Virulence comparison of 4 porcine circovirus type 2 (PCV-2) genotypes: 2a, 2b, 2d, and 2e with a single infection and co-infection with PCV-2 and porcine reproductive and respiratory syndrome virus (PRRSV).

The objective of this study was to compare the virulence of 4 porcine circovirus type 2 (PCV-2) genotypes (2a, 2b, 2d, and 2e) in pigs singly infected with 1 of these 4 PCV-2 genotypes and pigs dually infected with a combination of 1 of the 4 PCV-2 genotypes and porcine reproductive and respiratory syndrome virus (PRRSV). Virulence was determined based on levels of PCV-2 loads in the blood and lymph nodes and the severity of lymphoid lesion. Within the singly infected groups, PCV-2a, PCV-2b, and PCV-2d resulted in a similar virulence to each other and all were more virulent than the PCV-2e groups. Within the dually infected groups, the combination of PCV-2d and PRRSV was more virulent than the other 3 PCV-2 genotypes (2a, 2b, and 2e), each in combination with PRRSV. Both PCV-2a+PRRSV and PCV-2b+PRRSV were more virulent than PCV-2e+PRRSV in dually infected pigs. This increased virulence of PCV-2d compared to the other 3 PCV-2 genotypes (2a, 2b, and 2e) may be attributed to an extra amino acid (lysine residue) found within open reading frame 2 (ORF2) of PCV-2d. In contrast, extra amino acids in ORF2 may decrease the virulence of PCV-2e when compared to the other 3 PCV-2 genotypes (2a, 2b, and 2d). The results of this study demonstrated that PCV-2d was the most virulent PCV-2 genotype in pigs co-infected with PRRSV. The results also suggest that genetic differences in the ORF2 of PCV-2 may affect the virulence of PCV-2 genotypes.