Experimental Efficacy of an Alphavirus Vectored RNA Particle Vaccine Against Porcine Parainfluenza Virus-1 in Conventional Weaned Pigs

Parainfluenza viruses are a common cause of respiratory illness in many species. In this study, experimental, alphavirus-derived RNA particle vaccines either with or without adjuvant were evaluated against porcine parainfluenza virus 1 (PPIV1) challenge and compared to live virus exposure. Groups of ten, three-week-old pigs were vaccinated intramuscularly with an adjuvanted RNA particle (RPAdj/C) or non-adjuvanted RP (RP/C) or administered an intranasal live exposure (LE/C) dose of PPIV1 at 0- and 21-days post vaccination (DPV) followed by challenge with PPIV1 at 40 DPV. In addition, two groups were included as non-vaccinated, non-challenged (NV/NC) and non-vaccinated, challenged (NV/C) controls. Intranasal virus exposure and RP vaccination, regardless of adjuvant, reduced PPIV1 shedding in nasal swabs by 5 days post inoculation (DPI). All vaccinated or exposed pigs seroconverted as shown by enzyme-linked immunosorbent assay and serum virus neutralization. The antibody isotype detected in bronchoalveolar lavage fluid (BALF) LE/C was predominantly IgA while RP vaccination induced an IgG response. Reduced PPIV1 antigen was observed in the LE/C, RP/C and RPAdj/C groups in lung, trachea, or nasal turbinate epithelium. Additionally, the RPAdj vaccine significantly reduced nasal shedding compared to NV/C pigs although not as much as LE/C pigs. These results suggest vaccination could mitigate PPIV1 infection in commercial systems.