antigenic variation of foot and mouth disease virus of the last three isolates in Egypt

ABSTRACT

Three FMD viral isolates had been isolated from different outbreaks at three governorates [Sharquia, Suez, and Agga locality] during 1972, 1987, and 1993 from cattle respectively. The isolates were tested by coinplement fixation test [CFT] angainst the seven serotypes and the results revealed that all strains were of the type [O] FMD virus. The studied isolates were adapted after the 3[rd] and 4[th] passages to BEK cell cultures, they yielded infective titers ranging between 4 and 5.5 log 10 TCID[50] and complement fixing titers between 1.37-1.75 log[10] CFU/ml. Antigenic relationship and dominating state studies for the three isolates using the crosswise C.F.T. revealed that isolates [O[1]/72 and O[1] /87] and [O[1]/72] and O[1]/93] showing a little antigenic variation and can be classified as [Subtype similar but still different] and have a percentage between [32% to 70%] while isolates [O[1]/87 and O[1] /93] classified as [Subtype Similar] and have percentage between [70%-100%]. The dominance determination for isolated strains showed that isolate strain [O[1]/87] is dominating strain [O[1]/72 and O[1] /93] and strain O[1]/72 is dominating strain O[1]/93. The nucleotide sequence data of VPI of the isolated strains [O[1]/72, O[1]/87 and O[1]/93] revealed that the homology% FMD virus [O[1]/72, O[1] 87 with O[1]/93] were 86% and 88% respectively, while the homology% between O/87 and O/93 was 94%. This indicates a closer relationship between O[1]/87 and O[1]/93 isolates thorn to O[1]/72. The variation of the results between CF test and nucleotide sequence homology may be attnbuted to the fact that CF test is carried on the whole FMDV while the nucleotide sequence homology carried out on the level of VPI gene. However, this difference is not of a significant value that necessitates the change of the already applicable vaccinal strain