Impact of porcine reproductive and respiratory syndrome virus and porcine circovirus-2 infection on the potency of the classical swine fever vaccine (LOM strain)

• The antibodies levels in LOM-vaccinated pigs were not affected by infection of PRRSV or/and PCV2.
• Co-infection with both PRRSV and PCV2 may affect LOM strain replication or viral activity.
• The LOM strain might replicate with high titer and promote the spread of disease to other tissues.
• CSF vaccine (LOM strain) can afford to protect complete against virulence CSFV infection.

The classical swine fever (CSF) vaccine, which is derived from the LOM strain of the CSF virus (CSFV), induces protective immunity against CSFV infection. However, several factors influence vaccine efficacy. Evidence suggests that infection by porcine reproductive and respiratory syndrome virus (PRRSV) and/or porcine circovirus 2 (PCV2) reduces the efficacy of several vaccines. Here, we examined the effect of PRRSV or PCV2 alone or co-infection by PRRSV/PCV2 on the potency of the LOM vaccine in pigs. Neither CSFV antibody levels nor the period during which CSFV antigens were detectable in LOM-vaccinated pigs were negatively affected by infection by PRRSV or PCV2. However, co-infection with PRRSV/PCV2 may affect the replication or activity of the CSF vaccine virus in pigs vaccinated with the LOM strain, although CSFV antibody levels were not negatively affected. Nevertheless, the LOM vaccine afforded complete protection against a virulent strain of CSFV.