Detection of antibodies against a conserved capsid epitope as the basis of a novel universal serological test for foot-and-mouth disease

Abstract

16Diagnostic tests for foot-and-mouth disease (FMD) include the detection of antibodies 17 against either the viral non-structural proteins or the capsid. The detection of antibodies against 18 the structural proteins (SP) of the capsid can be used to monitor seroconversion in both infected 19 and vaccinated animals. However, SP tests need to be tailored to the individual FMD virus 20 serotype and their sensitivity performances may be affected by antigenic variability within each 21 serotype and mismatching between tests reagents. As a consequence, FMD Reference 22 Laboratories need to maintain contingency to employ multiple type-specific assays for large-23 scale serological surveillance and post-vaccination monitoring in the event of FMD outbreaks. 24 In this study, a highly conserved region in the N terminus of FMDV capsid protein VP2 (VP2N) 25 was characterised using a panel of intertypic-reactive monoclonal antibodies. This revealed a 26 universal epitope in VP2N which could be used as a peptide antigen to detect FMDV-specific 27 antibodies against all types of the virus. A VP2-peptide ELISA (VP2-ELISA) was optimised 28 using experimental and reference antisera from immunized, convalescent and negative animals 29 (n=172). The VP2-ELISA is universal, simple and provided sensitive (98.6 %) and specific 30 (93%) detection of antibodies to all FMDV strains used in this study. We anticipate that this 31 SP test could have utility for sero-surveillance during virus incursions in FMD-free countries 32 and as an additional screening tool to assess FMD virus circulation in endemic countries. 33 34 Keywords: FMDV, conserved capsid epitope, ELISA, diagnosis, serology. 35 36 37 Foot-and-mouth disease (FMD) is an economically devastating viral disease of cloven-38 hoofed animals with a global distribution. It limits access to markets for developing countries 39 and outbreaks in otherwise FMD-free countries are expensive to control (as in the UK in 2001, 40 Japan in 2010 and the Republic of Korea in 2010 and 2011) [1, 2]. FMD virus (FMDV) is a 41 single-stranded, positive-sense, RNA virus belonging to the genus Aphthovirus in the family 42 Picornaviridae. The virus exists as seven serotypes (O, A, C, Asia 1, South African Territories 43 (SAT)1, SAT2 and SAT3) as well as numerous and constantly evolving strains showing a 44 spectrum of antigenic diversity. 45The non-enveloped picornavirus capsid has icosahedral symmetry, a diameter of 46 approximately 30 nm and is composed of 60 copies of each of the capsid proteins VP1, VP2, 47 VP3 and VP4. VP1, VP2 and VP3 are the major components of the capsid, while VP4 is a 48 small (approximately (12 kDa) internal protein which lies on the inside surface of the capsid 49 around the five-fold axes of symmetry, where it is thought to stabilise interactions between 50 pentameric capsid subunits [3, 4]. During the replication cycle of FMDV, eight different viral 51 non-structural proteins (NSPs; and additional precursors) are generated which are potential 52 serological...