Risk and Mitigation of African Swine Fever Virus in Feed

Biosecurity Insights from the United States Swine Health Improvement Plan: Analyzing Data to Enhance Industry Practices

Biosecurity practices aim to reduce the frequency of disease outbreaks in a farm, region, or country and play a pivotal role in fortifying the country's pork industry against emerging threats, particularly foreign animal diseases (FADs). This article addresses the current biosecurity landscape of the US swine industry by summarizing the biosecurity practices reported by the producers through the United States Swine Health Improvement Plan (US SHIP) enrollment surveys, and it provides a general assessment of practices implemented. US SHIP is a voluntary, collaborative effort between industry, state, and federal entities regarding health certification programs for the swine industry. With 12,195 sites surveyed across 31 states, the study provides a comprehensive snapshot of current biosecurity practices. Key findings include variability by site types that have completed Secure Pork Supply plans, variability in outdoor access and presence of perimeter fencing, and diverse farm entry protocols for visitors. The data also reflect the industry's response to the threat of FADs, exemplified by the implementation of the US SHIP in 2020. As the US SHIP program advances, these insights will guide industry stakeholders in refining biosecurity practices, fostering endemic re-emerging and FAD preparedness, and ensuring the sustainability of the swine industry in the face of evolving challenges.

Thermostable T Cell Multiepitope Nanoparticle Antigens Inducing Potent Immune Responses against the Swine Fever Virus

African swine fever (ASF) is caused by the African swine fever virus (ASFV) and is a highly contagious, acute, febrile disease that has high morbidity and mortality rates in domestic and wild swine. However, a safe and effective vaccine against ASF remains unavailable as single antigens fail to provide sufficient protection. Therefore, a combination of multiple antigens with an efficient delivery system might be an alternative strategy. Herein, a de novo-designed antigen with multiple T-cell epitopes (TEPs) of ASFV was conjugated for surface display on self-assembled nanoparticles (NPs) of Aquifex aeolicus lumazine synthase (AaLS) and Quasibacillus thermotolerans encapsulin (QT) through the SpyCatcher/SpyTag system to construct nanovaccines (TEP-Spy-NPs). TEP-Spy-NPs exhibited significantly more thermal, storage, and freeze-thaw stability in comparison to TEP monomers. TEP-Spy-NPs were highly immunogenic and induced strong polyclonal antibody responses in mice and pigs. The specific antibody titers against the TEP of the TEP-Spy-AaLS and TEP-Spy-QT groups were significantly higher than those of the TEP monomer immune group after the second booster immunization. The antibody titer against TEP of the TEP-Spy-QT group was approximately twice that of the TEP-Spy-AaLS group in mice. ELISpot analysis demonstrated that more IFN-γ- and IL-2-secreting splenic lymphocytes were produced by TEP-Spy-AaLS- and TEP-Spy-QT-immunized mice than by TEP monomer-immunized mice. TEP-Spy-NPs elicited stronger cellular immunity and in vivo immunity in immunized pigs than did TEP monomers. Thus, the TEP nanovaccine successfully induced strong humoral and cellular immune responses in mice and pigs, and TEP-Spy-NPs have the potential as candidate vaccines for ASFV.

Spatiotemporal relative risk distribution of porcine reproductive and respiratory syndrome virus in the United States

Porcine reproductive and respiratory syndrome virus (PRRSV) remains widely distributed across the U.S. swine industry. Between-farm movements of animals and transportation vehicles, along with local transmission are the primary routes by which PRRSV is spread. Given the farm-to-farm proximity in high pig production areas, local transmission is an important pathway in the spread of PRRSV; however, there is limited understanding of the role local transmission plays in the dissemination of PRRSV, specifically, the distance at which there is increased risk for transmission from infected to susceptible farms. We used a spatial and spatiotemporal kernel density approach to estimate PRRSV relative risk and utilized a Bayesian spatiotemporal hierarchical model to assess the effects of environmental variables, between-farm movement data and on-farm biosecurity features on PRRSV outbreaks. The maximum spatial distance calculated through the kernel density approach was 15.3 km in 2018, 17.6 km in 2019, and 18 km in 2020. Spatiotemporal analysis revealed greater variability throughout the study period, with significant differences between the different farm types. We found that downstream farms (i.e., finisher and nursery farms) were located in areas of significant-high relative risk of PRRSV. Factors associated with PRRSV outbreaks were farms with higher number of access points to barns, higher numbers of outgoing movements of pigs, and higher number of days where temperatures were between 4°C and 10°C. Results obtained from this study may be used to guide the reinforcement of biosecurity and surveillance strategies to farms and areas within the distance threshold of PRRSV positive farms.

Innovative Research Offers New Hope for Managing African Swine Fever Better in Resource-Limited Smallholder Farming Settings: A Timely Update

African swine fever (ASF) in domestic pigs has, since its discovery in Africa more than a century ago, been associated with subsistence pig keeping with low levels of biosecurity. Likewise, smallholder and backyard pig farming in resource-limited settings have been notably affected during the ongoing epidemic in Eastern Europe, Asia, the Pacific, and Caribbean regions. Many challenges to managing ASF in such settings have been identified in the ongoing as well as previous epidemics. Consistent implementation of biosecurity at all nodes in the value chain remains most important for controlling and preventing ASF. Recent research from Asia, Africa, and Europe has provided science-based information that can be of value in overcoming some of the hurdles faced for implementing biosecurity in resource-limited contexts. In this narrative review we examine a selection of these studies elucidating innovative solutions such as shorter boiling times for inactivating ASF virus in swill, participatory planning of interventions for risk mitigation for ASF, better understanding of smallholder pig-keeper perceptions and constraints, modified culling, and safe alternatives for disposal of carcasses of pigs that have died of ASF. The aim of the review is to increase acceptance and implementation of science-based approaches that increase the feasibility of managing, and the possibility to prevent, ASF in resource-limited settings. This could contribute to protecting hundreds of thousands of livelihoods that depend upon pigs and enable small-scale pig production to reach its full potential for poverty alleviation and food security.

Determination of African swine fever virus viability in meat during long-term storage and sous-vide cooking using cell culture and real-time PCR combined with palladium compound pre-treatment methods

African swine fever virus is the causative agent of an acute and highly contagious disease affecting domestic and wild members of the family Suidae. The virus can be transmitted by direct contact among infected animals or via a contaminated environment or feed. Since the contaminated meat or products thereof have been characterised as the most probable vehicle in several outbreaks, the aim of the present study was to define viability of the virus in meat under conditions of freezing and chilling (−25 °C and 6 °C) and low temperature cooking (55 °C for 2.5 h and for 1 h). Two independent methods were employed; cell culture as a reference and real-time polymerase chain reaction combined with palladium compound (BB-PdCl2 and PdCl2COD) pre-treatment as an alternative method. Obtained results demonstrated a minimal decrease in the infectious virus titre during storage at −25 °C, and a remaining amount of viruses in meat stored at 6 °C for 14 months that can cause a disease after ingestion. The results obtained by both methods applied on the samples corresponded to each other. In contrast, results related to the virus’ persistence in thermal-treated meat indicated much lower stability than previously thought; infectious viruses were not detected by infectivity assay after the treatment at 55 °C for 1 h. The observed difference of one order of magnitude of virus detected using palladium compound pre-treatment suggests presence of intact rather than infectious viruses. A better suitability of PdCl2COD compared to BB-PdCl2 pre-treatment was demonstrated.

Stability of African swine fever virus in feed during environmental storage

African swine fever virus (ASFV) causes high case fatality in pigs and a trade-limiting disease resulting in significant economic losses to pork production. ASFV is resistant to environmental degradation and maintains infectivity in feed ingredients exposed to transoceanic shipment conditions. As ASFV is transmissible through consumption of contaminated feed, the objective of this study was to evaluate the stability of ASFV Georgia 2007 in three feed matrices (complete feed, soybean meal, ground corncobs) exposed to three environmental storage temperatures (40°F, 68°F, 95°F) for up to 365 days. ASFV DNA was highly stable and detectable by qPCR in almost all feed matrices through the conclusion of each study. Infectious ASFV was most stable in soybean meal, maintaining infectivity for at least 112 days at 40°F, at least 21 days at 68°F and at least 7 days at 95°F. These data help define risk of ASFV introduction and transmission through feed ingredients.

Antimicrobial monoglycerides for swine and poultry applications

The development of natural, broadly acting antimicrobial solutions to combat viral and bacterial pathogens is a high priority for the livestock industry. Herein, we cover the latest progress in utilizing lipid-based monoglycerides as feed additives to address some of the biggest challenges in animal agriculture. The current industry needs for effective antimicrobial strategies are introduced before discussing why medium-chain monoglycerides are a promising solution due to attractive molecular features and biological functions. We then critically analyze recent application examples in which case monoglycerides demonstrated superior activity to prevent feed transmission of viruses in swine and to mitigate bacterial infections in poultry along with gut microbiome modulation capabilities. Future innovation strategies are also suggested to expand the range of application possibilities and to enable new monoglyceride delivery options.

Modeling between-farm transmission dynamics of porcine epidemic diarrhea virus: Characterizing the dominant transmission routes

The role of transportation vehicles, pig movement between farms, proximity to infected premises, and feed deliveries has not been fully considered in the dissemination dynamics of porcine epidemic diarrhea virus (PEDV). This has limited efforts for disease prevention, control and elimination restricting the development of risk-based resource allocation to the most relevant modes of PEDV dissemination. Here, we modeled nine pathways of between-farm transmission represented by a contact network of pig movements between sites, farm-to-farm proximity (local transmission), four distinct contact networks of transportation vehicles (trucks that transport pigs from farm-to-farm and farm-to-markets, as well as trucks transporting feed and staff), the volume of animal by-products in feed diets (e.g., fat and meat-and-bone-meal) to reproduce PEDV transmission dynamics. The model was calibrated in space and time with weekly PEDV outbreaks. We investigated the model performance to identify outbreak locations and the contribution of each route in the dissemination of PEDV. The model estimated that 42.7% of the infections in sow farms were related to vehicles transporting feed, 34.5% of infected nurseries were associated with vehicles transporting pigs between farms, and for both farm types, local transmission or pig movements were the next most relevant transmission routes. On the other hand, finishers were most often (31.4%) infected via local transmission, followed by the vehicles transporting feed and pigs between farms. Feed ingredients did not significantly improve model calibration metrics, sensitivity, and specificity; therefore, it was considered to have a negligible contribution in the dissemination of PEDV. The proposed modeling framework provides an evaluation of PEDV transmission dynamics, ranking the most important routes of PEDV dissemination and granting the swine industry valuable information to focus efforts and resources on the most important transmission routes.

Modelling and assessing additional transmission routes for porcine reproductive and respiratory syndrome virus: Vehicle movements and feed ingredients

Accounting for multiple modes of livestock disease dissemination in epidemiological models remains a challenge. We developed and calibrated a mathematical model for transmission of porcine reproductive and respiratory syndrome virus (PRRSV), tailored to fit nine modes of between-farm transmission pathways including: farm-to-farm proximity (local transmission), contact network of batches of pigs transferred between farms (pig movements), re-break probabilities for farms with previous PRRSV outbreaks, with the addition of four different contact networks of transportation vehicles (vehicles to transport pigs to farms, pigs to markets, feed and crew) and the amount of animal by-products within feed ingredients (e.g., animal fat or meat and bone meal). The model was calibrated on weekly PRRSV outbreaks data. We assessed the role of each transmission pathway considering the dynamics of specific types of production (i.e., sow, nursery). Although our results estimated that the networks formed by transportation vehicles were more densely connected than the network of pigs transported between farms, pig movements and farm proximity were the main PRRSV transmission routes regardless of farm types. Among the four vehicle networks, vehicles transporting pigs to farms explained a large proportion of infections, sow = 20.9%; nursery = 15%; and finisher = 20.6%. The animal by-products showed a limited association with PRRSV outbreaks through descriptive analysis, and our model results showed that the contribution of animal fat contributed only 2.5% and meat and bone meal only .03% of the infected sow farms. Our work demonstrated the contribution of multiple routes of PRRSV dissemination, which has not been deeply explored before. It also provides strong evidence to support the need for cautious, measured PRRSV control strategies for transportation vehicles and further research for feed by-products modelling. Finally, this study provides valuable information and opportunities for the swine industry to focus effort on the most relevant modes of PRRSV between-farm transmission.

Early‐phase risk assessments during the first epidemic year of African swine fever outbreaks in Vietnamese pigs

Background

Objectives

Methods

Results

Conclusions

Persistence of African swine fever virus on porous and non-porous fomites at environmental temperatures

Background

African swine fever (ASF) is a lethal contagious disease affecting both domestic pigs and wild boars. Even though it is a non-zoonotic disease, ASF causes economic loss in swine industries across continents. ASF control and eradication are almost impossible since effective vaccines and direct antiviral treatment are not available. The persistence of ASFV on fomites plays an important role in the indirect transmission of ASFV to pigs encountering ASFV-contaminated fomites. ASFV persistence on porous and non-porous fomites (glass, metal, rubber, and cellulose paper) at different environmental temperatures was determined. The persistence of ASFV of fomites was determined by the rate of ASFV inactivation in terms of D_T, or the time required to reduce ASFV per 1 log at each selected environmental temperature (T). D_T is used to compare the persistence of ASFV on the fomites.

Results

The mean D₂₅, D₃₃, and D₄₂, of dried infectious ASFV on glass, metal, rubber, and paper were in the ranges 1.42–2.42, 0.72–1.94, and 0.07–0.23 days, respectively. The multiple D_T were used to develop a D_T model to predict the D_T for some other environmental temperatures. The D_T models to predict the persistence of dried infectious ASFV on glass, metal, rubber, and paper are log D_T = (− T/21.51) + 1.34, log D_T = (− T/20.42) + 1.47, log D_T = (− T/14.91) + 2.03, and log D_T = (− T/10.91) + 2.84, respectively. A spreadsheet as a quick and handy tool predicting the persistence time of dried infectious ASFV on fomites at various environmental temperatures based on these D_T models is available for public to download.

Conclusion

Persistence of dried infectious ASFV on paper are significantly the longest at lower environmental temperatures whereas that of dried infectious ASFV on paper is significantly the shortest at higher environmental temperature.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40813-022-00277-8.

The SLI-SC Mathematical Model of African Swine Fever Transmission among Swine Farms: The Effect of Contaminated Human Vector

In this paper, a mathematical model for African swine fever is modified by considering the swine farm with the contaminated human vector that is able to infect and spread the disease among swine farms. In the developed model, we have divided the swine farm density into three related groups, namely the susceptible swine farm compartment, latent swine farm compartment, and infectious swine farm compartment. On the other hand, the human vector population density has been separated into two classes, namely the susceptible human vector compartment and the infectious human vector compartment. After that, we use this model and a quarantine strategy to analyze the spread of the infection. In addition, the basic reproduction number R0 is determined by using the next-generation matrix, which can analyze the stability of the model. Finally, the numerical simulations of the proposed model are illustrated to confirm the results from theorems. The results showed that the transmission coefficient values per unit of time per individual between the human vector and the swine farm resulted in the spread of African swine fever.

Invited review: strategic adoption of antibiotic-free pork production: the importance of a holistic approach

The discovery of the use of antibiotics to enhance growth in the 1950s proved to be one of the most dramatic and influential in the history of animal agriculture. Antibiotics have served animal agriculture, as well as human and animal medicine, well for more than seven decades, but emerging from this tremendous success has been the phenomenon of antimicrobial resistance. Consequently, human medicine and animal agriculture are being called upon, through legislation and/or marketplace demands, to reduce or eliminate antibiotics as growth promotants and even as therapeutics. As explained in this review, adoption of antibiotic-free (ABF) pork production would represent a sea change. By identifying key areas requiring attention, the clear message of this review is that success with ABF production, also referred to as "no antibiotics ever," demands a multifaceted and multidisciplinary approach. Too frequently, the topic has been approached in a piecemeal fashion by considering only one aspect of production, such as the use of certain feed additives or the adjustment in health management. Based on the literature and on practical experience, a more holistic approach is essential. It will require the modification of diet formulations to not only provide essential nutrients and energy, but to also maximize the effectiveness of normal immunological and physiological capabilities that support good health. It must also include the selection of effective non-antibiotic feed additives along with functional ingredients that have been shown to improve the utility and architecture of the gastrointestinal tract, to improve the microbiome, and to support the immune system. This holistic approach will require refining animal management strategies, including selection for more robust genetics, greater focus on care during the particularly sensitive perinatal and post-weaning periods, and practices that minimize social and environmental stressors. A clear strategy is needed to reduce pathogen load in the barn, such as greater emphasis on hygiene and biosecurity, adoption of a strategic vaccine program and the universal adoption of all-in-all-out housing. Of course, overall health management of the herd, as well as the details of animal flows, cannot be ignored. These management areas will support the basic biology of the pig in avoiding or, where necessary, overcoming pathogen challenges without the need for antibiotics, or at least with reduced usage.

Effects of Pelleting and Long-Term High-Temperature Stabilization on Vitamin Retention in Swine Feed

The objective of this study was to study the effect of pelleting and long-term high-temperature stabilization on the retention of vitamin A, vitamin E, vitamin B2, and vitamin B6 in swine feed. Piglet diets (diet 1 and 3) were pelleted after conditioning at 83 °C for 120 s, and were high-temperature stabilized at 90 °C for 8.5 min after pelleting; the finishing pig diets (diet 2, 4, and 5) were pelleted after conditioning at 82 °C for 90 s, and were high-temperature stabilized at 85 °C for 9 min after pelleting; the samples were obtained before condition, after condition, after pelleting, and after cooling. The contents of vitamin A and vitamin E in diets 1−5 and vitamin B2, and vitamin B6 in diets 3−5 were detected. The results showed that: (1) the conditioning process had no significant effect on the retention of vitamin A, vitamin E, vitamin B2, and vitamin B6 in all experimental diets (p > 0.05); (2) the pelleting process and high-temperature stabilization process after pelleting had different degrees of influence on vitamins, among which the stabilization process had a more significant effect on the retention of vitamins. After pelleting and long-term high-temperature stabilization, the retention of vitamin A, vitamin E, and B2, and vitamin B6 were 68.8−77.3%, 56.9−90.1%, 63.8−70.3%, and 60.1−67.0%, respectively. In the process of pelleting and long-term high-temperature stabilization, the retention of vitamin A, vitamin E, vitamin B2, and vitamin B6 in the feed were significantly reduced (p < 0.05). Therefore, vitamin loss during high temperature and over a long period of time is worth considering, and vitamins must be over-supplemented.

Diagnostic sensitivity of porcine biological samples for detecting African swine fever virus infection after natural consumption in feed and liquid

African swine fever virus (ASFV) is a global threat to swine production and sustainable pork supply. Without a commercially available vaccine, prevention of ASFV entry and spread is reliant on biosecurity and early detection of infection. Although ASFV ingestion in swill or feed by naïve pigs is a likely route of initial introduction, controlled experimental studies rarely utilize natural consumption as the infection route. In the current study, we utilized biological samples collected from pigs 5 days after natural consumption of ASFV in feed and liquid to assess diagnostic sensitivity for early detection of virus infection. Biological samples (serum, spleen, lymph nodes, tonsils, and faeces) were assessed for the presence of ASFV using quantitative PCR and virus isolation. Statistical methods modelled the detection sensitivity of each sample type with each diagnostic assay in individual samples. Our results provide important information that can be incorporated into ASFV surveillance programs.

Pacmanvirus S19, the Second Pacmanvirus Isolated from Sewage Waters in Oran, Algeria

Acanthamoeba castellanii is an amoeba host that was used to isolate a novel strain named pacmanvirus S19. This isolate is the second strain reported and belongs to the extended Asfarviridae family. Pacmanvirus S19 harbors a 418,588-bp genome, with a GC content of 33.20%, which encodes 444 predicted proteins and a single Ile-tRNA.

Feed safety collaborations: Experiences, progress and challenges

Concerns were raised regarding the role feed and feed ingredients play for risk of disease introduction and dissemination after PEDV was first identified mid-2013. Subsequently there has been a body of research and reviews completed. The results suggest a subset of contaminated feed ingredients could serve as vehicles for transboundary disease introduction into the United States. That has led to the development of biosecurity information from the pork and feed industry associations. At this time, implementation is voluntary. In 2019, representatives from pork producers, veterinarians, pork and other agriculture commodity associations and animal food industry associations formed a feed safety task force. The United States Department of Agriculture, the United States Food and Drug Administration and the Canadian Food Inspection Agency were also invited and attended. The task force operates under the premise that all participants agree there is risk of introduction of pathogens into and within the US via imported feed products. It is agreed that any actions should be achievable, are based on science and should minimize trade disruptions. The pork and feed industries have the same goal - a healthy, productive US swine herd. While our two industry sectors may have different ideas on how to prevent the introduction of diseases via imported feed ingredients, there is agreement that the general foundation for these approaches must be science based, cost effective and minimize negative impacts on market and international trade. Noncompliance with voluntary mitigation measures puts the entire pork industry at risk, all allied industries, and the US agricultural economy in general. Because of that it is essential to continue to evaluate the role of effective regulation to ensure risk of introduction is minimized through implementation of programs that will be broadly and uniformly applied.

Evaluating the distribution of African swine fever virus within a feed mill environment following manufacture of inoculated feed

It is critical to understand the role feed manufacturing may have regarding potential African swine fever virus (ASFV) transmission, especially given the evidence that feed and/or ingredients may be potential vectors. The objective of the study was to evaluate the distribution of ASFV in a feed mill following manufacture of contaminated feed. To accomplish this, a pilot-scale feed mill consisting of a mixer, bucket elevator, and spouting was constructed in a BSL-3Ag facility. First, a batch of ASFV-free feed was manufactured, followed by a batch of feed that had an ASFV-contaminated ingredient added to feed, which was then mixed and discharged from the equipment. Subsequently, four additional ASFV-free batches of feed were manufactured using the same equipment. Environmental swabs from 18 locations within the BSL-3Ag room were collected after each batch of feed was discharged. The locations of the swabs were categorized into four zones: 1) feed contact surface, 2) non-feed contact surface < 1 meter away from feed, 3) non-feed contact surface > 1 meter from feed, and 4) transient surfaces. Environmental swabs were analyzed using a qPCR specific for the ASFV p72 gene and reported as genomic copy number (CN)/mL of environmental swab processing buffer. Genomic copies were transformed with a log₁₀ function for statistical analysis. There was no evidence of a zone × batch interaction for log₁₀ genomic CN/mL (P = 0.625) or cycle threshold (Ct) value (P = 0.608). Sampling zone impacted the log₁₀ p72 genomic CN/mL (P < 0.0001) and Ct values (P < 0.0001), with a greater amount of viral genome detected on transient surfaces compared to other surfaces (P < 0.05). This study illustrates that once ASFV enters the feed mill environment it becomes widespread and movement of people can significantly contribute to the spread of ASFV in a feed mill environment.

African swine fever risk and plant-based feed ingredients: Canada's approach to risk management of imported feed products

As a result of unprecedented spread of African swine fever (ASF) since 2018, Canada has taken additional steps to prevent introduction of the virus. While the role of plant‐based feed in the transmission of ASF is not completely understood, it was identified that no mitigation measures were in place to address this uncertain risk. A risk analysis process was conducted with collaboration between government and industry, including an assessment of the costs and benefits of various risk mitigation options. Using existing legislative tools, requirements must now be met before the importation of plant‐based feed ingredients of concern is permitted. Even with an uncertain risk, countries such as Canada that would suffer severe consequences should ASF be introduced, need to consider appropriate, risk‐based mitigation measures.

Detection of African swine fever virus in feed dust collected from experimentally inoculated complete feed using quantitative PCR and virus titration assays

African swine fever virus (ASFV) is a current threat to global pork production due to its high case fatality rate, lack of efficacious vaccine and recent transboundary spread into new regions of the world. Preventing introduction and further spread of ASFV is critical for countries currently negative for the virus. ASFV is stable in feed ingredients subjected to transoceanic conditions and transmission occurs through the natural consumption of contaminated feed. In this study, we investigated the use of feed dust collected from experimentally inoculated feed as a novel diagnostic sample type for ASFV detection. Moist swabs were used to collect dust from creep feeders after natural consumption of feed inoculated with 3.1-5.4 log₁₀ TCID₅₀ /g ASFV Georgia 2007 in the presence and absence of antimicrobial feed additives. Results validate the potential use of feed dust swabs as a novel diagnostic surveillance tool for detection and quantification of viral nucleic acid and infectious virus titre in ASFV-contaminated feed.