Viral load, lung lesions, and average daily gain in a porcine reproductive and respiratory syndrome virus-2 challenge model

Abstract

Objective: To determine viremia, percentage lung lesions, average daily gain (ADG), and their associations after a porcine reproductive and respiratory syndrome virus-2 (PRRSV-2) lineage 1 (open reading frame 5 restriction fragment length polymorphism 1-7-4 [ORF5 RFLP 1-7-4]) challenge in pigs vaccinated with either a PRRSV-2 lineage 8 modified live virus (MLV) vaccine, a PRRSV-2 lineage 1 MLV vaccine, or not vaccinated. Materials and methods: Pigs were vaccinated with either Fostera PRRS (n = 52), Prevacent PRRS (n = 50), or sterile water (nonvaccinated; n = 47). Four weeks after vaccination, all animals were challenged with PRRSV-2 lineage 1 ORF5 RFLP 1-7-4. Viremia was determined at 3-, 6-, and 12-days post challenge. Body weights were recorded to determine ADG throughout the experiment. Percentage lung lesions were assessed on day 40 (12 days post challenge). Results: Vaccination with either vaccine reduced (P < .001) lung lesions, increased (P < .001) ADG post challenge, and better controlled viremia (P < .001) compared to nonvaccinated pigs. Implication: A commercially available PRRSV-2 lineage 8 vaccine was as effective as a PRRSV-2 lineage 1 vaccine against a heterologous PRRSV-2 lineage 1 viral challenge.