1

Literature Review: Non-animal Origin Feed 

Ingredients and the Transmission of Viral 

Pathogens of Swine 

United States Department of Agriculture

Animal and Plant Health Inspection Service 

Veterinary Services

March 2019
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Table of Contents

1 Executive Summary...............................................................................................................................3

2 Acronyms ..............................................................................................................................................6

3 Introduction ..........................................................................................................................................7

4 Methods of the Literature Review......................................................................................................10

4.1 Overview .....................................................................................................................................10

4.2 Identification of studies and study selection..............................................................................10

4.3 Data extraction and quality assessment.....................................................................................12

4.4 Data synthesis and report writing...............................................................................................12

5 Animal-origin Feed Ingredients...........................................................................................................13

5.1 Spray-dried porcine plasma ........................................................................................................13

6 Literature Review Results ...................................................................................................................15

6.1 Risk factors for transmission and fomite survivability................................................................15

6.1.1 Risk factors for virus transmission ......................................................................................15

6.1.2 Virus survival in contact with fomites.................................................................................17

6.1.3 Summary of findings...........................................................................................................19

6.2 Epidemiology and outbreak investigations – PEDV and PDCoV .................................................20

6.2.1 Epidemiological reports, reviews and surveys....................................................................20

6.2.2 Feed and feed ingredients..................................................................................................24

6.2.3 Summary of findings...........................................................................................................26

6.3 Experimental studies on feed transmission with swine bioassays.............................................27

6.3.1 Experimental studies with swine bioassays using field-sourced challenge virus...............27

6.3.2 Experimental studies with swine bioassays using laboratory-sourced challenge virus .....29

6.3.3 Summary of findings...........................................................................................................33

7 Discussion............................................................................................................................................35

8 Appendix I: Sample data extraction form...........................................................................................39

9 Appendix II: Data synthesis table........................................................................................................41

10 References ......................................................................................................................................60
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1 Executive Summary

The United State Department of Agriculture (USDA) Animal and Plant Health Inspection Service (APHIS) 

Veterinary Services (VS) has conducted a literature review on the scientific evidence regarding whether 

non-animal origin ingredients of commercial swine feed could introduce or transmit viral pathogens of 

swine into or within the United States. The purpose of this literature review was to identify, evaluate, 

and summarize the current scientific knowledge published through March 2018 regarding this topic and 

to identify information gaps, thereby, making the available evidence more accessible to decision makers, 

other stakeholders, and the scientific community. The results may support future scientific research 

and/or risk quantifying models for evaluating the risk (or likelihood) of entry of exotic viral pathogens via 

specific feed ingredients from source countries and subsequent exposure to United States (U.S.) swine 

populations. 

The methodology of this literature review follows the basic framework of a qualitative systematic review 

and has four main components: 1) identifying and selecting research evidence, 2) data extraction and 

quality assessment, 3) data synthesis, and 4) report writing [1]. Twenty-six published articles were 

included in the literature review. The major findings and information gaps are highlighted below: 

• A subset of the studies reviewed provided experimental evidence that swine viruses can survive 

in non-animal origin feed ingredients under various experimental conditions. Virus survival

times were variable (range: 7 days to > 180 days) and dependent on the simulated 

environmental conditions applied (e.g., temperature and relative humidity) and the virusingredient combination. Additional research is needed to verify virus survival times (and 

infectivity) in complete feed and feed ingredients, with various virus-ingredient combinations 

under various environmental conditions, including actual field conditions.

• Several experimental studies provided evidence that feed contaminated with virus can transmit 

disease to naive piglets. However, the experimental methods used in these studies such as 

spiking feed ingredients with a predetermined virus load or inoculating piglets via methods 

other than natural feeding behaviors do not necessarily reflect the field setting and results may 

not be generalizable to field conditions, particularly the large, commercial swine production 

setting. Additional laboratory and field-based studies are needed to determine the extent of 

reproducibility and applicability of these experimental findings to field settings.

• Several studies have investigated whether some individual feed ingredients are more likely than 

others to support virus survivability. Viable virus (meaning positive by virus isolation test and/or 

bioassay) was detected in the following non-animal origin ingredients that were experimentally 

spiked with virus: organic and conventional soybean meal, dried distillers grain with solubles

(DDGS), lysine HCL, D/L methionine, choline chloride, and vitamin D. Two experimental studies, 

using different experimental conditions, observed porcine epidemic diarrhea virus (PEDV) 

viability in three PEDV-spiked ingredients: conventional soybean meal, lysine, and choline 

chloride. Virus viability (and infectivity) as determined in separate swine bioassays was observed 
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with choline chloride and two swine viruses: PEDV and Seneca virus A. The implications of these 

findings for field settings are unclear. 

• A major knowledge gap exists with respect to potential source(s) of contamination and where 

feed or feed ingredients may be contaminated, particularly for non-animal origin ingredients 

sourced outside the United States. Current studies have produced little scientific evidence of 

how, or if, non-animal origin feed ingredients could become contaminated with swine viruses in 

regions outside the United States. The critical point(s) of susceptibility to contamination along 

the feed production, processing, and distribution continuum, from harvesting the plant-derived 

feed ingredients in the field to on-farm delivery of feed to swine premises, have not been 

identified. Neither the contamination route of exotic swine pathogens into non-animal origin 

feed (ingredients) nor the virus entry route into the United States has been decisively proven.

• Under laboratory-simulated model conditions, both the formaldehyde-based liquid 

antimicrobial SalCURB® and a medium chain fatty acid blend were concluded to be effective 

chemical mitigants against PEDV. The real-world application of these mitigants for eliminating 

swine viruses or decreasing their level of infectivity under field conditions has yet to be 

determined. Additional mitigation strategies should continue to be explored, including other 

chemical treatments, the application of heat or pressure (pelleting) to feed and of various

holding times to feed or feed ingredients. 

• When considering non-animal origin feed ingredients as potential fomites for swine virus 

transmission, a major knowledge gap exist with how the primary transmission pathways (e.g., 

exposure to infected live pigs, contaminated transport vehicles, personnel, etc.) interface with 

one another, particularly how the production and distribution of feed interact with other 

potential sources of virus contamination (e.g., infected live pigs, contaminated transport 

vehicles, personnel, etc.) to contribute, if at all, to disease transmission. 

• Reliable and validated assays and sampling techniques capable of detecting infective virus (i.e., 

to determine the level of contamination is sufficient to transmit disease) in large quantities of 

(bulk) ingredients are not available. 

• The entry of PEDV (and new or emerging swine viruses) onto presumably biosecure commercial 

premises suggests that current biosecurity standards may be insufficient to prevent virus 

incursion. Virus characteristics and the characteristics of the commercial swine industry

(globalization of trade, intensification and vertical integration of production, and extensive 

movement of pigs and related production components) could contribute to biosecurity 

breaches. Robust biosecurity measures may be the only tool, in the absence of effective 

vaccines or treatments, to prevent the entry and spread of some diseases. Thus, biosecurity 

strategies, particularly the extensive movement of production inputs, need to be re-evaluated 

and adjusted to meet today’s swine industry paradigm.

While investigators have addressed some critical experimental questions pertaining to transmission of 

swine viruses via feed and feed ingredients, the current body of scientific knowledge has yet to provide 

conclusive evidence for the source(s) of contamination of non-animal origin feed ingredients with swine 

viruses and the epidemiology of virus transmission to swine under field conditions. If the primary 
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concern of the swine industry and associated stakeholders lies in the importation of contaminated feed 

and feed ingredients, then additional research and investigative studies of how ingredients are sourced, 

processed, and transported prior to importation into the United States are needed. However, the lack of 

feed and feed ingredient diagnostic assays capable of detecting virus in large volumes of material limits 

our ability to determine if and at what point non-animal origin feed or feed ingredients may become 

contaminated with viruses and limits our ability to establish critical control points in feed production, 

distribution, and storage to mitigate risk(s). Until these data are available, it is difficult to evaluate the 

biosecurity risk posed by non-animal origin feed and feed ingredients. Moving forward, studies designed 

to examine the likely source(s) of contamination and virus mitigation steps in processing and postprocessing may be the most fruitful focus of research.
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2 Acronyms

APHIS Animal and Plant Health Inspection Service

ASF(V) African swine fever (virus)

CSFV classical swine fever virus

Ct cycle threshold

DDGS dried distillers grain with solubles

DPI day(s) post-inoculation

EFSA European Food Safety Authority

FMDV foot and mouth disease virus

HP-PRRS highly pathogenic porcine reproductive and respiratory syndrome

IAV-S influenza A virus of swine

LA liquid antimicrobial

MBM meat and bone meal

MCFA medium chain fatty acid blend

OIE World Organization for Animal Health

PCR polymerase chain reaction

PCV2 porcine circovirus type 2

PDCoV porcine delta coronavirus

PED(V) porcine epidemic diarrhea (virus)

PHFD porcine high fever disease

PRRS(V) porcine reproductive and respiratory syndrome (virus)

PRV pseudorabies virus

RBC red blood cells

RNA ribonucleic acid

RT-PCR reverse transcription-polymerase chain reaction

SDPP spray-dried porcine plasma

SVDV swine vesicular disease virus

TCID50 tissue culture infectious dose 50

TGEV transmissible gastroenteritis virus

U.S. United States

VESV vesicular exanthema of swine virus

VI virus isolation

VSV vesicular stomatitis virus

VTM vitamin/trace mineral
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3 Introduction

Over the past three decades, the swine industry in the United States has experienced several significant

disease outbreak events with highly pathogenic viral pathogens, including porcine reproductive and 

respiratory syndrome virus (PPRSV), porcine circovirus type 2 (PCV2), and, most recently, the swine 

enteric coronaviruses, including porcine delta coronavirus (PDCoV) and porcine epidemic diarrhea virus

(PEDV) [2-5]. These disease events have resulted in significant clinical consequences with increased 

morbidity and mortality, in some cases reaching 100%, as well as economic devastation to the swine 

industry with financial losses estimated in the hundreds of millions to billions of dollars [4, 6]. Among 

other shared characteristics, all three causative agents had been previously known to cause mild or nonpathogenic disease in swine prior to the re-emergence event. Additionally, novel agents, such as PEDV, 

may be present yet remain undetected for some time, contributing to (wide) spread transmission 

amongst the industry and hindering local containment. Thus, once identified, the unforeseen emergence 

of swine diseases with high morbidity and mortality and rapid, transboundary spread brings about

fundamental questions (how, what, why, when, and from where) as well as an immediate need to find 

solutions for both short- and long-term response activities and mitigation strategies to control the 

outbreak and prevent future events [5].

During the 2013 - 2014 outbreak of porcine epidemic diarrhea (PED) in North America, contaminated 

feed and feed ingredients were suspected as a potential introduction and/or transmission route for 

spread as early cases of PED in Canada were linked to a common feed source containing spray-dried 

porcine plasma (SDPP) [7]. Additionally, genetic and phylogenetic analyses revealed that United States

(U.S.) strains were closely related to Chinese PEDV strains, particularly the 2012 strain from the Anhui 

Province in China [8], fueling concerns that imported (contaminated) commodities from China may have 

been the route of introduction into the United States. Growing anecdotal evidence and early 

investigative studies [9] have further implicated feed and feed ingredients as the possible transmission 

vehicle for PEDV although a definitive introductory cause remains unknown. Compounded by the recent 

outbreaks of African swine fever (ASF) in China and the European Union [10], there is rising concern that 

contaminated imported commodities, particularly non-animal origin feed ingredients of commercial 

swine feed, could introduce and transmit viral pathogens of significant concern to the United States

(U.S.) swine industry. 

The Animal and Plant Health Inspection Service (APHIS) has conducted two analyses concerning the 

introduction of exotic swine diseases into the United States. The scope of each assessment included 

feed and feed ingredients. In 2014, APHIS completed the Pathways Assessment: Entry Assessment for 

Exotic Viral Pathogens of Swine. This assessment estimated the likelihood of entry of exotic swine 

viruses via several import pathways based on the quantity of the commodity imported, the likelihood 

that a hazard would be associated with the pathway, and the likelihood that a hazard would persist 

under current import mitigation procedures. Several pathways were estimated to pose a nonnegligible risk of introducing exotic viral pathogens of swine into the United States, including animal 
8

feed ingredients derived from unprocessed plants or plant products; however, significant gaps in 

knowledge and available data prohibited a conclusive assessment. In 2015, APHIS completed the Swine 

Enteric Coronavirus Introduction to the United States: Root Cause Investigation Report. This report 

investigated several plausible import pathway scenarios including flexible intermediate bulk containers

(FIBC or tote bags) used to transport feed ingredients from China as a possible pathway for the 

introduction of PEDV into the United States [11].

Despite extensive investigative work in the field and the laboratory, the specific mode of introduction of 

exotic viral pathogens such as PEDV, into the United States and, subsequently, into domestic swine 

premises remains unknown. In order for feed or feed ingredients to be a route of disease introduction

into the United States, it must become contaminated with the causative agent; avoid inactivation 

through (trans-ocean) travel, feed manufacturing, processing, and distribution processes; and be 

ingested at a dose sufficient to cause infection in a susceptible pig (see Figure below). 

Figure 1: Simple generic pathway for transmission of pathogens in feed

The risk of disease transmission via contaminated feed and feed ingredients is non-zero as pathogens 

such as Salmonella are known to be transmitted via swine feed [12, 13]. However, questions regarding 

the true risk level that contaminated feed and feed ingredients pose in the introduction and subsequent

transmission of PEDV and other exotic swine viruses remain unanswered, particularly in comparison to

other recognized risk factors such as movement of infected pigs, transport vehicles, personnel, and 

waste feeding of unprocessed or improperly processed animal products. Thus, making sound decisions 

regarding risk mitigation measures in the face of an uncertain risk level is challenging. Additionally, the 

economic costs and downstream impacts of broadly banning certain feed ingredients or applying other 

mitigation measures to feed and feed ingredients without objective data may outweigh the costs of 

direct production losses from a disease event [5].

The emergence of PEDV in North America and growing concerns of introduction of ASF from China, the 

European Union, or other affected regions has put a spotlight on the possible role of contaminated feed 

and feed ingredients in the introduction and transmission of viral swine pathogens. The characteristics 

of modern swine production – globalization of trade (including significant increases in the volume of 

Feed commodity 

becomes 

contaminated with 

pathogen

Pathogen avoids 

inactivation during 

shipping, feed 

manufacturing, 

processing, and 

distribution 

processes

Exposure of 

susceptible animal 

with infective dose 

results in disease 
9

imported bulk feed ingredients), intensification and vertical integration of production, and extensive 

movement of pigs and related production components (e.g., transport vehicles, feed, personnel) – and 

the trend of emerging swine pathogens in new geographic ranges (e.g., ASF) and/or with increased 

pathogenicity (e.g., PEDV) suggests that the critical production inputs along with existing biosecurity and 

mitigating measures that have historically delivered an acceptable level of protection may need to be reevaluated.

In order to better inform policy-makers, the U.S. swine industry, and associated stakeholders, APHIS has 

conducted a literature review on the scientific evidence regarding whether non-animal origin 

ingredients of commercial swine feed could introduce or transmit viral pathogens of swine into or within 

the United States. This literature review was prepared by APHIS Veterinary Services at the request of the 

swine industry and other associated stakeholders. The goal of the literature review is to understand the 

current scientific knowledge and to identify information gaps. The results may support future scientific 

research and/or risk quantifying models for evaluating the risk (or likelihood) of entry of exotic viral 

pathogens via specific feed ingredients from source countries and subsequent exposure to U.S. swine 

populations.
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4 Methods of the Literature Review

4.1 Overview

The methodology of this literature review follows the basic framework of a qualitative systematic review

[1]. The literature review aims to identify, evaluate, and summarize the findings of relevant research 

studies, thereby making the available evidence more accessible to decision makers, other stakeholders, 

and the scientific community. When appropriate, combining the results of several studies gives a more 

reliable and precise estimate of the available knowledge, intervention, or control measure’s 

effectiveness than one study alone. This literature review aims to answer the following research 

question: 

What evidence is available in published scientific literature regarding whether non-animal origin 

ingredients of commercial swine feed could transmit viral pathogens of swine into or within the 

United States? 

The methodology of the literature review has four main components: 1) identifying and selecting 

research evidence, 2) data extraction and quality assessment, 3) data synthesis, and 4) report writing 

[1].

4.2 Identification of studies and study selection

A systematic search of the National Library of Medicine/PubMed, National Agricultural Library/PubAg, 

National Agricultural Library/Navigator (including major databases: AGRICOLA, AGRIS, BIOSIS, CABI, 

EBSCO Environment Complete, GEOBASE, GeoRef, MEDLINE, Scopus, Web of Science, and Zoological 

Record) and Google Scholar was conducted to identify published scientific literature pertaining to 

evidence regarding whether non-animal origin ingredients of commercial swine feed could transmit viral 

pathogens of swine into or within the United States. Studies published any time through March 2018 

were identified. 

The study selection process was performed in two stages. In the first stage, an initial screening of search 

results was performed based on title and abstract. In the second stage, the full text of the preliminary 

list of studies was evaluated. Additional articles were obtained through manual review of reference 

citations in the relevant literature. Figure 2 provides an overview of the study selection process. Studies 

were excluded that did not meet the purpose statement of the literature review. Reasons for exclusion 

include: 

 Focus on non-viral pathogens (e.g., Salmonella, toxoplasmosis, etc.)

 Focus on disease transmission routes other than feed and feed ingredients (e.g., airborne)

 Animal origin feed ingredients (e.g., swill, SDPP, etc.)

 Focus on mitigations/treatment/disinfection of equipment or sanitizing feed

 No English translation available

 Full text not available (e.g., abstract or conference proceeding only)
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 Duplicate publication

 Subject matter outside the scope of the review. 

Figure 2: Overview flow chart of study selection process

Studies identified 

through database 

searching

n = 209

Titles/abstracts screened

n = 219

Full-text screened

n = 96

Included studies

n = 26

Excluded

n = 70

Additional studies 

identified by swine 

industry

n = 10

Excluded

n = 132

Manual citation 

searches

n = 9
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The two-stage study selection resulted in retention of 26 included studies. The most common reasons 

for exclusion (in descending order) included: focus on disease transmission routes other than feed or 

feed ingredients; focus on mitigations/treatment/disinfection of equipment or sanitizing feed; subject 

matter outside the scope of the review; and focus on animal origin feed ingredients.

4.3 Data extraction and quality assessment

The data extraction component is the process by which research reviewers obtain the necessary 

information about study characteristics, methods, and findings from the included studies. The quality 

assessment component aims to identify internal and external validity of the selected studies. 

Standardized data extraction provides consistency in a literature review, thereby reducing potential bias 

and improving validity and reliability. 

A fillable, pdf data extraction form was created for the purpose of this literature review. Twenty-six 

published articles were included in the data extraction and quality assessment process. Six reviewers 

worked in pairs to perform the data extraction and quality assessment. Each article was reviewed for 

general information, study characteristics, and outcome results. For the quality assessment portion, the 

reviewers reported on potential sources of bias, shortfalls in the statistical and analyses methodology, 

the quality of reporting, and the generalizability of the study to the commercial swine industry in the 

United States. An example of the form is provided in Appendix I.

4.4 Data synthesis and report writing

A qualitative, narrative approach was used for the data synthesis and report writing. The information 

extracted in the data extraction process was summarized into data synthesis tables. These tables are 

provided in Appendix II. From the data synthesis tables, relevant information from the individual studies 

was collated and summarized in the Literature Review Results section below. 
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5 Animal-origin Feed Ingredients

Although outside of the scope of this literature review, the exploration of animal-origin feed ingredients 

as possible vehicles for pathogen transmission, in particular swine-origin ingredients such as SDPP, has 

been on-going. Recent studies have associated SDPP with the transmission of PEDV. Many of the studies 

reviewed in this literature review included swine-origin feed ingredients as part of the experimental 

data and/or the overall study discussion. Some studies more broadly or generically used the term “feed” 

without distinguishing whether animal origin ingredients were excluded. Thus, several recent studies on 

the transmission of PEDV via feed are summarized below to provide context for the discussion of the 

epidemiological role, if any, of contaminated animal-origin feed and feed ingredients in pathogen 

transmission.

5.1 Spray-dried porcine plasma

Several experimental studies and epidemiological investigations have been conducted on the role of 

PEDV-contaminated SDPP in the transmission of PED with inconsistent conclusions [7, 14-20]. In 

particular, the first outbreak of PED in Canada in January 2014 focused on imported SDPP from the 

United States as the possible transmission vehicle. Using complete feed and SDPP samples associated 

with the positive case herds in Canada, Pasick et al. (2014) conducted a swine bioassay with PEDV 

polymerase chain reaction (PCR)-positive SDPP and feed mixed with PEDV PCR-positive SDPP. The results 

provided evidence that the PEDV PCR-positive SDPP [cycle threshold (Ct)1 value range 36.35 – 36.69]

was infectious as clinical signs of diarrhea were observed and significant amounts of PEDV were shed in 

the feces of piglets inoculated with the PEDV PCR-positive SDPP. In contrast, the bioassay results from 

the piglets challenged with the feed matrix2 containing PEDV PCR-positive SDPP (Ct value range 37.22 –

42.88) were inconclusive and, thus, infectivity could not be definitely demonstrated [7]. In a 

retrospective case-control study, Perri et al. (2018) investigated the role of feed and other factors in the

Canadian outbreak. The authors found that the odds of PED occurrence in herds receiving feed from a 

specific feed company that provided potentially contaminated feed was 38.1 times greater than for 

herds that did not receive that feed. The number of live pig movements, semen deliveries, and the 

frequency of dead stock pickups were not identified as risk factors for PED [20]. Similarly, Aubry et al. 

(2017) determined the attack rate for farms with confirmed consumption of feed containing SDPP was 

28.1% while the attack rate of unexposed farms was estimated at 0.17%. The strength of association 

increased with increasing concentration of SDPP in feed [18]. In a separate study, spatiotemporal 

findings included that cases were more likely to neighbor cases than controls, and the pattern of spread 

indicated point source introduction with secondary transmission [17]. 

 1 A cycle threshold (Ct) of less than 38 is considered PEDV positive (Dee et al. 2014). 

2 Food matrix (plural matrices) as defined by the USDA National Agricultural Library is the nutrient and nonnutrient components of foods and their molecular relationships, i.e. chemical bonds, to each other. The glossary 

can be accessed at https://agclass.nal.usda.gov/glossary.shtml. 
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Collectively, these studies of the epidemiological investigation of the Canadian PED outbreak concluded 

that a single lot of SDPP imported from the United States was the vehicle of infection and found that the 

proportion of cases exposed to creep and nursery feeds contaminated with this product was 

significantly higher than expected. The investigation of the initial cases found no association with other 

exposures, such as feed providers, transporters, a rendering company or livestock haulers [7, 17, 18]. 

Despite previous evidence that the spray-drying process is effective at inactivating viruses, including 

PEDV [16, 21-23], the investigations into the Canadian PED cases suggest that a breach of good 

manufacturing practices and/or biosecurity practices led to contamination of the SDPP during 

processing, or post-processing contamination occurred during packaging, storage, and transportation of 

the SDPP and subsequent mixing into the complete swine feed [18].

However, independent studies on the same single lot of SDPP (provided directly from the plasma 

manufacturer not affected farms) by the Food and Drug Administration and the North American Spray 

Dried Blood and Plasma Producers Association determined the PEDV PCR-positive SDPP was not 

infectious; pigs remained negative as determined by PCR and serology testing. To account for low 

sensitivity of the bioassay and to mimic commercial feeding practices, two additional bioassay studies

were performed with longer feeding times (14 and 28 days, respectively); both determined that pigs fed

a diet with 5% SDPP that was PCR-positive for PEDV (Ct values of 30.1 and 30.0, respectively) did not 

contain infectious PEDV and did not transmit PEDV to pigs [16]. Similarly, Opriessnig et al. (2014) found 

that a commercial feed containing 5% commercial SDPP confirmed positive for PEDV ribonucleic acid

(RNA) (SDPP diet contained 3.3±0.3 log10 PEDV RNA copies/g) was not infective and not capable of 

transmitting PEDV to pigs [14]. Dee et al. (2015) were also not able to reproduce or support the Pasick et 

al. (2014) findings despite repeat bioassays with high viral load (Ct value of 16.34) [7, 15]. Given the 

varying results, the role, if any, of SDPP and other swine origin feed ingredients in the general 

epidemiology of PEDV requires further investigation, particularly in identifying the critical points in the 

production and distribution processes where contamination may occur and the likely sources for the 

viral contamination.
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6 Literature Review Results

The core studies included in this literature review have been collated into three categories: background 

information on risk factors for transmission and fomite survivability, epidemiology and outbreak 

investigations, and experimental studies with swine bioassays. Studies were grouped into the best-fit 

category. Information extracted from the core studies may overlap into one or more categories and, 

thus, may be discussed in more than one section. Additionally, the study summaries provided in this 

section are not meant to be detailed and fully comprehensive but rather are focused on the information 

pertinent to this literature review, namely, non-animal origin feed ingredients. Studies conducted on 

feed and feed ingredients containing animal-origin ingredients, such as SDPP, are summarized in Section 

5. For additional study details, please see Appendix II or consult the full-text paper (see References). 

6.1 Risk factors for transmission and fomite survivability

Numerous investigators have reviewed the epidemiology and impact of swine viral pathogens and 

analyzed industry expert opinion and outbreak information to identify risk factors for transmission of 

swine pathogens. Additionally, several studies have looked at the survivability of viruses on various 

fomites related to swine production and husbandry, including feed and feed ingredients. Methods used 

by these investigators include expert elicitation, questionnaire-based post-hoc outbreak investigations, 

and experimental studies of the survival of viruses in contact with fomites. Here, we summarize such 

investigations and their findings, focusing on non-animal origin feed and feed ingredients. The studies 

are grouped into two categories: risk factors for virus transmission and virus survival in contact with 

fomites. The virus scope of these studies includes African swine fever virus (ASFV), porcine high fever 

disease, (highly pathogenic) porcine reproductive and respiratory syndrome virus (PRRSV), pseudorabies 

virus (PRV), Aujeszky’s disease virus, and blue eye disease virus.

6.1.1 Risk factors for virus transmission

Three studies examined the epidemiology of specific swine pathogen(s) or outbreak events in various 

regions of the world [24-26]. The pathogens covered include porcine high fever disease virus in Vietnam 

and ASFV in Nigeria and Eastern Europe. One study used expert elicitation methods to identify risk 

factors for transmission of highly pathogenic porcine reproductive and respiratory syndrome (HP-PRRS) 

into and within Australia [27].

• A study by Le et al. (2012) examined risk factors that may have contributed to the spread of 

porcine high fever disease (PHFD) from China to Vietnam in 2008. PHFD is considered a PRRSrelated syndrome. A survey was administered to individual households in a southern province of 

Vietnam which included questions regarding observed clinical signs in the owner’s swine herd, 

suggestive of PHFD, as well as various risk factors that could contribute to the spread of this 

virus. Probability incidence of PHFD was estimated based on description of clinical signs but 

presence of the virus was not confirmed with diagnostics. Investigators found that, among other 

things, the presence of ducks and the feeding of water green crops, together, were positively
16

associated with clinical signs consistent with PHFD in swine. Water green crops are fed directly 

to pigs after harvest, without processing. Authors hypothesize that ducks potentially amplify the 

virus, similar to data shown for PRRSV, and contaminate the water green crops fed to pigs. It is 

also believed that PHFD virus can persist in water further contaminating the greens before 

harvest. The findings of this study suggest that unprocessed non-animal origin feed ingredients 

could be contaminated with virus by other animals and transmitted to swine [25]. 

• The study by Fasina et al. (2012) sought to identify risk factors associated with ASF outbreaks in 

Nigerian swine herds. Investigators conducted a matched case control investigation of farms

that experienced ASF outbreaks between 2006 and 2009. Case farms met OIE (World 

Organization for Animal Health) guidelines for confirmation of ASF including clinical signs, 

pathological signs, and laboratory diagnostic confirmation of ASF. Control farms were selected 

based on farm characteristics, similarity in operations and biosecurity measures, and absence of 

ASFV infection. An epidemiological questionnaire was administered to all participating farm 

owners and a number of factors associated with increased risk of ASF were identified. These 

included but were not limited to purchase of untested pigs from neighboring farms, presence of 

an abattoir in the community, wild bird access to pig pens, sharing of equipment between farms, 

and unprotected feed sources (rodent access). The use of commercial feed on farm, instead of 

swill feeding, was negatively associated (protective) with ASF risk. The final logistical regression 

model showed that protecting food and water sources, separation of sick and healthy pigs, and 

washing/disinfecting equipment were negatively associated (protective) with ASF infection. 

These findings indicate that preventing rodent access to feed sources and the use of commercial 

feeds, as opposed to swill feeding, were potentially protective measures in the farms studied. 

The investigators of this study conducted extensive statistical analysis on a wide range of ASF 

risk factors found on small and large swine farms. This study was conducted in a developing 

country; thus, direct application of findings to large scale, industrial swine farms in the United 

States may be limited [24]. 

• The review by Guinat et al. (2016) summarizes findings of ASFV transmission studies performed 

in Eastern European and Baltic countries. In respect to feed-to-pig transmission pathways, the 

authors referenced a European Commission (2014) epidemiological report in Latvia and 

Lithuania suggesting that fresh grass and seeds may have been contaminated by wild boar feces 

containing ASFV and transmitted the virus to domestic backyard pigs. A similar study focused on 

ASF in Latvia also suggested that feeding potentially contaminated (via wild boar) fresh grass or 

crops was a risk factor for ASF disease in backyard holdings; however, swill feeding could not be 

excluded as a source [28]. A study conducted in Kenya in 1921 demonstrated that ASFV could be 

transmitted to pigs when they consumed infected feces and urine but failed to transmit when 

contaminated sweet potatoes or bananas were consumed [29]. Several references were 

provided for documented transmission of ASFV to domestic pigs through feeding of swine-origin 
17

feed ingredients such as preserved or uncooked meat products; some primary references from 

the review were not accessible to the reviewers, making it difficult to gauge the robustness of 

the referenced studies. However, the studies referenced demonstrated that there is very little 

field data exploring the relationship of ASFV transmission and non-animal origin feed ingredients

[26]. 

• Brookes et al. (2015) elicited industry expert opinions to identify entry and exposure routes with 

the highest probability of occurrence for introduction of HP-PRRS from south-east Asia to 

Australia. Pig industry experts attending the Australian Pig Veterinarians' Annual Conference in 

Melbourne, Australia in June 2013 were given a questionnaire and asked to indicate the

probability of occurrence of 28 entry routes and 36 exposure routes within fixed probability 

ranges over one year. Agreement between participants was assessed using a chi-squared 

statistical test by comparing the frequency distribution of probability ranges for each route with 

a random distribution of probability ranges. There was statistically significant agreement on 29 

exposure routes; the routes with the highest estimated probability of occurrence all involved 

disposal of waste to feral or backyard pigs. The highest probability exposure route for 

commercial pigs was thought to be contact with a human acting as a fomite or access to animal 

feed/additives from south-east Asia. (Note: the definition of "animal feed/additives" was not 

provided and it is unclear if this term refers to non-animal origin feed, individual ingredients, or 

complete feed.) There was significant agreement on 16 entry routes; however, there were fewer 

consistent agreements or patterns of responses regarding a high proportion of entry routes in 

comparison to the exposure routes. This may be due to the fact that participant knowledge was 

of the pig industry and associated biosecurity practices, not border security or trade policy. The 

entry routes with the highest probability of occurrence and statistically significant agreement 

among participants included entry of HP-PRRS by humans or animal feed acting as fomites (and 

traveling or being shipped by air) and raw pork entering through the postal service or by a 

private individual. There was not agreement on the probability of entry of these fomites 

traveling or being shipped by sea. [27]. 

6.1.2 Virus survival in contact with fomites

Three studies examined virus survivability on various swine-related fomites, including feed and feed 

ingredients [30-32]. The viruses covered by these studies were PRV, PRRSV, Aujeszky’s disease virus, and 

blue eye disease virus. 

• Schoenbaum et al. (1991) investigated the survival duration of PRV in contact with various solid 

and liquid fomites commonly found in hog-raising environments. Feed or feed ingredients 

included in the study were green grass, whole corn, pelleted feed, and alfalfa. The authors did 

not report whether the feed included any animal-origin ingredients. The authors mixed stock 

PRV with various diluents, namely saline, swine saliva, or swine nasal washings, and inoculated 

fomites with those mixtures. After incubating the inoculated fomites at 25 °C for up to 14 days, 
18

the authors tested for virus activity through use of a cell-culture-based assay. They found that, 

in general, the quantity of infectious virus decreased over time. Of the combinations of PRV and 

diluent with feed or non-animal origin feed ingredients, the combination of PRV/saline/whole 

corn remained infectious the longest at 7 days with an estimated half-life of 36.3 hours. The 

durations of infectiousness of the other combinations of PRV/diluent/feed or non-animal origin 

feed ingredients were shorter, ranging from 1 to 4 days with an estimated half-life of 1.0 hour to 

5.1 hours. The conditions of this study do not reliably reproduce field conditions. The fomites 

were inoculated with stock virus at doses that might not reflect contamination levels under field 

conditions. The authors used liquid diluents in all experiments and deliberately avoided field 

conditions (drying and ultraviolet light exposure) deleterious to virus activity. Similarly, the 

authors acknowledged that virus survival time is impacted by temperature, and speculated that 

virus survival times would be longer at lower temperatures and shorter at higher temperatures

[30]. 

• Pirtle and Beran (1996) investigated the survival time of PRRSV in contact with various liquid and 

solid fomites. Feed and non-animal origin feed ingredients included in the study were ground 

corn, pelleted swine starter feed mix, and alfalfa. The authors did not report whether the feed 

included any animal-origin ingredients. The authors mixed stock PRRSV with saline, and 

inoculated fomites with those mixtures. After incubating the inoculated fomites at 25 to 27 °C 

for up to 11 days, the authors tested for virus activity through use of a cell culture based assay. 

In the PRRSV-spiked alfalfa sample, the authors detected PRRSV only on day 0. They did not 

detect any virus in the PRRSV-spiked starter feed mix and ground corn samples. The authors 

speculated that the pH (<7) of the samples tested and/or unknown substances present in the 

samples could have contributed to virus inactivation. The conditions of this study do not reliably 

reproduce field conditions. The addition of saline to each of the samples increased the moisture 

content of the samples and might have impacted the virus survival kinetics. In addition, the feed 

and feed ingredient samples were inoculated with stock virus at doses that might not reflect 

contamination levels under field conditions [31].

• Martínez-Gamba et al. (2001) examined the persistence of bacterial and viral pathogens in feces 

fermented for use in animal feed (silage). Feces from 30 pigs was collected, inoculated with 

Aujeszky’s disease virus and blue eye disease virus, and mixed with molasses and sorghum for 

fermentation. Flasks of ensilage were incubated at room temperature for 0, 7, 14, 28, and 56 

days. Presence of virus was detected by cytopathic effects on cellular monolayers and indirect 

immunofluorescence. Samples were positive for virus on day 0 but not at any subsequent time 

point. The findings indicate that fermentation is sufficient for the inactivation of the viruses 

tested and could be an acceptable means for eliminating harmful pathogens from feces used for 

animal feed. These results may not be applicable to viruses of other families [32]. 
19

6.1.3 Summary of findings

In summary, most of the reports and studies summarized above were not specifically designed to focus 

on non-animal origin feed and feed ingredients as a potential vehicle for virus transmission; however, 

feed and feed ingredients were included in the study design or discussion. In some cases, the author did 

not clearly state or define whether the feed includes animal-origin ingredients. Similarly, some findings 

in this group of studies may not be generalizable to other virus families or the commercial swine 

industry in the United States. Given these limitations, several key points are highlighted below. 

Le et al. (2012) identified owning ducks and using water green crop as pig feed (together) as being 

associated with an increased risk of PHFD, speculating that unprocessed non-animal origin feed 

ingredients could be contaminated with virus by other animals and transmitted to swine [25]. Fasina et 

al. (2012) identified food and water control to be significantly associated with decreased risk of ASF 

infection in Nigeria, noting that feed and water biosecurity practices can prevent virus contamination by 

rodents and wild birds [24]. Consistent with these findings, expert opinion conducted in Australia found 

industry representatives believed commercial pigs were most likely to be exposed to HP-PRRS through 

access to contaminated animal feed and feed additives imported from southeast Asia [27]. These studies 

suggest that protecting unprocessed non-animal origin feed ingredients from contact with animals may

decrease the likelihood of pathogen contamination. This may be particularly important for ingredients 

that are not processed before being fed to animals. 

Several investigators have examined the persistence of viral activity in the presence of various fomites, 

including non-animal origin feed ingredients. In experiments in which they spiked fomites with stock 

virus, they found, in general, that viral activity did not persist for long periods of time under the 

experimental conditions used. Schoenbaum et al. (1991) found that the combination of 

PRV/saline/whole corn remained infectious the longest at 7 days with an estimated half-life of 36.3 

hours [30]. Similarly, Pirtle and Beran (1996) detected PRRSV activity only on day 0 in the PRRSV-spiked 

alfalfa sample [31]. Interestingly, Martínez-Gamba et al. (2001) found that fermentation is sufficient for 

the inactivation of Aujeszky’s disease virus and blue eye disease virus [32]. Collectively, these studies 

suggest that, under certain conditions, swine viruses can survive in non-animal origin feed ingredients.

Among the knowledge gaps identified in these studies are the need for a comprehensive evaluation of 

transmission pathways involving non-animal origin feed ingredients and swine viruses. The scientific 

literature regarding the survival times for various non-animal origin feed ingredient/pathogen 

combinations as well as determination of infectivity is incomplete and warrants further studies along 

with documented replication of studies. Furthermore, the likelihood of non-animal origin feed 

ingredients incurring contamination and documented scenarios in which cross-contamination occurs 

under field conditions is unknown. 
20

6.2 Epidemiology and outbreak investigations – PEDV and PDCoV

In 2013, swine enteric coronaviruses, such as PEDV and PDCoV, emerged as pathogens of significance 

for the swine industry in the United States and several other countries. Efforts were made to describe 

the epidemiology of the outbreaks which included a focus on the source of virus introduction and 

transmission. Among other things, feed and non-animal origin feed ingredients were suspected as one 

possible route of virus introduction and spread. The following section summarizes reports pertaining

primarily to PEDV and PDCoV outbreak investigations, findings related to feed and feed ingredients, and 

experimental studies that sought to determine the survivability of swine viruses in feed and feed 

ingredients. 

Studies reviewed in this section have been separated into two major categories: 1) epidemiological 

reports, reviews and surveys and 2) feed and feed ingredient studies. These studies are primarily 

focused on PEDV and PDCoV; however, other swine pathogens are included such as transmissible 

gastroenteritis virus (TGEV), PRRSV, and PCV2. The epidemiological reports collated information from 

literature and descriptive reviews, disease outbreak analyses, as well as information from retrospective 

surveys [5, 11, 33-38]. 

Studies focused on virus-contaminated feed and non-animal origin feed ingredients evaluated the ability 

of these materials to serve as fomites for virus introduction and spread. The studies are grouped into 

descriptive and experimental reports. The descriptive studies obtained samples from feed, feed facilities 

and feed transport vehicles linked to disease outbreaks and analyzed them for presence of viral RNA [39, 

40]. Experimental studies included in this section investigated survivability of swine viruses on feed 

fomites by adding virus to the feed or non-animal origin feed ingredient and examining virus titers over 

time [41, 42]. 

6.2.1 Epidemiological reports, reviews and surveys

Eight epidemiological reports examining the global outbreaks of PED and PDCoV have been reviewed. 

The geographic scope of these reports include Europe, Asia, and North America [5, 11, 33-38]. The 

authors sought to describe the outbreaks and describe associations between risk factors for 

transmission and disease status.

• In 2014 and 2016, the European Food Safety Authority (EFSA) published two reports pertaining 

to PED and PDCoV [33, 34]. In 2014, EFSA published a scientific opinion on PEDV and PDCoV

based on a review of the scientific literature published in the preceding 10 years [34]. In regards 

to the global epidemiologic picture of PEDV and PDCoV, the authors found that only limited 

active monitoring is conducted for PED in Europe, Asia, and the Americas. Few outbreaks of PED

have been reported in Europe (Germany and Italy 2014); in Asia, multiple outbreaks have been 

reported in several countries. In the Americas, the first outbreak of PED in the United States was 

reported in May 2013 with rapid spread within the country and reports in North, Central and 
21

South America. The authors found no clear evidence that PDCoV is causing significant impacts 

on animal health [34].

When examining the possible geographic differences in PEDV strains and the potential for 

immunologic cross-protection, the authors found a high level of sequence identity between 

PEDV in Germany and Italy and the PEDV in the Americas. Findings of retrospective studies 

suggest that at least two PEDV strains were introduced into the United States at similar times. 

Differences in the nucleotide sequence of PEDV have been identified but their effects on 

virulence, if any, are unknown. Serological cross-reactivity between PEDV in Europe and the 

Americas is reported; no data regarding cross-protection are available. For reasons not well 

understood, outbreaks of PEDV in Asia and the United States seem to be more severe than 

those in Europe. However, it’s difficult to compare impacts in different regions because of 

differences in age group of affected pigs, production systems, biosecurity, farm management, 

herd size, and immune status and sanitary status of the herd population [34].

In a literature review covering the preceding 10 years (2004 – June 2014), EFSA concluded that 

the scientific literature supports the following statements [34]:

 Infected live animals and feces are reported to transmit PEDV. 

 PEDV can survive in slurry but the epidemiologic role of this matrix is unknown. 

 High levels of infectious PEDV are shed in feces, contributing to contamination of various 

fomites, including vehicles, humans, and feed.

 The transmission of PEDV via feed has been shown but more data are required to assess its 

epidemiologic importance. 

 PEDV RNA has been detected at low levels in serum but the role of this epidemiologic matrix 

is unknown. 

 Fecal cross-contamination of blood during collection at the slaughterhouse cannot be 

excluded. 

 Manufacturing techniques for SDPP can inactivate PEDV; however, different spray-drying 

techniques exist and variations in SDPP manufacturing procedures or breach in quality 

control (e.g., inadequate time and temperature holding times) may result in incomplete 

inactivation of PEDV. For example, infectious SDPP was detected in one study, but the origin 

of the PEDV in the SDPP is unknown (post-processing cross-contamination versus 

inadequate SDPP processing).

 Infectious PEDV has been detected in air under experimental conditions and virus may be 

transmitted via air over short distances.
22

 Swill, particularly untreated pig intestines, can contain PEDV but the role of this 

epidemiologic matrix is unknown. 

 There is no data on the presence of PEDV in embryos, pork meat, or other swine-derived 

feed components such as red blood cells (RBC), hydrolyzed proteins, fat, gelatin and 

collagen. 

In 2016, EFSA published a scientific report of PEDV epidemiology and impact as reported in 

scientific literature in 2014 and 2015, together with an analysis of PED cases in the European 

Union [33]. The goals of the report were to provide guidance on PEDV data to be collected by 

European Union Member States in order to optimize response coordination, and an analysis of 

the epidemiologic data to quantify PED impact on pig production in the European Union. Also, 

an updated literature search was conducted to obtain data from October 2014 to October 2015

to update information in the EFSA scientific opinion report from 2014. Transmission of PEDV via

feed or feed ingredients was not directly addressed in this report; thus, a summary of the report 

is not provided. However, the major recommendation(s) relevant to feed and non-animal origin 

feed ingredients included the importance of strict biosecurity, in particular with vehicles, to 

prevent introduction of PEDV onto the farm [33]. 

• Although PEDV was first identified in Japan in the 1990s, Japan experienced renewed outbreaks 

of the disease in 2013. Scientists determined that the strain of PEDV in Japan was highly similar 

to the viral strain affecting the United States. In a retrospective questionnaire-based casecontrol study, Sasaki et al. (2016) focused on risk factors associated with these new outbreaks of 

PEDV in Japan. The investigators tested the hypothesis that epidemiologic factors associated 

with a high risk of PEDV infection at swine farms located within 5 km of at least one other 

infected farm (locally exposed farms) differ from factors associated with high risk of infection at 

farms more distant from other infected farms (non-locally exposed farms). Using logistic 

regression analyses, they found that on locally exposed farms, PED was associated with a larger 

total number of swine, shorter distance to the nearest PEDV-positive farm, and a disinfectant 

contact time of less than 20 min. On non-locally exposed farms, PED was associated with 

increased feed truck visits to the farm, no visit by a veterinarian, and a disinfectant contact time 

of less than 20 min. Feed or non-animal origin feed ingredients were not explicitly included in 

the scope of this study. Feed-related items included on the questionnaire included feed truck 

visits and artificial milk. The authors found neither to be significantly associated with PED on 

either type of farm [36].

• In the descriptive report by Davies (2015), the first half of the article discusses the similarities of 

3 major disease epidemics in the swine industry caused by PRRSV, PCV2, and PEDV. All three 

share the following features: highly host specific, rapid rates of mutation, and appear to be 

associated with swine as non-pathogenic (or associated with mild disease) for years before 
23

becoming highly pathogenic. The author suggests that the proximate source of the highly 

pathogenic variants of the 3 viruses was the extant swine virome. The emergence of these 3 

highly pathogenic viruses over 25 years may be considered extremely rare events but the author 

argues that intensive single species food production systems along with globalization, 

intensification, and extensive movements of pigs have contributed to the geographic expansion 

of these viral agents and points to the likelihood that future "new" viruses in swine are likely to 

emerge from already recognized (non-pathogenic or ignored) swine viruses. 

The second half of the article discusses the risk of feeding animal products (SDPP) to swine and 

whether or not the true risk warrants excluding animal origin products (or other ingredients)

from swine diets. The author concludes that the risk of PEDV survival in SDPP is extremely low, 

but non-zero. The challenge lies in how to manage a non-zero risk. The likelihood of transmitting 

PEDV via feed in comparison to transmitting PEDV via infected animals is likely extremely low. 

However, the consequences of a disease outbreak are significant and the trend toward

increasing herd sizes (and assuming fixed biosecurity practices) in developed countries such as 

the United States along with greater flux of inputs (animals, semen, feed, water, personnel, 

vehicles, etc.) leads to a higher temporal frequency of adverse events. The author argues that a 

blanket ban on certain ingredients in swine feed (of swine origin) may not be the solution. A 

comprehensive evaluation of transmission pathways as well as cost-benefit analyses of 

managing feed-related risks and balancing risks with nutritional value are needed [5]. 

• In the review by Lowe (2014), the author summarized aspects of the U.S. outbreak of PEDV in 

2013, including factors that were found to be associated with greater risk of PEDV transmission. 

The author concluded that current research supports transmission of PEDV through livestock 

transportation, movement of people, vehicles, and other contaminated fomites as well as 

shared resources and equipment among farms [35]. The author cited reports by the Canadian 

Food Inspection Agency and others that demonstrated the level of PEDV found in SDPP added to 

feed around the time of the outbreak was not sufficient to transmit virus to naïve pigs [7, 14]. It 

is stated that feed was not likely a primary transmission route of PEDV in 2013 [35]; however,

Lowe cites other clinical studies and epidemiological investigations that provide evidence that 

feed can serve as a fomite for PEDV if contaminated during the manufacturing, storage, and 

transport processes [35]. 

• In 2014, the United States experienced the emergence of a second novel swine enteric 

coronavirus, PDCoV. McCluskey et al. (2016) administered a retrospective survey to 42 U.S. 

swine breeding herd operations that experienced a confirmed outbreak of PDCoV in order to 

identify factors that may have contributed to the introduction and spread of the virus. Among 

other things, the source and timing of feed delivered to the affected farms in the 10 days prior 

to the outbreak of PDCoV was examined. All farms surveyed had a delivery of complete feed or 
24

feed ingredients in the 10 days prior to the outbreak; 60% of those had a delivery of SDPP while 

40% received blood products or pork fat. One third of the farms received feed components from 

outside of the United States. There was no common source of feed or SDPP for the farms 

surveyed [37].

• In April/May of 2013, PEDV was first identified in the United States. Scott et al. (2016) addressed 

the question of how PEDV entered the United States, through various methods including 

scenario development, post hoc investigations, epidemiologic surveys, a case control study, 

brainstorming, and speculation. They used previously collected epidemiologic data to develop 

scenarios and identify hypothetical routes of PEDV introduction into the United States and 

conducted follow-up studies to gather evidence for the most plausible scenarios. The follow-up 

studies included testing organic soybeans and pet jerky treats imported from China and archived 

serum samples opportunistically collected from feral swine; all results were negative. The 

authors did not identify a proven source or route of PEDV introduction into the United States. 

However, it was suggested that incomplete farm feed/ration records negatively impacted 

investigators’ ability to thoroughly evaluate the potential epidemiologic role of feed or feed 

ingredients. The authors identified totes used to transport bulk feed as providing “the simplest 

explanation” for the investigation findings [11].

• A retrospective survey was administered to U.S. swine veterinarians and producers in 2017 to 

collect opinions regarding, among other things, the suspected source of PEDV and PDCoV 

introduction into the United States in 2013-2014. The majority of respondents believed trucks 

coming onto the farm (26%), feed (29%), and variable biosecurity protocols (18%) were 

responsible for virus introduction. Survey participants were also asked about control measures 

implemented in response to outbreaks. None of the participants noted a change in feed 

practices although 56% implemented enhanced biosecurity protocols. At the time of the survey 

the majority of respondents had either never experienced an outbreak of PEDV or PDCoV 

(28.9%) or reported that the virus had been eliminated from their farms (56.6%) [38].

6.2.2 Feed and feed ingredients

Feed and feed ingredients have been hypothesized to serve as fomites for virus introduction and spread, 

leading several investigators to examine environmental samples (feed, fomites etc.) for the presence of 

virus and/or to conduct assays testing the ability of feed to serve as a fomite for virus. The following 

summarizes the reported findings.

Descriptive

• Associated with the U.S. outbreak of PED in 2013, an epidemiological investigation was 

conducted at an affected Ohio swine operation to determine the source of virus introduction. 

The timing of the outbreak coincided with a switch to a new out-sourced feed pellet. 
25

Environmental samples were obtained and analyzed by real-time RT-PCR. The investigators 

report that PEDV RNA was detected in newly opened bags of pellets on-farm; and in pellets and 

individual ingredients sampled at the source (supplier) facility. No virus isolation (VI) assays were 

performed on these samples. In the bioassay conducted, pigs were observed to be healthy and 

no clinical signs of disease were observed [39].

• A retrospective case study by Greiner (2016) investigating PEDV and PDCoV outbreaks in the 

United States found a positive association between feed truck visits to farms and presence of 

PEDV. To investigate the role of feed and feed mills in these outbreaks, environmental sampling 

was conducted at 24 feed mills, some of which served farms known to be positive for PEDV or 

PDCoV. The investigators swabbed office floors, bulk ingredient pit grates (exterior surfaces), 

mixer/pellet coolers, incoming bagged-ingredient truck trailers, the interior of feed 

compartments on trucks servicing farms, and feed truck foot pedals. None of the samples 

obtained were positive for PEDV RNA, 5% of truck foot pedals and 1% of bulk ingredient pit 

grates were suspect for PDCoV RNA, and 3.4% and 2.2% of truck foot pedals and office floors, 

respectively, were positive for PDCoV. All other samples were negative for PDCoV. There were 

no significant associations between viral RNA at feed mills and the disease status of farms 

served. Further, with the exception of the 3.4% of suspect samples, none of the incoming 

ingredient trucks, bulk ingredient pits, or outgoing feed compartments were positive for PEDV 

or PDCoV RNA [40].

Experimental

• Trudeau et al. (2017a and 2017b) conducted experimental assays to investigate inactivation 

kinetics of PEDV, PDCoV, and TGEV in feed and feed ingredient matrices and on solid surfaces. 

Feed and non-animal origin feed ingredients used in these studies included complete feed, corn, 

soybean meal, corn dried distillers grains with solubles, and vitamin and trace mineral premix. 

The authors mixed stock virus with liquid medium, and then spiked samples of feed and feed 

ingredients with the mixture and incubated the combinations at various temperatures. In one 

study, they incubated the spiked samples at room temperature (approximately 25 °C) for 0 to 56 

days [42]. In another study, they incubated the spiked samples at 60 to 90 °C for up to 30 min

[41]. The authors used a cell culture based assay and model fitting to estimate a delta value, 

calculated as an indicator of the time necessary to reduce virus concentration by 1 log. For the 

spiked samples incubated at room temperature, the largest delta values were obtained for 

PDCoV and TGEV in soybean meal, at approximately 42 days each. Soybean meal at room 

temperature also provided the highest delta value for PEDV, at 7.5 days. Other findings 

indicated that at room temperature, moisture and ether content were important determinants 

of virus survival. The authors found no difference in virus survival in feed or non-animal origin

feed ingredients incubated at temperatures higher than 70 °C. The maximum level of virus

inactivation occurred upon heating the spiked samples at 90 °C for 30 minutes [41, 42].
26

6.2.3 Summary of findings

Of the retrospective studies, epidemiological investigations and reviews conducted in the aftermath of 

the PEDV and PDCoV outbreaks in 2013-2014, none found definitive evidence linking the transmission of 

PEDV and PDCoV to non-animal origin feed ingredients [11, 34-37]. Scott et al. (2016) proposed 

imported virus-contaminated feed totes as a possible scenario for the source of PEDV introduction into 

the United States in 2013; however, no conclusive data were presented to support this hypothesis [11]. 

The perception by the swine industry, however, that feed could have been the source of virus 

introduction is reflected in the results of the 2017 survey administered to veterinarians and swine 

producers, in which 29 percent of respondents believed feed was linked to virus entry and spread. 

Trucks (26%) and variable biosecurity protocols (18%) were also believed to be linked with PED spread 

[38]. The EFSA 2014 scientific opinion report notes that while transmission of PEDV via feed has been 

experimentally demonstrated [9], more data are needed for reliable assessment of the epidemiologic 

importance of this route in the field [34]. 

Lowe (2014) concluded that feed was not a primary transmission route in the spread of PEDV in the 

United States [35]. However, on further investigation, Lowe et al. (2014) found evidence that transport 

vehicles moving in and out of collection points, such as harvest facilities and livestock auction markets, 

served as a source of contamination of other transport vehicles, noting that the cost-saving industry 

practice of consolidating resources such as sharing building maintenance, manure handling equipment, 

personnel, and livestock transportation equipment likely contributed to the spread of the PED outbreak

across multiple geographic regions in the United States [43]. Similarly, McCluskey et al. (2016) reported 

on findings that movement of feed trucks onto farms was significantly associated with PED status. 

Collectively, these studies suggest that biosecurity measures on the farm and at the feed manufacturing 

plant as well as limiting the movement of animals, people, vehicles, and other shared inputs could serve 

as critical control points to stop the transmission of PEDV between herds [35, 37, 43].

Two studies conducted environmental sampling of feed, feed facilities, and feed transport vehicles to 

determine whether these items contributed to the cause of the PEDV and PDCoV outbreaks in the 

United States [39, 40]. Collectively, the findings indicate that none of the source ingredients nor the 

outgoing feed at the feed mills sampled were positive for viral RNA, suggesting the non-animal origin 

ingredients and feed were not contaminated with PEDV or PDCoV. However, experimental studies by 

Trudeau et al. (2017a and 2017b) did show that feed ingredients spiked with PEDV, PDCoV, and TGEV in 

a laboratory setting could maintain live virus for a period of time at room temperature. The authors also 

found that different ingredients produced different virus survival periods which they believe may be due 

to moisture and ether content or pH of each ingredient. These data indicate that, under certain 

conditions, swine enteric coronaviruses are able to survive in feed ingredients [41, 42].

In summary, the epidemiologic investigations and outbreak studies did not definitively link (or exclude) 

transmission of PEDV or PDCoV with non-animal origin feed or feed ingredients. Inconsistent findings 

impart uncertainty towards feed or feed ingredients as a transmission pathway [35, 37, 39, 40, 43]. The 
27

most common mechanical fomite implicated in this group of studies was transport vehicles, including a 

positive association between feed truck movements onto farms and disease status [34-38, 40, 43]. Two 

experimental studies reviewed did demonstrate that virus added to feed can survive for a period of time 

under certain conditions [41, 42]. However, these studies did not investigate nor were able to 

demonstrate that virus present in feed could be transmitted to naïve animals through normal feeding 

behavior.

Among the knowledge gaps identified in these studies are the identification of critical control points for 

pathogen contamination of feed and/or non-animal origin feed ingredients and consensus on the feedbased transmission pathways for PEDV and PDCoV. The point source(s) for virus contamination of feed 

or non-animal origin feed ingredients are not clearly defined. 

6.3 Experimental studies on feed transmission with swine bioassays

The rapid spread of PED in commercial swine in North America in 2013-2014 prompted several 

experimental (non- randomized) studies with in vivo biological assays (bioassays) to be conducted. The

bioassays were used to assess the biological activity or potency of the pathogen(s) of interest by 

measuring the magnitude of response such as observed clinical signs consistent with the study 

disease(s) and/or positive findings to diagnostic testing and necropsy examination. Most studies 

included in this section of the literature review used swine bioassays to determine the infectivity of the 

pathogen(s) of interest in feed or feed ingredients subsequent to detection by PCR of virus nucleic acid 

in the matrix (feed or feed ingredients) under examination. 

For the purposes of discussion, the experimental studies with swine bioassays have been collated into 

two categories: field-based experimental studies with bioassays [9, 39, 44], and laboratory-controlled 

experimental studies with bioassays [15, 45-48]. In general, the bioassays involved naïve piglets of 

various ages, ranging from four days old to 21 days old [9, 48]; in some studies, pigs were re-used after a 

negative bioassay and the subsequent ages at re-introduction to the bioassay were not easily 

discernable [15, 47]. Piglets were sourced from healthy herds and tested by PCR and serological assays 

to confirm negative status to the respective pathogen(s) prior to the initiation of the bioassay. Exposure 

routes of the challenge matrix to the piglets varied, including ad libitum (natural) feeding [9, 39], oral 

administration via syringe [15, 47, 48], orogastric gavage [44-46], intramuscular injection, and intranasal 

administration [48]. In most studies, the bioassays consisted of daily diagnostic monitoring, lasting 6-7 

days post-inoculation, culminating with euthanasia and complete necropsy examinations of piglets. 

6.3.1 Experimental studies with swine bioassays using field-sourced challenge virus 

Three experimental studies with swine bioassays exposed piglets to challenge feed samples inoculated 

with field-sourced virus from an index farm or contaminated feed facility. Prior to the bioassay, the virus 
28

material was further processed or prepared in the laboratory before inoculating the challenge matrix. 

The bioassay results yielded mixed findings [9, 39, 44]. 

• Pillatzki et al. (2015) used a swine bioassay to investigate whether PEDV PCR-positive samples of 

complete feed, feed pre-mix, and SDPP (Ct values of 33.8, 34.2, and 30.0, respectively) that had 

been retained by feed manufacturers could serve as a source of PEDV transmission to neonatal 

swine. The piglets inoculated with the PEDV-positive feed samples along with the negativecontrol piglets remained negative for PEDV by PCR and clinically healthy throughout the study 

period. In contrast, only the positive-control piglets (Ct value = 25.5) developed clinical signs of 

PED; PEDV RNA was detected in fecal swabs; villous atrophy was observed in the ileum; and 

PEDV was detected in the ileum by immunohistochemistry [44]. 

• Bowman et al. (2015) conducted a swine bioassay on a newly started pelleted diet that was 

implicated as the transmission vehicle of PEDV into an Ohio swine operation. PEDV was 

detected by RT-PCR in the interior of the unopened bags of the new supplier’s pellets, 

suggesting contamination occurred prior to delivery of the feed to the farm. Additionally, the 

source facility (supplier) tested positive for PEDV as well as individual ingredients at the source 

facility. Piglets were provided ad libitum access to the RT-PCR positive mash3 (mean Ct = 36.5) 

along with dry pellets from the same lot for 7 days and observed for clinical signs of PEDV. 

During the bioassay, none of the pigs developed clinical signs of disease. Environmental and 

rectal swabs collected daily during the study were negative for PEDV as determined by RT-PCR. 

Microscopic examination of intestinal tissues collected from the piglets at the end of the study 

revealed no significant morphologic lesions [39].

• Following an outbreak of PED on three breeding herd premises in the United States, Dee et al. 

(2014) used a novel on-farm sampling method to collect remnants of feed samples from empty 

feed bins that previously contained feed consumed by the index populations. Analysis of feed 

material across the 3 affected sites by real-time RT-PCR indicated the presence of PEDV RNA 

with Ct values ranging from 19.50-22.20. For the swine bioassay, piglets were divided into three 

groups: the treatment group was fed 454 g of the challenge feed (natural feeding method)

(pooled Ct value = 20.65); the positive-control group was challenged with feed spiked with stock 

PEDV (Ct value = 18.23); and the negative-control group was fed a placebo feed. The challenge 

feed for the treatment group was prepared using 30 g of feed material from the PCR-positive bin 

samples from the 3 affected sites and diluted in 30 mL of sterile phosphate buffered saline. The 

solution was vortexed and centrifuged. The supernatant was mixed with 454 grams of PEDV-free 

feed. Clinical signs consistent with PED were observed in piglets in the treatment group and the 

positive-control group. At necropsy, rectal swabs and intestinal tract samples from the 

treatment group and the positive-control group were positive for PEDV by PCR and 

 3 Mash refers to dry pellets, grain or meal mixed with (hot) water to form a moist, pulpy feed. 
29

immunohistochemistry with evidence of microscopic lesions. In the negative group, clinical 

signs, viral shedding, or PEDV-positive intestinal tract samples were not observed. Molecular 

sequencing of viral RNA obtained from treatment and positive control groups confirmed 

consumption of feed and not cross-contamination as the source of infection [9].

6.3.2 Experimental studies with swine bioassays using laboratory-sourced challenge virus

Five experimental studies with swine bioassays involved laboratory-controlled experimental studies in 

which piglets were exposed to the challenge matrix spiked with a predetermined pathogen dose 

sourced from laboratory stock viruses [15, 45-48]. Goyal (2014) and Schumacher et al. (2016) conducted 

experimental studies with a swine bioassay aimed at determining PEDV survivability in various organic 

materials and minimum infectious dose, respectively. 

• Goyal (2014) investigated the survival of PEDV and TGEV in fresh feces, manure slurry, animal 

feed, and water. Stock PEDV prepared from pigs infected experimentally with a field strain of 

PEDV and a laboratory strain of TGEV were inoculated into samples of fresh feces, slurry, dry 

and wet swine feed, and drinking water and the mixtures were incubated at various humidity 

percentages and temperatures and for up to 14 days. PEDV and TGEV could be detected by PCR 

in fresh feces for 1-7 or 14 days, respectively, depending on temperature and humidity. Both 

viruses could be detected in slurry, non-chlorinated water, and dry and wet feed samples for ≥ 

28 days at room temperature [45].

For the bioassay, a subset of pigs were inoculated via orogastric gavage with virus aliquots 

obtained from 7 day old fresh feces, ≥ 28 day old room temperature slurry samples and wet 

feed samples, 7 day old dry feed samples, and two week old water samples. Bioassay results 

showed that PEDV survives in fresh feces for 1-7 days. Infective virus was recovered from 

inoculated slurry samples stored for ≥ 14 days at various temperatures, suggesting that 

spreading of manure could disseminate virus onto fields. The findings of this study also suggest 

that PEDV inoculated into wet and dry swine feed can remain infective for up to 28 days and 7 

days, respectively [45]. 

• Schumacher et al. (2016) used a swine bioassay to estimate the minimum infectious dose of 

PEDV in virus-inoculated feed. The authors mixed serial dilutions of stock PEDV with feed, and 

administered the mixtures to 10-day-old piglets by orogastric gavage. The feed used in the study 

was corn- and soybean meal-based and included vitamin and trace mineral premixes and a 

source of phytase. The lowest concentration of virus in feed to cause infection in the piglets was 

5.6 x 101 tissue culture infectious dose 50 (TCID50)/g which corresponds to a Ct value of 37. 

Based on this infective dose, the authors estimated that 1 g of fecal matter could contaminate 

up to 450,000 kg of feed. The authors noted that there was a 10 unit difference in PCR Ct value 

for PEDV mixed with feed (Ct value of 37) in comparison to an equivalent dose of PEDV mixed 

with tissue culture medium (Ct value of 27). The authors proposed a variety of mechanisms that 
30

might account for this difference, such as differences in the methods of dilution and virus 

extraction, differential RNA degradation, or enhanced viral persistence through binding of virus 

particles or RNA to feed particles [46].

Three experimental studies with swine bioassays reported by the same primary author examined the 

infectivity of PEDV in common swine feed ingredients in the presence or absence of a formaldehydebased liquid antimicrobial SalCURB® (LA) [15]; the infectivity of PEDV in common swine feed ingredients 

with or without LA and 2% custom medium chain fatty acid blend (MCFA) following a simulated transPacific shipment from China to the United States [47]; and the infectivity of select viral pathogens in 

common swine feed ingredients following two simulated transportation conditions across two different 

regions of the world [48]. 

• Dee et al. (2015) examined PEDV viability in various feed ingredients common in swine diets in 

the presence or absence of LA. Eighteen common swine feed ingredients were selected: corn, 

conventional soybean meal (SBM), dried distillers grain with solubles (DDGS), SDPP, purified 

plasma, intestinal mucosa, meat and bone meal (MBM), RBC, 3 vitamin/trace mineral (VTM) 

mixes, choice white grease, soy oil, lysine HCL, D/L methionine, threonine, limestone, and dry 

choline chloride. Sixteen 30 g samples of each ingredient were divided into two groups in 

replicate. One group was treated with 0.1 mL of LA (treated group) and the other group was 

treated with saline (non-treated group). The samples were spiked with 2 mL PEDV to reach a Ct 

mean of 25 (range 19-30) following mixing. There were 32 control samples of complete feed 

inoculated with PEDV (16 positive controls) or saline (16 negative controls). Also, 8-10 mL 

samples of stock PEDV served as stock virus controls. The samples were stored outside in winter 

conditions in plastic totes. At 1, 7, 14, and 30 days post-inoculation (DPI), samples were

removed for diagnostic testing. The samples were tested for PEDV, PDCoV, and TGEV by RT-PCR.

The presence of viable virus was determined by VI. Viable PEDV (positive VI) on 30 DPI was 

detected from non-treated SBM, DDGS, RBCs, MBM, lysine HCL, and D/L methionine. Nontreated choice white grease, threonine, and limestone were positive on VI at varying sampling 

days. Only SBM and MBM remained PCR positive at day 30; all LA-treated ingredients were VI 

negative [15].

The swine bioassay was used for PCR positive but VI negative feed samples. This included the 

non-treated ingredients of corn, 3 VTM mixes, intestinal mucosa, soy oil, choline chloride, SDPP, 

purified plasma, as well as the LA-treated ingredients. Choice white grease, limestone, and 

threonine were tested as well. Piglets (n = 24) of 5-7 days old were divided into groups of four. 

Each pig received 1 mL of the designated inoculum orally via syringe. Pigs were observed for 7 

days for clinical signs and rectal swabs were collected daily. If clinical signs were observed, 

swabs were collected from diarrhea and vomit samples and tested by PCR. Following completion 

of the bioassay, viable PEDV was detected only in piglets challenged with non-treated choline 

and choice white grease [15].
31

• Dee et al. (2016) designed a model to evaluate the transboundary risk of PEDV-contaminated 

swine feed ingredients during a simulated shipment from China to the United States and tested 

the effect of two mitigation strategies on the reduction of PEDV in feed using LA and 2% custom 

MCFA. Fourteen swine feed ingredients commonly imported from China to the United States 

were selected: organic and conventional soybeans and soybean meal (SBM), lysine HCL, D/L 

methionine, tryptophan, vitamins A, D, & E, choline chloride, rice hulls, corn cobs, and feedgrade tetracycline. The samples were organized into four batches, each representing a specific 

segment of the 37 day shipping journey. Each ingredient was allocated into each of the four 

batches in two replicates. Each batch of ingredients had a positive control group (non-treated), a 

negative control group (PEDV-negative ingredients), a LA-treated group (LA and PEDV spiked), 

and a MCFA-treated group (MCFA and PEDV spiked). The samples were housed in a 

programmed environmental chamber based on the temperature and percent relative humidity 

for each segment of the shipping journey. For exposure to ambient air, two holes were drilled 

into each plastic container. At designated DPI, samples were removed and submitted for 

diagnostic testing by RT-PCR and VI. Viable PEDV (positive VI) in batch 4 (representing shipment 

to and storage in Iowa) was found in non-treated organic and conventional SBM, lysine, and 

vitamin D [47]. 

The swine bioassay was used to test ingredients that were PCR-positive for PEDV but negative 

by VI. This included non-treated ingredients vitamins A and E, tryptophan, D/L methionine, 

soybeans (organic and conventional) and choline chloride. Ingredients treated with LA or MCFA

included soybean meal (conventional and organic), lysine, vitamin D, and choline chloride. 

Piglets (n = 24) of 5-7 days old were divided into groups of four. All four piglets in each unit 

received the same ingredient. Samples from batch 4 (to represent ingredients that would travel 

the entire 37-day journey to Iowa) were prepared for the bioassay. Piglets received 1 mL of the 

designated inoculum orally via syringe. Pigs were observed for 7 days for clinical signs and daily 

rectal swabs were taken and, if clinical, swabs were collected from diarrhea and vomit samples 

and tested by PCR. If diagnostic samples were PEDV-positive by PCR, all animals swabbed were 

euthanized and piglets re-stocked. If pigs remained PEDV-negative, the pigs were added to a 

different experimental group and inoculated with a different ingredient (re-used). Positive

bioassay findings were observed in piglets that were administered non-treated choline chloride. 

None of the piglets fed LA- or MCFA-treated ingredients spiked with PEDV were positive on the 

swine bioassay [47]. 

• Dee et al. (2018) evaluated the survival of select viral pathogens in feed ingredients using 

models designed to simulate transportation conditions across two different regions of the 

world. Eleven viruses were selected: foot and mouth disease virus (FMDV), classical swine fever 

virus (CSFV), ASFV, influenza A virus of swine (IAV-S), PRV, Nipah virus, PRRSV, swine vesicular 

disease virus (SVDV), vesicular stomatitis virus (VSV), PCV2, and vesicular exanthema of swine 
32

virus (VESV). Surrogate viruses were used for FMDV, CSFV, PRV, VESV, Nipah virus, and SVDV. 

Eleven feed ingredients were selected: organic and conventional SBM, soy oil cake, DDGS, lysine 

HCL, vitamin D, choline chloride, moist cat food, moist dog food, dry dog food, and pork sausage 

casings. Two transboundary shipping journeys were modeled: trans-Pacific (per Dee et al., 2016) 

to simulate travel between China and the United States and trans-Atlantic to simulate travel 

between Europe (Poland) and the United States (for ASFV only). The samples were organized 

into four batches, each representing a specific segment of each trans-ocean shipping journey. 

Duplicate samples of each ingredient were organized into the batches. Five gram samples of 

gamma-irradiated ingredients were spiked with 100 μL of minimum essential media containing 1 

X 105 TCID50/g of each virus. All samples were incubated in a programmed environmental 

chamber regulated for temperature and percent relative humidity. Samples of each 

ingredient/virus combination were removed from each batch at the predetermined DPI and 

tested by RT-PCR and VI. A wide variation in viability was observed across the virus-ingredient 

combinations from batch 4 [48].

The swine bioassay was used to determine infectivity of feed ingredients that tested positive by 

PCR but negative on VI in cell culture. The bioassay was performed with Seneca virus A (FMDV

surrogate), PRRSV, porcine sapelovirus (SVDV surrogate), PCV2, ASFV, and IAV-S in selected 

virus-ingredient combinations. Pigs were inoculated by various methods, including orally via 

syringe, intramuscularly, and intranasally. A positive bioassay was observed for the following 

virus-ingredient combinations: PRRSV and conventional SBM; PRRSV and DDGS; Seneca virus A 

and choline; and PCV2 and lysine, choline, and vitamin D. The finding of Senecavirus A in choline 

was not detailed in the discussion section [48]. 

The investigators reported that from the virus-ingredient combinations subjected to various 

simulated environmental conditions, 7 viruses remained in a viable form in 2 or more 

ingredients: Seneca virus A, ASFV, PRRSV, porcine sapelovirus, PCV2, feline calicivirus (surrogate 

to VESV), bovine herpesvirus-1 (surrogate to PRV), and PEDV. The highest degree of stability was 

for Seneca virus A as viable virus was recovered from 10 of 11 ingredients. ASFV stock virus was 

the only virus to survive the simulated 30-day shipping journey in the absence of feed matrix. 

Half-life was calculated for Seneca virus A, porcine sapelovirus, feline calicivirus, bovine 

herpesvirus-1, and ASFV for each virus-ingredient combination. Feline calicivirus and Seneca 

virus A had extended half-lives in conventional SBM, 26.6 days and 9.7 day, respectively, as 

compared to other virus-ingredients combinations. Feline calicivirus had the longest half-life in 

conventional SBM at 26.6 days but much shorter half-life in other ingredients. In contrast, 

Seneca virus A had the least variability of half-life in feed, ranging from 1.7 to 9.7 days across 10 

ingredients. The non-animal origin feed ingredients that supported survival of multiple viruses 

(n) included conventional SBM (n = 7), lysine (n = 5), vitamin D (n = 4), choline (n = 4), organic 
33

SBM (n = 3), and DDGS (n = 2). The findings suggest that viruses can survive in feed but survival

duration is variable and dependent on virus properties and feed matrix [48]. 

6.3.3 Summary of findings

For the experimental studies using field-sourced challenge virus, the swine bioassays in the Pillatzki et al. 

(2015) and Bowman et al. (2015) studies failed to demonstrate the infectivity of PEDV PCR-positive feed. 

Pillatzki et al. (2015) provides several plausible explanations, including the nucleic acid detected in the 

feed samples did not represent infectious virus; the feed samples had relatively high Ct values (range: 

30.0 – 36.5); and an extended storage time between collection of the sample and the bioassay may have 

reduced or eliminated the infectivity of the PEDV. Similar explanations were provided by Bowman et al. 

(2015), adding that the small number of piglets used in the bioassay and the short feeding trial period 

lowered the sensitivity of the bioassay and did not realistically reflect the field setting. Despite the 

negative findings, Bowman et al. (2015) maintains that the contaminated feed pellets were the source of 

the outbreak in the Ohio swine operation. Pillatzki et al. (2015) also concluded that feed contaminated 

with infectious PEDV can serve as a vehicle for disease transmission, citing as evidence that the positivecontrol piglets that were administered spiked feed did develop clinical signs of PED and PEDV fecal 

shedding. The findings in Pillatzki et al. (2015) are consistent with the findings of Dee et al. (2014). Both 

studies produced challenge feeds with a low Ct value (range: 18.23 – 25.5) and the bioassay conducted 

with the PEDV-contaminated feeds produced disease. 

For the experimental studies using laboratory-sourced challenge virus, Goyal (2014) produced 

preliminary evidence that under laboratory conditions, PEDV can survive in PEDV-spiked wet and dry 

feed at room temperature and remain infectious for ≥ 28 days and 7 days, respectively [45]. Other

studies on PEDV survival in individual swine feed ingredients support these findings [15, 41, 42, 47]. 

Schumacher et al. (2016) produced preliminary evidence on the minimum infectious dose of PEDVinoculated feed as 5.6 x 101 TCID50/g with Ct values ranging from 27 – 37 [46]. 

The findings in three studies, under different experiment conditions, suggest that virus survival is 

ingredient-dependent. Varying physical and chemical characteristics of feed ingredients may enhance or 

protect virus survival [15, 47, 48]. Dee et al. (2015) noted several interesting or novel findings, including 

an extended survival time observed in conventional SBM; recovery of viable PEDV from (all non-treated) 

DDGS, 3 synthetic amino acids, and dry choline chloride; and the inability to recover viable PEDV from 

SDPP [in contrast to Pasick et al. (2014)] or the 3 VTM mixes. Dee et al. (2016) study also found viable 

PEDV in PEDV-spiked conventional SBM, lysine, and choline. Additionally, PEDV did survive and remain 

infectious in vitamin D [47]. Both formaldehyde-based LA and MCFA treatment rendered virus inactive, 

regardless of ingredient type, suggesting these mitigants might be useful as part of a risk management 

strategy for reducing viral load in feed ingredients [15, 47]. 

Building upon the shipping model methods developed in the Dee et al. (2016) study, the Dee et al. 

(2018) study expanded the selection of viral pathogens as well as added an additional trans-oceanic 
34

shipping route from Europe (Poland) to the United States for ASFV. Like the two preceding studies, Dee 

et al. (2018) found that certain feed ingredient matrices enhance or protect viral survival. Of interest, 

the authors noted that virus viability in organic SBM could not be demonstrated. This finding could 

discount previous speculation that the rise in organic swine farming may have contributed to PEDV 

introduction in to the United States. Additionally, the authors noted that ASFV demonstrated strong 

survivability characteristics, remaining viable under laboratory-simulated conditions with or without the 

feed matrix [48]. 

In summary, the infective dose of PEDV is low and, experimentally, infectivity of the feed material is 

dependent on viral load (e.g., Ct value). Additionally, experimental evidence indicates that the duration 

of virus survival in swine feed ingredients is dependent on the ingredient matrix and the virus-ingredient 

combination. The feed ingredients that have shown to support virus survivability and viability include 

conventional soybean meal, lysine, choline chloride, and vitamin D. ASFV demonstrated strong 

survivability characteristics. 

Among the knowledge gaps identified in these studies are the identification of vulnerable (risky) nonanimal origin feed ingredients for viral contamination, ingredient (matrix) characteristics that support or 

hinder virus survival, and identification of the critical point(s) in the transboundary feed production and 

distribution continuum where (fecal) contamination of non-animal origin ingredients could occur. There 

is a paucity of field data demonstrating if, how, and when non-animal origin feed ingredients may 

become contaminated with swine viruses. Further, although some field epidemiological investigations 

have associated contaminated feed (PCR positive) with the source of virus introduction on affected 

farms, to date, experimental studies designed to prove causation of virus transmission via feed and feed 

ingredients have yielded inconsistent data. It is also unknown what characteristics of non-animal origin 

feed ingredients may contribute to virus survival, if present. Additionally, the development of diagnostic 

assays and sampling techniques, capable of testing large volumes of non-animal origin feed ingredients

to determine whether the level of contamination is sufficient to transmit disease is required to better 

assess the frequency with which these materials are contaminated with virus, which viruses are present, 

and at what concentration. Subsequent assays to determine contamination of the final, processed feed 

product would be useful to determine the likelihood that contaminated non-animal origin feed 

ingredients would transmit virus to swine and to what degree feed should be prioritized as a biosecurity 

risk. 
35

7 Discussion

The objective of this literature review was to gather and analyze the evidence in published scientific 

literature regarding whether non-animal origin ingredients of commercial swine feed could introduce 

and transmit viral pathogens of swine into or within the United States. The goal was to understand the 

current scientific knowledge and to identify information gaps to better inform decision makers, other 

stakeholders, and the scientific community. To achieve this, the basic steps of a systematic review

methodology were followed [1], resulting in a qualitative summary report of findings. 

The results of the literature review demonstrate that a limited number of studies currently address

swine viral pathogen transmission through non-animal origin feed and feed ingredients. Of the studies 

available, several suffered from limitations that hinder generalizing the findings to real-world 

commercial swine scenarios. For example, studies were limited by small feed sample volumes (as small 

as 5 grams) which does not directly equate to the quantities (tonnage) in actual swine production and 

feed scenarios; small sample sizes (2 replicates) which reduced statistical strength and confidence of 

findings; low sensitivity in swine bioassays; experimental methods which do not mimic natural feeding 

behaviors of swine or large-scale commercial swine production; and environmental scenarios that

cannot be easily extrapolated to other seasons or geographical regions. Bioassays, including those 

reviewed in this document, often suffer from low sensitivity due to low number of subject animals (n = 4 

in the studies reviewed); health status of subject animals often does not reflect the immune status 

variability observed in the field setting; and subject animals are typically exposed or inoculated once 

(single-hit concept) whereas multiple or on-going exposures occur in the field setting. Thus, results of 

the bioassay may not equate to real-life scenarios. Other studies, particularly those with retrospective 

questionnaire or survey components, were limited by inherent sources of internal bias such as selection 

and recall bias. Furthermore, robust replication of studies in independent laboratories and field settings 

to validate or corroborate findings has not occurred. Thus, conclusions drawn from these studies should 

be interpreted with caution until repeatability of the findings can be demonstrated, particularly under 

conditions that mimic the field setting.

Despite the small number of published studies, several key themes have emerged, many of which

warrant additional exploration and research: 

• A subset of the studies reviewed provided experimental evidence that swine viruses can survive 

in non-animal origin feed ingredients under various experimental conditions [15, 30, 45, 47, 48]. 

Virus survival times were variable (ranging from 7 days to > 180 days) and dependent on the 

simulated environmental conditions applied (e.g., temperature and relative humidity) and the 

virus-ingredient combination. Others concluded that duration of virus survival (and infectivity) is 

ingredient-dependent and certain feed ingredients provide a more favorable matrix than others

for extended survival [15, 47, 48]. Additional research is needed to verify virus survival times 

(and infectivity) in complete feed and feed ingredients, with various virus-ingredient 

combinations under various environmental conditions, including actual field conditions.
36

• Several authors speculated that characteristics of the ingredient such as the physical supportive 

matrix and/or the chemical (bromatological) composition contributed to virus survival [15, 30, 

31, 48]. However, the specific characteristic(s) of the ingredient that contribute to viral 

persistence have not been identified or proven. 

• A subset of experimental studies provided evidence that feed contaminated with virus can 

transmit disease to naive piglets [9, 15, 45-48]. However, the experimental methods used in 

these studies such as spiking ingredients with predetermined virus load or inoculating piglets via 

methods other than natural feeding behaviors, do not reflect the field setting and results may 

not be generalizable to field conditions, particularly large-scale commercial swine facilities. 

Additional laboratory and field-based studies are needed to determine the extent of finding 

reproducibility and applicability to field settings.

• A subset of studies have attempted to identify individual feed ingredients that may be more 

likely than others to support virus survivability [15, 47, 48]. Viability and infectivity of each virus 

were assessed through VI and/or swine bioassay. The presence of a viable form (meaning a 

positive VI and/or bioassay) of virus (at ≥ 30 days) was confirmed in the following non-animal 

origin ingredients that had been experimentally spiked with virus inoculate: organic and 

conventional SBM, DDGS, lysine HCL, D/L methionine, choline chloride, and vitamin D [15, 47, 

48]. Extended survival was observed in virus-spiked conventional SBM [15]. Two experimental 

studies, using different experimental conditions, observed PEDV viability in three PEDV-spiked 

ingredients: conventional SBM, lysine, and choline chloride. [15, 47]. Virus viability (and 

infectivity) as determined in separate swine bioassays was observed with PEDV-contaminated 

choline chloride [15, 47] and Seneca virus A-contaminated choline chloride [48].

• A major knowledge gap exists in sources of potential contamination and where feed or feed 

ingredients may be contaminated. These experimental studies conducted with inoculated nonanimal origin feed ingredients do not address the question of whether these ingredients are 

contaminated with swine viruses under field conditions. The critical point(s) of susceptibility to 

contamination along the feed production, processing, and distribution continuum, from 

harvesting the plant-derived feed ingredients in the field to on-farm delivery of feed to swine 

premises, have not been identified.

• Neither the contamination route of exotic swine pathogens into non-animal origin feed 

(ingredients) nor the virus entry route into the United States has been decisively proven.

• Under the laboratory-simulated model conditions, both LA and MCFA were concluded to be 

effective chemical mitigants against PEDV in individual feed ingredients stored under simulated 

shipping conditions, suggesting they might be useful for reducing viral load in feed ingredients 

[15, 47]. The real-world application of LA and MCFA for eliminating swine viruses or decreasing 

their level of infectivity under field conditions has yet to be determined. If field-contamination 

of non-animal origin ingredients is determined to be a concern for pathogen transmission, 

additional mitigation strategies should continue to be explored, including other chemical 

treatments, the application of heat or pressure (pelleting) to feed, and holding times for feed or 

feed ingredients. 
37

• Some of the outbreak epidemiological investigations provided evidence that the transmission 

route(s) for swine viruses onto the index farm may differ from the transmission route(s) among 

housing units within the index farm and between secondary farms. Similarly, the entry route

(e.g., for PEDV) into the United States may differ from the transmission route(s) among 

domestic swine farms. Thus, as with other infectious diseases, multi-modal transmission 

mechanisms are likely occurring. When considering non-animal origin feed ingredients as a 

potential fomite for swine virus transmission, it’s important to understand how the primary

transmission pathways (e.g., infected live pigs, contaminated transport vehicles, personnel, etc.) 

interface with one another, particularly how the production and distribution of feed interacts

with other sources of virus contamination (e.g., infected live pigs, contaminated transport 

vehicles, personnel, etc.) to contribute, if at all, to disease transmission. 

• Similarly, it’s important to understand the relative risks of various transmission pathways and 

where feed ingredients fit in among broadly accepted risk pathways such as movement of 

infected pigs and fecal contamination of fomites (e.g., transport vehicles). By understanding the 

magnitude of the risk of feed ingredients, one can better balance the costs of sourcing “safe” 

feed ingredients and the nutritional needs of pigs with the costs of applying various mitigation 

strategies to potentially contaminated feed (e.g., heat or chemical treatment or feed holding 

times). 

• Reliable and validated assays and sampling techniques capable of detecting infective virus (i.e., 

to determine the level of contamination is sufficient to transmit disease) in large quantities of

(bulk) ingredients are not available. 

• As mentioned above, the critical point(s) of contamination along the feed production, 

processing, and distribution continuum, from harvesting the plant-derived feed ingredients in 

the field to on-farm delivery of feed to swine premises, have not been identified. Because of this

some of the experimental studies reviewed were performed under the assumption that 

ingredients are contaminated in the post-processing stage of feed production. Very little 

information is available on how non-animal origin feed ingredients are produced and sourced 

outside the United States and current studies have produced little scientific evidence of how, or 

if, non-animal origin feed ingredients could become contaminated with swine viruses in regions 

outside the United States. Taking a systematic approach to the entire (transboundary) feed 

production system, similar to the hazard analysis and critical control points process used in food 

safety, may help to identify vulnerabilities in the production process, better inform the

development and application of mitigation measures to reduce viral contamination risks, and 

help stakeholders allocate resources towards mitigation measures based on the likelihood of 

virus contamination. 

• Over the past several decades, the U.S. commercial swine industry has improved biosecurity 

measures on commercial premises to prevent transmission of economically significant viruses 

such as PCV2, PRRSV, and PEDV. Many commercial swine operations use the absence of PRRS on 

the farm as an indicator of thorough implementation and enforcement of biosecurity measures. 

In the studies reviewed, many favorably described their biosecurity measures and echoed 

sentiments expressed by Bowman et al. (2015) that the “effectiveness of the biosecurity 
38

measures in place was evidenced by the absence of PRRS cases”. However, the entry of PEDV 

(and new or emerging swine viruses) onto presumably biosecure commercial premises suggests 

that current biosecurity standards are insufficient to prevent virus incursion. Virus 

characteristics and the characteristics of the commercial swine industry (globalization of trade, 

intensification and vertical integration of production, and extensive movement of pigs and 

related production components) could contribute to biosecurity breaches. Robust biosecurity 

measures may be the only tool, in the absence of effective vaccines or treatments, to prevent 

the entry and spread of some diseases. Thus, biosecurity strategies, particularly the extensive 

movement of production inputs, need to be re-evaluated and adjusted to meet today’s swine 

industry paradigm.

While investigators have addressed some critical experimental questions pertaining to transmission of 

swine viruses via feed and feed ingredients, the current body of scientific knowledge has yet to provide 

conclusive evidence for the source(s) of contamination of non-animal origin feed ingredients with swine 

viruses and the epidemiology of virus transmission to swine under field conditions. If the primary 

concern of the swine industry and associated stakeholders lies in the importation of contaminated feed 

and feed ingredients, then additional research and investigative studies of how ingredients are sourced, 

processed, and transported prior to importation into the United States are needed. However, the lack of 

feed and feed ingredient diagnostic assays and sampling techniques capable of detecting virus in large 

volumes of material limits our ability to determine if and at what point non-animal origin feed or feed 

ingredients may become contaminated with viruses and limits our ability to establish critical control 

points in feed production, distribution, and storage to mitigate risk(s). Until these data are available, it is 

difficult to evaluate the biosecurity risk posed by non-animal origin feed and feed ingredients. Moving 

forward, studies designed to examine the likely source(s) of contamination and virus mitigation steps in 

processing and post-processing may be the most fruitful focus of research.
39

8 Appendix I: Sample data extraction form
40
41

9 Appendix II: Data synthesis table

Study Study Design

and Funding

Source(s)

Viral 

Pathogen(s)

Fomite4 Study Description Core Outcomes Methodological 

Comments

Bowman et al., 

2015 [39]

Epidemiological 

case report with 

bioassay

Funding provided 

by National Pork 

Checkoff, PIC 

North America, 

and USDA.

PEDV Feed, starter 

feed pellets

Through epidemiological 

investigation of a swine 

operation in Ohio, 

contaminated feed (starter 

feed pellets) was identified 

as the likely source of PEDV 

introduction. The feed and 

feed source was RT-PCRpositive for PEDV. A 

bioassay was performed 

with samples of 

cryopreserved feed.

Authors determined

the starter pellet to 

be the source of PEDV 

introduction. PEDV 

RNA was detected 

inside unopened bags 

of new pellets, at the 

source facility 

(supplier), and in 

individual ingredients 

at the source facility. 

For the bioassay, 

naive pigs fed PCRpositive feed from the 

supplier remained 

negative for PEDV. 

The results of the 

bioassay were negative 

but experimental 

conditions may not 

reflect field conditions. 

The authors made several 

hefty assumptions 

regarding biosecurity at 

the affected farm and 

ruled out other possible 

transmission routes 

without providing the 

supporting data. 

Brookes et al., 

2015 [27]

Expert elicitation

Funding provided 

by Australian Pork 

Limited.

PRRSV Multiple Through expert elicitation, 

authors examine the most 

probable route of 

introduction of highly 

pathogenic PRRSV from 

southeast Asia into 

Australia. Participant 

answers were analyzed for 

commonalities and 

Overall, significant 

agreement of 

respondents’ opinions 

for exposure routes 

involved disposal of 

waste to feral and 

backyard pigs. For 

commercial pigs, the 

highest probability 

exposure route was 

The study design has 

several sources of 

potential bias, including 

participant selection, 

response/cognitive bias, 

framing bias, and recency 

bias. Authors examine 

multiple entry and 

exposure routes to 

analyze perceived risks by 

 4 A fomite is defined as an inanimate object or material that is likely to carry infection such as animal feed, feed ingredients, organic substrates, transport 

vehicles, boots, etc. 
42

Study Study Design

and Funding

Source(s)

Viral 

Pathogen(s)

Fomite4 Study Description Core Outcomes Methodological 

Comments

agreements were grouped 

and ordered. 

human fomite or 

access to animal 

feed/additives from 

SE Asia (very low). 

Less agreement on 

entry routes; animal 

feed/additives were 

given moderate 

probability.

industry experts’ 

opinions. Thus, specific 

pathways (e.g. animal 

feed/additives) are not 

adequately defined or 

examined to the level of 

detail needed for indepth analysis. 

Davies, 2015 

[5]

Review article 

Funding source not

listed. 

PRRSV, PCV2 

and PEDV

Feed, SDPP The article describes 3 

major swine diseases, 

including PRRSV, PCV2 and 

PEDV. Similarities among 

the viruses are discussed. 

The virus transmission 

likelihood resulting from 

feeding animal products 

(SDPP) to swine and 

whether or not the true risk 

warrants excluding animal 

origin products from swine 

diets is examined. 

The author suggests 

that "new" viruses in 

swine are likely to 

emerge from already 

recognized (nonpathogenic or 

ignored) swine 

viruses. The likelihood 

of PEDV survival in 

SDPP is extremely 

low, but not zero. A 

blanket ban on certain 

ingredients in swine 

feed may not be the 

solution. A 

comprehensive 

evaluation of 

transmission 

pathways as well as 

cost-benefit analyses 

of managing feedrelated risks and 

The discussion focused on 

SDPP; however, key 

points can be generalized 

to non-animal origin 

ingredients. Increasing 

herd sizes (and assuming 

fixed biosecurity 

practices) along with 

greater flux of inputs 

translates to a higher

temporal frequency of 

adverse events. The 

features of modern swine 

production (global trade, 

intense production, 

extensive movements) 

have contributed to the 

emergence of these 

pathogenic strains and 

we should expect this 

trend to continue. 
43

Study Study Design

and Funding

Source(s)

Viral 

Pathogen(s)

Fomite4 Study Description Core Outcomes Methodological 

Comments

nutritional value is 

needed. 

Dee et al., 2014 

[9]

Experimental with 

bioassay

Funding provided 

by Pipestone 

Applied Research.

PEDV Complete feed At-risk feed bins were 

sampled on 3 index farms. 

Feed bins at 4 PEDVnegative farms were also 

sampled. All samples were 

tested for PEDV by RT-PCR. 

For the bioassay, 11 pigs 

were divided into 3 groups 

– a treatment group fed 

PCR-positive feed bin 

samples, a positive control 

group fed PEDV- spiked 

feed, and a negative 

control group fed a 

placebo. Groups were fed 

PCR-positive feed or 

placebo feed (ad libitum) 

on day 0 and PCR-negative 

feed throughout the 

remainder of the study. 

Pigs were necropsied on 

day 7 post- challenge.

Assessment of feed 

material in the at-risk 

bins across the 3 sites 

were PCR-positive for 

PEDV. All samples 

from control bins and 

PEDV-negative sites 

were PCR-negative.

For the bioassay, 

treatment and 

positive control 

groups exhibited 

clinical signs of PED 

and were PCRpositive for virus. The 

negative control 

group displayed no 

clinical signs of 

disease and were 

PCR-negative.

The bioassay sought to 

mimic on-farm 

transmission conditions 

by using PCR-positive 

feed material from 

confirmed PED affected 

farms and using a natural 

feeding method (ad 

libitum). An 

acknowledged limitation 

was that the in vivo study 

was not designed to 

estimate the frequency of 

feed-related PEDV 

infections. Results were 

based on a very small 

populations of pigs and 

cannot be extrapolated to 

today’s commercial farm 

and field conditions. 

Dee et al., 2015 

[15]

Experimental with 

bioassay

Kemin Industries

and Dr. Mark 

Bienhoff were 

PEDV Feed 

ingredients: 

corn, SBM, 

DDGS, SDPP, 

purified 

plasma, 

intestinal 

Common swine feed 

ingredients (18) were 

divided into two groups in 

replicate – LA treatment 

group and a non-treated 

group. Controls included 

complete feed spiked with 

Only LA-treated 

samples of SBM and 

MBM remained PEDVpositive at 30 DPI. 

Supplementary 

testing of SBM (nonLA treated) was 

The study assumes postprocessing contamination 

of ingredients; the index 

step or point of 

contamination in feed 

manufacturing/feed 

delivery is relatively 
44

Study Study Design

and Funding

Source(s)

Viral 

Pathogen(s)

Fomite4 Study Description Core Outcomes Methodological 

Comments

acknowledged for 

providing technical 

expertise, funding 

and in-kind 

resources.

mucosa, MBM, 

RBC, 3 VTM 

mixes, white 

grease, soy oil, 

lysine HCL, D/L 

methionine, 

threonine, 

limestone, dry 

choline 

chloride 

PEDV (positive) or saline 

(negative). The samples 

were stored outside in 

winter conditions in plastic 

totes. At 1, 7, 14 and 30 

DPI, feed samples were 

removed and were tested 

for PEDV, PDCoV, and TGE 

by RT-PCR. The presence of 

viable virus was tested by 

VI. A swine bioassay was 

conducted for PCR 

positive/VI negative feed 

samples. Piglets 5-7 days 

old were divided into 

groups of 4. Pigs received 

the designated inoculum 

orally via syringe and were 

observed for 7 days. The 

negative control group was 

given saline PO. If clinical 

signs observed, swabs were 

taken of diarrhea and 

vomit. Swabs were tested 

by PCR. If PEDV positive, all 

animals swabbed were 

euthanized; units were 

cleaned and piglets restocked as needed. 

negative by PCR and 

VI for up to 210 days. 

PEDV was not 

detected in other 

treated ingredients. 

The following 

ingredients were used 

in the bioassay: (nonLA treated) corn, 3 

VTM mixes, intestinal 

mucosa, soy oil, 

choline chloride, 

SDPP, purified plasma; 

(LA-treated) white 

grease, limestone, 

and threonine. Viable 

PEDV was detected 

only in piglets given 

choline and choice 

white grease. 

PEDV viability may be 

influenced by 

ingredient type. 

Extended virus 

survival observed in 

SBM. LA is effective in 

rendering PEDV 

inactive, independent 

of ingredient type. 

unknown. Only 2 

replicates per ingredient 

were used; confidence 

intervals and confidence 

levels were not provided. 

Small ingredient samples 

(30 g) may not equate to 

the quantities (tonnage) 

in actual swine 

production and feed 

scenarios. Outdoor 

winter weather 

conditions in this study 

may not be extrapolated 

to other climates or time 

periods. For the bioassay, 

pooled sampling was 

used across days 7, 14, 

and 30 DPI (not daily 

testing of samples) and 

piglets were re-used 

following negative 

bioassays. Bioassay 

inoculums were given 

orally via syringe which 

does not mimic normal 

feeding habits and may 

not correlate to field 

conditions. 

Dee et al., 2016 

[47]

Experimental with 

bioassay

PEDV Feed 

ingredients: 

The shipping journey from 

Beijing, China to Des 

First proof of concept 

study indicating PEDV 

The shipping timetable 

was based on one 
45

Study Study Design

and Funding

Source(s)

Viral 

Pathogen(s)

Fomite4 Study Description Core Outcomes Methodological 

Comments

Kemin Industries, 

APC, Inc. and 

National Pork 

Board were 

acknowledged for 

providing technical 

expertise, funding 

and in-kind 

resources.

organic and 

conventional 

soybeans, 

SBM, Lysine 

HCL, D/L 

methionine, 

tryptophan, 

Vitamin A, D, 

& E, choline 

chloride, rice 

hulls, corn 

cobs, and 

feed-grade 

tetracycline

Moines, Iowa was divided 

into 4 travel segments, 

represented by 4 sample 

batches. Two replicates of 

the 14 ingredients were 

allocated into the 4 travel 

segments. Each batch had a 

positive control group 

(PEDV with no LA 

treatment), LA-treated 

group and MCFA-treated 

group. Also negative 

controls (PEDV-negative 

feed with saline) and stock 

PEDV samples. Samples 

were housed in a 

programmed 

environmental chamber to 

mimic weather between 

China and Iowa in Dec 

2012/Jan 2013. At 

designated DPI, samples 

were submitted for 

diagnostic testing with RTPCR and VI. A bioassay was 

performed for PCR-positive, 

VI-negative samples. Piglets 

(5 days old) received 

inoculum (from batch 4) 

orally via syringe and were 

observed for 7 days. If 

survival in specific 

feed ingredients 

under modeled 

shipping conditions 

(China to US). After 

37-day period, viable 

PEDV found (via VI) in 

Vitamin D, lysine 

hydrochloride, organic 

and conventional 

SBM. For the 

bioassay, piglets 

became PEDV-positive 

when administered 

non LA-treated 

choline chloride. Both 

LA and MCFA were 

concluded to be 

effective chemical 

mitigations as a

means to reduce the 

risk of PEDV in feed 

ingredients. 

website, not (multiple) 

data from actual shipping 

times and may not reflect 

real-life scenarios. Small 

ingredient samples (30 g) 

may not equate to the 

quantities (tonnage) in 

actual swine production 

and feed scenarios. 

Simulated environmental 

conditions may not be 

extrapolated to other 

environmental 

conditions. Bioassay 

inoculums were given 

orally via syringe which 

does not mimic normal 

feeding habits. In the 

discussion, authors may 

have overstated (or did 

not adequately provide 

justifications for) the 

“risk” of organic farming 

and imported soybean 

products. Similar 

inferences were not 

stated in the discussion 

for ingredients commonly 

used in commercial swine

despite similar study 

results. 
46

Study Study Design

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Source(s)

Viral 

Pathogen(s)

Fomite4 Study Description Core Outcomes Methodological 

Comments

clinical, swabs were taken 

of diarrhea and vomit and 

tested by PCR. If PCRpositive, animals swabbed 

were euthanized; units 

cleans and piglets restocked as needed. 

Dee et al., 2018 

[48]

Experimental with 

bioassay

Funding provided 

by Swine Health 

Information Center 

(SHIC); American 

Association of 

Swine 

Veterinarians

Foundation; State 

of Kansas National 

Bio and Agrodefense Facility

Fund; SDSU Animal 

Disease Research 

and Diagnostic 

Laboratory. 

Salaries of four 

authors paid by

SVA (FMDV)5, 

bovine viral 

diarrhea virus 

(CSFV), BHV-1 

(pseudorabies 

virus), canine 

distemper 

virus (Nipah 

virus), PSV 

(SVDV), FCV 

(vesicular 

exanthema of 

swine virus), 

ASFV, IAV-S, 

PRRSV, 

vesicular 

stomatitis

virus, and 

PCV2.

Feed 

ingredients: 

organic & 

conventional 

SBM, soy oil 

cake, DDGS, 

lysine HCL, 

Vitamin D, 

choline 

chloride, moist 

cat food, moist 

dog food, dry 

dog food and 

pork sausage 

casings

Similar shipping model to 

Dee et al. 2016 employed. 

Two shipping routes: TransAtlantic (Poland to US) for 

ASFV and Tran-Pacific 

(China to US) for all other 

viruses. Eleven 

ingredient/11 virus 

combinations were 

assembled for trip 

segments. Five gram, 

gamma-irradiated samples 

were spiked with virus; 

stored in environmentallycontrolled chambers. Each 

ingredient/virus combo 

was tested by RT-PCR and 

VI on the appropriate day 

(based on simulated 

travel). A bioassay was 

performed for PCR-positive, 

Seven of 11 viruses 

remained viable in 2 

or more ingredients 

(SVA, ASFV, PRRSV, 

PSV, PCV2, FCV and 

BHV-1). SVA was 

recovered from 10 of 

11 ingredients. ASFV 

samples survived the 

simulated 30-day

shipping in the 

absence of feed 

matrix. FCV and SVA 

had extended halflives in conventional 

SBM; SVA had the 

most stable half-life 

range (1.7 to 9.7 days 

across 10 ingredients). 

FCV had the longest 

survival in 

Small ingredient samples 

(5 g) may not equate to 

the quantities (tonnage) 

in actual swine 

production and feed 

scenarios. Confidence 

intervals were not 

calculated due to too few 

replications. Samples 

were spiked with the 

same amount of virus 

which may not reflect 

proposed field 

contamination. Bioassay 

inoculums were given IM, 

IN or orally via syringe 

which does not mimic 

normal feeding habits. 

Results seem to negate 

previous reports (Dee et 

al. 2016) that organic 

 5 Surrogate viruses were used for viruses listed in parentheses. For other viruses listed, actual virus was used.
47

Study Study Design

and Funding

Source(s)

Viral 

Pathogen(s)

Fomite4 Study Description Core Outcomes Methodological 

Comments

Pipestone Applied 

Research.

VI-negative samples, which 

included SVA, PRRSV, PSV, 

PCV2, ASFV, and IAV-S.

conventional SBM 

(26.6 days). Findings 

indicate viruses can 

survive in feed; 

survival duration is 

variable and 

dependent on virus 

properties and feed 

matrix. Data indicates 

non-enveloped 

viruses are more 

resistant in the 

environment than 

enveloped.

soybean products pose 

an increased “risk” of 

virus transmission 

compared to non-organic 

ingredients. 

EFSA AHAW 

Panel, 2014 

[34]

Descriptive; 

qualitative 

literature review 

2004-2014

Funding source not 

listed. 

PEDV, PDCoV N/A At the request of the 

European Commission, 

EFSA AHAW Panel was 

tasked to deliver a scientific 

opinion on the current 

scientific evidence, 

epidemiological situation, 

and knowledge/data gaps 

regarding PEDV and PDCoV.

Transmission of these 

viruses in feed or feed 

ingredients was not 

directly addressed in 

this report. Overall, 

the major 

recommendation(s) 

relevant to NOFI 

included the 

importance of strict 

biosecurity, in 

particular with 

vehicles, to prevent 

introduction of PEDV 

onto the farm. 

Comprehensive 

summation of the current 

knowledge of PEDV from 

2004 to September 2014. 
48

Study Study Design

and Funding

Source(s)

Viral 

Pathogen(s)

Fomite4 Study Description Core Outcomes Methodological 

Comments

EFSA, 2016 [33] Descriptive; 

qualitative 

literature review 

Oct 2014 - Oct 

2015

Funding source not 

listed. 

PEDV N/A The European Commission 

requested EFSA to 1) 

provide guidance on PEDV 

data to be collected by EU 

Member States in order to 

optimize coordination of 

response, and 2) analyze 

the epidemiological data 

from EU Member States

and in the scientific 

literature. The review 

focused on occurrence of 

infection with different 

PEDV strains, 

morbidity/mortality rates 

and severity of clinical 

disease. 

Conclusions and 

recommendations 

starts pg. 20 & many 

annexes collate the 

findings and data 

from the updated 

literature review.

EU-centric report; 

however, 

recommendations pg. 20-

21 are generalizable to 

US. For the impact of 

PEDV to EU farms, the 

authors noted in Table 3 

that data were missing 

and analysis is difficult for 

non-reportable diseases. 

Due to the missing data, 

results in Table 3 must be 

interpreted with caution. 

Fasina et al., 

2012 [24]

Retrospective 

case-control study

Funding source not 

listed.

ASFV Feed (swill), 

water, 

rodents, 

equipment, 

people

A survey of farm 

characteristics, farm 

operations, and selfreported biosecurity 

measures was 

administered to case and 

control farm owners. 

Statistical analysis was 

performed on responses 

and risk factors using 

univariable and 

multivariable conditional 

logistic regression models.

Protection of feed and 

water (from rodents) 

and purchasing of 

commercial feed (vs 

swill feeding) was 

negatively associated 

(protective) with 

acquiring ASFV. 

Presence of abattoir 

in the community and 

infected neighboring 

farms was positively 

associated with risk 

for ASFV. 

The study examined 

associative relationships 

between farm practices 

and risk of ASFV. Swill 

feeding was not defined 

but presumably swill 

would contain both 

animal and non-animal 

origin feed components. 

Self-reporting and recall 

bias is possible given 

study design. 
49

Study Study Design

and Funding

Source(s)

Viral 

Pathogen(s)

Fomite4 Study Description Core Outcomes Methodological 

Comments

Goyal, S.M., 

2014 [45]

Experimental; 

quasi-experimental

Funding provided 

by Pork Checkoff.

PEDV; TGE 

virus

Feces, slurry, 

wet and dry 

feed, water

PEDV and TGE virus were 

inoculated into animal feed 

(dry and wet) and water. 

Feces and slurry from 

infected animals were 

tested for virus. Spiked 

feed was incubated and 

instilled into the esophagus 

of piglets. Animals were 

scored for signs of PED/TGE 

and sacrificed.

PEDV and TGE virus 

were detected by RTPCR in dry and wet 

feed, feces samples, 

slurry and water. All 

piglets inoculated 

with spiked feed 

became infected with 

PEDV at viral dilutions 

up to 10-9

.

The study used a small 

sample set for the 

bioassay (12 piglets). No 

statistical analyses were 

performed for the 

experiments. Bioassay 

inoculation performed by 

gavage instead of free 

feed. Author 

demonstrates that virus 

can survive in various 

organic materials and 

that pooled samples of 

spiked feed can infect 

piglets with PEDV. 

Authors attempt to 

extrapolate findings to 

infections that occur in 

the field but this is 

unsubstantiated. 

Greiner, L.L., 

2016 [40]

Descriptive

Funding provided 

by the National 

Pork Board. 

PEDV; PDCoV Feed mill 

fomites: office 

floors, bulk 

ingredient pit 

grates, trucks 

carrying 

bagged 

ingredients, 

mixer/pellet 

cooler, inside 

feed 

Fomites at 24 US feed mills 

were swabbed for 5 

consecutive days. Samples 

were analyzed by PCR at 1 

of 4 laboratories. Eighteen 

of the 24 feed mills 

serviced farms known to be 

positive for PEDV; 5 

delivered to PDCoVpositive farms.

No samples tested 

positive for PEDV 

RNA; 5% of truck foot 

pedals and 1% of bulk 

ingredient pits were 

suspect for PDCoV 

RNA; 3.4% of truck 

foot pedals and 2.2% 

of office floors were 

positive for PDCoV 

RNA. No bulk 

The study examined 

various control/entry 

points for virus at feed 

mills. Authors did not find 

a positive correlation 

between virus presence 

at the feed mill and 

probability of PEDV 

infection on farms 

serviced. 
50

Study Study Design

and Funding

Source(s)

Viral 

Pathogen(s)

Fomite4 Study Description Core Outcomes Methodological 

Comments

compartment 

on feed truck, 

foot pedals of 

feed delivery 

truck

ingredient pits or 

mixer/coolers were 

positive for either 

virus.

Guinat et al., 

2016 [26]

Review Article

Funding provided 

by the European 

Seventh 

Framework 

Programme. 

ASFV Review 

examining 

ASFV 

transmission 

(pig-to-pig, 

fomites, ticks, 

feed)

Research summarized 

describes transmission of 

ASFV via feeding of 

contaminated animal meat. 

ASFV was not transmitted 

by contaminated sweet 

potatoes or bananas (1921 

study). It was reported that 

a study in East Africa 

showed that ASFV was not 

transmitted by consuming 

non-animal origin feed 

(review 1969). 

Authors conclude 

current research 

supports transmission 

of ASFV in feed 

containing 

contaminated swine 

products. 

Transmission through 

non-animal origin 

feed is less conclusive. 

Additional studies are 

required to determine 

if transmission occurs 

in feed not containing 

swine products.

In the section on feed, 

authors conclude viral 

strain may impact 

transmission via this 

route. In this respect, 

extrapolation of findings 

to other viruses/different 

feeds may not be 

appropriate. 

Le et al., 

2012 [25]

Retrospective 

survey

Funding source not 

listed.

PHFDV N/A Retrospective survey 

classified cases of PHFD in 

southern Vietnam. 

Statistical analysis was 

conducted to identify 

potential risk factors 

associated with disease 

status at household level.

The study found 

PHFDV prevalence 

was 33.4% and risk 

factors included: 

higher numbers of 

sows and finishing 

pigs, receiving pigs 

from an external 

source and the 

interaction between 

using ‘water green 

The smaller study area 

limits extrapolation of 

results to other areas. 

Case identification was 

based only on clinical 

signs and no diagnostic 

assays were used. Farm 

size is a confounding 

factor.
51

Study Study Design

and Funding

Source(s)

Viral 

Pathogen(s)

Fomite4 Study Description Core Outcomes Methodological 

Comments

crop’ as pig feed and 

owning ducks with or 

without direct contact 

with pigs. 

Lowe, J. F.

2014 [35]

Review article

Funding source not 

listed.

PEDV Feed, vehicles, 

people, and 

other fomites

The article reviews the US 

PED outbreak in 2013. The 

author summarizes clinical 

signs, virus shedding, 

immune responses, 

epidemiology, origin of the 

outbreak and risk factors 

contributing to 

transmission such as 

herd/farm management, 

transportation and fomites.

In this outbreak, PEDV 

was transmitted by 

livestock transport, 

movement of people, 

vehicles, and other 

contaminated 

fomites, and shared 

resources/equipment. 

The author suggests 

feed contaminated 

with infectious fecal 

material could 

transmit virus and 

that enhanced control 

procedures may 

provide protection 

against outbreaks of 

PED or other novel 

diseases in the future. 

None 

MartinezGamba et al., 

2001 [32]

Experimental

Funding provided 

by PAPIIT-UNAM 

Project # 

INI210997.

Aujeszky's 

Disease virus; 

Blue Eye 

Disease virus

Ensilages (solid 

fraction of pig 

feces)

Swine feces was obtained 

from 30 pigs to prepare 

ensilage. A serological 

survey of the animals was 

performed to see if they 

were free of both 

pathogens. ADV and BEDV 

were inoculated into microNo animals had 

antibodies against 

either the ADV or the 

BEDV and all samples 

obtained from microsilos at different times 

of ensilage were 

negative for both 

Due to the small sample 

set (1 farm, 30 animals, 

and 5-15 samples from 

each area) the study is 

not easily extrapolated to 

other farms/conditions. 

Ensilage appears to 
52

Study Study Design

and Funding

Source(s)

Viral 

Pathogen(s)

Fomite4 Study Description Core Outcomes Methodological 

Comments

silos and tested by viral 

identification methods.

viruses. 

Immunofluorescence 

and electron 

microscopy were 

positive only at 60 

min after inoculation. 

inactivate both viruses 

examined. 

McCluskey et 

al.,

2016 [37]

Retrospective 

testing; case series 

study

Funding source not 

listed.

PDCoV Feed, feed 

components, 

trucks, 

equipment 

and drivers, 

farm 

employees, 

and visitors

Banked samples (feces, 

fecal swabs, intestines, or 

oral fluids) from 

commercial swine farms in 

27 states were tested by 

PCR to estimate initial time 

point of PDCoV 

introduction. A survey was 

conducted to examine 

biosecurity practices and 

disease status over time. 

Only 4 samples out of 

2286 were PCRpositive for PDCoV. 

Nearly 29% of sites 

with ill gestating sows 

and gilts that 

purchased feed 

delivered in the 10 

days prior to onset of 

PDCoV sourced feed 

ingredients from 

outside the US.

The authors conclude 

that the earliest 

detections in August 

and October 2013 

may have had limited 

spread due to warm 

summer and fall 

temperatures.

The study examined a 

small number of 

operations (42 breeding 

farms). Authors did not 

discuss potential sources 

of bias – (e.g. survey and 

recall biases). 

Niederwerder 

and Hesse,

2018 [38]

Review article PEDV, PDCoV Feed, trucks Review examined SECV 

detection, epidemiology, 

and control efforts in the 

U.S. and Canada. 

Transmission and risk 

The authors conclude 

that fecal–oral is the 

primary transmission 

route for SECV. Those 

surveyed (73.6%) 

Survey results cannot be 

extrapolated due to the 

low number of 

respondents (40) and 
53

Study Study Design

and Funding

Source(s)

Viral 

Pathogen(s)

Fomite4 Study Description Core Outcomes Methodological 

Comments

Funding provided 

by the National 

Pork Board.

factors for introduction 

were also discussed. A 

survey of U.S. swine 

veterinarians and managers 

was conducted to compile 

information related to SECV 

including suspected 

sources of introduction. 

believed truck 

movements onto 

farms, feed and 

biosecurity issues 

were the most likely 

routes of SECV 

introduction. 

small number of herds 

(83). 

Pillatzki et al., 

2015 [44]

Experimental with 

bioassay

Funding provided 

by the American 

Association of 

Swine 

Veterinarians.

PEDV Complete 

feed, feed premix, and dried 

porcine 

plasma 

retained by 

feed 

manufacturers 

from April and 

May 2013

Investigators obtained 3 

PEDV feed samples -

complete feed, feed premix and SPDD. After 

confirming the feed 

samples were PCR-positive, 

they performed a swine 

bioassay. Piglets were 

separated into 5 groups 

and inoculated with 

untreated feed (negative 

control), one of the PEDVcontaminated feeds (3 

experimental groups), or 

feed spiked with PEDV 

stock virus (positive 

control). Feed samples 

were mixed with saline and 

supernatants were instilled 

into animals by gavage. 

Rectal swabs were 

collected daily. Pigs were 

euthanized on day 7, 

No clinical signs were 

observed in piglets 

from the negative 

controls or treatment 

groups inoculated 

with PCR-positive premix feed, SDPP, or 

complete feed. Also, 

fecal swabs collected 

from these groups 

were PEDV-negative, 

no histologic lesions 

were, and PEDV was 

not detected by IHC. 

The positive control 

group developed 

clinical signs at 3 DPI, 

and feces was PCRpositive. No histology 

or IHC results were 

presented for positive 

controls.

The extended storage of 

the feed samples might 

have impacted virus 

viability. Authors suggest 

that these contaminated 

feed samples might not 

have been representative 

of the overall 

concentration of PEDV in 

the entire batch of feed. 

The method of 

inoculation for the 

bioassay (gastric gavage) 

does not reflect natural 

field transmission 

conditions. 
54

Study Study Design

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Source(s)

Viral 

Pathogen(s)

Fomite4 Study Description Core Outcomes Methodological 

Comments

necropsied, and small 

intestine and colon samples 

were collected for analysis. 

Pirtle and 

Beran, 1996 

[31]

Experimental

Funding provided 

by Iowa Pork 

Producers. 

PRRSV Solid- stainless 

steel, plastic, 

boot rubber

Porousground corn, 

pelleted swine 

starter feed 

mix, wood 

shavings, 

alfalfa, straw, 

denim cloth 

Liquid- PBSS, 

saline G, well 

water, city 

water, and 

swine urine, 

saliva, and 

fecal slurry 

Three solid fomites, 6 

porous fomites, and 7 

liquids (25-27 °C) were 

contaminated with PRRSV. 

Samples were obtained on 

day 0 through day 11 for VI, 

cell culture assay, and 

fluorescent antibody 

staining.

Only the day 0 

samples of the 3 solid 

fomites contained 

PRRSV. PRRSV was 

isolated only at day 0 

for 3 porous fomites 

(alfalfa, wood 

shavings, and straw) 

and not detected in 

any samples for 3 

porous fomites (corn, 

swine starter feed and 

denim cloth). PRRSV 

was isolated only at 

day 0 from all swine 

secretions (urine, 

saliva, fecal slurry). 

PRRSV was detected 

in two buffer 

solutions through 

days 4 and 6; in well 

water through day 9; 

and in city water 

through day 11. 

Fomites were spiked with 

stock virus at doses that 

may not reflect 

contamination levels 

under field conditions, 

therefore, extrapolation 

to field conditions is 

limited. 

Sasaki et al., 

2016 [36]

Retrospective 

case-control study

PEDV People, trucks, 

equipment, 

feed, artificial 

Japanese swine producers 

were surveyed for 

information regarding herd 

management practices for 

For locally-exposed 

farms, 8 of 20 

variables were 

associated with PED 

Authors report that 

participants selected for 

this study may not be 

representative of the 
55

Study Study Design

and Funding

Source(s)

Viral 

Pathogen(s)

Fomite4 Study Description Core Outcomes Methodological 

Comments

Funding provided 

by a KAKENHI

Grants-in-Aid for 

Scientific Research)

from the Japan 

Society for the 

Promotion of 

Science.

milk, manure, 

pests 

a two-week time period 

relevant to PEDV exposure. 

The goal of the study was 

to test the hypothesis that 

factors associated with high 

risk of PEDV infection were 

different for locally 

exposed farms (within 5 km 

of another PEDV-infected 

premises) than for nonlocally exposed farms 

(greater than 5 km of 

another PEDV-infected 

farm). Investigators sought 

to quantify the dynamics of 

PEDV spread and support 

the design and 

implementation of PED 

prevention and control 

measures in Japan.

status such as, 

increased farm size, 

shorter distances to 

the closest PEDVpositive farm, and a 

disinfectant contact 

time of less than 20 

minutes. In nonlocally exposed farms, 

PED status was 

associated with 

increased feed truck 

visits to the farm, 

visits by a 

veterinarian, and 

disinfectant contact 

time of less than 20 

minutes. 

overall Japanese swine 

industry. Results should 

be interpreted cautiously. 

Schoenbaum et 

al., 1991 [30]

Experimental study

Funding provided 

by a grant from 

USDA APHIS. 

PRV Swine nasal 

washings, 

saliva, & urine, 

swine lagoon 

water and pit 

effluent, swine 

bile, 

chlorinated 

water, well 

water, heatsterilized 

Fomites were spiked with 

stock virus, and the 

combinations were 

incubated at 25 °C. Samples 

were collected on days 0, 1, 

2, 3, 4, 7, and 10, or until a 

PRV titer of < 10 PFU/ml 

was obtained. Swine bile 

was also sampled at 1 h, 

and swine urine on day 14. 

Virus titers were 

Of the combinations 

of PRV and diluent 

with feed or nonanimal origin feed 

ingredients, the 

combination of 

PRV/saline/whole 

corn remained 

infectious longest, at 

7 days with an 

estimated half-life of 

Generalizability of study 

findings to field 

conditions is poor. Nonanimal origin feed and 

feed ingredients were 

mixed with diluents prior 

to spiking with virus. Field 

conditions detrimental to 

virus activity (drying and 

UV light exposure) were 

deliberately not used. 
56

Study Study Design

and Funding

Source(s)

Viral 

Pathogen(s)

Fomite4 Study Description Core Outcomes Methodological 

Comments

chlorinated 

water, heatsterilized PBSS, 

steel, 

concrete, 

polypropylene 

plastic, vinyl 

rubber, denim 

cloth, loam 

soil, green 

grass, whole 

corn, pelleted 

feed (starter 

and finisher), 

MBM, alfalfa, 

straw, wood, 

swine feces

determined by counting 

plaques in cell culture.

36.3 hours. The 

durations of 

infectiousness of the 

other combinations of 

PRV/diluent/feed or 

non-animal origin 

feed ingredients 

ranged from 1 to 4 

days with an 

estimated half-life of 

1.0 h to 5.1 h. Authors 

report that the 

“quantity of infectious 

virus decreased 

logarithmically” over 

time. The rate of 

decrease varied 

among fomites.

Schumacher et 

al., 2016 [46]

Experimental with 

bioassay 

Funding provided 

by the National 

Pork Board.

PEDV Feed 

containing 

corn, SBM, 

VTM, and a 

source of 

phytase

Feed was mixed with stock 

PEDV at various doses, and 

the mixtures were 

administered to pigs by 

orogastric gavage. Fecal 

swab specimens were 

collected. Pigs were 

euthanized at 7 days after 

exposure. Fecal swab 

samples, tissue samples, 

and cecal contents were 

analyzed by PCR, histology, 

and/or 

The lowest 

concentration of virus 

in feed to cause 

infection in pigs was 

5.6 x 101 TCID50/g. The 

PCR cycle threshold 

value was 10 units 

lower for PEDV mixed 

with feed than for an 

equivalent dose of 

PEDV mixed with 

tissue culture 

medium. 

Generalizability of study 

findings to field 

conditions is poor; virusspiked feed was 

administered to pigs by 

orogastric gavage. 
57

Study Study Design

and Funding

Source(s)

Viral 

Pathogen(s)

Fomite4 Study Description Core Outcomes Methodological 

Comments

immunohistochemistry. 

Virus titers were 

determined by RT-

(quantitative) PCR.

Scott et al., 

2016 [11]

Scenario 

development, post 

hoc investigation, 

epidemiologic 

survey, 

case/control, 

brainstorming and 

speculation

Funding source not 

listed.

PEDV, SECV Products or 

equipment 

identified as 

having the 

potential to 

carry PEDV or 

other SECVs: 

feed totes, 

organic 

soybeans, pet 

treats, SDPP, 

biologicals, 

plant 

materials, 

amino acid 

supplements, 

and VTM

The authors used 

previously collected 

epidemiologic data to 

develop scenarios and 

identify possible routes of 

PEDV introduction into the 

United States, and initiated 

follow-up studies “to 

gather more evidence for 

the most plausible 

scenarios”. 

No PEDV was 

detected in imported 

organic soybeans, pet 

jerky treats, or feral 

swine samples. Source 

of epidemic was not 

identified. Authors 

identified totes used 

to transport bulk feed 

as providing the 

simplest explanation 

for the investigation 

findings. 

Unclear objective(s) and 

reporting. Appears to be

an emphasis or 

assumption towards 

identifying Asia or China 

as the location of origin

and towards imported 

organic soybeans as the 

point source feed 

ingredient. 

Trudeau et al., 

2017a [42] 

Experimental study

Funding provided 

by the National 

Pork Board.

PEDV, PDCoV, 

TGEV

Complete

feed, SDPP, 

meat meal, 

MBM, blood 

meal, corn, 

SBM, and 

DDGS.

Fomites were spiked with 

stock virus, and the 

combinations were 

incubated at room 

temperature for 0 to 56 

days. Virus titers were 

determined through use of 

a cell-culture-based assay.

The first log decrease 

in PDCoV and TGEV 

activity took longest 

in SBM. Moisture and 

ether content were 

indicated as being 

important 

determinants of virus 

survival in feed 

ingredients.

Generalizability to field 

conditions is poor. 

Fomites were spiked with 

stock virus. Increased 

moisture content due to 

virus inoculation likely 

altered virus survival 

kinetics. 
58

Study Study Design

and Funding

Source(s)

Viral 

Pathogen(s)

Fomite4 Study Description Core Outcomes Methodological 

Comments

Trudeau et al., 

2017b [41]

Experimental study

Funding provided 

by the National 

Pork Board.

PEDV SBM, swine 

growingfinishing

VTM, SDPP, 

meat meal, 

MBM, blood

meal, corn, 

and DDGS,

complete feed, 

galvanized 

steel, stainless 

steel, 

aluminum, 

plastic

Feed and feed ingredients 

were spiked with stock 

virus, and the combinations 

were incubated at various 

temperatures for 0-30 min. 

Four fomite surfaces were 

spiked with stock virus and 

held at various 

temperatures for 0-10 

days. Virus titers were 

determined through use of 

a cell-culture-based assay.

The authors found no 

difference in virus 

survival in feed or 

feed ingredients at 

temperatures higher 

than 70 °C. Maximum 

virus decrease 

occurred upon 

heating at 90 °C for 30 

min. Inactivation 

kinetics did not differ 

among the surfaces 

tested.

Generalizability to field 

conditions is poor. 

Fomites were spiked with 

stock virus. Increased 

moisture content due to 

virus inoculation likely 

altered virus survival 

kinetics. 
59

Acronyms - Data synthesis table 

ADV Aujeszky’s disease virus

AHAW Animal Health and Welfare

BEDV blue eye disease virus

Ct cycle threshold

DDGS distillers dried grains with solubles

DPI day(s) post-inoculation

EFSA European Food Safety Authority

EU European Union

FCV feline calicivirus

FMDV foot and mouth disease virus

IAV-S influenza A virus of swine

LA liquid antimicrobial

MBM meat and bone meal

MCFA medium chain fatty acid

PBSS phosphate buffered saline solution

PCV2 porcine circovirus 2

PDCoV porcine deltacoronavirus

PED(V) porcine epidemic diarrhea (virus)

PHFDV porcine high fever disease virus

PRV pseudorabies virus

PSV porcine sapelovirus

RBC red blood cells

(RT)-PCR (real time)-polymerase chain reaction

RNA ribonucleic acid

SBM soybean meal

SDPP spray dried porcine plasma

SECV swine enteric coronavirus

SVA Seneca virus A

SVDV Swine vesicular disease virus

TCID50 tissue culture infectious dose 50

TGE(V) transmissible gastroenteritis (virus)

VI virus isolation

VTM vitamin/trace mineral 
60

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