Thesis (M.Sc.) - Cairo University - Faculty of Veterinary Medicine - Department of Virology

Foot and mouth disease (FMD) is responsible for serious economic losses in Egypt. Although vaccination is practiced as the main control strategy, failure of vaccination has been reported in many cases. Selection of FMD antigenic variants under the immune pressure of partially immunized animals has been previously recorded. The current study aimed to isolate and characterize foot and mouth disease virus (FMDV) strains circulating in the Egyptian vaccinated animals. Serotype O, A and SAT2 FMDVs were detected in different Egyptian governorates during 2015, 2016 and 2017. We report here the successful isolation of 15 FMDVs of the three serotypes. Phylogenetic analysis based on VP1 gene placed all serotype O isolates with EA-3 prototypes. There was a variation in 15-17 amino acids between serotype O isolates of 2015 and (2016 & 2017). Serotype A isolates belonged to 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. Virus neutralization test (VNT) using serotype-specific sera confirmed the serotyping of the isolated viruses and determined the antigenic relatedness between the isolates and the currently used vaccine strains. A drop in the neutralizing antibody titer of some serotype O and A isolates could be attributed to mutation in critical amino acids in the neutralizing antigenic sites. Hence, this work suggests the significance of amino acids substitution within the virus antigenic sites in antibody neutralization and immune escape

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