Evaluation of Extended Storage of Swine Complete Feed for Inactivation of Viral Contamination and Effect on Nutritional, Microbiological, and Toxicological Profiles.

The extended storage of feed ingredients has been suggested as a method to mitigate the risk of pathogen transmission through contaminated ingredients. To validate the approach of extended storage of complete swine feed for the inactivation of swine viruses, an experiment was conducted wherein swine feed was inoculated with 10 mL of 1 × 105 TCID50/mL of porcine reproductive and respiratory syndrome virus (PRRSV), porcine epidemic diarrhea virus (PEDV), and Senecavirus A (SVA) and stored for 58 d at 23.9 °C. Measures of feed quality were also evaluated at the initiation and conclusion of the storage period including screening for mycotoxins, characterization of select microbiological measures, and stability of phytase and dietary vitamins. Storing feed for 58 d under either ambient or anaerobic and temperature-controlled storage conditions did not result in substantial concerns related to microbiological profiles. Upon exposure to the feed following 58 d of storage in a swine bioassay, previously confirmed naïve pigs showed no signs of PEDV or SVA replication as detected by the PCR screening of oral fluids and serum antibody screening. Infection with SVA was documented in the positive control room through diagnostic testing through the State of Minnesota. For PRRSV, the positive control room demonstrated infection. For rooms consuming inoculated feed stored for 58 d, there was no evidence of PRRSV infection with the exception of unintentional aerosol transmission via a documented biocontainment breach. In summary, storing feed for 58 d at anaerobic and temperature-controlled environmental conditions of 23.9 °C validates that the extended storage of complete swine feed can be a method to reduce risks associated with pathogen transmission through feed while having minimal effects on measures of nutritional quality.

Improvements in swine herd biosecurity reduce the incidence risk of porcine reproductive and respiratory syndrome virus in breeding herds in the Midwestern United States.

OBJECTIVE: Porcine reproductive and respiratory syndrome (PRRS) is a significant disease of swine. The purpose of this study was to determine whether application of a comprehensive, science-based approach to breeding herd biosecurity, known as next-generation biosecurity (NGB), could reduce PRRS incidence risk across a large commercial production company. ANIMALS: Pigs (381,404 sows across 76 breeding herds). METHODS: From 2009 to 2020, the annual incidence risk of PRRS in sow farms managed by the same company averaged 33%, ranging from 20% to 50%. To measure the effect of NGB on PRRS incidence risk, a retrospective cohort study was conducted from July 1, 2021, to June 30, 2023, across breeding herds managed by the same company. During the analysis, 2 groups of herds emerged: those that implemented protocols for all phases of NGB (NGB COMPLETE), and those that implemented all described protocols of biosecurity except for air filtration (NGB INCOMPLETE). RESULTS: During the 2-year assessment period, 56 breeding herds were classified as NGB COMPLETE, while 20 herds were NGB INCOMPLETE. The PRRS incidence risk in NGB COMPLETE herds was 8.9% as compared to 40.0% in NGB INCOMPLETE herds. From disease year 1 (July 1, 2021, to June 30, 2022) and disease year 2 (July 1, 2022, to June 30, 2023), system-wide PRRS incidence risk was 8.6% and 9.2%, respectively. The association between NGB status and PRRS incidence risk for the 2-year period was statistically significant at a P value of .006. CLINICAL RELEVANCE: Results of the present report provided evidence that improvements in biosecurity result in lower PRRS incidence risk under large-scale commercial swine production conditions.

Transmission of porcine reproductive and respiratory syndrome virus in domestic pigs via oral ingestion of feed material.

OBJECTIVE: The purpose of this case study was to describe the transmission of porcine reproductive and respiratory syndrome virus (PRRSV) under field and experimental conditions via the consumption of PRRSV-positive swine feed. ANIMALS: 1 domestic swine breeding herd and 20 laboratory-maintained experimental domestic pigs. CLINICAL PRESENTATION, PROGRESSION, AND PROCEDURES: A 2,500-sow PRRSV-naïve biosecure breeding herd became infected during the autumn months. It experienced a feed outage involving a specific bin on October 23 (day 0), with the bin refilled on October 24 (day 1). From October 28 to 30 (days 5 to 7), signs of anorexia and hyperemia were observed in 30 gestating sows after consuming feed from this bin. On November 1 (day 9), blood samples from 10 affected sows were PRRSV positive by reverse transcriptase PCR. In contrast, sows in the same room that had consumed feed from other bins were clinically normal and PRRSV negative. To investigate whether the feed delivery introduced PRRSV to the herd, on November 2 (day 10) 4 samples of feed material from the interior walls of the index bin were collected and tested by reverse transcriptase PCR. TREATMENT AND OUTCOME: All 4 samples were positive for PRRSV RNA with cycle threshold values ranging from 26 to 29. Nucleic acid sequencing indicated that the open reading frame 5 region of the PRRSV in feed samples was 100% homologous to PRRSV from index cases. To assess viability of the virus, PRRSV-naïve pigs were allowed to consume the index feed bin samples and became infected with PRRSV based on viral RNA in oral fluid samples, clinical signs, and postmortem lesions. CLINICAL RELEVANCE: These results suggest that feed was a likely source of PRRSV introduction to the herd. This is the first report of PRRSV transmission through feed.

Duration of Mycoplasma hyopneumoniae detection in pigs following purposeful aerosol exposure.

Swine disease elimination programs for Mycoplasma hyopneumoniae are commonly applied in the North American swine industry and may include the aerosolization of medium containing lung tissue to achieve population exposure prior to start. Field data has indicated M. hyopneumoniae PCR detection in pigs beyond 240 days post-herd closure (dphc; planned end of an elimination program) and is thought to contribute to disease elimination programs' failure. Here, the duration of M. hyopneumoniae detection in sows and replacement gilts following aerosolized lung homogenate exposure, as part of a dual disease elimination program, was determined. A subset of sows and gilts from a commercial sow herd and off-site gilt development unit were longitudinally sampled to collect deep tracheal catheter secretions at various times post-exposure. Samples were tested for M. hyopneumoniae using a species-specific real-time PCR. A proportion of 58, 51, 52, 19, and 2% females were detected positive at 30, 60, 120, 180 and 240 dphc, respectively. Noteworthy, a greater proportion of gilts exposed at the off-site GDU were detected PCR positive for M. hyopneumoniae at each sampling event, compared to sows. In this study, assaying for genetic material in live female pigs showed extended detection of M. hyopneumoniae until at least 240 dphc. This data suggests persistence of M. hyopneumoniae longer than previously reported and highlights the importance of performing diagnostic testing to confirm negativity to the bacterium, prior to opening sow herds, especially late in the herd closure timeline.

Will swine veterinarians lead by meeting the next-generation needs of our industry?

The US swine industry is currently challenged by the potential of transboundary animal disease (eg, African swine fever) entry to the national herd and the relentless pressures of domestic diseases (eg, porcine reproductive and respiratory syndrome). The task of the swine veterinarian is to biosecure both the national herd and their customers' local farms to mitigate these risks. This Viewpoint raises 4 questions that swine veterinarians, including practicing (private and corporate), industry, research, academic, and regulatory (state and federal) veterinarians who spend a portion of their time controlling, treating, preventing, or eradicating diseases of swine, must answer to meet the needs of their farms to compete globally and survive. In addition, it appears that there is sufficient science-based information to move forward in a collaborative manner and that the goals of prevention of African swine fever and elimination of porcine reproductive and respiratory syndrome virus are technically possible. Therefore, as previous generations of swine veterinarians led the US industry in the elimination of foot-and-mouth disease virus, classical swine fever virus, and pseudorabies virus from the national herd, the central challenge is whether the next generation of veterinarians will provide the necessary leadership to deal with the current industry and its next-generation challenges.

Survival of a surrogate African swine fever virus-like algal virus in feed matrices using a 23-day commercial United States truck transport model.

African swine fever virus (ASFV) is a member of the nucleocytoplasmic large DNA viruses (NCLDVs) and is stable in a variety of environments, including animal feed ingredients as shown in previous laboratory experiments and simulations. Emiliania huxleyi virus (EhV) is another member of the NCLDVs, which has a restricted host range limited to a species of marine algae called Emiliania huxleyi. This algal NCLDV has many similar morphological and physical characteristics to ASFV thereby making it a safe surrogate, with results that are applicable to ASFV and suitable for use in real-world experiments. Here we inoculated conventional soybean meal (SBMC), organic soybean meal (SBMO), and swine complete feed (CF) matrices with EhV strain 86 (EhV-86) at a concentration of 6.6 × 107 virus g-1, and then transported these samples in the trailer of a commercial transport vehicle for 23 days across 10,183 km covering 29 states in various regions of the United States. Upon return, samples were evaluated for virus presence and viability using a previously validated viability qPCR (V-qPCR) method. Results showed that EhV-86 was detected in all matrices and no degradation in EhV-86 viability was observed after the 23-day transportation event. Additionally, sampling sensitivity (we recorded unexpected increases, as high as 49% in one matrix, when virus was recovered at the end of the sampling period) rather than virus degradation best explains the variation of virus quantity observed after the 23-day transport simulation. These results demonstrate for the first time that ASFV-like NCLDVs can retain viability in swine feed matrices during long-term transport across the continental United States.

The impacts of viral infection and subsequent antimicrobials on the microbiome-resistome of growing pigs.

BACKGROUND: Antimicrobials are used in food-producing animals for purposes of preventing, controlling, and/or treating infections. In swine, a major driver of antimicrobial use is porcine reproductive and respiratory syndrome (PRRS), which is caused by a virus that predisposes infected animals to secondary bacterial infections. Numerous antimicrobial protocols are used to treat PRRS, but we have little insight into how these treatment schemes impact antimicrobial resistance (AMR) dynamics within the fecal microbiome of commercial swine. The aim of this study was to determine whether different PRRS-relevant antimicrobial treatment protocols were associated with differences in the fecal microbiome and resistome of growing pigs. To accomplish this, we used a metagenomics approach to characterize and compare the longitudinal wean-to-market resistome and microbiome of pigs challenged with PRRS virus and then exposed to different antimicrobial treatments, and a group of control pigs not challenged with PRRS virus and having minimal antimicrobial exposure. Genomic DNA was extracted from pen-level composite fecal samples from each treatment group and subjected to metagenomic sequencing and microbiome-resistome bioinformatic and statistical analysis. Microbiome-resistome profiles were compared over time and between treatment groups. RESULTS: Fecal microbiome and resistome compositions both changed significantly over time, with a dramatic and stereotypic shift between weaning and 9 days post-weaning (dpw). Antimicrobial resistance gene (ARG) richness and diversity were significantly higher at earlier time points, while microbiome richness and diversity were significantly lower. The post-weaning shift was characterized by transition from a Bacteroides-dominated enterotype to Lactobacillus- and Streptococcus-dominated enterotypes. Both the microbiome and resistome stabilized by 44 dpw, at which point the trajectory of microbiome-resistome maturation began to diverge slightly between the treatment groups, potentially due to physical clustering of the pigs. Challenge with PRRS virus seemed to correspond to the re-appearance of many very rare and low-abundance ARGs within the feces of challenged pigs. Despite very different antimicrobial exposures after challenge with PRRS virus, resistome composition remained largely similar between the treatment groups. Differences in ARG abundance between the groups were mostly driven by temporal changes in abundance that occurred prior to antimicrobial exposures, with the exception of ermG, which increased in the feces of treated pigs, and was significantly more abundant in the feces of these pigs compared to the pigs that did not receive post-PRRS antimicrobials. CONCLUSIONS: The fecal microbiome-resistome of growing pigs exhibited a stereotypic trajectory driven largely by weaning and physiologic aging of the pigs. Events such as viral illness, antimicrobial exposures, and physical grouping of the pigs exerted significant yet relatively minor influence over this trajectory. Therefore, the AMR profile of market-age pigs is the culmination of the life history of the individual pigs and the populations to which they belong. Disease status alone may be a significant driver of AMR in market-age pigs, and understanding the interaction between disease processes and antimicrobial exposures on the swine microbiome-resistome is crucial to developing effective, robust, and reproducible interventions to control AMR. Video Abstract.

Evaluating the effect of temperature on viral survival in plant-based feed during storage.

Viruses of veterinary significance are known to survive for extended periods in plant-based feed ingredients imported into North America. To reduce the likelihood of virus introduction, high-risk ingredients, such as oil seed meals, are stored in designated facilities for extended periods under controlled environmental conditions to minimize viral infectivity prior to use in diets. While 30 days has become a standard storage period, the required ambient temperature to inactivate viruses during this time is not known. To address the question, 1-metric tonne totes of conventional soybean meal were inoculated with PRRSV 144 lineage 1C variant and SVA prior to storage for 30 days at 23.9°C, 15.5°C or 10°C, and feeding to pigs. Virus infectivity was evaluated through detection of viral RNA in oral fluid samples, along with clinical signs. Results indicated that inactivation of both viruses occurred in soy stored at 23.9°C. In contrast, SVA infectivity was observed in soy stored at both 15.5°C and 10°C, while PRRSV 144 L1C variant infectivity was only observed in soy stored at 10°C. These results suggest that a storage period of 30 days and a temperature of 23.9°C may assist in the reduction of the risk of virus contaminated plant-based feed ingredients, such as soybean meal.

A Molecular and Epidemiological Description of a Severe Porcine Reproductive and Respiratory Syndrome Outbreak in a Commercial Swine Production System in Russia.

Porcine reproductive and respiratory syndrome (PRRS) is an economically devastating disease of swine in many parts of the world. Porcine reproductive and respiratory syndrome virus (PRRSV) type 1 is endemic in Europe, and prevalence of the subtypes differ spatially. In this study, we investigated a severe PRRS outbreak reported in 30 farms located in eastern Russia that belong to a large swine production company in the region that was also experiencing a pseudorabies outbreak in the system. Data included 28 ORF5 sequences from samples across 18 of the 25 infected sites, reverse transcriptase real-time polymerase chain reaction (RT-qPCR) results from diagnostic testing, reports of clinical signs, and animal movement records. We observed that the outbreak was due to two distinct variants of wildtype PRRSV type 1 subtype 1 with an average genetic distance of 15%. Results suggest that the wildtype PRRSV variants were introduced into the region around 2019, before affecting this production system (i.e., sow farms, nurseries, and finisher farms). Clinical signs did not differ between the variants, but they did differ by stage of pig production. Biosecurity lapses, including movement of animals from infected farms contributed to disease spread.

Evidence of viral survival in representative volumes of feed and feed ingredients during long-distance commercial transport across the continental United States.

The hypothesis that feed ingredients could serve as vehicles for the transport and transmission of viral pathogens was first validated under laboratory conditions. To bridge the gap from the laboratory to the field, this current project tested whether three significant viruses of swine could survive in feed ingredients during long-distance commercial transport across the continental US. One-metric tonne totes of soybean meal (organic and conventional) and complete feed were spiked with a 10 ml mixture of PRRSV 174, PEDV and SVA and transported for 23 days in a commercial semi-trailer truck, crossing 29 states, and 10,183 km. Samples were tested for the presence of viral RNA by PCR, and for viable virus in soy-based samples by swine bioassay and in complete feed samples by natural feeding. Viable PRRSV, PEDV and SVA were detected in both soy products and viable PEDV and SVA in complete feed. These results provide the first evidence that viral pathogens of pigs can survive in representative volumes of feed and feed ingredients during long-distance commercial transport across the continental United States.

Monoglyceride reduces viability of porcine epidemic diarrhoea virus in feed and prevents disease transmission to post-weaned piglets.

Outbreaks of African swine fever virus (ASFv) and porcine epidemic diarrhoea virus (PEDv) have revealed the susceptibility of livestock to disease transmitted through feed. Several viruses, including PEDv, survive in feed and may introduce disease that causes significant morbidity and mortality. In 2013, PEDv, which causes severe diarrhoea and vomiting, reached North America after spreading for decades across Eurasia. The global exchange of ingredients has created demand for products that prevent disease transmission from feed. Formaldehyde-based products are highly effective at inactivating enveloped viruses when applied at 3.25 kg/t. Alternative products to formaldehyde, including carboxylic acids, essential oils and medium chain fatty acids (MCFAs), have exhibited mixed efficacy against PEDv and require application rates higher than formaldehyde. Amphiphilic molecules like MCFAs disrupt the bilayer-lipid membranes that protect viral nucleic acids through the formation of micelles. Monoglycerides form micelles at lower concentrations than MCFAs, which suggests they may be more potent against enveloped viruses. The potential efficacy of monoglycerides against enveloped viruses in feed led to the development and examination of an experimental monoglyceride blend. The proprietary monoglyceride blend significantly (p < .0001) reduced PEDv viability in vitro after application to feed at 1.5, 2.5 and 3.5 kg/t. The monoglyceride was tested in a natural feeding behaviour challenge model in piglets. The feed was contaminated with ice-blocks containing viable PEDv, and the piglets were exposed to PEDv through the feed bin for 20 days. At the end of the 20-day challenge period, all pigs were rectally swabbed and tested for PEDv by qPCR. In the untreated control group 54.8% of the piglets tested positive for PEDv, whereas none of the MCFA-treated feed (10 kg/t inclusion) transmitted PEDv. Strikingly, the monoglyceride-treated groups (1.5, 2.5 and 3.5 kg/t) all exhibited 100% protection from PEDv. These data support the use of this proprietary monoglyceride blend in mitigation and prevention of viral disease transmission to piglets from contaminated feed.

Stability of Senecavirus A in animal feed ingredients and infection following consumption of contaminated feed.

Animal feed and feed ingredients have recently been investigated as sources of pathogen introduction to farms and as a potential source of infection to animals post-consumption of contaminated feed. Survival of several viruses for a prolonged period has been demonstrated in feed. Here, we determined the rate of decay of Senecavirus A (SVA) in swine feed ingredients as a function of time and temperature and established half-life estimates for the virus. Select feed ingredients were spiked with a constant amount of SVA (105 median tissue culture infectious dose 50) and incubated at 4, 15 and 30°C for up to 91 days. Virus viability and the presence of viral RNA were assessed in samples collected over time. At the three different temperatures investigated, dried distillers' grains with solubles (DDGS) and soybean meal (SBM) provided the most stable matrices for SVA, resulting in half-lives of 25.6 and 9.8 days, respectively. At 30°C, SVA was completely inactivated in all feed ingredients and in the control sample, which did not contain a feed matrix. Although virus infectivity was lost, viral RNA remained stable and at consistent levels throughout the experimental period. Additionally, the ability of SVA to infect swine via ingestion of contaminated feed was investigated in 3-week-old, weaned pigs. Animals were provided complete feed spiked with three concentrations of SVA (105 , 106 and 107 per 200 g of feed) and allowed to naturally consume the contaminated feed. This procedure was repeated for three consecutive days. Infection of pigs through consumption of contaminated feed was confirmed by virus neutralization assay and the detection of SVA in serum, feces and in the tonsil of exposed animals by real-time reverse transcriptase PCR. Our findings demonstrate that feed matrices are able to extend the survival of SVA, protecting the virus from decay. Additionally, we demonstrated that consumption of contaminated feed can lead to productive SVA infection.

The risk and mitigation of foot-and-mouth disease virus infection of pigs through consumption of contaminated feed.

Transboundary movement of animal feed and feed ingredients has been identified as a route for pathogen incursions. While imports of animals and animal-derived products are highly regulated for the purpose of infectious disease prevention, there has been less consideration of the viability of infectious agents in inanimate products, such as feed. This study investigated the ability of foot-and-mouth disease virus (FMDV) to remain infectious as a contaminant of commercial whole pig feed and select pig feed ingredients, and to establish the minimum infectious dose (MIDF ) required to cause foot-and-mouth disease (FMD) in pigs that consumed contaminated feed. FMDV viability in vitro varied depending on virus strain, feed product, and storage temperature, with increased duration of infectivity in soybean meal compared to pelleted whole feed. Specifically, both strains of FMDV evaluated remained viable through to the end of the 37 day observation period in experimentally contaminated soybean meal stored at 4 or 20°C . The MIDF for pigs consuming contaminated feed varied across virus strains and exposure duration in the range of 106.2 to 107 TCID50 . The ability of FMDV to cause infection in exposed pigs was mitigated by pre-treatment of feed with two commercially available feed additives, based on either formaldehyde (SalCURB®) or lactic acid (Guardian™). Our findings demonstrate that FMDV may remain infectious in pig feed ingredients for durations compatible with transoceanic transport. Although the observed MIDF was relatively high, variations in feeding conditions and biophysical characteristics of different virus strains may alter the probability of infection. These findings may be used to parameterize modelling of the risk of FMDV incursions and to regulate feed importation to minimize the risk of inadvertent importation.

Evaluation of the Impact of Antimicrobial Use Protocols in Porcine Reproductive and Respiratory Syndrome Virus-Infected Swine on Phenotypic Antimicrobial Resistance Patterns.

A longitudinal study was conducted to assess the impact of different antimicrobial exposures of nursery-phase pigs on patterns of phenotypic antimicrobial resistance (AMR) in fecal indicator organisms throughout the growing phase. Based on practical approaches used to treat moderate to severe porcine reproductive and respiratory syndrome virus (PRRSV)-associated secondary bacterial infections, two antimicrobial protocols of differing intensities of exposure [44.1 and 181.5 animal-treatment days per 1000 animal days at risk (ATD)] were compared with a control group with minimal antimicrobial exposure (2.1 ATD). Litter-matched pigs (n = 108) with no prior antimicrobial exposure were assigned randomly to the treatment groups. Pen fecal samples were collected nine times during the wean-to-finish period and cultured for Escherichia coli and Enterococcus spp. Antimicrobial-susceptibility testing was conducted using NARMS Gram-negative and Gram-positive antibiotic panels. Despite up to 65-fold difference in ATD, few and modest differences were observed between groups and over time. Resistance patterns at marketing overall remained similar to those observed at weaning, prior to any antimicrobial exposures. Those differences observed could not readily be reconciled with the patterns of antimicrobial exposure. Resistance of E. coli to streptomycin was higher in the group exposed to 44.1 ATD, but no aminoglycosides were used. In all instances where resistances differed between time points, the higher resistance occurred early in the trial prior to any antimicrobial exposures. These minimal impacts on AMR despite substantially different antimicrobial exposures point to the lack of understanding of the drivers of AMR at the population level and the likely importance of factors other than antimicrobial exposure. IMPORTANCE Despite a recognized need for more longitudinal studies to assess the effects of antimicrobial use on resistance in food animals, they remain sparse in the literature, and most longitudinal studies of pigs have been observational. The current experimental study had the advantages of greater control of potential confounding, precise measurement of antimicrobial exposures which differed markedly between groups and tracking of pigs until market age. Overall, resistance patterns were remarkably stable between the treatment groups over time, and the differences observed could not be readily reconciled with the antimicrobial exposures, indicating the likely importance of other determinants of AMR at the population level.

An assessment of enhanced biosecurity interventions and their impact on porcine reproductive and respiratory syndrome virus outbreaks within a managed group of farrow-to-wean farms, 2020-2021.

Introduction: Porcine reproductive and respiratory syndrome virus (PRRSV) has been a challenge for the U.S. swine industry for over 30 years, costing producers more than $600 million annually through reproductive disease in sows and respiratory disease in growing pigs. In this study, the impact of enhanced biosecurity practices of site location, air filtration, and feed mitigation was assessed on farrow-to-wean sites managed by a large swine production management company in the Midwest United States. Those three factors varied in the system that otherwise had implemented a stringent biosecurity protocol on farrow-to-wean sites. The routine biosecurity followed commonplace activities for farrow-to-wean sites that included but were not limited to visitor registration, transport disinfection, shower-in/shower-out procedures, and decontamination and disinfection of delivered items and were audited. Methods: Logistic regression was used to evaluate PRRSV infection by site based on the state where the site is located and air filtration use while controlling for other variables such as vaccine status, herd size, and pen vs. stall. A descriptive analysis was used to evaluate the impact of feed mitigation stratified by air filtration use. Results: Sites that used feed mitigates as additives in the diets, air filtration of barns, and that were in less swine-dense areas appeared to experience fewer outbreaks associated with PRRSV infection. Specifically, 23.1% of farms that utilized a feed mitigation program experienced PRRSV outbreaks, in contrast to 100% of those that did not. Sites that did not use air filtration had 20 times greater odds of having a PRRSV outbreak. The strongest protective effect was found when both air filtration and feed mitigation were used. Locations outside of Minnesota and Iowa had 98.5-99% lesser odds of infection as well. Discussion: Enhanced biosecurity practices may yield significant protective effects and should be considered for producers in swine-dense areas or when the site contains valuable genetics or many pigs.

Modeling transmission dynamics and effectiveness of worker screening programs for SARS-CoV-2 in pork processing plants.

Pork processing plants were apparent hotspots for SARS-CoV2 in the spring of 2020. As a result, the swine industry was confronted with a major occupational health, financial, and animal welfare crisis. The objective of this work was to describe the epidemiological situation within processing plants, develop mathematical models to simulate transmission in these plants, and test the effectiveness of routine PCR screening at minimizing SARS-CoV2 circulation. Cumulative incidence of clinical (PCR-confirmed) disease plateaued at ~2.5% to 25% across the three plants studied here. For larger outbreaks, antibody prevalence was approximately 30% to 40%. Secondly, we developed a mathematical model that accounts for asymptomatic, pre-symptomatic, and background "community" transmission. By calibrating this model to observed epidemiological data, we estimated the initial reproduction number (R) of the virus. Across plants, R generally ranged between 2 and 4 during the initial phase, but subsequently declined to ~1 after two to three weeks, most likely as a result of implementation/compliance with biosecurity measures in combination with population immunity. Using the calibrated model to simulate a range of possible scenarios, we show that the effectiveness of routine PCR-screening at minimizing disease spread was far more influenced by testing frequency than by delays in results, R, or background community transmission rates. Testing every three days generally averted about 25% to 40% of clinical cases across a range of assumptions, while testing every 14 days typically averted 7 to 13% of clinical cases. However, the absolute number of additional clinical cases expected and averted was influenced by whether there was residual immunity from a previous peak (i.e., routine testing is implemented after the workforce had experienced an initial outbreak). In contrast, when using PCR-screening to prevent outbreaks or in the early stages of an outbreak, even frequent testing may not prevent a large outbreak within the workforce. This research helps to identify protocols that minimize risk to occupational safety and health and support continuity of business for U.S. processing plants. While the model was calibrated to meat processing plants, the structure of the model and insights about testing are generalizable to other settings where large number of people work in close proximity.

Phylogenetically Distinct Near-Complete Genome Sequences of Porcine Reproductive and Respiratory Syndrome Virus Type 2 Variants from Four Distinct Disease Outbreaks at U.S. Swine Farms over the Past 6 Years.

Porcine reproductive and respiratory syndrome virus (PRRSV) continues to mutate, causing disruptive PRRS outbreaks in farms that lead to reproductive failure and respiratory disease-associated mortality. We present four new PRRSV type 2 variants in the United States belonging to four distinct orf5 sublineages within lineage 1.

Use of a demonstration project to evaluate viral survival in feed: Proof of concept.

In 2014, the hypothesis that feed ingredients could serve as vehicles for the transport and transmission of viral pathogens was proposed and evaluated by multiple investigators under laboratory conditions. In an attempt to validate these data, we used a demonstration project to test whether three significant viruses of swine could survive in feed ingredients under real-world shipping conditions. Samples of soya bean meal (organic and conventional), lysine, choline and vitamin A were spiked with a mixture of PRRSV 174, PEDV and SVA and transported for 21 days in the trailer of a commercial transport vehicle, encompassing 14 states and 9,741 km. Samples were tested for viral genome and viability at the end of the transit period. Regarding viability, PRRSV, PEDV and SVA were all detected as infectious in bioassays following inoculation with both soy products. In addition, viable PRRSV and SVA were detected by bioassay pigs inoculated with samples of vitamin A, and infectious SVA was detected in pigs inoculated with samples of lysine and choline. These results provide further evidence that select viral pathogens of pigs can survive in certain feed ingredients during commercial transit.