role of feed with ASFv
Specifically, the minimum infectious dose of ASFv Georgia 2007 in liquid was 100
(TCID50), whereas 104 TCID50
50% tissue culture infectious dose was the dose necessary for
infection in feed. Statistical modelling of repeated exposures to small vol- umes over time (i.e. consuming a contaminated batch of feed or drinking contaminated water) revealed an increased likelihood of infection as the number of exposures or total consumption volume rises. Taken together, ASFv is orally transmitted through natural consumption of contaminated plant-based feed, with the infection probability depend- ent on the quantity of virus present and the volume of feed consumed.
3
Can ASFv risks be reduced by feed biosecurity? As a relatively new area of specialisation in the bios- ecurity realm, feed biosecurity has become an im-
portant and widely recognised biosecurity target critical for the prevention of porcine viral disease entry onto farms. When examining feed ingredients as a potential pathogen source, several factors influence this biosecurity risk. • First, inclusion of the ingredient should be confirmed as nec- essary for swine health and growth, and it should lack a suitable, cost-effective and lower risk alternative.
• Second, the disease status of the country of origin for each ingredient should be considered, including swine disease outbreaks in specific regions or endemic diseases of widespread prevalence.
• As a third consideration, the environmental stability of the virus in the feed ingredient plays a role in risk.
• Finally, the agricultural or manufacturing practices used to produce the ingredient impact risk.
Feed, ingredient and feed mill biosecurity is essential for reducing infectious disease risks at all stages of swine pro- duction, and implementation of biosecurity procedures focused on feed can help address these risks. Breaches in feed biosecurity can result in virus contamination during the growing, harvesting, processing or post-processing of crops intended for swine feed. Many current biosecurity pro- tocols for swine farms can be directly translated to the feed mill environment.
4
How can ASFv risk be mitigated in feed? In addition to biosecurity and sourcing considera- tions, physical and chemical treatments of feed or
ingredients can be tools for risk mitigation of ASFv. Implementing feed quarantine, or storage of ingredients after import from high-risk countries and regions, is one strategy intended to allow virus decay prior to incorporation of the ingredients into swine diets. Heat treatments and storage of crops and plant-based ingre- dients have demonstrated experimental efficacy in reducing the infectivity of swine viruses such as ASFv and PEDv. For example, research in 2020 by Melina Fischer and others from the German Friedrich-Loeffler-Institut contaminated field crops, including wheat, barley, rye, triticale, corn and peas, with ASFv Armenia 2008 prior to subjecting the crops to a two-hour drying period at 20°C. After two hours of storage at room temperature, no infectious virus could be isolated from the unprocessed crops.
▶ ALL ABOUT FEED | Volume 29, No. 4, 2021 7
Feed ingredients can be of par- ticular concern as a potential source of spreading viruses.
PHOTO: SHUTTERSTOCK
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