Control Of African Swine Fever Research Articles

Deletion of African Swine Fever Virus (ASFV) H240R Gene Attenuates the Virulence of ASFV by Enhancing NLRP3-Mediated Inflammatory Responses.

African swine fever (ASF) is a highly contagious infectious disease of domestic pigs and wild boars caused by African swine fever virus (ASFV), with a mortality rate of up to 100%. In order to replicate efficiently in macrophages and monocytes, ASFV has evolved multiple strategies to evade host antiviral responses. However, the underlying molecular mechanisms by which ASFV-encoded proteins execute immune evasion are not fully understood. In this study, we found that ASFV pH240R strongly inhibits transcription, maturation, and secretion of interleukin-1β (IL-1β). Importantly, pH240R not only targeted NF-κB signaling but also impaired NLRP3 inflammasome activation. In this mechanism, pH240R interacted with NF-kappa-B essential modulator (NEMO), a component of inhibitor of kappa B kinase (IKK) complex and subsequently reduced phosphorylation of IκBα and p65. In addition, pH240R bonded to NLRP3 to inhibit NLRP3 inflammasome activation, resulting in reduced IL-1β production. As expected, infection with H240R-deficient ASFV (ASFV-ΔH240R) induced more inflammatory cytokine expression both in vitro and in vivo than its parental ASFV HLJ/18 strain. Consistently, H240R deficiency reduced the viral pathogenicity in pigs compared with its parental strain. These findings reveal that the H240R gene is an essential virulence factor, and deletion of the H240R gene affects the pathogenicity of ASFV HLJ/18 by enhancing antiviral inflammatory responses, which provides insights for ASFV immune evasion mechanisms and development of attenuated live vaccines and drugs for prevention and control of ASF. IMPORTANCE African swine fever (ASF), caused by African swine fever virus (ASFV), is a highly contagious and acute hemorrhagic viral disease of domestic pigs, with a high mortality approaching 100%. ASFV has spread rapidly worldwide and caused huge economic losses and ecological consequences. However, the pathogenesis and immune evasion mechanisms of ASFV are not fully understood, which limits the development of safe and effective ASF attenuated live vaccines. Therefore, investigations are urgently needed to identify virulence factors that are responsible for escaping the host antiviral innate immune responses and provide a new target for development of ASFV live-attenuated vaccine. In this study, we determined that the H240R gene is an essential virulence factor, and its depletion affects the pathogenicity of ASFV by enhancing NLRP3-mediated inflammatory responses, which provides theoretical support for the development of an ASFV attenuated live vaccine.

Simulating Hunting Effects on the Wild Boar Population and African Swine Fever Expansion Using Agent-Based Modeling.

African swine fever (ASF) is a viral hemorrhagic fever fatal to animals of the Suidae family. It has spread from Africa to Europe and Asia, causing significant damage to wildlife and domesticated pig production. Since the first confirmed case in South Korea in September 2019, the number of infected wild boars has continued to increase, despite quarantine fences and hunting operations. Hence, new strategies are needed for the effective control of ASF. We developed an agent-based model (ABM) to estimate the ASF expansion area and the efficacy of infection control strategies. In addition, we simulated the agents' (wild boars) behavior and daily movement range based on their ecological and behavioral characteristics, by applying annual hunting scenarios from past three years (2019.09-2022.08). The results of the simulation based on the annual changes in the number of infected agents and the ASF expansion area showed that the higher the hunting intensity, the smaller the expansion area (24,987 km2 at 0% vs. 3533 km2 at 70%); a hunting intensity exceeding 70% minimally affected the expansion area. A complete removal of agents during the simulation period was shown to be possible. In conclusion, an annual hunting intensity of 70% should be maintained to effectively control ASF.

The First Eighteen Months of African Swine Fever in Wild Boar in Saxony, Germany and Latvia—A Comparison

African swine fever (ASF) emerged in Latvia in 2014. In 2020, the virus has been detected in the German federal state, Saxony. In both regions, the virus was probably introduced by infected wild boar coming from affected neighboring countries. As the current ASF control strategy at EU level had not yet been developed at the time of ASF introduction into Latvia, disease control measures in both study areas differed over time. Assessing the course of ASF in Saxony and the implemented control strategies, the first 18 months of the ASF epidemic were epidemiologically compared between Saxony and Latvia. ASF wild boar surveillance data were analyzed and the prevalence of ASF virus-positive wild boar was estimated. For estimating the wild boar density, the numbers of wild boar per km² were calculated for the respective geographical areas. The number of samples collected from hunted wild boar and wild boar found dead was higher in Saxony. The ASF virus prevalence in Latvia was significantly higher than in Saxony, indicating that Saxony has had more time for getting prepared for dealing with an ASF incursion. Experience from other countries and the rapid implementation of new control strategies may have helped Saxony deal with ASF.

The Indirect ELISA and Monoclonal Antibody against African Swine Fever Virus p17 Revealed Efficient Detection and Application Prospects.

Since 2018, the outbreak and prevalence of the African swine fever virus (ASFV) in China have caused huge economic losses. Less virulent ASFVs emerged in 2020, which led to difficulties and challenges for early diagnosis and control of African swine fever (ASF) in China. An effective method of monitoring ASFV antibodies and specific antibodies against ASFV to promote the development of prevention techniques are urgently needed. In the present study, ASFV p17 was successfully expressed in CHO cells using a suspension culture system. An indirect enzyme-linked immunosorbent assay (ELISA) based on purified p17 was established and optimized. The monoclonal antibody (mAb) against p17 recognized a conservative linear epitope (3TETSPLLSH11) and exhibited specific reactivity, which was conducive to the identification of recombinant porcine reproductive and respiratory syndrome virus (PRRSV) expressing p17. The ELISA method efficiently detected clinical ASFV infection and effectively monitored the antibody levels in vivo after recombinant PRRSV live vector virus expressing p17 vaccination. Overall, the determination of the conserved linear epitope of p17 would contribute to the in-depth exploration of the biological function of the ASFV antigen protein. The indirect ELISA method and mAb against ASFV p17 revealed efficient detection and promising application prospects, making them ideal for epidemiological surveillance and vaccine research on ASF.

Spatio-Temporal Epidemiology of the Spread of African Swine Fever in Wild Boar and the Role of Environmental Factors in South Korea.

Since the first confirmation of African swine fever (ASF) in domestic pig farms in South Korea in September 2019, ASF continues to expand and most notifications have been reported in wild boar populations. In this study, we first performed a spatio-temporal cluster analysis to understand ASF spread in wild boar. Secondly, generalized linear logistic regression (GLLR) model analysis was performed to identify environmental factors contributing to cluster formation. In the meantime, the basic reproduction number (R0) for each cluster was estimated to understand the growth of the epidemic. The cluster analysis resulted in the detection of 17 spatio-temporal clusters. The GLLR model analysis identified factors influencing cluster formation and indicated the possibility of estimating ASF epidemic areas based on environmental conditions. In a scenario only considering direct transmission among wild boar, R0 ranged from 1.01 to 1.5 with an average of 1.10, while, in another scenario including indirect transmission via an infected carcass, R0 ranged from 1.03 to 4.38 with an average of 1.56. We identified factors influencing ASF expansion based on spatio-temporal clusters. The results obtained would be useful for selecting priority areas for ASF control and would greatly assist in identifying efficient vaccination areas in the future.

A Novel Tool to Assess the Risk for African Swine Fever in Hunting Environments: The Balkan Experience.

In Europe, African swine fever (ASF) can be sustained within wild boar populations, thus representing a constant source of virus and a huge challenge in the management of the disease. Hunters are the key stakeholders for the prevention, detection and control of ASF in wild boar. Their behavior and the biosecurity standards applied in infected or at-risk hunting grounds have a huge impact on disease dynamics and management. The Food and Agriculture Organization (FAO) has developed a semi-quantitative survey-based novel tool to assess the risk of ASF in hunting grounds (namely the risks of introduction and spread into and between hunting grounds, and the risk of not detecting the infection) and how such risks could be reduced if mitigation or corrective measures were applied at low, medium and high effort. The weight of risk factors was determined through an expert knowledge elicitation (EKE). The surveys for each hunting ground were filled in by their respective managers. The tool's outputs allow users to visualize the different ASF risks of hunting grounds, whether as numerical values or color-coded maps, at sub-national, national and regional levels. These outputs can be used to guide policy makers, highlighting gaps or geographical areas to prioritize. The tool was used to assess hunting grounds in Kosovo1 (1 As per United Nations Security Council resolution 1244). Montenegro and Serbia, showing overall a high risk.

A qualitative assessment of alternative eradication strategies for African swine fever in the Dominican Republic.

Since its recent detection in July 2021, the reintroduction of African swine fever (ASF) in the Dominican Republic (DR) has generated much discourse on various measures for its effective control. Strategies range from complete depopulation of the swine population, as was done in 1978, to a system of passive surveillance with endemicity, with many in-between. Currently, ASF-decision makers need a peer evaluation and comparison and contrast of these potential strategies that incorporates both private and public perspectives. To achieve this, we used strengths, weaknesses, opportunities, and threats (SWOT) analysis to evaluate three different theoretical ASF control scenarios with the aim of contributing evaluations of alternatives strategies to mitigate the epidemic's impact. These included total depopulation of all pigs in the DR, partial depopulation, and continuation of current control measures. Relevant experts from the DR private swine industry were identified through "snowball sampling" techniques. Five experts completed the SWOT questionnaire and additional questions considering aspects of financial cost, social impact, feasibility, animal welfare, and regional policy. The summarized responses were presented to the full group of experts initially nominated for final review and later to representatives of the DR government. The SWOT analysis highlighted that although there are certain benefits associated with each of the proposed strategies, there are also important drawbacks and disadvantages for all. This analysis is a tool for facilitating cooperating between the private-public industries, and ultimately it supports the development of strategies that will reduce ASF burden in the DR in a way suitable for all relevant stakeholders.

Alternative approaches to the diagnosis of African swine fever in the Russian Federation in 2017–2021

Prevention and control of African swine fever (ASF) transmission on the territory of the Russian Federation requires monitoring based on testing of samples from pigs and wild boars. Specific anti-ASFV antibodies are rarely detected in samples during routine serological diagnostics. Although, ASF isolates with weakened virulence were confirmed in Russia and neighboring countries.The aim of this work was to determine the possibility of using alternative samples for ASF diagnosis and evaluate the effectiveness of the diagnostic methods used on the territory of Russia. Biological materials obtained from experimentally infected animals and samples collected in the "field" conditions were used in this study. Complex testing (RT-PCR and ELISA) is a more effective approach to diagnose chronic and asymptomatic forms of ASF compared to the separate use of these techniques. The possibility and efficiency of using alternative samples in diagnostics are demonstrated. It was confirmed that IPT method overcomes ELISA by high diagnostic sensitivity and detection of antibodies on earlier stages in extended range of samples. Anti-ASFV antibodies were detected in domestic and wild pigs in five regions of Russia. Samples from infected pigs that are negative in RT-PCR can be positive for anti-ASFV antibodies. The detection of antibodies in samples from shot wild boars (negative or uncertain in RT-PCR test) suggests the existence of animals surviving ASF infection. The data obtained suggest a revision of the ASF surveillance strategy, by introducing complex diagnostic methods aimed at detection of both the virus genome and anti-ASFV antibodies simultaneously.

One-Step Rapid and Sensitive ASFV p30 Antibody Detection via Nanoplasmonic Biosensors.

African swine fever (ASF) is one of the most serious transnational swine diseases in the world. The case fatality rate of susceptible pigs is up to 100%. Currently, no commercial vaccine is available, so the prevention and control of ASF mainly relies on early diagnosis and culling of infected pigs. As the ASF virus continues to evolve, develop, and diversify, nucleic acid testing becomes less efficient. Here, we developed a method for the rapid and direct optical measurement of African swine fever virus (ASFV) antibody in vitro. This one-step procedure requires nearly no sample preparation and involves p30 protein-specific label-free integration into standard 96-well plates. Using a nanoplasmonic biosensor with extraordinary optical transmission (EOT) effect, one-step sample addition, ASFV antibody was detected within 20 min. The positive antibody showed a satisfactory sensitivity and linear relationship in the dilution ratio of 1:100-1:16000. It was used for the detection of clinical serum samples with a coincidence rate of 96.6%. The measurement results can be automatically analyzed and displayed on a conventional microplate meter computer and connected device. Our detection method can be widely applied in point-of-care testing (POCT) of ASFV antibody in pig farms. IMPORTANCE African swine fever (ASF) is a serious transnational disease caused by the African swine fever virus (ASFV), which is highly contagious in wild boars and domestic pigs. There is currently no available vaccine for ASF; therefore, development efforts are a key priority as ASFV continues to evolve and diversify. The ASF antibody rapid detection platform comprising the nanoplasmonic biosensor with extraordinary optical transmission effect can greatly reduce the detection time and improve detection flux while maintaining detection sensitivity and specificity. The one-step sample addition can effectively avoid cross contamination of samples in the detection process. The detection method provides a solution for the rapid and accurate real-time monitoring of ASF in pig farms.

Prospects for the application of infectious virus detection technology based on propidium monoazide in African swine fever management.

African swine fever (ASF) is a hemorrhagic and often fatal disease occurring in domestic pigs and wild boars. ASF can potentially greatly impact the global trade of pigs and pork products and threaten global food security. Outbreaks of ASF must be notified to the World Organization for Animal Health. In this study, we analyzed the feasibility of applying propidium monoazide (PMA) pretreatment-based infectious virus detection technology to ASF prevention and control and investigated the prospects of applying this technology for epidemic monitoring, disinfection effect evaluation, and drug development. PMA as a nucleic acid dye can enter damaged cells and undergo irreversible covalent crosslinking with nucleic acid under halogen light to prevent its amplification. Although this technology has been widely used for the rapid detection of viable bacteria, its application in viruses is rare. Therefore, we analyzed the theoretical feasibility of applying this technology to the African swine fever virus (ASFV) in terms of gene and cell composition. Rapid infectious ASFV detection technology based on PMA pretreatment would greatly enhance all aspects of ASF prevention and control, such as epidemic monitoring, disinfection treatment, and drug development. The introduction of this technology will also greatly improve the ability to prevent and control ASF.

Estimation of basic reproduction number (R0) of African swine fever (ASF) in mid-size commercial pig farms in Vietnam.

African swine fever (ASF) is a devastating disease affecting the global swine industry. Recently, it has spread to many countries in Africa, Europe, Asia, and the Caribbean, leaving severe damage to local, regional, national, and global economies. Due to its highly complex molecular characteristics and pathogenesis, the development of a successful vaccine has been an unmet challenge. Therefore, ASF control relies solely on biosecurity, rapid detection, and elimination. Epidemiological information obtained from natural ASF outbreaks is critical for designing and implementing ASF control measures. Basic reproduction number (R0), an epidemiological metric used to describe the contagiousness or transmissibility of infectious agents, is an important epidemiological tool. In this study, we have calculated R0 for the in-farm spread of ASF among fattening pigs and sows in two midsize commercial pig farms, HY1 and HY2, that practice the spot removal approach in controlling ASF outbreaks in Vietnam. The R0 values for the sows and fattening pigs were 1.78 (1.35–2.35) and 4.76 (4.18–5.38) for HY1 and 1.55 (1.08–2.18) and 3.8 (3.33–4.28) for HY2. This is the first study to evaluate the transmission potential of ASF in midsize commercial pig farms in Vietnam. Based on the R0 values, we predict that the spot removal approach could be used to successfully control ASF outbreaks in midsize commercial sow barns but not in fattening pens.

Detection of African swine fever virus antibodies in serum using a pB602L protein-based indirect ELISA.

African Swine Fever (ASF) is an acute, highly contagious and deadly infectious disease that has a huge impact on the swine industry. It is caused by the African swine fever virus (ASFV). The most acute forms of ASF in domestic pigs have mortality rates of up to 100%. The lack of a commercial vaccine and effective therapeutic drugs has brought great challenges to the prevention and control of ASF. Current, the African swine fever virus requires a huge amount of detection, so there is a need for more sensitive and accurate detection technology. The protein pB602L, as a late non-structural protein, has a high corresponding antibody titer and strong antigenicity in infected swine. In this research, the B602L gene was constructed into the pColdI prokaryotic expression vector, and prokaryotic expression of the soluble pB602L protein was induced by IPTG. Western blot analysis demonstrated that the protein had strong immunogenicity. We established an indirect ELISA method for the detection of anti-ASFV using purified recombinant pB602L protein as antigen. The detection method showed excellent specificity without cross-reactions with antibodies against PRRSV, CSFV, JEV, and GETV. The method could detect anti-ASFV in serum samples that were diluted up to 6,400 times, showing high sensitivity. The coefficients of variation of the intra-assay and inter-assay were both <10%. The assays had excellent specificity, sensitivity, and repeatability. In summary, we developed an accurate, rapid, and economical method for the detection of anti-ASFV in pig serum samples with great potential for ASF monitoring and epidemic control.

Development of a highly sensitive Gaussia luciferase immunoprecipitation assay for the detection of antibodies against African swine fever virus.

In recent years, African swine fever (ASF) has caused a devastating blow to the swine industry globally. Since no effective vaccine is available, strict biosafety measures and rapid diagnosis are the most effective strategies for ASF control. ASFV p30 is one of the most antigenic viral proteins that have been widely used in the field for serological diagnosis of ASF infection. In this study, we developed a luciferase immunoprecipitation system (LIPS) assay for the detection of ASFV antibodies in pig serum using Gaussia luciferase (GLuc)-tagged p30 as a diagnostic antigen. The optimal GLuc-p30 input of 107 luminance units (LU) and optimal serum dilution factor of 1/100 were set to achieve the highest P/N ratio. Based on 87 ASFV-positive and negative pig sera, the cutoff value of the S/N ratio could be set between 2.298 and 30.59 to achieve 100% sensitivity and 100% specificity. Moreover, the diagnostic sensitivity of this LIPS is comparable to that of a commercial enzyme-linked immunosorbent assay (ELISA) and the specificity of LIPS is even superior to the tested ELISA. In conclusion, we have established a LIPS assay for ASFV antibody detection, which could be a potential method for ASFV diagnosis in laboratories and farms.

Development of an indirect ELISA for the identification of African swine fever virus wild-type strains and CD2v-deleted strains

African swine fever (ASF) is a potent infectious disease with detrimental effects on the global swine industry and no currently vaccine available. The emergence of low-virulence CD2v-deleted mutants manifested as non-hemadsorption (non-HAD) strains represents a significant challenge to the prevention and control of ASF. In this study, we aimed to establish an indirect ELISA (IELISA) method for the identification of ASFV wild-type and CD2v-deleted strains. We integrated the CD2v protein extracellular domain sequence (CD2v-Ex, 1–588 bp) of the highly pathogenic strain China/2018/AnhuiXCGQ into the genome of suspension culture-adapted Chinese hamster Ovary-S (CHO-S) cells using lentivirus vectors (LVs). By screening, we identified a monoclonal CHO-S cell line that stably expressed secretory CD2v-Ex Protein. We then used the purified CD2v-Ex Protein as the detection antigen to establish an indirect ELISA method (CD2v-IELISA) for identification of the ASFV wild-type and CD2v-Deleted (CD2v−) strains. The CD2v-IELISA method showed excellent specificity with no cross-reaction with serum samples infected with ASFV (CD2v−), porcine reproductive and respiratory syndrome virus (PRRSV), classical swine fever virus (CSFV), porcine circovirus (PCV), porcine pseudorabies virus (PRV), swine foot and mouth disease virus (FMDV) and porcine epidemic diarrhea virus (PEDV). Furthermore, this method showed high sensitivity, allowing identification of ASFV-infected clinical serum samples up to a dilution of 1:2,560. The coefficient of variation both in and between batches was <10% with good reproducibility and a high compliance rate of 99.4%. This CD2v-IELISA method developed here is of great significance for the prevention, control and purification of ASFV.

Implications of partial culling on African swine fever control effectiveness in Vietnam.

The introduction of the African swine fever (ASF) into previously unaffected countries often overwhelms veterinary authorities with the resource demanding control efforts that need to be undertaken. The approach of implementing total stamping out of affected herds is taken as “default” control measure in many countries, regardless of the transboundary animal disease addressed, leading to a variety of challenges when implemented. Apart from the organizational challenges and high demand for human and financial resources, the total stamping out approach puts a high burden on the livelihoods of the affected farmers. After the spread of ASF throughout the country in 2019, Vietnam changed the culling approach enabling partial culling of only affected animals in the herd, in order to save resources, and reduce the environmental impact because of the carcass disposal and allow farmers to protect valuable assets. Until now, field data comparing these disease control options in their performance during implementation has not been evaluated scientifically. Analyzing the effect of the change in a control policy, the present study concludes that partial culling can on average save over 50% of total stock with an 8-day prolongation of the implementation of control measures. With 58% of farms undergoing partial culling scoring high on a time-livelihoods matrix, while total stamping out fails to score on livelihoods, much-needed clarity on the livelihood-protecting effects of alternative culling strategies is given. In the future, this will allow veterinary authorities to adjust control measures according to differing priorities, targeting peculiarities of ASF and acknowledging resource constraints faced.

Flow cytometry-based multiplexing antibody detection for diagnosis of African swine fever virus

African swine fever (ASF) is an infectious disease that has a mortality rate of nearly 100% in domestic pigs. To date, no vaccine or effective treatment for ASF is available, necessitating the development of an accurate and sensitive diagnostic method to monitor ASF virus (ASFV) antibodies for prevention and control. Herein, a reliable and sensitive suspension microarray technology-based multiplexing method was developed for ASFV antibody detection using recombinant CD2v, p30, p54, and p22 antigen protein coated size-encoded microbeads as probes to capture the target antibody. Compared to commercial ELISA kits, the newly developed method showed a 16-fold improvement in detection sensitivity. Differential diagnosis of CD2v-unpressed low-virulence mutant (genotype II) and wild-type ASFV (genotype II) was readily achieved by fluorescence signal analysis of the CD2v-coated probe in the microbead mixture solution. In addition, the real serum assay revealed a 97% consistency rate between the novel method and commercial ELISA kits, demonstrating excellent potential for ASF epidemic surveillance and control.

Pigkeepers’ knowledge and perceptions regarding African swine fever and the control measures in Estonia

African swine fever (ASF) has been present in Estonia since 2014, and pigkeepers play a major role in controlling the spread of viral infection in domestic pigs. Participatory epidemiology may provide insight into livestock keepers’ existing attitudes and compliance with implementing control strategies. By conducting focus group discussions and using participatory epidemiology tools, this study aimed to reveal pigkeepers’ knowledge and awareness of ASF clinical signs, transmission routes, and preventive measures. Furthermore, opinions including trust in stakeholders in ASF control, acceptability of ASF eradication, and control measures by pigkeepers in Estonia were identified. The most indicative ASF signs in pigs were “increased mortality” and “fever, inappetence, lethargy”. The highest risk of virus introduction into the herd was designated to “agricultural machinery, vehicles”, “rodents, birds, insects”, and “people”. “Fencing” was the most liked ASF preventive measure, while “training of staff in biosecurity and informing the visitors” was considered the most effective measure. The least accepted ASF eradication measure was “culling of all animals on the farm”. Generally, pigkeepers perceived that healthy animals should not be culled but only ASF-infected pigs. Additionally, healthy pigs could be slaughtered and used for the production of heat-treated canned meat. “Destroying the feed” of ASF-infected farms was not favoured because some pigkeepers proposed using it for other animal species. Regarding ASF territorial restrictions (zoning), “lower meat prices” and “economic losses” were regarded as consequences with the greatest impact. Pigkeepers ranked trust in “Veterinary Authority and Ministry of Rural Affairs” regarding their role in ASF prevention and control as high while perceiving themselves as the most trustworthy stakeholder within the ASF network. This study demonstrates a generally good level of awareness among the pigkeepers in Estonia concerning the clinical manifestation of ASF, the most relevant transmission routes of the virus for their farms, and preventive measures for ASF. Pigkeepers are aware of their own role in preventing ASF, and there is a high level of trust between them and government authorities. Additional efforts are needed from authorities to communicate better the purpose of some ASF control and eradication measures to the pigkeepers. Further incentives are required to support the implementation of costly biosecurity measures, assure compliance, and mitigate the consequences of these measures.

Exploring the hurdles that remain for control of African swine fever in smallholder farming settings.

To honour the 100 years anniversary of the first publication about African swine fever (ASF) a webinar with a particular focus on disease control in the smallholder sector was organized. This article is based on the webinar, summarizing the early history of ASF research, reflecting on the current global disease situation and bringing forward some suggestions that could contribute towards achieving control of ASF. The first description of ASF by R. Eustace Montgomery in 1921 laid the foundations for what we know about the disease today. Subsequent research confirmed its association with warthogs and soft ticks of the Ornithodoros moubata complex. During the latter half of the 21st century, exponential growth of pig production in Africa has led to a change in the ASF-epidemiology pattern. It is now dominated by a cycle involving domestic pigs and pork with virus spread driven by people. In 2007, a global ASF epidemic started, reaching large parts of Europe, Asia and the Americas. In Europe, this epidemic has primarily affected wild boar. In Asia, wild boar, smallholders and industrialized pig farms have been affected with impact on local, national and international pig value chains. Globally and historically, domestic pigs in smallholder settings are most frequently affected and the main driver of ASF virus transmission. Awaiting a safe and efficacious vaccine, we need to continue focus on other measures, such as biosecurity, for controlling the disease. However, smallholders face specific challenges linked to poverty and other structural factors in implementing biosecurity measures that can prevent spread. Improving biosecurity in the smallholder sector thus remains an important tool for preventing and controlling ASF. In this regard, interdisciplinary research can help to find new ways to promote safe practices, facilitate understanding and embrace smallholders' perspectives, engage stakeholders and adjust prevention and control policies to improve implementation.

Eight Years of African Swine Fever in the Baltic States: Epidemiological Reflections

African swine fever (ASF) was first detected in Lithuania, Latvia, and Estonia in 2014 and has since been circulating in the Baltic States with a similar epidemiological course characterized by persistence of the disease in the wild boar population and occasional spill-over infections in domestic pigs. The aim of the present study was to evaluate surveillance data on ASF in wild boar from the three countries to improve our understanding of the course of the disease. ASF surveillance and wild boar population data of the countries were analyzed. In all three countries, a decrease in the prevalence of ASF virus-positive wild boar was observed over time. Although somewhat delayed, an increase in the seroprevalence was seen. At the same time, the wild boar population density decreased significantly. Towards the end of the study period, the wild boar population recovered, and the prevalence of ASF virus-positive wild boar increased again, whereas the seroprevalence decreased. The decreasing virus prevalence has obviously led to virus circulation at a very low level. Together with the decreasing wild boar population density, the detection of ASF-infected wild boar and thus ASF control has become increasingly difficult. The course of ASF and its continuous spread clearly demonstrate the necessity to scrutinize current ASF surveillance and control strategies fundamentally and to consider new transdisciplinary approaches.

Surveillance and Control of African Swine Fever in the Early Phase of the COVID-19 Pandemic, March-May 2020: A Multi-Country E-Survey

Stringent COVID-19 public health and social measures (PHSMs) have challenged the work of animal health professionals, especially in the early phase of the pandemic. We aimed to qualitatively describe how COVID-19 PHSMs have affected the surveillance and control of African swine fever (ASF) in Europe, assess how professionals engaged in these activities perceived the impact of the COVID-19 crisis, and identify potential areas of improvement. An online questionnaire was proposed via email between 9 December 2020 and 22 January 2021 to professionals engaged in ASF-related activities in Europe and Eastern neighboring countries. The questionnaire contained questions pertaining to ASF surveillance and control activities between March and May 2020, respondent's perception of the impact of COVID-19 PHSMs on these activities, and respondent's opinion on potential improvements to prepare for future crises. Economic and sanitary variables were used to describe the national contexts over the study period. Twenty-seven respondents from 24 countries participated to the study. Essential activities related to surveillance and management of ASF were reduced and/or adapted but maintained in most surveyed countries. Communication was mentioned as the first area of improvement during crisis while maintenance of efficient veterinary services and surveillance activities were cited second and third top priorities. The need for the development of remote procedures was also recognized. Some respondents highlighted difficulties in ensuring biosecurity and biosafety of the field actors due to shortage in protective equipment. Only a small majority (52%) of the survey participants agreed that their institution/working group is better prepared to future lockdown-type situations. Our study emphasizes that short-term measures were globally successful to tackle the immediate impacts of the COVID-19 crisis on the routine duties of professionals involved in ASF surveillance and control. Our findings suggest that country-specific improvements are necessary to support and advance the preparedness of the actors involved in infectious animal disease surveillance and control in case lockdown-like measures are implemented. Overall, our results highlight the crucial importance of recognizing animal health services as essential activities during crisis.