GENETIC-VARIATION OF FOOT-AND-MOUTH-DISEASE VIRUS FROM FIELD OUTBREAKS TO LABORATORY ISOLATION

Foot-and-mouth disease virus (FMDV), by nature of its RNA genome, poss esses a high rate of mutation during replication. This results in exte nsive genetic polymorphism of virus populations in nature. The emergen ce of FMDV variants during replication has been reported. Genetic chan ges in the viral capsid protein (VP1) gene can result in amino acid ch anges affecting the immunodominant epitopes of FMDV. The genetic heter ogeneity of FMDV in the field and the antigenic variants observed afte r cell culture isolation has been investigated by PCR sequencing and r eactivity with monoclonal antibodies. These methods were applied to vi ruses causing two different outbreaks of FMD before and after replicat ion in cell culture and in the animal host. The VP1 region of the geno me was amplified by PCR and sequenced to reveal variant sequences iden tified after passage and to determine their presence in the original f ield tissue. In one case, reactivity with monoclonal antibodies was lo st after passage as a result of an amino acid change in the subpopulat ion. These findings suggest that host cells can select specific virus genetic and antigenic subpopulations during virus isolation and propag ation.