SHIC Study Examines Mitigant Efficacy in Pathogen-Contaminated Feed

March 25, 2020 — Paul Sundberg

The Swine Health Information Center (SHIC) funded a study to evaluate the mitigation potential of chemical feed additives following natural consumption of contaminated and mitigated feed. Prompted by concern over feed biosecurity and other research results suggesting feed can harbor viable viral pathogens and potentially serve as source of infection to susceptible pigs, this study was recently completed and the full report is posted on the SHIC website. Results showed chemical mitigation alone may not be able to completely prevent transmission of pathogens through feed.

During the laboratory phase of another project feed additives were screened against several swine pathogens. Results from that study showed that a select group of feed additives have the potential to be used as chemical mitigants to decrease the risk of pathogen transmission through feed. Limitations of the laboratory study, however, included the fact that: 1) mitigation results were based mostly on laboratory assays; 2) a single contamination dose was used (105 TCID50) for each pathogen; 3) the reduction in titers observed after mitigation may not be sufficient to prevent infection/transmission of those pathogens after ingestion of feed.

Researchers addressed these limitations by performing a feed trial experiment in which animals were allowed to ingest contaminated feed (Senecavirus A (SVA) and porcine epidemic diarrhea virus (PEDV)) or contaminated feed (SVA and PEDV) with a mitigant (A, B, and C) for three consecutive days. For this animal trial, the top three candidate mitigants, A (a medium chain fatty acid), B (a blend of organic acids and methionine hydroxy analogue (HMTBa)), and C (a blend of medium chain fatty acids), from the previous laboratory mitigation project were selected. After feeding, each animal was sampled individually and levels of viremia, virus shedding, and viral load in tissues were determined by RT-qPCR. Importantly, animals in each treatment group were fed mitigated feed during the entire experimental period (14 days).

Results showed that under the conditions used in the animal clinical trial, in which every animal in the study ingested contaminated feed via natural feeding the efficacy of the mitigants was low. Out of the three mitigants tested, only mitigant A reduced SVA infection when a low contamination dose (105) of the virus was used, as evidenced by lower levels of virus shedding and viral load in tonsil of exposed animals. When the contamination levels were increased to 106 and 107 TCID50, no significant differences were observed between the mitigated and non-mitigated treatment groups, with all animals presenting similar levels of virus shedding and viral load in tonsil.

These results suggest that chemical mitigation alone (with mitigants A, B, and C) may not be able to prevent transmission of pathogens through feed. Factors that may affect and/or complicate pathogen mitigation in feed include:

1. the contamination dose, which in this trial were relatively high;
2. the fact that the chemical mitigants don't reduce viral load in feed to levels that are non-infectious to susceptible pigs; and
3. possible poor contact and/or short contact time of the mitigant with the virus.

Consequently, if or when these compounds gain FDA approval for feed viral mitigation, adding them onto alternative strategies such as storage time and importation of feed ingredients from known and trusted sources should be considered to safeguard the US swine industry from unwanted viral pathogens. Additionally, studies on the mechanism of action of potential mitigants may also allow selection of those compounds that present the greatest chance of virus inactivation in the feed matrix or that modulate the pig immune responses, thus reducing the risk of potential pathogen transmission through feed.

Funded by America's pork producers to protect and enhance the health of the US swine herd, SHIC focuses its efforts on prevention, preparedness, and response. As a conduit of information and research, SHIC encourages sharing of its publications and research for the benefit of swine health. Forward, reprint, and quote SHIC material freely. For more information, visit http://www.swinehealth.org or contact Dr. Sundberg at psundberg@swinehealth.org.

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Paul Sundberg, Executive Director, Swine Health Information Center