A Review of African Swine Fever and the Potential for Introduction into the United States and the Possibility of Subsequent Establishment in Feral Swine and Native Ticks

Biological Containment for African Swine Fever (ASF) Laboratories and Animal Facilities: The Italian Challenge in Bridging the Present Regulatory Gap and Enhancing Biosafety and Biosecurity Measures

The African Swine Fever Virus (ASFV) is a DNA virus of the Asfarviridae family, Asfivirus genus. It is responsible for massive losses in pig populations and drastic direct and indirect economic impacts. The ever-growing handling of ASFV pathological material in laboratories, necessary for either diagnostic or research activities, requires particular attention to avoid accidental virus release from laboratories and its detrimental economic and environmental effects. Recently, the Commission Delegated Regulation (EU) 2020/689 of 17 December 2019 repealed the Commission Decision of 26 May 2003 reporting an ASF diagnostic manual (2003/422/EC) with the minimum and supplementary requirements for ASF laboratories. This decision generated a regulatory gap that has not been addressed yet. This paper aims to describe the Italian National Reference Laboratory (NRL) efforts to develop an effective and reliable biological containment tool for ASF laboratories and animal facilities. The tool consists of comprehensive and harmonized structural and procedural requirements for ASF laboratories and animal facilities that have been developed based on both current and repealed legislation, further entailing a risk assessment and internal audit as indispensable tools to design, adjust, and improve biological containment measures.

Vaccines for African swine fever: an update

African swine fever (ASF) is a fatal infectious disease of swine caused by the African swine fever virus (ASFV). Currently, the disease is listed as a legally notifiable disease that must be reported to the World Organization for Animal Health (WOAH). The economic losses to the global pig industry have been insurmountable since the outbreak of ASF. Control and eradication of ASF are very critical during the current pandemic. Vaccination is the optimal strategy to prevent and control the ASF epidemic, but since inactivated ASFV vaccines have poor immune protection and there aren't enough cell lines for efficient in vitro ASFV replication, an ASF vaccine with high immunoprotective potential still remains to be explored. Knowledge of the course of disease evolution, the way of virus transmission, and the breakthrough point of vaccine design will facilitate the development of an ASF vaccine. In this review, the paper aims to highlight the recent advances and breakthroughs in the epidemic and transmission of ASF, virus mutation, and the development of vaccines in recent years, focusing on future directions and trends.

Identification of Two Novel Linear B Cell Epitopes on the CD2v Protein of African Swine Fever Virus Using Monoclonal Antibodies

African swine fever virus (ASFV) is a highly infectious viral pathogen that endangers the global pig industry, and no effective vaccine is available thus far. The CD2v protein is a glycoprotein on the outer envelope of ASFV, which mediates the transmission of the virus in the blood and recognition of the virus serotype, playing an important role in ASFV vaccine development and disease prevention. Here, we generated two specific monoclonal antibodies (mAbs), 6C11 and 8F12 (subtype IgG1/kappa-type), against the ASFV CD2v extracellular domain (CD2v-ex, GenBank: MK128995.1, 1-588 bp) and characterized their specificity. Peptide scanning technology was used to identify the epitopes recognized by mAbs 6C11 and 8F12. As a result, two novel B cell epitopes, 38DINGVSWN45 and 134GTNTNIY140, were defined. Amino acid sequence alignment showed that the defined epitopes were conserved in all referenced ASFV strains from various regions of China including the highly pathogenic, epidemic strain, Georgia2007/1 (NC_044959.2), with the same noted substitutions compared to the four foreign ASFV wild-type strains. This study provides important reference values for the design and development of an ASFV vaccine and useful biological materials for the functional study of the CD2v protein by deletion analysis.

Development and characterization of monoclonal antibodies against the extracellular domain of African swine fever virus structural protein, CD2v

African swine fever virus (ASFV), a DNA double-stranded virus with high infectivity and mortality, causing a devastating blow to the pig industry and the world economy. The CD2v protein is an essential immunoprotective protein of ASFV. In this study, we expressed the extracellular region of the CD2v protein in the 293F expression system to achieve proper glycosylation. Monoclonal antibodies (mAbs) were prepared by immunizing mice with the recombinant CD2v protein. Eventually, four mAbs that target the extracellular region of the ASFV CD2v protein were obtained. All four mAbs responded well to the ASFV HLJ/18 strain and recognized the same linear epitope, 154SILE157. The specific shortest amino acid sequence of this epitope has been accurately identified for the first time. Meaningfully, the 154SILE157 epitope was highly conformed in the ASFV Chinese epidemic strain and Georgia2008/1 strains according to the analysis of the conservation and have a fair protective effect. These findings contribute to further understanding of the protein function of CD2v and provide potential support for the development of diagnostic tools and vaccines for ASFV.

The study of antigen carrying and lesions observed in pigs that survived post African swine fever virus infection

African swine fever (ASF) is a dangerous infectious disease of domestic pigs and wild boar caused by African swine fever virus (ASFV). In Vietnam, the ASF epidemic is gradually turning into an endemic status with several recovered pigs post infection, but there were not many studies evaluating the role of these pigs in the epidemiological context in Vietnam. The aim of this study was to evaluate the viral antigen distribution and lesions in recovered pigs post ASFV infection. Ten pigs recovered from ASF at 6 weeks of age were monitored and assessed for anti-ASFV antibodies and viremia until slaughter. The five major organs (lung, liver, spleen, kidney, and lymph nodes) of these pigs were evaluated for microscopic lesions and viral antigen distribution. Anti-ASFV antibody was consistently observed to be high (S/P% ≥ 80) until slaughter, while viremia levels were very high (7 log₁₀ copies/mL) at 6 weeks of age and gradually decreased to undetectable levels at 12 weeks of age (6th week post-infection). At slaughter, the ASFV-associated lesions in the organs of these pigs were mild and nonspecific. Seven out of ten pigs recovering from ASF still carried the virus in surveyed organ tissues, although not in the serum. These findings suggest that ASF-recovered pigs may be potential carriers of the virus, contributing to the increased complexity in the current endemic status in Vietnam.

Optimizing response to an introduction of African swine fever in wild pigs

African swine fever virus (ASFv) is a virulent pathogen that threatens domestic swine industries globally and persists in wild boar populations in some countries. Persistence in wild boar can challenge elimination and prevent disease-free status, making it necessary to address wild swine in proactive response plans. In the U.S., invasive wild pigs are abundant and found across a wide range of ecological conditions that could drive different epidemiological dynamics among populations. Information on size of control areas required to rapidly eliminate ASFv in wild pigs and how this area should change with management constraints and local ecology are needed to optimize response planning. We developed a spatially-explicit disease transmission model contrasting wild pig movement and contact ecology in two ecosystems in southeastern U.S. We simulated ASFv spread and determined optimal response area (reported as radius of a circle) for eliminating ASFv rapidly over a range of detection times (when ASFv is detected relative to true date of introduction), culling capacities (proportion of wild pigs in the culling zone removed weekly), and wild pig densities. Large radii for response areas (14 km) were needed under most conditions but could be shortened with early detection (≤ 8 weeks) and high culling capacities (≥ 15% weekly). Under most conditions ASFv was eliminated in less than 22 weeks using optimal control radii, although ecological conditions with high rates of wild pig movement required higher culling capacities (≥ 10% weekly) for elimination within one year. Results highlight the importance of adjusting response plans based on local ecology and show wild pig movement is a better predictor of optimal response area than numbers of ASFv cases early in the outbreak trajectory. Our framework provides a tool for determining optimal control plans in different areas, guiding expectations of response impacts, and planning resources needed for rapid elimination. This article is protected by copyright. All rights reserved.

Development of a Blocking ELISA Kit for Detection of ASFV Antibody Based on a Monoclonal Antibody against Full Length p72

BACKGROUND

African swine fever virus (ASFV) is the etiologic agent of African swine fever (ASF), a disease of highly contagious and significant threat to pork production. At present, the sensitive detection methods are the keys to the disease control.

OBJECTIVE

Full length p72 is produced by eukaryotic system and its monoclonal antibody (mAb) 34C10 is subsequently recovered. A blocking ELISA kit for detection of ASFV antibody is developed based on p72 trimers and 34C10.

METHODS

Full length p72 is expressed and is used as immunogen to prepare a panel of monoclonal antibodies. The mAb 34C10 is verified by immunofluorescent and tested by ELISAs with positive serums. The constant affinity of 34C10 is then confirmed. A blocking ELISA kit is further developed and is compared with two commercial kits.

RESULTS

The mAb 34C10 is specifically bound to p72 protein, and it exhibits blocking affection to positive serum. IFA experiment shows that 34C10 could bind to p72 expressed by baculoviruses and the binding affinity of 34C10 is found to be as high as 1.85 × 1011 L/mol. The blocking ELISA kit shows high coincidence with a commercial ELISA kit. The sensitivity between these two kits is 97.6% (95%, CI: 90.65-99.58) and the specificity between them is 100% (95%, CI: 98.34-100).

CONCLUSION

The blocking ELISA developed in this study may have great potential for diagnosis of ASF. The structure of the antigen p72 is found to be a key factor for the performance of the kit.

HIGHLIGHTS

For the first time, the eukaryotic expressed full-length p72 protein is utilized to recover the monoclonal antibody and it is coated as antigen during the development of the blocking ELISA kit. This study sheds new light on the development of the blocking ELISA kits, especially for the development of diagnostic kit for the contagious virus with bio-safety problems.

Assessment of soy-based imports into the United States and associated foreign animal disease status

Soy-based products are known to pose a viable risk to U.S. swine herds because of their ability to harbour and transmit virus. This publication aimed to evaluate soy imports into the United States as a whole and from foreign animal disease positive (FAD-positive) countries to determine which products are being imported in the highest quantities and observe potential trends in imports from FAD-positive countries. Import data were accessed through the United States International Trade Commission website (USITC DataWeb) and summarized using R (version 4.0.2, R core team, Vienna, Austria). Twenty-one different Harmonized Tariff Schedule (HTS) codes were queried to determine quantities (metric tonnes, MT) and breakdown of different soy product types being imported into the United States from 2015 to 2020. A total of 78 different countries exported soy products to the United States in 2019 and 2020 with top contributors being Canada (546,467 and 481,497 MT, respectively), India (397,858 and 430,621 MT, respectively) and Argentina (122,116 and 79,471 MT, respectively). Soy oilcake (582,273 MT) was imported in the largest quantities, followed by organic soybeans (270,194 MT) and soy oil (134,436 MT) for 2020. Of the 78 countries, 46 had cases of FAD reported through the World Organization for Animal Health (OIE) World Animal Health Information Database (WAHIS). Top exporters of soy products to the United States from FAD-positive countries in 2019 and 2020 were India (397,858 and 430,621 MT, respectively), Argentina (122,116 MT in 2019) and Ukraine (40,293 and 56,392 MT, respectively). The risk of FAD introduction to the United States through soy imports can fluctuate based on where FAD outbreaks are occurring, shipping methods and end usage of products. A system to monitor these factors could help make future decisions about trade and risk of FAD introduction to U.S. swine herds.

Models to assess the risk of introduction of selected animal viral diseases through the importation of live animals as a key part of risk analysis

Introduction of an animal viral disease, especially a notifiable disease, into an importing country or region free from the disease may lead to serious epidemiological consequences and economic losses. Trade in live animals is historically considered one of the most important risk pathways. To estimate the magnitude of such risk, the likelihood of a virus’ entry into a country and the consequences of this event should be jointly evaluated. Depending on data availability, the urgency of the problem and the detail level of the objectives, a risk assessment may be conducted in a qualitative, semi-quantitative or quantitative way. The purpose of this review was firstly to provide a brief description of each step of the risk analysis process, with particular emphasis on the risk assessment component, and subsequently to supply examples of different approaches to the assessment of the risk of the introduction of selected animal viral diseases. Based on the reviewed models, the overall likelihood of introduction of particular diseases was generally estimated as low. The output risk value was strongly dependent on the duration of the silent phase of the epidemic in the country of origin. Other parameters with some bearing upon the risk derived from the epidemiological situation in the country of origin and the biosecurity or mitigation measures implemented in the country of destination. The investigated models are universal tools for conducting assessment of the risk of introduction of various animal diseases to any country. Their application may lead to timely implementation of appropriate measures for the prevention of the spread of a disease to another country or region.

An extensive evaluation of codon usage pattern and bias of structural proteins p30, p54 and, p72 of the African swine fever virus (ASFV)

African swine fever virus (ASFV) belongs to the family of Asfarviridae to the genus Asfivirus. ASF virus causes hemorrhage illness with a high mortality rate and hence, commercial loss in the swine community. The ASFV has been categorized by variation in codon usage that is caused by high mutation rates and natural selection. The evolution is caused mainly due to the mutation pressure and regulating the protein gene expression. Based on publicly accessible nucleotide sequences of the ASFV and its host (pig & tick), codon usage bias analysis was performed since an approved effective vaccination is not available to date, it is very important to analyze the codon usage bias of the p30, p54, and p72 proteins of ASFV to produce an effective and efficient vaccine to control the disease. Even though the codon usage bias analyses have been evaluated earlier, the evaluation of the codon usage pattern specific to p30, p54, and p72 of ASFV is inadequate. In all the protein-coding sequences, nucleotide base and codons terminating with base T were most frequent and the mean effective number of codons (Nc) was high, indicating the presence of codon usage bias. The GC contents and dinucleotide frequencies also indicated the codon usage bias of the ASFV pig and tick. The Nc plot, parity plot, neutrality plot analysis, revealed natural selection, as well as mutation pressure, were the major constraints in altering the codon bias of ASF virus. codon usage bias analysis was performed with no substantial differences in codon usage of the ASFV in pig and tick.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13337-021-00719-x.

Is the COVID-19 pandemic impacting on the risk of African Swine Fever virus (ASFV) introduction into the United States? A short-term assessment of the risk factors

African swine fever (ASF) is a contagious disease with high mortality in domestic and feral swine populations. Although it is not a zoonosis, its spread may have severe socio-economic and public health consequences. The activities of veterinary services are essential for controlling ASF outbreaks within a country, but also for diminishing its threat of spread to neighbouring countries, and for recognizing its entry into countries that are currently free. ASF requires quick responses and permanent monitoring to identify outbreaks and prevent spread, and both aspects can be heavily undercut during the COVID-19 pandemic. This paper analyses changing patterns of the main drivers and pathways for the potential introduction of ASFV into the United States during the COVID-19 pandemic, including international movements of people, swine products and by-products. Data on commercial flights and merchant ships was used as a proxy to indirectly assess the flow of illegal products coming from ASF affected countries. Results from this study highlight a decreasing trend in the legal imports of swine products and by-products from ASF affected countries (Sen's slope = -99, 95% CI: -215.34 to -21.26, p-value < 0.05), while no trend was detected for confiscations of illegal products at ports of entry. Additionally, increasing trends were detected for the monthly number of merchant ships coming from ASF affected countries (Sen's slope = 0.46, 95%CI 0.25-0.59), the monthly value of imported goods ($) through merchant ships (Sen's slope = 1513196160, 95%CI 1072731702-1908231855), and the monthly percentage of commercial flights (Sen's slope = 0.005, 95%CI 0.003-0.007), with the majority of them originating from China. Overall, the findings show an increased connection of the United States with ASF affected countries, highlighting the risk posed by ASF during a global public health crisis.

African Swine Fever in Wild Boar in Europe-A Review

The introduction of genotype II African swine fever (ASF) virus, presumably from Africa into Georgia in 2007, and its continuous spread through Europe and Asia as a panzootic disease of suids, continues to have a huge socio-economic impact. ASF is characterized by hemorrhagic fever leading to a high case/fatality ratio in pigs. In Europe, wild boar are especially affected. This review summarizes the currently available knowledge on ASF in wild boar in Europe. The current ASF panzootic is characterized by self-sustaining cycles of infection in the wild boar population. Spill-over and spill-back events occur from wild boar to domestic pigs and vice versa. The social structure of wild boar populations and the spatial behavior of the animals, a variety of ASF virus (ASFV) transmission mechanisms and persistence in the environment complicate the modeling of the disease. Control measures focus on the detection and removal of wild boar carcasses, in which ASFV can remain infectious for months. Further measures include the reduction in wild boar density and the limitation of wild boar movements through fences. Using these measures, the Czech Republic and Belgium succeeded in eliminating ASF in their territories, while the disease spread in others. So far, no vaccine is available to protect wild boar or domestic pigs reliably against ASF.

The Contribution of Wildlife Hosts to the Rise of Ticks and Tick-Borne Diseases in North America

Wildlife vertebrate hosts are integral to enzootic cycles of tick-borne pathogens, and in some cases have played key roles in the recent rise of ticks and tick-borne diseases in North America. In this forum article, we highlight roles that wildlife hosts play in the maintenance and transmission of zoonotic, companion animal, livestock, and wildlife tick-borne pathogens. We begin by illustrating how wildlife contribute directly and indirectly to the increase and geographic expansion of ticks and their associated pathogens. Wildlife provide blood meals for tick growth and reproduction; serve as pathogen reservoirs; and can disperse ticks and pathogens-either through natural movement (e.g., avian migration) or through human-facilitated movement (e.g., wildlife translocations and trade). We then discuss opportunities to manage tick-borne disease through actions directed at wildlife hosts. To conclude, we highlight key gaps in our understanding of the ecology of tick-host interactions, emphasizing that wildlife host communities are themselves a very dynamic component of tick-pathogen-host systems and therefore complicate management of tick-borne diseases, and should be taken into account when considering host-targeted approaches. Effective management of wildlife to reduce tick-borne disease risk further requires consideration of the 'human dimensions' of wildlife management. This includes understanding the public's diverse views and values about wildlife and wildlife impacts-including the perceived role of wildlife in fostering tick-borne diseases. Public health agencies should capitalize on the expertise of wildlife agencies when developing strategies to reduce tick-borne disease risks.

Risk of Introduction of Classical Swine Fever Into the State of Mato Grosso, Brazil

Classical swine fever (CSF) is considered one of the most important diseases of swine because of the far-reaching economic impact the disease causes to affected countries and regions. The state of Mato Grosso (MT) is part of Brazil's CSF-free zone. CSF status is uncertain in some of MT's neighboring States and countries, which has resulted in the perception that MT is at high risk for the disease. However, the risk for CSF introduction into MT has not been previously assessed. Here, we estimated that the risk for CSF introduction into the MT is highly heterogeneous. The risk associated with shipment of commercial pigs was concentrated in specific municipalities with intense commercial pig production, whereas the risk associated with movement of wild boars was clustered in certain municipalities located close to the state's borders, mostly in northern and southwestern MT. Considering the two pathways of possible introduction assessed here, these results demonstrate the importance of using alternative strategies for surveillance that target different routes and account for different likelihoods of introduction. These results will help to design, implement, and monitor surveillance activities for sustaining the CSF-free status of MT at times when Brazil plans to expand the recognition of disease-free status for other regions in the country.

New perspectives for evaluating relative risks of African swine fever virus contamination in global feed ingredient supply chains

There are no published reports indicating that the African swine fever virus (ASFV) has been detected in feed ingredients or complete feed. This is primarily because there are only a few laboratories in the world that have the biosecurity and analytical capabilities of detecting ASFV in feed. Several in vitro studies have been conducted to evaluate ASFV concentration, viability and inactivation when ASFV was added to various feed ingredients and complete feed. These inoculation studies have shown that some feed matrices support virus survival longer than others and the reasons for this are unknown. Current analytical methodologies have significant limitations in sensitivity, repeatability, ability to detect viable virus particles and association with infectivity. As a result, interpretation of findings using various measures may lead to misleading conclusions. Because of analytical and technical challenges, as well as the lack of ASFV contamination data in feed supply chains, quantitative risk assessments have not been conducted. A few qualitative risk assessments have been conducted, but they have not considered differences in potential scenarios for ASFV contamination between various types of feed ingredient supply chains. Therefore, the purpose of this review is to provide a more holistic understanding of the relative potential risks of ASFV contamination in various global feed ingredient supply chains and provide recommendations for addressing the challenges identified.

Predicting high-risk areas for African swine fever spread at the wild-domestic pig interface in Ontario

The probability of disease transmission among livestock premises via spillover from wildlife vectors depends on interacting ecological, demographic, and behavioural variables. Wild pigs (Sus scrofa) act as vectors and reservoirs of many diseases, including African Swine Fever (ASF), a highly lethal and contagious viral disease that affects both wild and domestic swine. Wild pigs play a significant role in the spread of ASF in geographic locations where the disease is present. Planning and preparedness will ensure that swift action can be taken to control ASF if it is introduced into North America. We used a network to predict the highest risk areas for ASF spread in Ontario, Canada given the distribution of wild pig sightings and other risk factors for wild pig presence and movement on the landscape. We used network nodes to represent the presence of domestic pig farms in a defined area, and we weighted network edges by the probability of ASF virus movement between nodes via movement of wild pigs. Our network models predicted that central Ontario has relatively high network closeness, suggesting that this area has a relatively high risk of virus exposure. These highly connected areas tended to also have the highest domestic pig farm density within a node. Central and eastern Ontario had the highest predicted network betweenness, suggesting that these areas are important for controlling virus flow across the province. We detected 10 communities or clusters within the overall network, where nodes were highly connected locally and relatively less connected to the rest of the network. Predicting areas with a high risk of exposure to the ASF virus due to wild pig movement in Ontario will guide managers on where to focus surveillance for ASF in the wild pig population and where to heighten biosecurity within commercial and backyard pig farms, ensuring that managers are prepared to act quickly to limit spread of ASF if the virus is introduced.

Evidence-Based African Swine Fever Policies: Do We Address Virus and Host Adequately?

African swine fever (ASF) is one of the most threatening diseases for the pig farming sector worldwide. Prevention, control and eradication remain a challenge, especially in the absence of an effective vaccine or cure and despite the relatively low contagiousness of this pathogen in contrast to Classical Swine Fever or Foot and Mouth disease, for example. Usually lethal in pigs and wild boar, this viral transboundary animal disease has the potential to significantly disrupt global trade and threaten food security. This paper outlines the importance of a disease-specific legal framework, based on the latest scientific evidence in order to improve ASF control. It compares the legal basis for ASF control in a number of pig-producing regions globally, considering diverse production systems, taking into account current scientific evidence in relation to ASF spread and control. We argue that blanket policies that do not take into account disease-relevant characteristics of a biological agent, nor the specifics under which the host species are kept, can hamper disease control efforts and may prove disproportionate.

An Isothermal Molecular Point of Care Testing for African Swine Fever Virus Using Recombinase-Aided Amplification and Lateral Flow Assay Without the Need to Extract Nucleic Acids in Blood

African swine fever (ASF) is a highly contagious and usually deadly porcine infectious disease listed as a notifiable disease by the World Organization for Animal Health (OIE). It has brought huge economic losses worldwide, especially since 2018, the first outbreak in China. As there are still no effective vaccines available to date, diagnosis of ASF is essential for its surveillance and control, especially in areas far from city with limited resources and poor settings. In this study, a sensitive, specific, rapid, and simple molecular point of care testing for African swine fever virus (ASFV) B646L gene in blood samples was established, including treatment of blood samples with simple dilution and boiling for 5 min, isothermal amplification with recombinase-aided amplification (RAA) at 37°C in a water bath for 10 min, and visual readout with lateral flow assay (LFA) at room temperature for 10–15 min. Without the need to extract viral DNA in blood samples, the intact workflow from sampling to final diagnostic decision can be completed with minimal equipment requirement in 30 min. The detection limit of RAA-LFA for synthesized B646L gene-containing plasmid was 10 copies/μl, which was 10-fold more sensitive than OIE-recommended PCR and quantitative PCR. In addition, no positive readout of RAA-LFA was observed in testing classical swine fever virus, porcine reproductive and respiratory syndrome virus, porcine epidemic diarrhea virus, pseudorabies virus and porcine circovirus 2, exhibiting good specificity. Evaluation of clinical blood samples of RAA-LFA showed 100% coincident rate with OIE-recommended PCR, in testing both extracted DNAs and treated bloods. We also found that some components in blood samples greatly inhibited PCR performance, but had little effect on RAA. Inhibitory effect can be eliminated when blood was diluted at least 32–64-fold for direct PCR, while only a 2–4 fold dilution of blood was suitable for direct RAA, indicating RAA is a better choice than PCR when blood is used as detecting sample. Taken together, we established an sensitive, specific, rapid, and simple RAA-LFA for ASFV molecular detection without the need to extract viral DNA, providing a good choice for point of care testing of ASF diagnosis in the future.

Development and characterization of monoclonal antibodies against the N-terminal domain of African swine fever virus structural protein, p54

African swine fever virus (ASFV), a re-emerging DNA virus, causes a highly contagious disease for domestic pigs. It is running rife worldwide and threatening the global swine industry. Protein p54 is an attractive candidate for ASFV diagnostic and vaccine design. In this work, we designed a peptide to mimic the N-terminal domain (NTD) of ASFV p54 and pretested it with sera from ASFV-infected pigs. The peptide could be well recognized by the sera, implying that the NTD of p54 contained some potential linear B cell epitopes. Then, the conjugates of the peptide with bovine serum albumin were used as the immunogen to generate monoclonal antibodies (mAbs). A total of six mAbs specific to the NTD of ASFV p54 protein were developed. Five of them well reacted with ASFV HLJ/18 strain and recognized a same linear B cell epitope ⁵FFQPV⁹. Furthermore, epitope ⁵FFQPV⁹ could be well recognized by ASFV-positive sera from natural infected pigs, suggesting that it was a natural linear B-cell epitope. Conservation analysis indicated that epitope ⁵FFQPV⁹ were highly conserved among ASFV epidemic isolates belonging to genotype I and II. Alanine-scanning mutagenesis further revealed that the residues (6F to 9V) of epitope ⁵FFQPV⁹ were the core binding sites for antibody recognition. This is the first research to characterize specific mAbs against NTD of p54 protein. These findings may help further understand the function of p54 protein and the improvement of ASFV diagnosis.

A stochastic network-based model to simulate farm-level transmission of African swine fever virus in Vietnam

African swine fever virus is highly contagious, and mortality rates reach up to 100% depending on the host, virus dose, and the transmission routes. The main objective of this study was to develop a network-based simulation model for the farm-level transmission of ASF virus to evaluate the impact of changes in farm connectivity on ASF spread in Vietnam. A hypothetical population of 1,000 pig farms was created and used for the network-based simulation, where each farm represented a node, and the connection between farms represented an edge. The three scenarios modelled in this way (baseline, low, and high) evaluated the impact of connectivity on disease transmission. The median number of infected farms was higher as the connectivity increased (low: 659, baseline: 968 and high: 993). In addition, we evaluated the impact of the culling strategy on the number of infected farms. A total of four scenarios were simulated depending on the timing of culling after a farm was infected. We found that the timing of culling at 16, 12, 8, and 6 weeks had resulted in a reduction of the number of median infected farms by 81.92%, 91.63%, 100%, and 100%, respectively. Finally, our evaluation of the implication of stability of ties between farms indicated that if the farms were to have the same trading partners for at least six months could significantly reduce the median number of infected farms to two (95th percentile: 413) than in the basic model. Our study showed that pig movements among farms had a significant influence on the transmission dynamics of ASF virus. In addition, we found that the either timing of culling, reduction in the number of trading partners each farm had, or decreased mean contact rate during the outbreaks were essential to prevent or stop further outbreaks.

African swine fever: a New Zealand perspective on epidemiological risk factors for its occurrence

This article reviews key epidemiological and clinical features of African swine fever (ASF). We identify particular aspects of New Zealand's pig populations (commercial, non-commercial, and wild) that may affect the risk of disease entry or spread. Review of published literature is supplemented by analysis of demographic and spatial aspects of the New Zealand commercial, non-commercial, and feral pig populations to provide context around risk factors for the disease that are most relevant to New Zealand. The current Eurasian outbreak of ASF, including recent spread into Oceania, has increased the risk of an incursion of the disease into New Zealand. Large volumes of fresh pork importation (including from countries affected by ASF), large non-commercial pig populations with substantial spatial overlap with the country's commercial industry, limited monitoring of compliance with waste food feeding regulations, and lack of mandatory premises identification for non-commercial pig holdings would likely contribute to the risk of spread of ASF in the event of an incursion. Awareness amongst veterinarians of these risk factors will contribute to national biosecurity and disease preparedness efforts in New Zealand.

Modelling the transmission and vaccination strategy for porcine reproductive and respiratory syndrome virus

Many aspects of the porcine reproductive and respiratory syndrome virus (PRRSV) between-farm transmission dynamics have been investigated, but uncertainty remains about the significance of farm type and different transmission routes on PRRSV spread. We developed a stochastic epidemiological model calibrated on weekly PRRSV outbreaks accounting for the population dynamics in different pig production phases, breeding herds, gilt development units, nurseries and finisher farms, of three hog producer companies. Our model accounted for indirect contacts by the close distance between farms (local transmission), between-farm animal movements (pig flow) and reinfection of sow farms (re-break). The fitted model was used to examine the effectiveness of vaccination strategies and complementary interventions such as enhanced PRRSV detection and vaccination delays and forecast the spatial distribution of PRRSV outbreak. The results of our analysis indicated that for sow farms, 59% of the simulated infections were related to local transmission (e.g. airborne, feed deliveries, shared equipment) whereas 36% and 5% were related to animal movements and re-break, respectively. For nursery farms, 80% of infections were related to animal movements and 20% to local transmission; while at finisher farms, it was split between local transmission and animal movements. Assuming that the current vaccines are 1% effective in mitigating between-farm PRRSV transmission, weaned pigs vaccination would reduce the incidence of PRRSV outbreaks by 3%, indeed under any scenario vaccination alone was insufficient for completely controlling PRRSV spread. Our results also showed that intensifying PRRSV detection and/or vaccination pigs at placement increased the effectiveness of all simulated vaccination strategies. Our model reproduced the incidence and PRRSV spatial distribution; therefore, this model could also be used to map current and future farms at-risk. Finally, this model could be a useful tool for veterinarians, allowing them to identify the effect of transmission routes and different vaccination interventions to control PRRSV spread.

Helminths of the Wild Boar (Sus scrofa) from Units of Conservation Management and Sustainable Use of Wildlife Installed in the Eastern Economic Region of Mexico

Wild boars (Sus scrofa) were introduced in Mexico for sport hunting and meat trading for human consumption, but the available data regarding their role in pathogen transmission are limited. This research and field work aimed to identify the helminths of the wild boar produced in three units of conservation management and sustainable use of wildlife placed in the eastern economic region of Mexico. Samples of feces and serum were collected from 90 animals that came from three different ranches. Stool examination and antibody determination to Fasciola hepatica, Taenia crassciceps, Ascaris suum, Toxocara canis (ELISA), and Trichinella spiralis (Western blot) were performed. In addition, 30 diaphragm samples from one ranch were obtained for artificial digestion. Eggs of Strongyloides sp. (72.2%), Metastrongylus sp. (57.7%), Oesophagostomum sp. (53.3%), and Trichuris sp. (37.7%) were found in addition to oocysts of Eimeria sp. (75.6%). Antibodies to Fasciola (8.9%), Taenia (4.4%), Ascaris (32.2%), Toxocara (20%), and Trichinella (5.5%) were found. The eggs of Strongyloides and Oesophagostomum were associated to female hosts. One nematode larva was found by artificial digestion. This is the first report to identify helminths from wild boars in Mexico. In addition, this study identifies the potential risk of the wild boar as a transmission channel of parasites that can have an impact on public health.

Risks of introduction and economic consequences associated with African swine fever, classical swine fever and foot-and-mouth disease: A review of the literature

African swine fever (ASF), classical swine fever (CSF) and foot-and-mouth disease (FMD) are considered to be three of the most detrimental animal diseases and are currently foreign to the U.S. Emerging and re-emerging pathogens can have tremendous impacts in terms of livestock morbidity and mortality events, production losses, forced trade restrictions, and costs associated with treatment and control. The United States is the world's top producer of beef for domestic and export use and the world's third-largest producer and consumer of pork and pork products; it has also recently been either the world's largest or second largest exporter of pork and pork products. Understanding the routes of introduction into the United States and the potential economic impact of each pathogen are crucial to (a) allocate resources to prevent routes of introduction that are believed to be more probable, (b) evaluate cost and efficacy of control methods and (c) ensure that protections are enacted to minimize impact to the most vulnerable industries. With two scoping literature reviews, pulled from global data, this study assesses the risk posed by each disease in the event of a viral introduction into the United States and illustrates what is known about the economic costs and losses associated with an outbreak.

Differential vector competence of Ornithodoros soft ticks for African swine fever virus: What if it involves more than just crossing organic barriers in ticks?

Background

Several species of soft ticks in genus Ornithodoros are known vectors and reservoirs of African swine fever virus (ASFV). However, the underlying mechanisms of vector competence for ASFV across Ornithodoros species remain to be fully understood. To that end, this study compared ASFV replication and dissemination as well as virus vertical transmission to descendants between Ornithodorosmoubata, O. erraticus, and O. verrucosus in relation to what is known about the ability of these soft tick species to transmit ASFV to pigs. To mimic the natural situation, a more realistic model was used where soft ticks were exposed to ASFV by allowing them to engorge on viremic pigs.

Methods

Ornithodoros moubata ticks were infected with the ASFV strains Liv13/33 (genotype I) or Georgia2007/1 (genotype II), O. erraticus with OurT88/1 (genotype I) or Georgia2007/1 (genotype II), and O. verrucosus with Ukr12/Zapo (genotype II), resulting in five different tick–virus pairs. Quantitative PCR (qPCR) assays targeting the VP72 ASFV gene was carried out over several months on crushed ticks to study viral replication kinetics. Viral titration assays were also carried out on crushed ticks 2 months post infection to confirm virus survival in soft ticks. Ticks were dissected. and DNA was individually extracted from the following organs to study ASFV dissemination: intestine, salivary glands, and reproductive organs. DNA extracts from each organ were tested by qPCR. Lastly, larval or first nymph-stage progeny emerging from hatching eggs were tested by qPCR to assess ASFV vertical transmission.

Results

Comparative analyses revealed higher rates of ASFV replication and dissemination in O. moubata infected with Liv13/33, while the opposite was observed for O. erraticus infected with Georgia2007/1 and for O. verrucosus with Ukr12/Zapo. Intermediate profiles were found for O. moubata infected with Georgia2007/1 and for O. erraticus with OurT88/1. Vertical transmission occurred efficiently in O. moubata infected with Liv13/33, and at very low rates in O. erraticus infected with OurT88/1.

Conclusions

This study provides molecular data indicating that viral replication and dissemination in Ornithodoros ticks are major mechanisms underlying ASFV horizontal and vertical transmission. However, our results indicate that other determinants beyond viral replication also influence ASFV vector competence. Further research is required to fully understand this process in soft ticks.

Genetic origins and diversity of bushpigs from Madagascar (Potamochoerus larvatus, family Suidae)

The island of Madagascar, situated off the southeast coast of Africa, shows the first evidence of human presence ~ 10,000 years ago; however, other archaeological data indicates a settlement of the modern peoples of the island distinctly more recent, perhaps > 1500 years ago. Bushpigs of the genus Potamochoerus (family Suidae), are today widely distributed in Madagascar and presumed to have been introduced from Africa at some stage by human immigrants to the island. However, disparities about their origins in Madagascar have been presented in the literature, including the possibility of endemic subspecies, and few empirical data are available. Furthermore, the separation of bushpigs in Madagascar from their mainland relatives may have favoured the evolution of a different repertoire of immune genes first due to a founder effect and then as a response to distinct pathogens compared to their ancestors. Molecular analysis confirmed the species status of the bushpig in Madagascar as P. larvatus, likely introduced from the central region of southern Africa, with no genetic evidence for the recognition of eastern and western subspecies as suggested from previous cranial morphology examination. Investigation of the immunologically important SLA-DQB1 peptide-binding region showed a different immune repertoire of bushpigs in Madagascar compared to those on the African mainland, with seventeen exon-2 haplotypes unique to bushpigs in Madagascar (2/28 haplotypes shared). This suggests that the MHC diversity of the Madagascar populations may have enabled Malagasy bushpigs to adapt to new environments.

Stability of African Swine Fever Virus in Carcasses of Domestic Pigs and Wild Boar Experimentally Infected with the ASFV "Estonia 2014" Isolate

Europe is currently experiencing a long-lasting African swine fever (ASF) epidemic, both in domestic pigs and wild boar. There is great concern that carcasses of infected wild boar may act as long-term virus reservoirs in the environment. We evaluated the tenacity of ASF virus (ASFV) in tissues and body fluids from experimentally infected domestic pigs and wild boar, which were stored on different matrices and at different temperatures. Samples were analysed at regular intervals for viral genome and infectious virus. ASFV was most stable in spleen or muscles stored at -20 °C and in blood stored at 4 °C. In bones stored at -20 °C, infectious virus was detected for up to three months, and at 4 °C for up to one month, while at room temperature (RT), no infectious virus could be recovered after one week. Skin stored at -20 °C, 4 °C and RT remained infectious for up to three, six and three months, respectively. In urine and faeces, no infectious virus was recovered after one week, irrespective of the matrix. In conclusion, tissues and organs from decomposing carcasses that persist in the environment for a long time can be a source of infection for several months, especially at low temperatures.

Selection for Favorable Health Traits: A Potential Approach to Cope with Diseases in Farm Animals

Disease is a global problem for animal farming industries causing tremendous economic losses (>USD 220 billion over the last decade) and serious animal welfare issues. The limitations and deficiencies of current non-selection disease control methods (e.g., vaccination, treatment, eradication strategy, genome editing, and probiotics) make it difficult to effectively, economically, and permanently eliminate the adverse influences of disease in the farm animals. These limitations and deficiencies drive animal breeders to be more concerned and committed to dealing with health problems in farm animals by selecting animals with favorable health traits. Both genetic selection and genomic selection contribute to improving the health of farm animals by selecting certain health traits (e.g., disease tolerance, disease resistance, and immune response), although both of them face some challenges. The objective of this review was to comprehensively review the potential of selecting health traits in coping with issues caused by diseases in farm animals. Within this review, we highlighted that selecting health traits can be applied as a method of disease control to help animal agriculture industries to cope with the adverse influences caused by diseases in farm animals. Certainly, the genetic/genomic selection solution cannot solve all the disease problems in farm animals. Therefore, management, vaccination, culling, medical treatment, and other measures must accompany selection solution to reduce the adverse impact of farm animal diseases on profitability and animal welfare.

An overview from the 2019 Swine Fever Exercise for Agriculture Response in Iowa

Iowa leads the United States in pork production, housing approximately one-third of the country's swine population. This puts Iowa at great economic risk if an outbreak of African swine fever, a disease that limits international trade opportunities, were to occur anywhere in the United States. To hone emergency response plans to combat an outbreak, the Iowa Department of Agriculture and Land Stewardship in September 2019 participated in a 4-day exercise with representatives from the other 13 top pork-producing states. This exercise involved a mock foreign animal disease response and helped to concisely summarize what pork producers could expect should a foreign animal disease be detected in Iowa.

Antibiotic Resistance: Moving From Individual Health Norms to Social Norms in One Health and Global Health

Antibiotic resistance is a problem for human health, and consequently, its study had been traditionally focused toward its impact for the success of treating human infections in individual patients (individual health). Nevertheless, antibiotic-resistant bacteria and antibiotic resistance genes are not confined only to the infected patients. It is now generally accepted that the problem goes beyond humans, hospitals, or long-term facility settings and that it should be considered simultaneously in human-connected animals, farms, food, water, and natural ecosystems. In this regard, the health of humans, animals, and local antibiotic-resistance-polluted environments should influence the health of the whole interconnected local ecosystem (One Health). In addition, antibiotic resistance is also a global problem; any resistant microorganism (and its antibiotic resistance genes) could be distributed worldwide. Consequently, antibiotic resistance is a pandemic that requires Global Health solutions. Social norms, imposing individual and group behavior that favor global human health and in accordance with the increasingly collective awareness of the lack of human alienation from nature, will positively influence these solutions. In this regard, the problem of antibiotic resistance should be understood within the framework of socioeconomic and ecological efforts to ensure the sustainability of human development and the associated human-natural ecosystem interactions.

Comparative Pathology of Domestic Pigs and Wild Boar Infected with the Moderately Virulent African Swine Fever Virus Strain "Estonia 2014"

Endemically infected European wild boar are considered a major reservoir of African swine fever virus in Europe. While high lethality was observed in the majority of field cases, strains of moderate virulence occurred in the Baltic States. One of these, "Estonia 2014", led to a higher number of clinically healthy, antibody-positive animals in the hunting bag of North-Eastern Estonia. Experimental characterization showed high virulence in wild boar but moderate virulence in domestic pigs. Putative pathogenic differences between wild boar and domestic pigs are unresolved and comparative pathological studies are limited. We here report on a kinetic experiment in both subspecies. Three animals each were euthanized at 4, 7, and 10 days post infection (dpi). Clinical data confirmed higher virulence in wild boar although macroscopy and viral genome load in blood and tissues were comparable in both subspecies. The percentage of viral antigen positive myeloid cells tested by flow cytometry did not differ significantly in most tissues. Only immunohistochemistry revealed consistently higher viral antigen loads in wild boar tissues in particular 7 dpi, whereas domestic pigs already eliminated the virus. The moderate virulence in domestic pigs could be explained by a more effective viral clearance.

Modelling the global economic consequences of a major African swine fever outbreak in China

African swine fever is a deadly porcine disease that has spread into East Asia where it is having a detrimental effect on pork production. However, the implications of African swine fever on the global pork market are poorly explored. Two linked global economic models are used to explore the consequences of different scales of the epidemic on pork prices and on the prices of other food types and animal feeds. The models project global pork prices increasing by 17-85% and unmet demand driving price increases of other meats. This price rise reduces the quantity of pork demanded but also spurs production in other parts of the world, and imports make up half the Chinese losses. Demand for, and prices of, food types such as beef and poultry rise, while prices for maize and soybean used in feed decline. There is a slight decline in average per capita calorie availability in China, indicating the importance of assuring the dietary needs of low-income populations. Outside China, projections for calorie availability are mixed, reflecting the direct and indirect effects of the African swine fever epidemic on food and feed markets.

Ecological drivers of African swine fever virus persistence in wild boar populations: Insight for control

Environmental sources of infection can play a primary role in shaping epidemiological dynamics; however, the relative impact of environmental transmission on host-pathogen systems is rarely estimated. We developed and fit a spatially explicit model of African swine fever virus (ASFV) in wild boar to estimate what proportion of carcass-based transmission is contributing to the low-level persistence of ASFV in Eastern European wild boar. Our model was developed based on ecological insight and data from field studies of ASFV and wild boar in Eastern Poland. We predicted that carcass-based transmission would play a substantial role in persistence, especially in low-density host populations where contact rates are low. By fitting the model to outbreak data using approximate Bayesian computation, we inferred that between 53% and 66% of transmission events were carcass-based that is, transmitted through contact of a live host with a contaminated carcass. Model fitting and sensitivity analyses showed that the frequency of carcass-based transmission increased with decreasing host density, suggesting that management policies should emphasize the removal of carcasses and consider how reductions in host densities may drive carcass-based transmission. Sensitivity analyses also demonstrated that carcass-based transmission is necessary for the autonomous persistence of ASFV under realistic parameters. Autonomous persistence through direct transmission alone required high host densities; otherwise re-introduction of virus periodically was required for persistence when direct transmission probabilities were moderately high. We quantify the relative role of different persistence mechanisms for a low-prevalence disease using readily collected ecological data and viral surveillance data. Understanding how the frequency of different transmission mechanisms vary across host densities can help identify optimal management strategies across changing ecological conditions.

Progress Toward Development of Effective and Safe African Swine Fever Virus Vaccines

African swine fever is a major concern due to its negative impact on pork production in affected regions. Due to lack of treatment and a safe vaccine, it has been extremely difficult to control this devastating disease. The mechanisms of virus entry, replication within the host cells, immune evasion mechanisms, correlates of protection, and antigens that are effective at inducing host immune response, are now gradually being identified. This information is required for rational design of novel disease control strategies. Pigs which recover from infection with less virulent ASFV isolates can be protected from challenge with related virulent isolates. This strongly indicates that an effective vaccine against ASFV could be developed. Nonetheless, it is clear that effective immunity depends on both antibody and cellular immune responses. This review paper summarizes the key studies that have evaluated three major approaches for development of African Swine Fever virus vaccines. Recent immunization strategies have involved development and in vivo evaluation of live attenuated virus, and recombinant protein- and DNA-based and virus-vectored subunit vaccine candidates. The limitations of challenge models for evaluating ASFV vaccine candidates are also discussed.

African Swine Fever in a Bulgarian Backyard Farm-A Case Report

African swine fever (ASF) is one of the most threatening diseases for the pig farming sector worldwide. As an effective vaccine is lacking, strict application of control measures is the only way to fight the disease in both industrial farms and backyard holdings. With generally low biosecurity standards, the latter are at particular risk for disease introduction and offer challenging conditions for disease control. In the following case report, we describe the overall course of an ASF outbreak in a Bulgarian backyard farm and the implemented control measures. Farm facilities and available data have been investigated to estimate the possible source, spread and time point of virus introduction. Contact with contaminated fomites entering the stable via human activities was regarded to be the most likely introduction route. The slow disease spread within the farm contributes to the hypothesis of a moderate contagiosity. As no further ASF outbreaks have been detected in domestic pig farms in the region, it could be demonstrated that successful disease control in small-scale farms can be reached. Thus, the report contributes to a better understanding of ASF in the backyard sector.

Nanoparticle-based vaccine development and evaluation against viral infections in pigs

Virus infections possess persistent health challenges in swine industry leading to severe economic losses worldwide. The economic burden caused by virus infections such as Porcine Reproductive and Respiratory Syndrome Virus, Swine influenza virus, Porcine Epidemic Diarrhea Virus, Porcine Circovirus 2, Foot and Mouth Disease Virus and many others are associated with severe morbidity, mortality, loss of production, trade restrictions and investments in control and prevention practices. Pigs can also have a role in zoonotic transmission of some viral infections to humans. Inactivated and modified-live virus vaccines are available against porcine viral infections with variable efficacy under field conditions. Thus, improvements over existing vaccines are necessary to: (1) Increase the breadth of protection against evolving viral strains and subtypes; (2) Control of emerging and re-emerging viruses; (3) Eradicate viruses localized in different geographic areas; and (4) Differentiate infected from vaccinated animals to improve disease control programs. Nanoparticles (NPs) generated from virus-like particles, biodegradable and biocompatible polymers and liposomes offer many advantages as vaccine delivery platform due to their unique physicochemical properties. NPs help in efficient antigen internalization and processing by antigen presenting cells and activate them to elicit innate and adaptive immunity. Some of the NPs-based vaccines could be delivered through both parenteral and mucosal routes to trigger efficient mucosal and systemic immune responses and could be used to target specific immune cells such as mucosal microfold (M) cells and dendritic cells (DCs). In conclusion, NPs-based vaccines can serve as novel candidate vaccines against several porcine viral infections with the potential to enhance the broader protective efficacy under field conditions. This review highlights the recent developments in NPs-based vaccines against porcine viral pathogens and how the NPs-based vaccine delivery system induces innate and adaptive immune responses resulting in varied level of protective efficacy.

Intramolecular [2 + 2] Photocycloaddition of Altrenogest: Confirmation of Product Structure, Theoretical Mechanistic Insight, and Bioactivity Assessment

While studying the environmental fate of potent endocrine-active steroid hormones, we observed the formation of an intramolecular [2 + 2] photocycloaddition product (2) with a novel hexacyclic ring system following the photolysis of altrenogest (1). The structure and absolute configuration were established by X-ray diffraction analysis. Theoretical computations identified a barrierless two-step cyclization mechanism for the formation of 2 upon photoexcitation. 2 exhibited progesterone, estrogen, androgen, and pregnane X receptor activity, albeit generally with reduced potency relative to 1.

Defining and combating antibiotic resistance from One Health and Global Health perspectives

Several interconnected human, animal and environmental habitats can contribute to the emergence, evolution and spread of antibiotic resistance, and the health of these contiguous habitats (the focus of the One Health approach) may represent a risk to human health. Additionally, the expansion of resistant clones and antibiotic resistance determinants among human-associated, animal-associated and environmental microbiomes have the potential to alter bacterial population genetics at local and global levels, thereby modifying the structure, and eventually the productivity, of microbiomes where antibiotic-resistant bacteria can expand. Conversely, any change in these habitats (including pollution by antibiotics or by antibiotic-resistant organisms) may influence the structures of their associated bacterial populations, which might affect the spread of antibiotic resistance to, and among, the above-mentioned microbiomes. Besides local transmission among connected habitats-the focus of studies under the One Health concept-the transmission of resistant microorganisms might occur on a broader (even worldwide) scale, requiring coordinated Global Health actions. This Review provides updated information on the elements involved in the evolution and spread of antibiotic resistance at local and global levels, and proposes studies to be performed and strategies to be followed that may help reduce the burden of antibiotic resistance as well as its impact on human and planetary health.

Risk of African Swine Fever Virus Sylvatic Establishment and Spillover to Domestic Swine in the United States

African swine fever virus (ASFV) causes a high-consequence foreign animal disease that has emerged along international trade routes. Owing to high lethality and resulting trade sanctions, establishment of this disease in the United States would have devastating economic consequences. ASFV can be transmitted by soft ticks in the genus Ornithodoros or directly between swine, including domestic, feral, and wild swine. Consequently, the spatial risk of ASFV establishment depends on where susceptible animals, with or without competent vectors, co-occur. We synthesized county-level historical records of soft tick occurrence, current maps of feral swine distribution, and domestic swine inventory to evaluate the risk of ASFV establishment and spillover in the United States. Areas of California, Florida, and much of the southwestern United States were classified as high risk for ASFV establishment and spillover should an introduction event occur. Our analyses indicate that California, Texas, Georgia, and Florida are high-priority candidates for proactive risk reduction strategies. Domestic swine are often produced in high-biosecurity environments, mitigating health risks associated with contacting infected hosts and vectors. However, small-scale and organic pig producers in much of the southern United States remain more vulnerable to disease emergence.

BOARD INVITED REVIEW: Prospects for improving management of animal disease introductions using disease-dynamic models

Management and policy decisions are continually made to mitigate disease introductions in animal populations despite often limited surveillance data or knowledge of disease transmission processes. Science-based management is broadly recognized as leading to more effective decisions yet application of models to actively guide disease surveillance and mitigate risks remains limited. Disease-dynamic models are an efficient method of providing information for management decisions because of their ability to integrate and evaluate multiple, complex processes simultaneously while accounting for uncertainty common in animal diseases. Here we review disease introduction pathways and transmission processes crucial for informing disease management and models at the interface of domestic animals and wildlife. We describe how disease transmission models can improve disease management and present a conceptual framework for integrating disease models into the decision process using adaptive management principles. We apply our framework to a case study of African swine fever virus in wild and domestic swine to demonstrate how disease-dynamic models can improve mitigation of introduction risk. We also identify opportunities to improve the application of disease models to support decision-making to manage disease at the interface of domestic and wild animals. First, scientists must focus on objective-driven models providing practical predictions that are useful to those managing disease. In order for practical model predictions to be incorporated into disease management a recognition that modeling is a means to improve management and outcomes is important. This will be most successful when done in a cross-disciplinary environment that includes scientists and decision-makers representing wildlife and domestic animal health. Lastly, including economic principles of value-of-information and cost-benefit analysis in disease-dynamic models can facilitate more efficient management decisions and improve communication of model forecasts. Integration of disease-dynamic models into management and decision-making processes is expected to improve surveillance systems, risk mitigations, outbreak preparedness, and outbreak response activities.

Simulation of transmission and persistence of African swine fever in wild boar in Denmark

African swine fever (ASF) is caused by ASF virus (ASFV) and is currently circulating in the eastern part of Europe posing a serious risk regarding transmission to western European countries. Wild boar is a main driver of the transmission and persistence of ASFV in the endemic infected countries in Europe. Some European countries free from ASF, such as Denmark and the Netherlands, have limited population sizes of wild boar, but have large swine productions. In these countries, the patterns of transmission and persistence of ASFV in the existing wild boar population, in case of introduction of ASFV, are unknown. It is important to get a better understanding of ASFV in these wild boar populations, in order to better manage the existing wild boar population and thereby minimize the risk of virus introduction and transmission to domestic pigs, in case of an ASFV incursion. We created an agent-based spatio-temporal model and simulated the transmission of ASFV within Danish wild boar populations, using actual landscape data. The model was run with 50 and 100 wild boar groups used as initial population sizes, respectively, either distributed across the southern part of the mainland (Jutland) or across both the southern and middle parts of Jutland, where wild boar groups are believed to exist. At first, the model was run without ASFV for 25 years to assess wild boar population dynamics in both regions. Thereafter, ASFV was added to the model 1 year after initiation and run for up to another 4 years. The model predicted that wild boar populations may increase drastically over the next 25 years, if wild boar groups were distributed across both southern and middle Jutland and no mitigation actions were taken, while the population sizes will be restricted, if groups were distributed only across the southern part of Jutland. The density of the population is an important factor affecting the transmission and persistency of the disease. Model results indicated that ASF epidemics in the simulated populations would generally persist for few months. However, due to the high stochasticity of the process, in certain situations the epidemics may last for more than one year, posing a serious risk of ASFV introduction to domestic pigs.

Transboundary spread of pig diseases: the role of international trade and travel

As globalization increases the interconnectedness between nations, economies, and industries, the introduction of diseases will continue to remain a prominent threat to the livestock sector and the trade of animals and animal products, as well as the livelihoods of farmers, food security and public health. The global pig sector, with its size and dichotomy between production type and biosecurity level, is particularly vulnerable to the transmission of transboundary animal diseases such as African and classical swine fever, foot and mouth disease, or porcine reproductive and respiratory syndrome. All of the above pose a constant threat to swine health, mainly as a result of both formal and informal international trade.Inspired in the risk assessment methodology, this paper classifies and provides an overview of the different pig disease introduction and exposure pathways, illustrated with abundant examples. Introduction pathways are classified as formal international trade (by product), informal international trade (by product), and spread through fomites. Formal trade of pigs and pork products is regulated by legislation and measures protecting animal populations from exotic diseases. Much more difficult to control is the transboundary swine disease transmission originating through informal trade, which entails illegal smuggling, but also the informal cross-border transfer of animals and products for personal use or within informal market chains. Meat products are most commonly mentioned, although fomites have also played a role in some cases, with live pigs, being more difficult to smuggle playing a role less frequently. The main exposure pathways are also described with the oral route playing a prominent role.Risk assessments can aid in the identification of pathways of pathogen introduction and exposure. However, quantitative information on informal disease introduction pathways remains very scarce and often incomplete, making it difficult to estimate the actual magnitudes of risks. Nevertheless, this knowledge is deemed essential to set up risk based awareness, prevention and surveillance programs that correspond to reality.

Reviewing the Potential Vectors and Hosts of African Swine Fever Virus Transmission in the United States

African swine fever virus (ASFV) continues to threaten global animal health and agricultural biosecurity. Mitigating the establishment of ASFV in the United States (U.S.) is contingent on (1) the identification of arthropod vectors and vertebrate hosts that are capable of viral maintenance and transmission in the U.S. and (2) knowledge of vector-host associations that may permit transmission. We aggregated data on vector competence, host competence and tick–host associations by systematic review of published articles and collection records to identify species that may support the invasion of ASFV in the U.S. Three species of competent soft ticks occur in the U.S., Ornithodoros coriaceus, Ornithodoros turicata, and Ornithodoros puertoricensis, however, vector competence for the majority of soft ticks in the U.S. remains unknown. Three species of competent vertebrate hosts currently occur in the U.S.: domestic pigs (Sus scrofa domesticus), feral hogs (Sus scrofa), and common warthogs (Phacochoerus africanus). Hierarchical hazard categories based on vector competence, tick–host contact rates, and vector abundance were used to semiquantitatively rank U.S. soft tick species by their relative risk for contributing to ASFV transmission to identify which soft tick species are a priority for future studies. High-risk vector and host species identified in this study can be used to focus ASFV risk assessments in the U.S., guide targeted surveillance and control strategies, and proactively prepare for an ASFV incursion event. Results indicate O. coriaceus, O. turicata, and O. puertoricensis demonstrate the highest relative risk for contributing to ASFV transmission in the U.S., however, many gaps in knowledge exist preventing the full evaluation of at least 30 soft tick species in the U.S. Further study is required to identify soft tick vectors that interact with feral swine populations, elucidate vector competence, and further understand the biology of soft tick species.

A preliminary molecular survey of Babesia divergens and first evidence of Theileria annulata in cattle from Saudi Arabia

Background and Aim

Babesia divergens causes human babesiosis in Europe where the parasite utilizes cattle as animal reservoir and Ixodes ricinus as tick vector. Importation of infected animals and passive carriage of infected ticks through migratory birds can lead to tick/pathogen geographic expansion and emergence of diseases in naïve land. Given the information that Saudi Arabia imports cattle from the European countries and that two global bird flyways pass through the country geographic coordinates, we speculate that B. divergens might be introduced into the Kingdom. Therefore, the aim of this preliminary study was to molecularly detect and characterize B. divergens and other piroplasms (including Theileria spp.) in cattle from Taif district, Kingdom of Saudi Arabia.

Materials and Methods

Blood samples from 20 cattle residing Taif district were collected, and polymerase chain reaction tested using wide and species-specific primers. Amplicons from a positive genus-wide reaction were purified, sequenced, and analyzed. Phylogenetic trees were constructed, and similarity to existing GenBank zoonotic piroplasms was also assessed.

Results

All samples were negative for B. divergens, and only one sample proved positive for Theileria annulata in a wide reaction. Phylogeny clustered our strain with T. annulata from Spanish dog and another one detected in a cow from France. BLAST analysis showed genetic distance from zoonotic piroplasms with identity ranged from 88% to 91%.

Conclusion

Although B. divergens was not detected, we are not able to rule out or affirm the existence of the pathogen in the country. On the other hand, identifying T. annulata strain with a southern European origin strongly supports our speculation that bovine zoonotic Babesia might be introduced into KSA. This study is not only the first molecular survey of B. divergens but also the first report of the molecular identity of T. annulata in Saudi Arabia. A national-wide bovine and tick surveillance are needed to further prove our speculation.