Effect of Different Inactivators on the Efficacy of Egyptian Foot and Mouth Disease SAT2 Vaccine

In 2012, Foot and Mouth Disease Virus (FMDV) of serotype SAT2 caused a devastating FMD epidemic in Egypt. In order to control it, a vaccine was produced, based on the Egyptian SAT2 field isolate. As it is often difficult to produce good vaccines from FMDV isolates of the SAT serotypes, a study was carried out to determine the optimal inactivation protocol for the Egyptian SAT2 strain. In comparison to the usual FMDV inactivation protocol with binary ethyleneimine (BEI) alone, an alternative protocol was employed which used formalin as an additional inactivating agent and possible antigen stabilizer in combination with BEI. Inactivation kinetics was recorded for both protocols and the preservation of the antigens were determined by complement fixation test (CFT). From both antigens trial vaccines were formulated with Montanide ISA 206 and tested in guinea pigs. While inactivation with 0.1 M BEI alone resulted in an inactivation rate of 0.53 log10 TCID50/hour, BEI combined with formalin (BEI-FA) resulted in a significantly higher inactivation rate of 2 log10 TCID50/hour. While BEI inactivation of the antigen led to a drop in CFT titer from 1/32 to 1/16, no such decline was found with the BEI-FA inactivation protocol. The BEI-FA protocol also resulted in a trial vaccine with higher immunogenicity in guinea pigs. For 28 days post vaccination (dpv) sera, SNT and ELISA titers of 1.8 and 2.05, respectively, were recorded for the BEI inactivated antigen while for BEI-FA inactivated antigen, SNT and ELISA titers of 2.1 and 2.3, respectively, were recorded. Finally it was clear that, the use of BEI-FA as an inactivator for FMDV (SAT2) reduces the time of inactivation and provides good and safe antigen content consequently higher post vaccinal antibody titer.)