This is our Friday rubric: every week a new Science Page from the Bob Morrison’s Swine Health Monitoring Project. The previous editions of the science page are available on our website.
Kansas State University researcher Allison K. Blomme, Tate L. Ackerman, Cassandra K. Jones, Jordan T. Gebhardt, Jason C. Woodworth, Chad B. Paulk, and Roman M. Pogranichniy share findings about how long PRRSV can be harbored in different feed products.
Introduction
Although the half-life of PRRSV is shorter in feedstuffs than in other matrix types, there is evidence that it can survive in feedstuffs, which could be a concern for the introduction of virus into a farm. The most common method for the detection of PRRSV or any other virus in animal feed is by using PCR and non-standardized extraction methods. An assay using MARC-145 cells to determine infectivity would allow for faster, more cost-effective identification of infectious PRRSV in animal feed. Therefore, we used virus isolation (VI) to determine tissue culture infectivity and RT-qPCR to determine the stability of PRRSV strain P129 in solvent-extracted soybean meal (SBM), dried distillers grains with solubles (DDGS), complete swine feed (FEED), or medium (DMEM) at 4°C, 23°C, or 37°C for up to 3 d.
Methods
Three feed matrices were used (SBM, DDGS, and FEED [a swine gestation diet with 78% corn, 17% soybean meal, and 0.5% fat]). 10 g of each were inoculated with 1 mL of type 2 PRRSV strain P129 with a concentration of 105.4 TCID50/mL for a final concentration of 104.4 TCID50/g of matrix and incubated at 3 temperatures (4, 23, and 37°C). Samples of each treatment were taken at regular intervals (1, 24, 48, and 72 h post-inoculation – hpi) and processed. Supernatant was titrated and used to inoculate confluent MARC-145 cells to determine infectivity. RNA was extracted from each supernatant sample and tested by RT-qPCR to determine any change in detectable virus RNA across matrix type, temperature, and time.
Results
An interaction (p = 0.028) was observed for matrix × temperature × hour for live virus detected by VI (Table 1). At 4°C, the concentration of infectious virus was greatest in DMEM, intermediate in SBM, and lowest in DDGS and FEED. DMEM also had the greatest concentration of infectious PRRSV at 23°C over time; a higher infectious virus concentration was maintained in SBM for longer than in DDGS or FEED. At 37°C, a greater concentration of infectious virus was sustained in DMEM than in the feedstuffs, with concentrations decreasing until 48 h post-inoculation. Only matrix type influenced the quantity of viral RNA detected by RT-qPCR (p = 0.032).
Conclusion
More viral RNA was detected in the virus control than in DDGS; SBM and FEED were intermediate. By VI, we found that infectious virus could be harbored in SBM, DDGS, and FEED for a short time.
The full paper can be found at: https://doi.org/10.1177/10406387231185080
