Scientific Opinion on African Swine Fever

Identifying risk clusters for African swine fever in Korea by developing statistical models

Introduction

African swine fever (ASF) is a disease with a high mortality rate and high transmissibility. Identifying high-risk clusters and understanding the transmission characteristics of ASF in advance are essential for preventing its spread in a short period of time. This study investigated the spatial and temporal heterogeneity of ASF in the Republic of Korea by analyzing surveillance data on wild boar carcasses.

Methods

We observed a distinct annual propagation pattern, with the occurrence of ASF-infected carcasses trending southward over time. We developed a rank-based statistical model to evaluate risk by estimating the average weekly number of carcasses per district over time, allowing us to analyze and identify risk clusters of ASF. We conducted an analysis to identify risk clusters for two distinct periods, Late 2022 and Early 2023, utilizing data from ASF-infected carcasses. To address the underestimation of risk and observation error due to incomplete surveillance data, we estimated the number of ASF-infected individuals and accounted for observation error via different surveillance intensities.

Results

As a result, in Late 2022, the risk clusters identified by observed and estimated number of ASF-infected carcasses were almost identical, particularly in the northwestern Gyeongbuk region, north Chungbuk region, and southwestern Gangwon region. In Early 2023, we observed a similar pattern with numerous risk clusters identified in the same regions as in Late 2022.

Discussion

This approach enhances our understanding of ASF spatial dynamics. Additionally, it contributes to the epidemiology and study of animal infectious diseases by highlighting areas requiring urgent and focused intervention. By providing crucial data for the targeted allocation of resources for disease management and preventive measures, our findings lay vital groundwork for improving ASF management strategies, ultimately aiding in the containment and control of this devastating disease.

Identification of predilection sites for wild boar carcass search based on spatial analysis of Latvian ASF surveillance data

Targeted search for wild boar carcasses is essential for successful control of African swine fever (ASF) in wild boar populations. To examine whether landscape conditions influence the probability of finding ASF-positive carcasses, this study analyzed Global Positioning System (GPS) coordinates of Latvian wild boar carcasses and hunted wild boar, extracted from the CSF/ASF wild boar surveillance database of the European Union, and random coordinates in Latvia. Geographic information system (GIS) software was used to determine the landscape type and landscape composition of carcass detection sites and to measure distances from the carcasses to nearest waterbodies, forest edges, roads and settlements. The results of the automated measurements were validated by manually analyzing a smaller sample. Wild boar carcasses were found predominantly in forested areas and closer to waterbodies and forest edges than random GPS coordinates in Latvia. Carcasses of ASF-infected wild boar were found more frequently in transitional zones between forest and woodland shrub, and at greater distances from roads and settlements compared to ASF-negative carcasses and random points. This leads to the hypothesis, that ASF-infected animals seek shelter in quiet areas further away from human disturbance. A detailed collection of information on the environment surrounding carcass detection sites is needed to characterize predilection sites more accurately.

Seasonal Occurrence of African Swine Fever in Wild Boar and Domestic Pigs in EU Member States

Since 2007, African swine fever (ASF) has spread widely within Europe and beyond. Most affected countries recorded outbreaks in domestic pigs and cases in wild boar. Outbreak data from 2014 to 2021 were used to investigate the seasonal pattern of ASF in domestic pigs and wild boar across affected member states of the European Union, since knowledge of seasonal patterns may provide the potential to adapt prevention, surveillance and control during times of increased risk. In domestic pigs, a yearly peak was observed in many European countries in summer (predominantly in July and August). In wild boar, the patterns showed more variability. In many countries, there was a seasonal peak of ASF occurrence in winter (predominantly in January and December), with an additional summer peak in the Baltic States (predominantly in July) and a further spring peak in Poland (predominantly in March). The observed seasonal effects may be related to the abundance and population dynamics of wild boar and to seasonality in pig farming. Moreover, ASF occurrence may also be influenced by human activities in both domestic pigs and wild boar.

Ten Years of African Swine Fever in Ukraine: An Endemic Form of the Disease in the Wild Boar Population as a Threat to Domestic Pig Production

(1) Background: African swine fever (ASF) has been present in Ukraine for more than ten years (2012-2022). The purpose of our study was to perform a retrospective analysis of the spread of ASF to assess the role of wild boar in the epizootic expansion in Ukraine. (2) Methods: Statistical materials were collected and the epizootic situation of ASF from 2012 to 2022 was examined. The potential sources of the African swine fever virus (ASFV) and transmission factors were analysed. The main factors exerting negative impacts on domestic pig production were also analysed. (3) Results: Consequently, from the results of the retrospective analysis of ASF outbreaks in Ukraine, the probability ratio of ASF outbreaks in the wild boar and domestic pig populations was determined. The data show a direct relationship between ASF outbreaks among wild boar and domestic pigs with the observed decay of wild boar outbreaks across the entire territory of Ukraine. At the same time, an increase in the number of wild boars has been observed in the Mykolaiv region, with a parallel spillover of outbreaks in domestic pigs. (4) Conclusions: The epidemiological situation observed for ASF in the wild boar population may suggest an endemic form of the disease. This may further complicate eradication programs and the protection of domestic pig farms from ASF outbreaks. An additional and major reason to control the ASF epizootic is the continuing military Russian offensive in Ukraine.

Temporal and Spatial Evolution of the African Swine Fever Epidemic in Vietnam

African swine fever (ASF) is a severe infectious disease affecting domestic and wild suids. Spatiotemporal dynamics analysis of the ASF is crucial to understanding its transmission. The ASF broke out in Vietnam in February 2019. The research on the spatiotemporal evolution characteristics of ASF in Vietnam is lacking. Spatiotemporal statistical methods, including direction analysis, spatial autocorrelation analysis, and spatiotemporal scan statistics were used to reveal the dynamics of the spatial diffusion direction and spatiotemporal aggregation characteristics of ASF in Vietnam. According to the cessation of the epidemic, it was divided into three phases: February to August 2019 (phase 1), April to December 2020 (phase 2), and January 2021 to March 2022 (phase 3). The ASF showed a significant spread trend from north to south in phase 1. The occurrence rate of the ASF aggregated spatially in phase 1 and became random in phases 2 and 3. The high−high ASF clusters (the province was a high cluster and both it and its neighbors had a high ASF occurrence rate) were concentrated in the north in phases 1 and 2. Four spatiotemporal high-risk ASF clusters were identified with a mean radius of 121.88 km. In general, there were significant concentrated outbreak areas and directional spread in the early stage and small-scale, high-frequency, and randomly scattered outbreaks in the later stage. The findings could contribute to a deeper understanding of the spatiotemporal spread of the ASF in Vietnam.

The Evolution of African Swine Fever in China: A Global Threat?

African swine fever (ASF) is one of the most critical diseases in the pig industry. In Asia, 15 countries have already reported an outbreak as of November 22, 2021. In 2021, China reported the genotype II lower virulent ASF virus (ASFV) and the emergence of genotype I ASFV. ASF is generally known as a contagious and lethal disease, but if chronic infection spreads, then disease control would be more difficult. In the current study, we highlighted the possibility of lower virulent virus distribution throughout China and the subsequent general risk of the virus being released from the country. The kernel density estimation showed that the two highest kernel density areas of ASF notification were located in Northeast and Midwest China. Four of the five provinces where lower virulent ASFV was isolated overlapped with areas of relatively high ASF notification density. In terms of the risk of ASFV spreading from China, eight of the 10 largest airports and three of the 10 largest seaports are located in areas of relatively high ASF notification density. There were flight flow from China to 67 countries and ship flow to 81 countries. Asia had the highest flight flow, followed by Europe, North America, Africa, and Oceania. The highest number of ship flows was also concentrated in Asia, but about 10% of ships head to Africa and South America. Chinese overseas residents were distributed in each continent in proportion to these results. Here, we highlight the potential risk of ASFV spread from China to the world.

Evaluation of a Lateral Flow Assay for Rapid Detection of African Swine Fever Virus in Multiple Sample Types

Antibody-based lateral flow assay (LFA) is a quick and inexpensive tool used to detect pathogens in field samples, especially in hard-to-reach remote areas that may have limited access to central laboratories during an outbreak or surveillance. In this study, we investigated the ability of a commercially available LFA, PenCheck^®, to detect African swine fever virus (ASFV) in clinical samples derived from pigs infected with highly virulent ASFV strains. The assay was specific and positively identified the majority of pigs showing high fever during the early stages (between 3 and 5 days) of infection. PenCheck^® LFA also detected ASFV in serum and tissue samples collected from pigs that succumbed to experimental ASFV infection and whole blood, plasma, and tissue samples from the field. The limit of detection of the assay was ASFV titer 10^7.80 TCID₅₀/mL, corresponding to ASFV real-time PCR values below 23 Ct. Although the sensitivity of the assay is less than that of the laboratory-based real-time PCR assays, the results obtained with the PenCheck^® LFA in this study suggest that it can be used as a herd-level, field-deployable, and easy-to-use diagnostic tool to identify ASF-affected farms when access to portable molecular assays or central laboratories is not possible.

Supporting control programs on African swine fever in Ukraine through a knowledge, attitudes, and practices survey targeting backyard farmers

A Knowledge, Attitudes, and Practices (KAP) questionnaire was designed to collect information on farmers' knowledge of ASF and their practices surrounding that could impact the spread of the disease. The questionnaire was distributed, and data collected, from 233 backyard farmers from five selected Oblasts (Rivne, Kharkiv, Odessa, Zakarpattia and Kiev). Kruskal-Wallis tests were conducted to identify factors that could influence knowledge, and Dunn tests were performed to determine differences between groups when the Kruskal-Wallis tests were significant. Spearman tests were carried out to explore the association between knowledge and risky practices. Results show that comprehensive knowledge on ASF is not common in backyard farmers and that risky practices that influence the spread of ASF are regularly performed. Of the respondents, 47% felt well-informed about how ASF can be transmitted and 31.8% felt confident about recognizing clinical signs of ASF. The independent variable "Oblast" was identified as a significant factor (p = 0.0015) associated with differences in knowledge on clinical signs. We demonstrated statistically significant differences of knowledge between backyard farmers from different Oblasts. Knowledge of preventive measures was positively correlated with risky handling practices related to edible pork products (p = 0.0053) and non-edible pork products (p = 0.0417). In conclusion, our results show that backyard farmers have knowledge gaps on ASF and practice various risky behaviours that might favour the spread of the disease in Ukraine. There are regional differences in ASF knowledge and risky practices that should be taken into consideration in future evidence-based ASF prevention and control programs, including public awareness activities.

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.

Research priorities to fill knowledge gaps in the control of African swine fever: possible transmission of African swine fever virus by vectors

The European Commission requested that EFSA provide study designs for the investigation of four research domains according to major gaps in knowledge identified by EFSA in a report published in 2019: (i) the patterns of seasonality of African Swine Fever (ASF) in wild boar and domestic pigs in the EU; (ii) the epidemiology of ASF in wild boar; (iii) survival of ASF virus (ASFV) in the environment and (iv) transmission of ASFV by vectors. In this Scientific Opinion, the fourth research domain on ASFV transmission by vectors is addressed. Eleven research objectives were proposed by the EFSA working group and broader ASF expert networks, such as ASF stop, ENETWILD, VectorNet, AHAW network and the AHAW Panel Experts. Of the 11 research objectives, six were prioritised based on the following set of criteria: (1) the impact on ASF management; (2) the feasibility or practicality to carry out the study; (3) the potential implementation of study results in practice; (4) a possible short time-frame study (< 1 year); (5) the novelty of the study and (6) if it was a priority for risk managers. The prioritised research objectives were: (I) Studies on the potential vector fauna at the pig-wild boar interface and the feeding preference of blood-feeding potential vectors in ASF-affected areas; (II) Assessment of the efficacy of insect screens on indoor/outdoor pig holdings to prevent the entry of blood-sucking vectors (i.e. Stomoxys) in ASF endemic areas; (III) Assess the role of mechanical vectors in the virus transmission in ASF-affected areas; (IV) Distribution of the potential mechanical transmission vectors in ASF-affected areas of the EU; (V) ASFV transmission by synanthropic birds; and (VI) Assessment on the presence/absence of the soft tick Ornithodoros erraticus in ASF-affected areas in Europe. For each of the selected research objectives, a research protocol has been proposed considering the potential impact on ASF management and the period of 1 year for the research activities.

ASF Exit Strategy: Providing cumulative evidence of the absence of African swine fever virus circulation in wild boar populations using standard surveillance measures

EFSA assessed the role of seropositive wild boar in African swine fever (ASF) persistence. Surveillance data from Estonia and Latvia investigated with a generalised equation method demonstrated a significantly slower decline in seroprevalence in adult animals compared with subadults. The seroprevalence in adults, taking more than 24 months to approach zero after the last detection of ASFV circulation, would be a poor indicator to demonstrate the absence of virus circulation. A narrative literature review updated the knowledge on the mortality rate, the duration of protective immunity and maternal antibodies and transmission parameters. In addition, parameters potentially leading to prolonged virus circulation (persistence) in wild boar populations were reviewed. A stochastic explicit model was used to evaluate the dynamics of virus prevalence, seroprevalence and the number of carcasses attributed to ASF. Secondly, the impact of four scenarios on the duration of ASF virus (ASFV) persistence was evaluated with the model, namely a: (1) prolonged, lifelong infectious period, (2) reduction in the case-fatality rate and prolonged transient infectiousness; (3) change in duration of protective immunity and (4) change in the duration of protection from maternal antibodies. Only the lifelong infectious period scenario had an important prolonging effect on the persistence of ASF. Finally, the model tested the performance of different proposed surveillance strategies to provide evidence of the absence of virus circulation (Exit Strategy). A two-phase approach (Screening Phase, Confirmation Phase) was suggested for the Exit Strategy. The accuracy of the Exit Strategy increases with increasing numbers of carcasses collected and tested. The inclusion of active surveillance based on hunting has limited impact on the performance of the Exit Strategy compared with lengthening of the monitoring period. This performance improvement should be reasonably balanced against an unnecessary prolonged 'time free' with only a marginal gain in performance. Recommendations are provided for minimum monitoring periods leading to minimal failure rates of the Exit Strategy. The proposed Exit Strategy would fail with the presence of lifelong infectious wild boar. That said, it should be emphasised that the existence of such animals is speculative, based on current knowledge.

What Do Lithuanian Hunters Think of African Swine Fever and Its Control-Perceptions

Simple Summary

Effectiveness and successful implementation of control measures greatly depend on hunters’ willingness and motivation to carry out these measures. Therefore, assessing their opinions regarding the current system is paramount in order to achieve the best possible results. The present study provides insights of hunters’ attitudes and perceptions about measures to control African swine fever (ASF) in wild boar in Lithuania. This study highlights several measures that are not supported by hunters (i.e., restriction of hunting, selective female hunting, ban of supplementary feeding, involvement of additional forces in ASF control) and possible motivational options (i.e., reduction of work, financial incentives and improved feedback and relationships with government officials). Considering these findings when planning and altering control measures for ASF could improve their successful implementation in the field.

Abstract

After the introduction of African swine fever (ASF) into Lithuania in 2014, continuous spread of the disease resulted in infection of the wild boar populations in most parts of Lithuania. The virus has been moving closer to other Western European countries where pig density is high. An efficient surveillance system detecting ASF cases early in domestic and wild animals is necessary to manage this disease. To make surveillance appropriate and effective, it is critical to understand how key players perceive the implemented control measures. This study investigated the attitudes and beliefs of hunters in Lithuania regarding currently implemented or proposed measures for the control of ASF in the wild boar population. Study data were collected through questionnaires distributed via the internet and by hunting associations in Lithuania. In total, 621 fully completed questionnaires were received and analyzed. All measures interfering with extensive hunting, like ban of driven or individual hunting or ban of supplementary feeding were considered as unacceptable and as ineffective measures to control ASF in wild boar. However, selective hunting of female wild boar was generally considered as an unethical act and therefore rejected. Some measures that seem to have been successful in other countries, like involvement of additional forces, were rejected by Lithuanian hunters, thus implementation of these measures could be difficult. The study highlighted that there is a need for improving important relationships with other stakeholders, since many hunters expressed a lack of trust in governmental institutions and regarded cooperation with them as insufficient. Hunters emphasized that their motivation to support passive surveillance measures could be improved with financial compensation and reduction of workload. The present study provides insights into hunters’ perceptions, which may be used as a foundation for additional discussions with these important stakeholders and for adapting measures to improve their acceptance if appropriate.

A Review of Risk Factors of African Swine Fever Incursion in Pig Farming within the European Union Scenario

African swine fever (ASF) is a notifiable viral disease of pigs and wild boars that could lead to serious economic losses for the entire European pork industry. As no effective treatment or vaccination is available, disease prevention and control rely on strictly enforced biosecurity measures tailored to the specific risk factors of ASF introduction within domestic pig populations. Here, we present a review addressing the risk factors associated with different European pig farming systems in the context of the actual epidemiological scenario. A list of keywords was combined into a Boolean query, “African swine fever” AND (“Risk factors” OR “Transmission” OR “Spread” OR “Pig farming” OR “Pigs” OR “Wild boars”); was run on 4 databases; and resulted in 52 documents of interest being reviewed. Based on our review, each farming system has its own peculiar risk factors: commercial farms, where best practices are already in place, may suffer from unintentional breaches in biosecurity, while backyard and outdoor farms may suffer from poor ASF awareness, sociocultural factors, and contact with wild boars. In the literature selected for our review, human-related activities and behaviours are presented as the main risks, but we also stress the need to implement biosecurity measures also tailored to risks factors that are specific for the different pig farming practices in the European Union (EU).

Quantitative Understanding of the Decision-Making Process for Farm Biosecurity Among Japanese Livestock Farmers Using the KAP-Capacity Framework

In a globalized world, the frequency of transboundary livestock infectious diseases is increasing, and strengthening of farm biosecurity is vital to stabilize food production. The aim of this study was to understand the decision-making process for farm biosecurity among Japanese livestock farmers. Postal surveys using structured questionnaires were conducted on beef, dairy, pig, and layer farms in Hokkaido and Saitama Prefectures, which represent the principal production area and peri-urban Tokyo, respectively, as well as randomly selected broiler farms across Japan. The question items included the attributes of farms and owners, disease experiences, related associations and sources of hygiene information, attitude toward hygiene management, and compliance with the Standards of Rearing Hygiene Management (SRHM). The compliance rates were compared between livestock sectors. Univariable analyses were conducted using combined data from both prefectures, with the compliance rate as the outcome variable and the questionnaire items as explanatory variables, in generalized linear models. Exploratory factor analyses were conducted using the variables with p < 0.2 in the univariable analyses. The factors identified were classified into knowledge, attitude, capacity, practice, and structural equation modeling (SEM) was performed. The questionnaires were completed and returned by 97 and 66 beef cattle, 86 and 136 dairy, 67 and 45 pig, 20 and 39 layer farmers in Hokkaido and Saitama Prefectures, respectively, and 95 broiler farms. The compliance rate was significantly higher among broiler farms (88.9%) compared with the other sectors, followed by pig (77.1%), layer (67.2%), dairy (63.8%), and beef (59.1%) farms in Hokkaido Prefecture, and layer (64.9%), pig (60.0%), dairy (58.5%), and beef (57.6%) farms in Saitama Prefecture. Based on SEM, the decision-making process from greater knowledge to higher attitude, and from higher attitude to greater compliance with the SRHM were significant (p < 0.01) in all sectors. Higher capacity was significantly associated with higher knowledge in dairy, pig,break and layer farms (p < 0.01), and with higher compliance in beef, pig, and layer farms (p < 0.05). These results suggest that the provision of targeted hygiene knowledge to livestock farmers and the support to smallholder farms would improve biosecurity through elevated attitudes and self-efficacy.

African swine fever virus survival in buried wild boar carcasses

Since the first introduction of African swine fever (ASF) into the European wild boar population in 1957, the question of virus survival in carcasses of animals that succumbed to the disease has been discussed. The causative African swine fever virus (ASFV) is known to be very stable in the environment. Thus, carcasses of infected wild boar could play a major role as ASFV reservoir and thereby help to locally maintain and spread the disease in wild boar populations. To minimize this risk, removal of wild boar carcasses in ASF affected areas is regarded to be crucial for effective disease control. If removal is not feasible, carcasses are usually disposed by burial on the spot to avoid direct contact of wild boar to the infection source. In this study, carcasses of ASFV infected wild boar buried in Lithuania at different time points and locations have been excavated and retested for the presence of infectious ASFV by in vitro assays and for viral genome by qPCR. Soil samples potentially contaminated by body fluids have been additionally tested for viral genome. In seventeen out of twenty burial sites, samples of excavated carcasses were positive for ASFV genome. However, in none of the carcass samples ASFV could be isolated. On seven sites soil samples contained ASF viral DNA. These results unexpectedly negate the long-term persistence of infectious ASFV in wild boar carcasses independent from the burial time. In this context, sensitivity of ASFV isolation from carcass samples versus susceptibility of animals and doses needed for oral inoculation has to be further investigated. Furthermore, research is required to consider alternative ASF infection sources and drivers in the infection cycle among wild boar.

The Risk of Infection by African Swine Fever Virus in European Swine Through Boar Movement and Legal Trade of Pigs and Pig Meat

African swine fever (ASF) is currently spreading westwards throughout Europe and eastwards into China, with cases occurring in both wild boar and domestic pigs. A generic risk assessment framework is used to determine the probability of first infection with ASF virus (ASFV) at a fine spatial scale across European Union Member States. The framework aims to assist risk managers across Europe with their ASF surveillance and intervention activities. Performing the risk assessment at a fine spatial scale allows for hot-spot surveillance, which can aid risk managers by directing surveillance or intervention resources at those areas or pathways deemed most at risk, and hence enables prioritization of limited resources. We use 2018 cases of ASF to estimate prevalence of the disease in both wild boar and pig populations and compute the risk of initial infection for 2019 at a 100 km2 cell resolution via three potential pathways: legal trade in live pigs, natural movement of wild boar, and legal trade in pig meat products. We consider the number of pigs, boar and amount of pig meat entering our area of interest, the prevalence of the disease in the origin country, the probability of exposure of susceptible pigs or boar in the area of interest to introduced infected pigs, boar, or meat from an infected pig, and the probability of transmission to susceptible animals. We provide maps across Europe indicating regions at highest risk of initial infection. Results indicate that the risk of ASF in 2019 was predominantly focused on those regions which already had numerous cases in 2018 (Poland, Lithuania, Hungary, Romania, and Latvia). The riskiest pathway for ASFV transmission to pigs was the movement of wild boar for Eastern European countries and legal trade of pigs for Western European countries. New infections are more likely to occur in wild boar rather than pigs, for both the pig meat and wild boar movement pathways. Our results provide an opportunity to focus surveillance activities and thus increase our ability to detect ASF introductions earlier, a necessary requirement if we are to successfully control the spread of this devastating disease for the pig industry.

[African swine fever]

African swine fever (ASF) is a hemorrhagic infectious disease of Suids, which is endemic in sub-Saharan area of African continent. ASF is usually circulating sub-symptomatically among wild species of Suidae family, such as warthogs and bush pigs, by mediating Ornithodoros soft ticks. Domestic pigs (Sus scrofa) are, however, highly sensitive to the infection and show severe clinical signs with a high mortality rate, resulting a huge impact on pork production. Currently, there is no treatment or vaccine available. The etiological agent, ASFV, is highly resistant to environmental conditions, and resides in unheated pork meat or pork meat products for a long period, which may be a chance of its long-distance spread. Since August 2018, ASFV has been circulating in East and Southeast Asian countries and may possibly be introduced into Japan. Here, I describe the outline of the disease and the etiology of the pathogen in order to remind the importance of "awareness" and "preparedness" for the disease.

Epidemiological considerations on African swine fever in Europe 2014-2018

In 2007 African swine fever (ASF) arrived at a Black Sea harbour in Georgia and in 2014 the infection reached the European Union (EU), where it still expands its territory. ASF is a fatal viral disease affecting domestic pigs and wild boar of all ages with clinical presentations ranging from per-acute to chronic disease, including apparently asymptomatic courses. Until the detection of the first case inside the EU, infections in the current epidemic were mainly seen among pig farms with generally low biosecurity, and with incidental spill over to the wild boar population. In the EU, however, the infection survived locally in the wild boar population independently from outbreaks in domestic pigs, with a steady and low prevalence. Apart from the wild boar population and the habitat, the current epidemic recognizes humans as the main responsible for both long distance transmission and virus introduction in the domestic pig farms. This underlines the importance to include social science when planning ASF-prevention, -control, or -eradication measures. Based on experiences, knowledge and data gained from the current epidemic this review highlights some recent developments in the epidemiological understanding of ASF, especially concerning the role of wild boar and their habitats in ASF epidemiology. In this regard, the qualities of three epidemiological traits: contagiousity, tenacity, and case fatality rate, and their impact on ASF persistence and transmission are especially discussed.

A rapid risk assessment of African swine fever introduction and spread in Japan based on expert opinions

A rapid risk assessment was conducted using a questionnaire composed of 10 questions asking experts in African swine fever (ASF) to identify and rank the potential risk factors associated with the introduction and spread of ASF in Japan. The experts participating in this risk assessment considered illegal food import, followed by transport routes and foreign workers, to be the most relevant pathway of ASF introduction into Japan. Kanto and Kyushu were identified as the most likely regions for ASF introduction. All experts agreed that China is the most likely source of ASF introduction into Japan. Most Japanese experts were of the view that the risk of ASF spread if introduced into Japan would be low, while foreign experts considered the risk to be moderate or high. Most experts answered that wild boars would play an important role in the persistence of ASF if the disease were to spread in Japan.

Relevant Measures to Prevent the Spread of African Swine Fever in the European Union Domestic Pig Sector

During the past decade, African swine fever (ASF) has spread from the Caucasus region to eastern European Union countries affecting domestic pig and wild boar populations. In order to avert ASF spread, mitigation measures targeting both populations have been established. However, despite these efforts, ASF has been reported in thirteen different countries (Georgia, Azerbaijan, Armenia, the Russian Federation, Ukraine, Belarus, Estonia, Latvia, Lithuania, Poland, Moldova, Czech Republic, and Romania). In the absence of an effective vaccine or treatment to ASF, introduction and spread of ASF onto domestic pig farms can only be prevented by strict compliance to control measures. This study systematically reviewed available measures to prevent the spread of ASF in the EU domestic pig sector distinguishing between commercial, non-commercial, and outdoor farms. The search was performed in PubMed and using a common browser. A total of 52 documents were selected for the final review process, which included scientific articles, reports, EU documents and official recommendations, among others. From this literature review, 37 measures were identified as preventive measures for the introduction and spread of ASF. Subsequently, these measures were assessed by ASF experts for their relevance in the mitigation of ASF spread on the three mentioned types of farms. All experts agreed that some of the important preventive measures for all three types of farms were: the identification of animals and farm records; strict enforcement of the ban on swill feeding; and containment of pigs, so as to not allow direct or indirect pig–pig and/or pig–wild boar contacts. Other important preventive measures for all farms were education of farmers, workers, and operators; no contact between farmers and farm staff and external pigs; appropriate removal of carcasses, slaughter residues, and food waste; proper disposal of manure and dead animals, and abstaining from hunting activities during the previous 48 h (allowing a 48 h interval between hunting and being in contact with domestic pigs). Finally, all experts identified that the important preventive measures for non-commercial and outdoor farms is to improve access of those farms to veterinarians and health services.

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

African swine fever (ASF) is caused by African swine fever virus (ASFV), which can cause substantial morbidity and mortality events in swine. The virus can be transmitted via direct and indirect contacts with infected swine, their products, or competent vector species, especially Ornithodoros ticks. Africa and much of Eastern Europe are endemic for ASF; a viral introduction to countries that are currently ASF free could have severe economic consequences due to the loss of production from infected animals and the trade restrictions that would likely be imposed as a result of an outbreak. We identified vulnerabilities that could lead to ASFV introduction or persistence in the United States or other ASF-free regions. Both legal and illegal movements of live animals, as well as the importation of animal products, byproducts, and animal feed, pose a risk of virus introduction. Each route is described, and current regulations designed to prevent ASFV and other pathogens from entering the United States are outlined. Furthermore, existing ASFV research gaps are highlighted. Laboratory experiments to evaluate multiple species of Ornithodoros ticks that have yet to be characterized would be useful to understand vector competence, host preferences, and distribution of competent soft tick vectors in relation to high pig production areas as well as regions with high feral swine (wild boar or similar) densities. Knowledge relative to antigenic viral proteins that contribute to host response and determination of immune mechanisms that lead to protection are foundational in the quest for a vaccine. Finally, sampling of illegally imported and confiscated wild suid products for ASFV could shed light on the types of products being imported and provide a more informed perspective relative to the risk of ASFV importation.

Behaviour of free ranging wild boar towards their dead fellows: potential implications for the transmission of African swine fever

The behaviour of free ranging wild boar (Sus scrofa) towards carcasses of their conspecifics potentially infected with African swine fever (ASF) may significantly influence the course of an ASF epidemic. This study aims to better understand the behaviour of wild boar towards their dead fellows. Thirty-two wild boar carcasses on nine study sites in northeast Germany were monitored under field conditions by photo-trapping from October 2015 until October 2016. During this period, a total of 122 160 pictures were taken, thereof 16 111 pictures of wild boar. In both winter and summer, wild boar seemed to be particularly interested in the soil next to and underneath the carcasses. About one third of the visits of wild boar led to direct contact with dead conspecifics. The contacts consisted mostly in sniffing and poking on the carcass. Under the given ecological and climatic conditions, there was no evidence for intra-species scavenging. However, piglets were observed several times chewing bare bones once skeletonization of the carcasses was complete. It must be assumed that all these types of contact may represent a risk of transmission. Both the high tenacity of ASF virus and the long time wild boar carcasses can remain in the environment, allow the persistence of the virus for several months or even years. We therefore consider the rapid detection and removal (or destruction on the spot) of contaminated carcasses as an important control measure against ASF in wild boar.

Update on the Risk of Introduction of African Swine Fever by Wild Boar into Disease-Free European Union Countries

Despite efforts to prevent the appearance and spread of African swine fever (ASF) in the European Union, several Member States are now affected (Lithuania, Poland, Latvia and Estonia). Disease appearance in 2014 was associated with multiple entrances linked to wild boar movement from endemic areas (EFSA Journal, 8, 2015, 1556), but the risk of new introductions remains high (Gallardo et al., Porcine Health Management, 1, and 21) as ASF continues to be active in endemic countries (Russian Federation, Belarus and Ukraine). Since 2014, the number of ASF notifications has increased substantially, particularly in wild boar (WB), in parallel with slow but constant geographical advance of the disease. This situation suggests a real risk of further disease spread into other Member States, posing a great threat to pig production in the EU. Following the principles of the risk-based veterinary surveillance, this article applies a methodology developed by De la Torre et al. (Transboundary and Emerging Diseases, 62, and 272) to assess the relative risk of new introductions of ASF by natural movements of WB according to the current epidemiological situation. This update incorporates the most recent available data and an improved version of the most important risk estimator: an optimized cartographic tool of WB distribution to analyse wild boar suitable habitat. The highest relative risk values were estimated for Slovakia (5) and Romania (5), followed by Finland (4), Czech Republic (3) and Germany (3). Relative risk for Romania and Finland is associated mainly with disease entrance from endemic areas such as the Russian Federation and Ukraine, where the disease is currently spreading; relative risk for Germany and Czech Republic is associated mainly with the potential progress of the disease through the EU, and relative risk for Slovakia is associated with both pathways. WB habitat is the most important risk estimator, whereas WB density is the least significant, suggesting that WB presence is more relevant than density. These results can provide actionable advice for dealing with risk. They can be directly used to inform risk-based national strategies and identify countries that may need to pay greater attention to surveillance or conduct additional evaluations at the subnational level.

African swine fever virus transmission cycles in Central Europe: Evaluation of wild boar-soft tick contacts through detection of antibodies against Ornithodoros erraticus saliva antigen

BACKGROUND

African swine fever (ASF) is one of the most complex viral diseases affecting both domestic and wild pigs. It is caused by ASF virus (ASFV), the only DNA virus which can be efficiently transmitted by an arthropod vector, soft ticks of the genus Ornithodoros. These ticks can be part of ASFV-transmission cycles, and in Europe, O. erraticus was shown to be responsible for long-term maintenance of ASFV in Spain and Portugal. In 2014, the disease has been reintroduced into the European Union, affecting domestic pigs and, importantly, also the Eurasian wild boar population. In a first attempt to assess the risk of a tick-wild boar transmission cycle in Central Europe that would further complicate eradication of the disease, over 700 pre-existing serum samples from wild boar hunted in four representative German Federal States were investigated for the presence of antibodies directed against salivary antigen of Ornithodoros erraticus ticks using an indirect ELISA format.

RESULTS

Out of these samples, 16 reacted with moderate to high optical densities that could be indicative of tick bites in sampled wild boar. However, these samples did not show a spatial clustering (they were collected from distant geographical regions) and were of bad quality (hemolysis/impurities). Furthermore, all positive samples came from areas with suboptimal climate for soft ticks. For this reason, false positive reactions are likely.

CONCLUSION

In conclusion, the study did not provide stringent evidence for soft tick-wild boar contact in the investigated German Federal States and thus, a relevant involvement in the epidemiology of ASF in German wild boar is unlikely. This fact would facilitate the eradication of ASF in the area, although other complex relations (wild boar biology and interactions with domestic pigs) need to be considered.

African swine fever: a global view of the current challenge

African Swine Fever (ASF) is an important contagious haemorrhagic viral disease affecting swine whose notification is mandatory due to its high mortality rates and the great sanitary and socioeconomic impact it has on international trade in animal and swine products.

This disease only affects porcine species, both wild and domestic, and produces a variety of clinical signs such as fever and functional disorders of the digestive and respiratory systems. Lesions are mainly characterized by congestive-haemorrhagic alterations. ASF epidemiology varies significantly between countries, regions and continents, since it depends on the characteristics of the virus in circulation, the presence of wild hosts and reservoirs, environmental conditions and human social behaviour. Furthermore, a specific host will not necessarily always play the same active role in the spread and maintenance of ASF in a particular area.

Currently, ASF is endemic in most sub-Saharan African countries where wild hosts and tick vectors (Ornithodoros) play an important role acting as biological reservoirs for the virus. In Europe, the disease has been endemic since 1978 on the island of Sardinia (Italy) and since 2007, when it was first reported in Georgia, in a number of Eastern European countries. It is also endemic in certain regions of the Russia Federation, where domestic pig and wild boar populations are widely affected. By contrast, in the affected eastern European Union (EU) countries where ASF is currently as epidemic, the on-going spread of the disease affects mainly wild boar populations located in restricted areas and, to a much less extent, domestic pigs. Unlike most livestock diseases, no vaccine or specific treatment is currently available for ASF. Therefore, disease control is mainly based on early detection and the application of strict sanitary and biosecurity measures. Epidemiology of ASF is very complex by the existence of different virus circulating, reservoirs and a number of scenarios, and the on-going spread of the disease through Africa and Europe. Survivor pigs can remain persistently infected for months which may contribute to virus transmission and thus the spread and maintenance of the disease, thereby complicating attempts to control it.

Experimental Infection of Ornithodoros erraticus sensu stricto with Two Portuguese African Swine Fever Virus Strains. Study of Factors Involved in the Dynamics of Infection in Ticks

African swine fever (ASF) is a frequently devastating hemorrhagic disease of domestic pigs and wild boar and Ornithodoros erraticus sensu stricto argasid ticks are the only biological vectors of African swine fever virus (ASFV) known to occur in Europe. Recently this disease emerged in Eastern Europe and Russian Federation, showing a huge potential for a rapid spread between countries. There is some risk of re-emergence of ASF in the countries where these ticks exist, that can contribute for the persistence of infection and compromise control measures. In this study we aimed to identify factors that determine the probability of infection and its dynamics in the tick vector Ornithodoros erraticus sensu stricto, with two Portuguese strains of ASFV. Our results suggest that these ticks have a high likelihood of excreting the two haemadsorbing ASF viruses of different host origins and that, in field surveys, the analysis of adults and 5th nymphal stage can provide the best chance of detecting virus infection. The results also indicate that infection of pigs with highly virulent ASF viruses will promote higher rates of infection and a higher likelihood for virus excretion by ticks. Nevertheless, there is also a risk, although lower, that ticks can become infected on pigs that have overcome the acute phase of infection, which was simulated in our study by membrane feeding ticks with low titres of virus. We believe these results can be valuable in designing and interpreting the results of ASF control programmes, and future work can also be undertaken as our dataset is released under open access, to perform studies in risk assessment for ASFV persistence in a region where O. erraticus sensu stricto ticks are present.

The Assessment of African Swine Fever Virus Risk to Belgium Early 2014, using the Quick and Semiquantitative Pandora Screening Protocol

A risk assessment was organized during the early EU ASF outbreaks of early 2014 (February-April) and performed in cooperation with 15 Belgian and European experts on ASFV and its epidemiology in pigs/wild boar. African swine fever (ASF) is considered as one of the most dangerous infectious pig diseases, causing many outbreaks. Since the end of 2013 - early 2014, several outbreaks within the European Union (Lithuania, Poland, Estonia and Latvia) were reported to OIE, which prompted several risk assessments by (inter)national bodies and scientists. In this study, the open source, semiquantitative Pandora risk assessment tool was used for a quick overall screening of the risk posed by ASF to Belgium early 2014. A set of integrated risk scores was calculated within the Pandora framework. Experts scored the questions and uncertainty levels in the Pandora modules individually, after which the calculations were performed and averaged scores were used within pre-defined risk scales to define and visualize the ASF risk to Belgium. Emergence risk was considered low (Pandora score 0.29), while disease consequences were deemed high (0.93); the resulting multiplicative overall risk of ASFV for Belgium was low (0.27). The Belgian experts tended to give lower risk scores than the European experts, especially for entry risk and trade/public opinion consequences. These risk scores are further interpreted with a due consideration of the qualitative data in the expert remarks and of other ASF risk assessments. The results are similar to more extensive and elaborate risk assessment models/procedures which may require more time and resources. The Pandora tool allows sequential updates to monitor (rates of) increasing risk and provides information for risk managers to organize targeted control.

Development of vaccines against Ornithodoros soft ticks: An update

Ticks are parasites of great medical and veterinary importance since they are vectors of numerous pathogens that affect humans, livestock and pets. Among the argasids, several species of the genus Ornithodoros transmit serious diseases such as tick-borne human relapsing fever (TBRF) and African Swine Fever (ASF). In particular, Ornithodoros erraticus is the main vector of these two diseases in the Mediterranean while O. moubata is the main vector in Africa. The presence of these Ornithodoros ticks in domestic and peridomestic environments may greatly hinder the eradication of TBRF and ASF from endemic areas. In addition, there is a constant threat of reintroduction and spreading of ASF into countries from where it has been eradicated (Spain and Portugal) or where it was never present (the Caucasus, Russia and Eastern Europe). In these countries, the presence of Ornithodoros vectors could have a tremendous impact on ASF transmission and long-term maintenance. Therefore, elimination of these ticks from at least synanthropic environments would contribute heavily to the prevention and control of the diseases they transmit. Tick control is a difficult task and although several methods for such control have been used, none of them has been fully effective against all ticks and the problems they cause. Nevertheless, immunological control using anti-tick vaccines offers an attractive alternative to the traditional use of acaricides. The aim of the present paper is to offer a brief overview of the current status in control measure development for Ornithodoros soft ticks, paying special attention to the development of vaccines against O. erraticus and O. moubata. Thus, our contribution includes an analysis of the chief attributes that the ideal antigens for an anti-tick vaccine should have, an exhaustive compilation and analysis of the scant anti-soft tick vaccine trials carried out to date using both concealed and salivary antigens and, finally, a brief description of the new reverse vaccinology approaches currently used to identify new and more effective protective tick antigens.

Dynamics of African swine fever virus shedding and excretion in domestic pigs infected by intramuscular inoculation and contact transmission

African swine fever virus (ASFV) is a highly virulent swine pathogen that has spread across Eastern Europe since 2007 and for which there is no effective vaccine or treatment available. The dynamics of shedding and excretion is not well known for this currently circulating ASFV strain. Therefore, susceptible pigs were exposed to pigs intramuscularly infected with the Georgia 2007/1 ASFV strain to measure those dynamics through within- and between-pen transmission scenarios. Blood, oral, nasal and rectal fluid samples were tested for the presence of ASFV by virus titration (VT) and quantitative real-time polymerase chain reaction (qPCR). Serum was tested for the presence of ASFV-specific antibodies. Both intramuscular inoculation and contact transmission resulted in development of acute disease in all pigs although the experiments indicated that the pathogenesis of the disease might be different, depending on the route of infection. Infectious ASFV was first isolated in blood among the inoculated pigs by day 3, and then chronologically among the direct and indirect contact pigs, by day 10 and 13, respectively. Close to the onset of clinical signs, higher ASFV titres were found in blood compared with nasal and rectal fluid samples among all pigs. No infectious ASFV was isolated in oral fluid samples although ASFV genome copies were detected. Only one animal developed antibodies starting after 12 days post-inoculation. The results provide quantitative data on shedding and excretion of the Georgia 2007/1 ASFV strain among domestic pigs and suggest a limited potential of this isolate to cause persistent infection.

Assessing the Risk of African Swine Fever Introduction into the European Union by Wild Boar

The presence of African swine fever (ASF) in the Caucasus region and Russian Federation has increased concerns that wild boars may introduce the ASF virus into the European Union (EU). This study describes a semi-quantitative approach for evaluating the risk of ASF introduction into the EU by wild boar movements based on the following risk estimators: the susceptible population of (1) wild boars and (2) domestic pigs in the country of origin; the outbreak density in (3) wild boars and (4) domestic pigs in the countries of origin, the (5) suitable habitat for wild boars along the EU border; and the distance between the EU border and the nearest ASF outbreak in (6) wild boars or (7) domestic pigs. Sensitivity analysis was performed to identify the most influential risk estimators. The highest risk was found to be concentrated in Finland, Romania, Latvia and Poland, and wild boar habitat and outbreak density were the two most important risk estimators. Animal health authorities in at-risk countries should be aware of these risk estimators and should communicate closely with wild boar hunters and pig farmers to rapidly detect and control ASF.

African swine fever (ASF): five years around Europe

Since African swine fever (ASF) was re-introduced into Eastern Europe in April 2007, the disease has spread through five countries, drastically changing the European ASF situation. This re-introduction has significant implications for the affected countries, and it puts the European Union (EU) at serious risk of ASF introduction. Numerous factors are complicating the control of ASF in the Russian Federation and neighboring areas, particularly the absence of a coordinated control program, the abundance of backyard pig units with low or no biosecurity and the traditional use of swill feeding. All these risk factors are driven in turn by socio-economic, political and cultural factors. Moreover, the lack of clear information regarding the current situation of ASF in the Trans-Caucasus countries such as Armenia and Georgia may be increasing the risk of ASF spread into neighboring areas. The ASF situation in Eastern Europe poses a constant risk of ASF entry into the EU, especially via routes that are difficult to control, such as wild boar movements, illegal movement of animals and animal products and movements of contaminated vehicles or other fomites. This paper reviews and discusses current ASF epidemiology in Eastern Europe, the factors that may contribute to disease endemicity in the area, the current challenges for disease control, and the risk of introduction into the EU.

African swine fever: an epidemiological update

African swine fever (ASF) is one of the most important swine diseases, mainly because of its significant sanitary and socioeconomic consequences. This review gives an update on the epidemiology of the disease and reviews key issues and strategies to improve control of the disease and promote its eradication. Several characteristics of ASF virus (ASFV) make its control and eradication difficult, including the absence of available vaccines, marked virus resistance in infected material and contaminated animal products, and a complex epidemiology and transmission involving tick reservoir virus interactions. The incidence of ASF has not only increased on the African continent over the last 15 years, so that it now affects West African countries, Mauritius and Madagascar, but it has also reached new areas, such as the Caucasus region in 2007. In fact, the rapid spread of the disease on the European continent and the uncontrolled situation in the Russian Federation places all countries at great risk as a result of intense global trade. The proximity of some affected areas to the European Union (EU) borders (<150 km) has increased concerns about the potential economic consequences of an ASF incursion into the EU pig sector. Establishing effective surveillance, control and eradication programmes that implicate all actors (veterinarians, farmers, and policy makers) is essential for controlling ASF. African swine fever -free countries should be aware of the potential risk of ASF incursion and implement risk reduction measures such as trade controls and other sanitary measures. This review will discuss lessons learnt so far about ASF control, current challenges to its control and future studies needed to support global efforts at prevention and control.

Development and inter-laboratory validation study of an improved new real-time PCR assay with internal control for detection and laboratory diagnosis of African swine fever virus

A real-time polymerase chain reaction (PCR) assay for the rapid detection of African swine fever virus (ASFV), multiplexed for simultaneous detection of swine beta-actin as an endogenous control, has been developed and validated by four National Reference Laboratories of the European Union for African swine fever (ASF) including the European Union Reference Laboratory. Primers and a TaqMan(®) probe specific for ASFV were selected from conserved regions of the p72 gene. The limit of detection of the new real-time PCR assay is 5.7-57 copies of the ASFV genome. High accuracy, reproducibility and robustness of the PCR assay (CV ranging from 0.7 to 5.4%) were demonstrated both within and between laboratories using different real-time PCR equipments. The specificity of virus detection was validated using a panel of 44 isolates collected over many years in various geographical locations in Europe, Africa and America, including recent isolates from the Caucasus region, Sardinia, East and West Africa. Compared to the OIE-prescribed conventional and real-time PCR assays, the sensitivity of the new assay with internal control was improved, as demonstrated by testing 281 field samples collected in recent outbreaks and surveillance areas in Europe and Africa (170 samples) together with samples obtained through experimental infections (111 samples). This is particularly evident in the early days following experimental infection and during the course of the disease in pigs sub-clinically infected with strains of low virulence (from 35 up to 70dpi). The specificity of the assay was also confirmed on 150 samples from uninfected pigs and wild boar from ASF-free areas. Measured on the total of 431 tested samples, the positive deviation of the new assay reaches 21% or 26% compared to PCR and real-time PCR methods recommended by OIE. This improved and rigorously validated real-time PCR assay with internal control will provide a rapid, sensitive and reliable molecular tool for ASFV detection in pigs in newly infected areas, control in endemic areas and surveillance in ASF-free areas.