Genetics And Variation Of Gene 3A Of Foot-and-Mouth Disease Virus By Sequential Passages In Mice

Foot-and-Mouth Disease in cattle was successfully controlled bythe usage of attenuated vaccine produced by sequential passages inmice in 1960s. However, it elicited and maintained long term epidemicsin pigs because of its high virulence to swine compared with lowervirulence to cattle. On our conjecture, Gene 3A may be the determinantof the virulence of FMDV. During the course of long term consecutivepassages, a deletion occurred in the nucleotide sequence of gene 3A. Thealtered nonstructural protein 3A possibly contributed to defining itsporcinophilic phenotype and decreased virulence in cattle.Six strains of Serotype 0 FMD viruses (P35~. P53~. P57~ P6l~ P70~P105) were cloned by routine techniques of molecularbiology, sequenced by automatic sequencing, compared and analyzed byGenedoc software to study their genetics and variation according tothe changes in the nucleotide sequence of gene 3A and to provide thebasic materials for further research in the aspects of virus virulenceand host range as well as the other functions of gene 3A.58By comparison with the nucleotide sequence of gene 3A of theseviruses, it was found that there was a 45-base-deletion in the sequence of P61, P70 and P105 in contrast with a single base change in P35, P53 and P57. This deletion located in the second half of gene 3A and the loci and the number of bases were completely identical. Surprisingly,it was also found that there was a deletion of 30 bases in the sequence of OZK/93,an epidemic Type 0 FMD virus strain. This may suggest apossible role of 3A in determining virus virulence and tropism to hogs.Besides this deletion, other changes were within the range of fivebases. The sequence of gene 3B had no changes in exception of one base difference between P35 and other viruses.A more detailed demonstration of the function of gene 3A will await further investigation.