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

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 (<i>P_inf</i> ) 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 <i>P_inf</i> < 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 <i>P_inf</i> 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 <i>P_inf</i> 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.