The timing was perfect for this question to be addressed, as April 2021 was the moment that 2 major reviews were launched related to this subject. The European Food Safety Authority (EFSA) published a Scientific Opinion to all kinds of risk factors in the spread of African Swine Fever virus and so did Dr Megan Niederwerder of Kansas State University in a great overview summarising years of scientific work to the role of feed in the spread of the virus. The recorded version of the presentation at the VAAFF can be found at the bottom of the blog.

With regard to ASF virus and the role of pig feed, to my knowledge I can see at least 4 different pathways that need some attention, with different degrees of liability.

ASF virus and swill feeding

A lot of debate about swill feeding is not necessary in this context. It is widely known that swill (or food waste) is a potential source of spreading viruses. The picture on the side shows the swill that brought African Swine Fever virus to Brazil in 1978 and it is thought that swill feeding may also have caused the introduction of ASF virus in China in 2018. Now surprise then that China forbade swill feeding in that year. In doing so, it followed the example of for instance the UK (2001, after Foot-and-Mouth Disease), the EU (2003), Brazil (2007) and the US (exact situation is different per state).

ASF virus and forage

Forage is a route that needs some discussion. In an interview with Prof Zygmunt Pejsak in 2018, he explained that one of the first (backyard) farms that got infected with ASF in Poland was due to the use of hay and straw. The EFSA opinion of April 2021 also clearly states that feeding forage from ASF affected areas to the pigs were risk factors for ASF incursion in backyard farms.

ASF virus and blood plasma

In this context it is good to give some attention to spray-dried porcine blood plasma as well, even though the opposite has become clear – when processed properly, this is not a route of transmission of ASFv. Yet in 2018, soon after the outbreaks of ASF virus in China, the authorities there suspended the use of porcine plasma. It was re-allowed in December 2018 after a series of checks by the Chinese Ministry of Agriculture and Rural Affairs.

These days, roughly 65% of the worldwide market is produced by companies being attached to the European Animal Protein Association (EAPA) or the North American Spray-Dried Blood Plasma Producers (NASDBPP). Sourcing and production guidelines of both organisations are very strict to exclude any potential risk. That again, was confirmed by the EFSA opinion.

ASF virus and mechanical carriers

Feed and raw materials can also act as mechanical carriers of swine viruses, so much has become clear in the United States since 2013. In that year, Porcine Epidemic Diarrhoea virus (PEDv) entered the US, and even though the real source of infection was never identified, feed bags might have been involved. That has caused a growing worry in the US about the role of feed ingredients in virus spreading, something which is reflected in a large number of publications in which often Kansas State University is involved.

In 2018, ASF virus was identified as a virus that could be transmitted through feed, which included e.g. different types of soybean meal as well as complete feed. ASF was found to be easily transmitted through consumption and it could also survive in a hypothetical 30-day oceanic voyage. Now, saying that it is possible is not the same as saying that it is likely, and the latter is exactly the message that the EFSA is giving in its scientific opinion of April 2021. “Other risk pathways are more likely to require risk management,” it stated.

The second question to be answered was whether pig feed could also be part of the solution for ASF. Again, I identified at least 3 different routes that are being discerned.

Feed mill biosecurity

At Kansas State University in 2020, a trial was done in which under biosecure circumstances it was tested whether or not ASF virus could spread inside a feed mill. The results were daunting, the scientists reported: “Once ASFv was experimentally introduced into a feed manufacturing environment, the virus became widely distributed throughout the facility.”

So what could feed mills do? Iowa feed mill manager Jarrod Plants, in a presentation given last year at the digital conference SwineTalks in 2020, spoke of a «biosecurity matrix,» i.e. being well prepared with a clear plan, depending on the level of emergency in relation to ASF virus, ranging from for the potential presence of ASF virus, from guarded to critical.

Secondly, being critical towards both necessity as well as the source of the ingredients can be a step, and thirdly there are various ways to inactivate the virus in feedstuffs, by e.g. quarantine or heat treatment. Each method, however, also has its own drawbacks.

Feed ingredients

In a study in 2020, Dr Megan Niederwerder identified 2 possible feed ingredients that could reduce virus infectivity. 1 of them includes the use of aqueous formaldehyde, the other applies the use of certain medium-chain fatty acids (MCFA), which disrupt the viral envelope, like for instance can be seen in the product Feedlock of Agrimprove. This presentation, also held at the VAAFF, discusses the mode of action of MCFA.

Another route could be to enhance the pigs’ immunity and that road is being taken by plasma producer APC which is working on trials with CReSA-IRTA in Barcelona, Spain. Preliminary trials, like explained in this video, hint towards a delay of disease onset using plasma.

Protection via the oral route

Various other options are being tested to offer protection via the oral route. In a recent trial in 2020 scientists at CReSA-IRTA supplied faecal material of warthogs to pigs to observe if that would enhance the pigs’ immunity. Another pathway that is followed is supplying wild boar with vaccine under development, hidden in bait. These tests are being taken into account by e.g. both the vaccine candidates of the Universidad Complutense in Madrid, Spain as well as the Agricultural Research Service of the USDA.

So all in all, yes, feed can play a role in the spread of the ASF virus, but the risk is getting lower in the case where an industry is more professional. When swine production is being executed at a good commercial level, normally elements like swill feeding or providing random forage would not occur and any porcine plasma used will come from credible sources, thus excluding the risk of transmission.

And yes, feed can also play a part in forming a solution to overcome ASF, yet it can only be that – a part of an overall solution. Major elements in that context should also be proper biosecurity, vaccination, and above all the right human behaviour, based on sound knowledge and transparent communication.