A comparison of the severity of reproductive failure between single and dual infection with porcine reproductive and respiratory syndrome virus (PRRSV)‐1 and PRRSV‐2 in late‐term pregnancy gilts

: The objective of this study was to compare the severity of reproductive failure caused by either a single or a dual infection with porcine reproductive and respiratory syndrome virus (PRRSV)-1 and PRRSV-2 in late-term pregnancy gilts. Pregnant gilts were intranasally administered PRRSV-1, PRRSV-2 or both at 3 weeks before the expected farrowing date (93 days of gestation). Regardless of single and dual infection, PRRSV-infected pregnant gilts experienced premature farrowing (103-109 days of gestation) compared with negative control gilts which carried their pregnancy to full term (114-115 days of gestation). Pregnant gilts infected with only PRRSV-1 had a significantly (p < 0.05) higher number of genomic copies of PRRSV-1 in their blood compared with dually infected gilts. Additionally, stillborn foetuses and live-born piglets from pregnant gilts infected with only PRRSV-1 had a significantly (p < 0.05) higher number of PRRSV-1-positive cells per unit area of tissue sections examined, compared to pregnant gilts dually infected with PRRSV-1 and PRRSV-2. In contrast, pregnant gilts infected with only PRRSV-2 showed no difference in the number of genomic copies of PRRSV-2 compared with dually infected pregnant gilts and there were no significant differences in PRRSV-2-positive cells per unit area in tissues of stillborn foetuses and live-born piglets from pregnant gilts infected with PRRSV-2 only compared with dually infected gilts. Interestingly, even though PRRSV-2 was shown to replicate more efficiently compared with PRRSV-1 in dually infected pregnant gilts, neither PRRSV type was able to exacerbate reproductive failure in pregnant gilts already dually infected with PRRSV-1 and PRRSV-2. Our results suggest that the severity of reproductive failure is similar between dual (PRRSV-1 and PRRSV-2) and single infection (PRRSV-1 or PRRSV-2).