Researchers update ASF holding times

Researchers update ASF holding times
Mar 02, 2020

Scientists have discovered that ASF can be viable in feed ingredients for longer than originally determined 

By Jackie Clark
Staff Writer

Researchers have revaluated the amount of time African swine fever (ASF) can stay viable in feed ingredients, resulting in extended holding times to ensure degradation of the virus in potentially infected feed.

The previous holding time values were determined in March 2018. That study, however, had several limitations.

“We calculate half lives based on the concentration of the virus and how it changes over time,” Dr. Megan Niederwerder told She’s the lead researcher and an assistant professor of diagnostic medicine and pathobiology at Kansas State University.

“In the first publication, essentially we were estimating the half lives based on titration only at the conclusion of the study and the viral inoculation. One of the factors that that doesn’t take into account is if the decay of the virus is non-linear. It also doesn’t take into account the differences in the ability to quantify the virus after inoculation, which is different between feed ingredients,” Niederwerder explained. Titrations are used to quantify the amount of virus present.

With that limited data, the scientists could not determine standard error or confidence intervals, so they wanted to repeat the study with more data collection points to ensure the accuracy of the half-life values.

“We repeated the entire study looking at the viral quantity over time, during the 30-day trans-oceanic model which simulates the variable temperature and humidity conditions that feed ingredients would be subjected to during trans-oceanic shipment,” Niederwerder said.

This time, the researchers quantified the virus four times: on day one, day eight, day 17 and day 30.

Multiple measurements over the 30 days “gave us more of an idea about how the virus decays over time. And what we see is that the virus seems to decay more rapidly early on. Then it has a slowed rate of decay in the second half of the model,” she explained.

“It looks more like an exponential decay rather than a linear decay,” she added.

The decreasing rate of decay of ASF in feed ingredients means that the virus remains viable for longer than originally thought. The scientists conducted this research using a strain like the one circulating in Asia and Europe, so their findings have implications for the current ASF crisis.

“What we think could potentially be contributing to this particular strain spreading to so many places is that there may be an increase of environmental stability of the virus, not only in feed ingredients, but potentially in other environmental conditions as well. (This), of course, would lengthen the amount of time that the virus is infectious,” Niederwerder said.

As a result of the study, “the holding times have increased for several of the ingredients,” she said.

This research is key to the development and upholding of feed biosecurity protocols.

Feed biosecurity includes “looking at where your feed ingredients are being imported from, and the likelihood of the contamination factor. … Do your due diligence for the feed manufacturing facilities,” Neiderwerder said.

The findings of the study of ASF in feed ingredients “not only increases the holding time but also re-emphasizes some of these other procedures and policies that can be put in place to reduce the risk through feed ingredients,” she explained.

Next, the team at Kansas State University wants “to look at whether there is a temperature in which we can recommend or reliably see that the virus decays at a faster rate,” Neiderwerder said.

Further research on temperature’s impact on virus stability may help adjust and specify holding times to the specific context of the feed ingredient’s harvest and transport.

Rat0007\iStock\Getty Images Plus photo  

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