Toward the calibration of serological assays using sera collected from cattle and sheep following a single dose of foot-and-mouth disease vaccine

Background and Aim: Serological assays are widely used to monitor the performance of foot-and-mouth disease (FMD) vaccines to estimate vaccination coverage and to ensure that vaccinated animals generate adequate immune responses. This study aimed to measure the FMD virus (FMDV)-specific responses in cattle and sheep after a single dose of a trivalent FMD vaccine containing serotypes A, O, and Asia-1, and to use these sera to calibrate virus neutralization tests (VNTs) and serotype-specific serological enzyme-linked immunoassays (ELISAs) that can measure post-vaccination responses. Materials and Methods: Sera were collected from cattle (n=10) and sheep (n=10) on 0, 21, and 56 days after immunization with an imported aqueous formulated FMD vaccine. These samples were tested by VNT using field FMDV isolates that are representative of the epidemiological risks in Central Asia (A/ASIA/Iran-05, A/ASIA/GVII, O/ME-SA/Ind-2001, O/SEA/Mya-98, O/ME-SA/PanAsia, and Asia-1 Shamir). Heterologous VNT antibody responses were compared to those measured using commercial FMDV-specific ELISAs for serotypes O, A, and Asia 1. Results: Administration of the FMD vaccine increased FMDV-specific antibody titers for both species in sera collected on day 21, but these elevated titers were short-lived and were decreased by day 56. Conclusion: These results highlight the short duration of immunity with a single dose of this aqueous vaccine and motivate further studies to assess immune responses in cattle and small ruminants after a two-dose course vaccination schedule. Further comparative data for VNT and serotype-specific ELISAs are needed to define cutoffs that can be used to monitor post-vaccination immune responses in low-containment laboratories where it is not possible to handle live FMDVs.