Negative impact of porcine reproductive and respiratory syndrome virus infection on the efficacy of classical swine fever vaccine

Recent findings suggest that porcine reproductive and respiratory syndrome virus (PRRSV) possesses immunomodulatory properties. To investigate the effect of PRRSV infection on classical swine fever (CSF) vaccine efficacy, 17-day-old pigs were divided into five groups. The experimental group was infected with a Thai PRRSV (US genotype) a week before CSF vaccination and challenged with a virulent CSF virus (CSFV) 3 weeks following vaccination. The control groups received no PRRSV infection, no CSF vaccination, no CSF challenge, or in combination were included. The results demonstrated that PRRSV infection significantly inhibited host immune response that resulted in vaccination failure in the subsequent CSFV exposure. Following CSF challenge, the PRRSV-infected, vaccinated pigs exhibited clinical, virological and pathological features resembled to those of the non-vaccinated groups. The findings indicated that CSF immunization during an acute phase of PRRSV infection could result in vaccination failure.