpv. (B) FMDV type O SP enzyme-linked immunosorbent assay antibody levels (1 − S/N values) in the negative control (NC) and commercial vaccine (Comm. Vac.) groups. *** p < 0.001, and **** p < 0.0001 versus the control group; ns, not significant. (C,D) Individual clinical scores and viral copy numbers in oral, nasal swabs from individual pigs in the NC and Comm. Vac. groups following challenge over the 7-dpc observation period.

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  Figure 4. Serum neutralizing antibody responses and cross-reactivity following the viral challenge. Serum virus neutralization (VN) titers in the negative control (NC; red circles) and commercial vaccine (Comm. Vac.; blue triangles) groups over the 7-dpc monitoring period. (A) VN titers against the recombinant challenge strain, O/CATH/APQA-V18. (B) VN titers against the commercial vaccine strain, O 3039. Data are presented as means with individual data points. * p < 0.05, ** p < 0.01, and **** p < 0.0001 versus the control group; ns, not significant.