Mutations in foot and mouth disease virus types A and O isolated from vaccinated animals

Foot and mouth disease (FMD) is responsible for serious economic losses in Egypt. Although vaccination is practised as the main control strategy, failure of vaccination has been reported in many cases, which can be due to a number of factors. Selection of FMD antigenic variants under the immune pressure of partially immunised hosts has been previously recorded. This study was designed to isolate and characterise foot and mouth disease viruses (FMDVs) circulating in Egyptian vaccinated animals. Serotype O, A and Southern African Territories (SAT) 2 FMDVs were detected in different Egyptian governorates during 2015, 2016 and 2017. The successful isolation of 15 FMDVs of the three serotypes is reported in this paper. Phylogenetic analysis based on the viral protein (VP) 1 gene showed that all serotype O isolates had East Africa (EA)-3 topotypes. There was variation in 15-17 amino acids between the serotype O isolates of 2015 and those of 2016 and 2017. The serotype A isolates belonged to the A-Iran-05 lineage, with the exception of one isolate of 2016 which clustered with the African strains of G-IV. Serotype SAT2 FMDV was detected in two samples of 2017 and both were of lineage Alx-12 of topotype VII. The virus neutralisation test using sera raised against vaccine strains confirmed the serotyping of the isolates and determined the antigenic relatedness between the isolates and the currently used vaccine strains. A decrease in the neutralising antibody titre of some serotype O and A isolates could be attributed to mutation in critical amino acids in the neutralising antigenic sites. Hence, this work supports previous studies describing the significance of amino acid substitutions within the antigenic sites of the virus in antibody neutralisation and immune escape.