Selection of Vaccine Candidate for Foot-and-Mouth Disease Virus Serotype O Using a Blocking Enzyme-Linked Immunosorbent Assay

Figures

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  Figure 1. Comparison of immunogenicity in pigs, cattle, and sheep. Pigs (10 animals for each strain), cattle (12–13 animals for each strain) and sheep (12–13 animals for each strain) were immunized with Foot-and-mouth disease virus (FMDV) O/Mya/98, SCGH/CHA/2016, O/Tibet/99, and O/XJ/CHA/2017 vaccines at day 0 and 21, respectively. Serum samples collected at 21 days post vaccination (dpv) were used to measure homologous antibodies by NA-ELISA (A) and serum samples collected at 42 dpv with boosted vaccination were used to measure homologous antibodies both by NA-ELISA (B) and virus neutralizing test (VNT) (C). The statistical significance of differences between groups was determined. * p < 0.05, ** p < 0.01, *** p < 0.001, **** p < 0.0001.

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  Figure 2. Cross-neutralization analysis. Serum samples collected at 21 dpv and 42dpv from pigs (A), cattle (B), and sheep (C) vaccinated with O/XJ/CHA/2017 vaccine were used to measure homologous antibodies with FMDV O/XJ/CHA/2017 and heterologous antibodies with FMDV O/Mya/98, SCGH/CHA/2016, and O/Tibet/99 by NA-ELISA, and sera collected at 42 dpv were also used to detect homologous and heterologous antibodies by VNT (D). Unpaired t-test was used to compare the differences between homologous antibodies and heterologous antibodies. * p < 0.05, ** p < 0.01, *** p < 0.001, **** p < 0.0001.

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  Figure 3. Vaccine matching test using vaccinated cattle sera. The r1-value between the O/XJ/CHA/2017 strain (homologous virus) and other viruses, namely, O/Mya/98, SCGH/CHA/2016, and O/Tibet/99 was calculated according to the cross-neutralization analysis results from serum samples collected from 13 cattle inoculated with the O/XJ/CHA/2017 vaccine at 42dpv both using NA-ELISA (A) and VNT (B).

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  Figure 4. Correlation of the titers obtained by the NA-ELISA and VNT using different FMDV strains. (A) FMDV SCGH/CHA/2016. (B) FMDV O/Mya/98. (C) FMDV O/Tibet/99. (D) FMDV O/XJ/CHA/2017. Pearson’s correlation coefficient was computed using GraphPad Prism (version 6.0) software (San Diego, CA, USA). n, number of serum samples tested; r, correlation coefficient. The P value is two-tailed. The dotted lines represent the cutoff values. **** p < 0.0001.

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  Figure 5. The relationship between NA-ELISA titers of vaccinated pigs and clinical protection against challenge with FMDV serotype O. Dispersion of individual values for protected pigs (open squares) and unprotected pigs (filled triangles). The dotted lines represent the cutoff value of NA-ELISA and n, number of pig sera tested.