Risk assessment of African swine fever transmission by spray-dried porcine plasma in piglet feed and the effect of UV irradiation treatment as an additional safety step

Clazien J. De Vos^1*Lourens Heres²Aldo Dekker¹Manon Swanenburg¹W Meindert Pelser²Jacob Post¹Marcel M Hulst¹

• ¹Wageningen Bioveterinary Research, Wageningen University and Research, Lelystad, Netherlands
• ²Sonac / Darling Ingredients, Son, Netherlands

The increase of African swine fever (ASF) outbreaks worldwide has raised concerns about the feeding of spray-dried porcine plasma (SDPP) to pigs. The processing of blood into SDPP should thus guarantee sufficient inactivation of ASF virus (ASFV) to render a safe product. The objective of this study was to evaluate (i) the required level of inactivation if blood of ASF-infected pigs would be processed into SDPP and fed to piglets, and (ii) the additional safety achieved if UV treatment is applied to plasma before spray-drying. A quantitative microbial risk assessment (QMRA) model was built to assess the infection probability (P_inf) of weaned piglets fed with SDPP produced from blood collected from a single ASF-infected herd. The inactivation of ASFV by UV treatment was quantified using a mobile, laboratory-scale “Cold Pasteurization” apparatus (Lyras inc, Aalborg, Denmark). Porcine plasma spiked with blood collected from pigs experimentally infected with ASFV was irradiated with different doses of UV-C and the log10 reduction factor (LRF) calculated. An average LRF of 2.2. was achieved by the highest dose of UV-C irradiation applied (~137 Joule/m2). QMRA model results indicate that an LRF of 5 needs to be achieved during processing to arrive at a median value of P_inf < 0.01, i.e. less than 1 out of 100 ASF-infected batches resulting in new infections. With an LRF of 8, also the 95th percentile value of P_inf is < 0.01. These results were compared to reported LRF values of spray-drying and dry storage of SDPP, which varied between 5.2 and 11.1. Applying UV-C irradiation as an additional step in SDPP production thus provides extra safety guarantees as the combined inactivation levels of spray-drying, dry storage and UV treatment are likely to result in an overall LRF  8, implying a very low risk of new ASF infections (median P_inf 7.310-6; 95th percentile 1.610-3). The QMRA model did not account for the probability that ASF-infected pigs are unintendedly processed into SDPP. This probability is low if SDPP is not sourced from pigs in ASF-infected areas, therewith further reducing the ASF infection risk of SDPP.