Classification of fetal resilience to porcine reproductive and respiratory syndrome (PRRS) based on temporal viral load in late gestation maternal tissues and fetuses.

•The fetal placenta is rapidly infected following PRRSV infection of the dam.•Fetal compromise was first observed about one week after infection.•Intra-uterine growth retarded fetuses are more resilient to PRRSV.•Viral load in fetal thymus is a strong predictor of PRRSV resilience.