PCV2 infection without manipulation does not cause clinical signs or post-weaning multisystemic wasting syndrome (PMWS), whereas, when PCV2 infection is combined with TTSuV1 infection, PMWS is produced. In addition, TTSuV1 co-infection with PRRSV is correlated with the development of porcine dermatitis and a nephropathy-syndrome-like condition in gnotobiotic pigs.