Marty Misener from South West Ontario Veterinary Services, Can ASFV Contamination of Field Crops be Eliminated with Drying and Heat Treatment?

The ASF virus (ASFV) is efficiently transmitted via blood and meat that is derived from infected animals. The virus is extremely stable in a wide range of environmental conditions and soil types. Field crops originating from areas with ASF in wild boar and thus with high environmental ASFV contamination may be at risk for virus introduction into domestic pig herds. This is a real threat for introduction of ASFV into North America as a number of feed ingredients such as organic soybean meal are currently may be imported from ASFV positive countries. Avoiding importation of feed ingredients from ASFV positive countries would significantly reduce the risk of introduction. There has also been a lot of discussion about the use of mitigants such as medium chain fatty acids in feed as a means of reducing the probability of virus transmission but these products are not always effective. These researchers at the Friedrich-Loeffler-Institute in Germany wanted to test the effect of drying and then further heat treatment on the inactivation of ASFV on six different types of field crops. The study included wheat, barley, rye, triticale, corn, and peas that were contaminated with infectious blood. Samples were analysed for the presence of viral DNA and infectious virus after 2 hr drying at room temperature or after drying and 1 hr exposure to moderate heat at a specific temperature between 40°C and 75°C .

The researchers found the following:

  • ASFV genome was detected in all samples by real-time polymerase chain reaction (PCR), including samples that had been dried for 2 hr and incubated for 1 hr at 75°C.
  • No infectious virus could be detected after 2 hr drying using virus isolation in porcine macrophages in combination with the detection of ASFV by the haemadsorption test (HAT).

Take Home Message:

  • The risk of ASFV transmission via contaminated crops is likely to be low if the crops are incubated for at least 2 hr minimum at room temperature or 1 hour at at 75°C.
  • The best way to minimize the risk of transmission of ASFV via crops from ASF-affected zones is to avoid importation of grains from ASFV positive zones.

Ref: Melina Fischer , Maarten Mohnke , Carolina Probst , Jutta Pikalo , Franz J Conraths , Martin Beer , Sandra Blome  Stability of African swine fever virus on heat-treated field crops   Transbound Emerg Dis . 2020 Nov;67(6):2318-2323. doi: 10.1111/tbed.13650. Epub 2020 Jun 8.