Improvement of foot-and-mouth disease virus vaccines and diagnostics through structural design

Abstract

Foot-and-mouth disease (FMD) is a contagious viral disease, which affects cloven-hoofed animals such as cattle, pigs, sheep, goats, and other artiodactyl species and ranks as one of the most economically important infectious diseases of animals according to the World Organisation for Animal Health (OIE). The occurrence of the disease not only affects international trade in livestock and animal products but also results in damaging consequences for the livelihoods of local farmers due to impacts upon productivity, food security, and losses of income. The disease is widely distributed in the developing world, in particular Africa and Asia. The key focus in FMD endemic regions, is reliable diagnosis and to control the disease through vaccination. However, due to the complexity of the FMD virus (FMDV) i.e. the causative agent, having seven serotypes, several topotypes and subtypes due to the lack of a proof-reading mechanism during viral RNA replication, vaccination against one serotype may not afford immune protection against another. Thus, improved FMD vaccines and diagnostic assays becomes imperative. This study focused on research gaps with these concepts as a key. FMDV acquires the ability to bind to cell surface heparan sulphate proteoglycans following serial cytolytic infections in cell culture and by utilizing comparative sequence analysis, the fixation of positively charged residues at amino acid positions 83-85 and 110-112 of the VP1 outer capsid protein was revealed to play a role. Through reverse genetics, eight chimeric field strain, mutant viruses were constructed with additional positive charges in symmetrical clusters on the virion surface. The data indicated that only positively charged residues at position 110- 112 of VP1 enhanced infectivity of BHK-21 cells. A FMD diagnostic assay that differentiates infected from vaccinated animals (DIVA) is based on the FMDV 3ABC non-structural protein (NSP). A 3ABC ELISA based on the FMDV SAT serotypes was developed with sensitivity and specificity comparable to the commercially available NSP assay and one in-house assay for the IZSLER Institute, Italy. In an extension of these studies, a na�ve chicken phage displayed antibody library was panned with SAT1 and SAT3 FMDV to select single chain variable fragments (scFvs) that can be used as diagnostic reagents. The soluble scFv resulting from the panning of a SAT1 virus was found to be favourable for detecting SAT1 viruses in an ELISA. The information gained from this study contributes to a greater understanding of strategies enabling the virus to generate novel receptor binding and alternative host-cell interactions and aid in more sensitive and specific diagnostic assays.