Restriction fragment length polymorphism of ORF6 and ORF7 genes of porcine reproductive and respiratory syndrome virus (PRRSV) vaccine strains registered in the Czech Republic

Restriction fragment length polymorphism (RFLP) of open reading frames 6 and 7 was applied to comparative genetic analysis of live attenuated vaccine strains (Amervac-PRRS/A3, Porcilis PRRS, Ingelvac PRRS) of porcine reproductive and respiratory syndrome virus (PRRSV), registered in the Czech Republic, six field viruses (L-588, L-1606, L-2053, L-3305, L-6558, L-6791), and three PRRSV local field isolates (CAMP V-502, CAMP V-503, VOS 2878) found in pig herds in the Czech Republic and Slovak Republic. The set of restriction enzymes Hae II, Alu I and BsaJ I allowed the differentiation of local field isolates, field viruses of PRRS, and vaccine strains of the European genotype from North American genotype, but could also distinguish between viruses of the same genotype. Five different RFLP patterns were obtained from twelve examined PRRS viruses by combination of the above restriction enzymes. RFLP code 1-1-1 was the most frequent digestion pattern within all PRRS field viruses (L-588, L-1606, L-2053, L-3305, L-6558, L-6791), CAMP V-502 isolate and vaccine strain Porcilis PRRS, which is suggestive of higher antigenic identity among the compared viruses. In the North American types (Ingelvac PRRS vaccine strain and VOS 2878 isolate), homogeneity in restriction patterns (code 2-x-4) was recorded. These studies indicate that PCR-based RFLP analysis of ORF6 and ORF7 of genes might be a suitable tool in epidemiological studies of PRRSV, similarly to the studies based on genetic analysis of ORF5 gene.