Environmental persistence of porcine epidemic diarrhea virus, porcine delta corona virus, and transmissible gastroenteritis in feed ingredients

Abstract Text:

Porcine epidemic diarrhea virus (PEDV), porcine delta corona virus (PDCoV), and transmissible gastroenteritis (TGEV) are major threats to swine production. Investigations of recent outbreaks confirmed that contaminated feed plays a role in virus transmission. This risk makes it necessary to evaluate the survival of such viruses in various feed ingredients. The objective of our experiment was to characterize the inactivation of PEDV, PDCoV, and TGEV in various feed and ingredient matrices. To determine differences in virus survival, 5 g samples of complete feed, spray-dried porcine plasma, meat meal, meat and bone meal, blood meal, corn, soybean meal, and low, medium, and high oil dried distillers grains with solubles were weighed into separate scintillation vials. These samples were inoculated with 1 mL of PEDV, PDCoV, or TGEV and incubated at room temperature for up to 56 d. At each time point, surviving virus was eluted and the supernatant was inoculated into vero-81 cells for PEDV, or swine testicular cells for PDCoV and TGEV. Cells were observed daily for 10 d for cytopathic effects, and this information was used to calculate a median tissue culture infectious dose (TCID₅₀) using the Karber method. Inactivation kinetics were determined using the Weibull model. A delta value was estimated from the model, indicating the time necessary to reduce virus concentration by 1 log. This delta value was then compared across ingredients using the mixed procedure of SAS, and correlations between ingredient proximate analysis data and delta values were determined. Results showed that soybean meal had the greatest delta value (7.50 d) for PEDV compared with other ingredients (P < 0.06). Likewise, PDCoV (42.04 d) and TGEV (42.00 d) delta values were highest in soybean meal (P < 0.001). There was a moderate positive correlation between moisture and the delta value for PDCoV (r = 0.49, P = 0.01) and TGEV (r = 0.41, P = 0.02). There was also a moderate negative correlation between lipid content and the delta value for TGEV (r = -0.51, P = 0.01), suggesting that TGEV is less stable in ingredients with greater lipid content compared to ingredients with less lipid content. In conclusion, these results indicate that the first log reduction of PDCoV and TGEV takes the greatest amount of time in soybean meal and it appears to be the result of greater moisture content.

Keywords:  Feed, inactivation kinetics, virus transmission