Inactivation of porcine reproductive and respiratory syndrome virus and Seneca virus A in cell culture using chemical feed additives

Abstract

Seneca virus A (SVA) and porcine reproductive and respiratory syndrome virus (PRRSV) have caused significant economic losses to swine production in the United States. Recently, contaminated feed and feed ingredients have been considered risk factors for swine virus transmission. The use of chemical feed additives has been discussed as one potential management strategy to mitigate this risk. The objective of this study was to evaluate the efficacy of medium chain fatty acid-based (MCFA) and formaldehyde-based (FORMALD) liquid antimicrobials against SVA and PRRSV in a cell culture model. Viral stocks of SVA and PRRSV (10⁶ 50% tissue culture infectious dose per ml, TCID₅₀/ml) were mixed with different concentrations of MCFA or FORMALD in minimum essential media. Ten-fold serial dilutions of each virus-mitigant mixture were performed in triplicate for inoculation onto confluent monolayers of porcine kidney (PK-15) and African green monkey kidney (MARC-145) cells for SVA and PRRSV, respectively. Viral titers after exposure to each mitigant were determined by the serial dilution endpoint method and calculated using the method of Reed and Muench. The differences between the titer of the control virus (no mitigant) and the mitigant-treated samples were used to measure antiviral activity. FORMALD reduced the titers of both SVA and PRRSV at concentrations above 0.6% and 0.15%, respectively. MCFA reduced the PRRSV titer at concentrations greater than 0.25%. No significant reduction of SVA titers were detected after exposure to MCFA up to 5%. This study provides evidence suggesting that both MCFA and FORMALD may be used as potential feed additives to mitigate the risk of SVA or PRRSV transmission through contaminated animal feed or ingredients.