Doug MacDougald from Southwest Ontario Veterinary Services, ASF Viral Load Required To Cause Infection Via Feed Is Low

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African  swine  fever  is  currently  one  of the  most  significant  threats  to  worldwide swine  production.  ASF  does  not  cause human   disease.   ASF   is   a   reportable disease that has a devastating effect on the health of infected  pigs.  The  closure  of  borders  to  trade  can have  a  catastrophic  effect  on  countries  that  rely  on exporting  a  significant  amount  of  their  production. Preventing  introduction  of  the  virus  into  countries that  are  still  free  of  the  disease  is  therefore  of primary importance. The global distribution of feed ingredients is one of many ways that this virus can move over very long distances.

Among  the  feed  ingredients  that  were identified  as  higher  risk,  unprocessed  grains  and oilseeds  (such  as  corn  and  soybeans)  and  their associated  meals  destined  for  livestock  feed  and which originate in countries that have reported cases of ASF in the last five  years have been deemed the highest risk. The Canadian Food Inspection Agency is  working  with  groups  such  as  ANAC  to  develop risk   reduction   programs   for   feed   ingredients imported  from  ASF  infected  countries. CFIA has also declared secondary control zones around major ports of entry and this provides authority to take steps to mitigate this risk. ANAC’s “National  Biosecurity  Guide  for  the  Livestock  and Poultry  Feed  Sector”  which  is  now  available,  is designed  to  help  the  feed  industry  develop  strong biosecurity protocols for the feed supply chain.

Dr. Megan Niederwerder at Kansas State University is  leading  a  team  that  is  adding  scientific  evidence that confirms how ASF could spread across borders via  feed  and  feed  ingredients.  This  research  is carried  out  in  the  Biosecurity  Research  Institute,  a biosafety  level-3  facility,  that  has  the  capability  of safely handling ASF. Their first study found that the ASF  virus  could  survive  in  a  simulated  overseas feed  shipment.  This  current  study  has  helped  to “connect the dots” by demonstrating that ASF virus can  be  transmitted  from  infected  feed  to  the  pig through   the   natural   oral   consumption   of   the contaminated feed and liquid.

The authors pointed out that proving the absence or presence of ASF virus in a batch of feed is difficult because the pockets of infection can be very small. It is not as simple as doing a viral detection test on suspect  loads  of  feed.  Sub-sample  selection  can make finding the ASF virus in a load of feed akin to “finding a needle in a hay stack”. Because pigs will consume  an  entire  load  of  feed,  however,  finding the  infection  after  it  is  fed  to  pigs  is  more  of  an eventuality.  It  is  a  bit  more  like  “chewing  on  the entire   hay   stack   until   you   bite   down   on   the needle”. It’s going to happen if the needle is there!

The next research will focus on identifying ways to reduce  or  eliminate  the  ASF  risk  in  feed  and  this will   include   evaluating   the   use   of   chemical additives,  storage  time,  heat  treatments  or  other steps

Take Home Message

ASF   infection   can   occur   via   natural   oral consumption of feed or water.

The “Connecting of The Dots” in a scientific way is continuing. The  feed  industry  needs  to  develop  strong  feed import  and  biosecurity  protocols  as  part  of  the best management practices for the supply chain.

Submitted by Doug MacDougald, DVM

Ref: Niederwerder MC, Stoian AMM, Rowland RRR, Dritz SS, Petrovan V, Constance  LA,  et  al.  Infectious  dose  of  African  swine  fever  virus  when consumed naturally in liquid or feed. Emerg Infect Dis. 2019 May [date cited]. https://doi.org/10.3201/eid2505.181495

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