Cost Implications of African Swine Fever in Smallholder Farrow‐to‐Finish Units: Economic Benefits of Disease Prevention Through Biosecurity

African swine fever remains the greatest limitation to the development of the pig industry in Africa, and parts of Asia and Europe. It is especially important in West and Central African countries where the disease has become endemic. Biosecurity is the implementation of a set of measures that reduce the risk of infection through segregation, cleaning and disinfection. Using a 122‐sow piggery unit, a financial model and costing were used to estimate the economic benefits of effective biosecurity against African swine fever. The outcomes suggest that pig production is a profitable venture that can generate a profit of approximately US$109 637.40 per annum and that an outbreak of African swine fever (ASF) has the potential to cause losses of up to US$910 836.70 in a single year. The implementation of biosecurity and its effective monitoring can prevent losses owing to ASF and is calculated to give a benefit‐cost ratio of 29. A full implementation of biosecurity will result in a 9.70% reduction in total annual profit, but is justified in view of the substantial costs incurred in the event of an ASF outbreak. Biosecurity implementation is robust and capable of withstanding changes in input costs including moderate feed price increases, higher management costs and marginal reductions in total outputs. It is concluded that biosecurity is a key to successful pig production in an endemic situation.     

Deathbed choice by ASF‐infected wild boar can help find carcasses

African swine fever (ASF) is a fatal disease infectious to wild and domesticated suids. This disease entered the European Union in 2014 and recently reached western Europe, with the first cases observed in Belgium in September 2018. Carcasses of ASF‐infected wild boar play an important role in the spread and persistence of the virus in the environment. Thus, rapidly finding and removing carcasses is a crucial measure for effective ASF control. Using distribution modelling, we investigated whether the fine‐scale distribution of ASF‐infected animals can be predicted and support wild boar carcass searches. Our results suggest that ASF‐infected wild boar selected deathbeds in cool and moist habitats; thus, deathbed choice was mostly influenced by topographic and water‐dependent covariates. Furthermore, we show that in the case of an epidemic, it is important to quickly collect a minimum of 75–100 carcasses with exact locations to build a well‐performing and efficient carcass distribution model. The proposed model provides an indication of where carcasses are most likely to be found and can be used as a guide to strategically allocate resources.     

High probability areas for ASF infection in China along the Russian and Korean borders

African swine fever (ASF) is a transcontinental, contagious, fatal virus disease of pig with devastating socioeconomic impacts. Interaction between infected wild boar and domestic pig may spread the virus. The disease is spreading fast from the west of Eurasia towards ASF‐free China. Consequently, prediction of the distribution of ASF along the Sino‐Russian‐Korean borders is urgent. Our area of interest is Northeast China. The reported ASF‐locations in 11 contiguous countries from the Baltic to the Russian Federation were extracted from the archive of the World Organization for Animal Health from July 19, 2007 to March 27, 2017. The locational records of the wild boar were obtained from literature. The environmental predictor variables were downloaded from the WorldClim website. Spatial rarefication and pair‐wise geographic distance comparison were applied to minimize spatial autocorrelation of presence points. Principal component analysis (PCA) was used to minimize multi‐collinearity among predictor variables. We selected the maximum entropy algorithm for spatial modelling of ASF and wild boar separately, combined the wild boar prediction with the domestic pig census in a single map of suids and overlaid the ASF with the suids map. The accuracy of the models was assessed by the AUC. PCA delivered five components accounting for 95.7% of the variance. Spatial autocorrelation was shown to be insignificant for both ASF and wild boar records. The spatial models showed high mean AUC (0.92 and 0.97) combined with low standard deviations (0.003 and 0.006) for ASF and wild boar, respectively. The overlay of the ASF and suids maps suggests that a relatively short sector of the Sino‐Russian border has a high probability entry point of ASF at current conditions. Two sectors of the Sino‐Korean border present an elevated risk.     

Clinical symptoms of African swine fever in domestic pig farms in the Republic of Korea, 2019

This study describes the clinical characteristics of the African swine fever (ASF) outbreaks in 14 domestic pig farms in the Republic of Korea. ASF outbreak was identified by farmers' notifications in 11 farms and by active surveillance in the remaining three. At the time of notification, farmers reported sudden death, abortion and anorexia in sows. Death was the primary symptom identified by farmers in fattener pigs. The number of animals exhibiting clinical symptoms did not exceed four heads at notification, and the number of asymptomatic virus positives was four heads per farm on average. As ASF virus was detected only in the same pig house (in a pen for fattener pigs) in each of 14 ASF outbreak farms, there has been no evidence of house‐to‐house viral spread within any of the ASF outbreak farms. This in turn supports our hypothesis that infection was successfully detected during its initial phase.     

Current status and evolving approaches to African swine fever vaccine development

African swine fever (ASF) is a highly lethal haemorrhagic disease of swine caused by African swine fever virus (ASFV), a unique and genetically complex virus. The disease continues to be a huge burden to the pig industry in Africa, Europe and recently in Asia, especially China. The purpose of this review was to recapitulate the current scenarios and evolving trends in ASF vaccine development. The unavailability of an applicable ASF vaccine is partly due to the complex nature of the virus, which encodes various proteins associated with immune evasion. Moreover, the incomplete understanding of immune protection determinants of ASFV hampers the rational vaccine design. Developing an effective ASF vaccine continues to be a challenging task due to many undefined features of ASFV immunobiology. Recent attempts on DNA and live attenuated ASF vaccines have been reported with promising efficacy, and especially live attenuated vaccines have been proved to provide complete homologous protection. Single‐cycle viral vaccines have been developed for various diseases such as Rift Valley fever and bluetongue, and the rational extension of these strategies could be helpful for developing single‐cycle ASF vaccines. Therefore, live attenuated vaccines in short term and single‐cycle vaccines in long term would be the next generation of ASF vaccines.     

An Investigation into the First Outbreak of African Swine Fever in the Republic of Mauritius

Outbreaks of African swine fever (ASF) have been reported from many countries, particularly in Sub‐Saharan Africa, but until 2007 the disease had never been reported from the Republic of Mauritius. This is the first report describing field epidemiological and laboratory investigations into the outbreak of the lethal pig disease on the island. The official index case displayed clinical and necropsy signs suggestive of ASF. Serological and agent identification methods used to confirm and investigate the outbreak yielded negative and a few positive results respectively. Phylogenetic analysis based on DNA sequencing clustered the outbreak strain within genotype II viruses. The outbreak was controlled by modified stamping out and risk assessment revealed the possibility of disease endemicity in the country.     

Why is African swine fever still present in Sardinia?

African swine fever (ASF ) is an infectious disease of swine that has been present in Sardinia since 1978. Soon after introduction of the disease, several control and eradication programmes were established with limited success. Some researchers attributed the persistence of the disease in central and eastern areas to certain socio‐economic factors, the existence of some local and traditional farming practices (i.e., unregistered free‐ranging pigs known as brado animals) and the high density of wild boar in the region. In the past, scarcity of swine data in Sardinia complicated the evaluation and study of ASF on the island. More complete, accurate and reliable information on pig farms has become available as a result of the most recent eradication programmes. Here, we perform statistical modelling based on these data and the known distribution of domestic pig and wild boar to identify the main risk factors that have caused ASF persistence in Sardinia. Our results categorized, identified and quantified nine significant risk factors, six of which have not been previously described. The most significant factors were the number of medium‐sized farms, the presence of brado animals and the combination of estimated wild boar density and mean altitude above sea level. Based on these factors, we identified regions in eastern and central Sardinia to be at greatest risk of ASF persistence; these regions are also where the disease has traditionally been endemic. Based on these risk factors, we propose specific control measures aimed at mitigating such risks and eradicating ASF from the island.     

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.     

Pre‐Clinical Evaluation of a Real‐Time PCR Assay on a Portable Instrument as a Possible Field Diagnostic Tool: Experiences from the Testing of Clinical Samples for African and Classical Swine Fever Viruses

African swine fever (ASF) and classical swine fever (CSF) are two highly infectious transboundary animal diseases (TADs) that are serious threats to the pig industry worldwide, including in China, the world's largest pork producer. In this study, a duplex real‐time PCR assay was developed for the rapid detection and differentiation of African swine fever virus (ASFV) and classical swine fever virus (CSFV). The assay was performed on a portable, battery‐powered PCR thermocycler with a low sample throughput (termed as ‘T‐COR4 assay’). The feasibility and reliability of the T‐COR4 assay as a possible field method was investigated by testing clinical samples collected in China. When evaluated with reference materials or samples from experimental infections, the assay performed in a reliable manner, producing results comparable to those obtained from stationary PCR platforms. Of 59 clinical samples, 41 had results identical to a two‐step CSFV real‐time PCR assay. No ASFV was detected in these samples. The T‐COR4 assay was technically easy to perform and produced results within 3 h, including sample preparation. In combination with a simple sample preparation method, the T‐COR4 assay provides a new tool for the field diagnosis and differentiation of ASF and CSF, which could be of particular value in remote areas.     

Reproductive Ratio for the Local Spread of African Swine Fever in Wild Boars in the Russian Federation

African swine fever (ASF) has caused the swine industry of the Russian Federation substantial economic losses over the last 7 years, and the disease spread from there to a number of neighbouring countries. Wild boar has been involved in the spread of the disease both at local and at transboundary levels. Understanding ASF dynamics in wild boars is prerequisite to preventing the spread and to designing and applying effective surveillance and control plans. The reproductive ratio (R₀) is an epidemiological indicator commonly used to quantify the extent of disease spread. Here, it was estimated in nine spatio‐temporal clusters of ASF in wild boar cases in the Russian Federation (2007–2013). Clusters were defined by exploring the maximum distance of association of ASF cases using K Ripley analysis and spatio‐temporal scan statistics. A maximum spatial association of 133 km in wild boar cases was identified which is within de the conventional radius of surveillance zone (100–150 km). The mean range value of R₀ = 1.58 (1.13–3.77) was lower compared to values previously estimated for ASF transmission within farms but similar to early estimates between farm (R₀ = 2–3), in domestic pigs using notification data in the Russian Federation. Results obtained provide quantitative knowledge on the epidemiology of ASF in wild boars in the Russian Federation. They identify the ASF transmission rate value in affected natural wild populations, for the first time, which could provide basis for modelling ASF transmission and suggest that current surveillance radius should be reviewed to make surveillance in wild nature more targeted and effective.     

Attitudes and Beliefs of Pig Farmers and Wild Boar Hunters Towards Reporting of African Swine Fever in Bulgaria,Germany and the Western Part of the Russian Federation

This study investigated the attitudes and beliefs of pig farmers and hunters in Germany, Bulgaria and the western part of the Russian Federation towards reporting suspected cases of African swine fever (ASF). Data were collected using a web‐based questionnaire survey targeting pig farmers and hunters in these three study areas. Separate multivariable logistic regression models identified key variables associated with each of the three binary outcome variables whether or not farmers would immediately report suspected cases of ASF, whether or not hunters would submit samples from hunted wild boar for diagnostic testing and whether or not hunters would report wild boar carcasses. The results showed that farmers who would not immediately report suspected cases of ASF are more likely to believe that their reputation in the local community would be adversely affected if they were to report it, that they can control the outbreak themselves without the involvement of veterinary services and that laboratory confirmation would take too long. The modelling also indicated that hunters who did not usually submit samples of their harvested wild boar for ASF diagnosis, and hunters who did not report wild boar carcasses are more likely to justify their behaviour through a lack of awareness of the possibility of reporting. These findings emphasize the need to develop more effective communication strategies targeted at pig farmers and hunters about the disease, its epidemiology, consequences and control methods, to increase the likelihood of early reporting, especially in the Russian Federation where the virus circulates.     

Monitoring of African Swine Fever in the Wild Boar Population of the Most Recent Endemic Area of Spain

Wild boars are natural hosts for African swine fever (ASF). The ASF virus (ASFV) can persist for long periods in the environment, such as in ticks and contaminated products, which may be sources of infection for wild boar populations. African swine fever was eradicated in domestic pig populations in Spain in 1995, after 35 years of significant effort. To determine whether ASFV can persist in wild boar hosts after it has been eradicated from domestic pigs and to study the role of wild boar in helping ASFV persist in the environment, we checked for the presence of ASFV in wild boars in Doñana National Park, one of the largest natural habitats of wild boar in Spain and one of the last areas where ASF was endemic prior its eradication. Samples from 158 animals collected between 2006 and 2010 were analysed using serological and nucleic acid‐based diagnostic techniques recommended by the World Organization for Animal Health (OIE). None of the samples was found to be positive. These results confirm the absence of disease in wildlife in what was once one of the areas most affected by ASF in Spain, and they suggest that wild boars play a limited role in ASFV persistence. These results confirm that ASFV cannot persist in isolated wild boar populations for long periods of time without the interaction of other factors such as re‐infection by contact with domestic pigs or by feeding on contaminated swill.     

Genetic Characterization of African Swine Fever Viruses from a 2008 Outbreak in Tanzania

Outbreaks of African swine fever (ASF) have been reported in the past from several countries in sub‐Saharan Africa. The aim of this study was to genotype ASF viruses (ASFVs) from the 2008 outbreak in Morogoro and Dar es Salaam regions of Tanzania. Tissue samples from domestic pigs that died as a result of severe haemorrhagic disease were collected and analysed with PCR and genome sequencing methods using ASFV‐specific primer sets. Nucleotide sequence data were obtained for the B646L (p72), E183L (p54) and the variable region of the B602L gene sequences. Phylogenetic analyses based on DNA sequences showed that the 2008 Tanzanian isolates belonged to p72 genotype XV and clustered together with those derived from the 2001 outbreak in Tanzania. Analysis of the tetrameric amino acid repeat regions within the variable region of the B602L gene showed that the repeat signature of the 2008 Tanzanian ASFV was unique and contained three novel tetramers (U = NIDT/NTDT and X = NTDI). Epidemiological investigation suggested that transportation of live pigs continues to play an active role in the epidemiology of ASF in Tanzania. It is recommended that future control of ASF spread in Tanzania should focus on the early detection and confirmation of the disease, prompt institution of quarantine measures, culling and proper disposal of infected and in‐contact animals and decontamination of affected premises.     

Diagnostic specificity of the African swine fever virus antibody detection enzyme‐linked immunosorbent assay in feral and domestic pigs in the United States

African swine fever (ASF) is a highly contagious haemorrhagic disease of pigs that has the potential to cause mortality nearing 100% in naïve animals. While an outbreak of ASF in the United States’ pig population (domestic and feral) has never been reported, an introduction of the disease has the potential to cause devastation to the pork industry and food security. During the recovery phase of an outbreak, an antibody detection diagnostic assay would be required to prove freedom of disease within the previously infected zone and eventually nationwide. Animals surviving an ASF infection would be considered carriers and could be identified through the persistence of ASF viral antibodies. These antibodies would demonstrate exposure to the disease and not vaccination, as there is no ASF vaccine available. A well‐established commercial enzyme‐linked immunosorbent assay (ELISA) detects antibodies against ASF virus (ASFV), but the diagnostic specificity of the assay had not been determined using serum samples from the pig population of the United States. This study describes an evaluation of the World Organization for Animal Health (OIE)‐recommended Ingezim PPA COMPAC ELISA using a comprehensive cohort (n = 1791) of samples collected in the United States. The diagnostic specificity of the assay was determined to be 99.4% (95% confidence interval (CI): [98.9, 99.7]). The result of this study fills a gap in understanding the performance of the Ingezim PPA COMPAC ELISA in the ASF naïve pig population of the United States.     

Re‐emergence of genotype I of African swine fever virus in Ivory Coast

In July 2014, an outbreak of severe haemorrhagic disease in a domestic pig population, was reported in San‐Pedro, the second seaport city of Ivory Coast. Animals of all age groups developed clinical signs consistent with African swine fever (ASF). Tissue and serum samples from dead pigs were sent to the laboratory for diagnostic confirmation and molecular characterization based on the partial B646L (p72), the full E183L (p54) gene and the central variable region of the B602L gene. The PCR results confirmed the outbreak of ASF. Phylogenetic analyses based on p72 and p54 sequences showed that the San‐Pedro 2014 outbreak virus strain belongs to p72 genotype I. The Analysis of the tetrameric amino acid repeat regions of the B602L gene showed two repeat signatures which differ by an extra A = CAST in the second signature. The ASFV sequence of the San‐Pedro 2014 outbreak strain is closely related to historical and recent ASFV strains collected in Angola and Cameroon whose ships have repeatedly visited the seaport of San‐Pedro from March to June 2014. The 2014 viruses are distinct from the strains involved in the previous ASF wave in 1996 in Ivory Coast.     

Surveillance for African Swine Fever in Nigeria, 2006–2009

African swine fever (ASF) has had significant economic and social impact in Nigeria since 1997. However, there has been no effective national response to bring it under control. In this report, we confirm that ASF is still prevalent and widespread in Nigeria. Results from both serosurveillance and virological analyses indicated that ASF is present in most of the agro‐ecological zones of the country. Nine per cent (9%) of serum samples and 48% of tissue samples were positive for ASF virus antibody and genome, respectively. Areas with high pig‐related activities (marketing, consumption and farming) have higher prevalences compared with areas with less pig activities. Farm‐gate buyers, marketing systems and transport of untested pigs within the country assist with the circulation of the virus. Only by putting in place a comprehensive routine surveillance and testing system, reorganizing the market and transportation systems for pigs, implementing on‐farm bio‐security protocols and considering the option of compensation will it be possible to achieve a significant reduction in ASF prevalence in Nigeria.     

Antigenic regions of African swine fever virus phosphoprotein P30

African swine fever (ASF) is one of the most complex and lethally haemorrhagic viral diseases of swine, affecting all breeds and ages of pigs. In the absence of ASF vaccines, reliable laboratory diagnosis and restricted biosecurity are critical for disease prevention and control. A detection of ASF‐specific antibodies in an unvaccinated pig is a good marker for the diagnosis of ASF. The immunoperoxidase test (IPT) is a sensitive test for detecting ASF virus (ASFV) antibodies. However, due to the complexity of the procedure, the IPT is only suitable to be used as a confirmatory test. The ASFV p30 protein‐based enzyme‐linked immunosorbent assay (ELISA) is widely used for ASFV antibody screening, but the sensitivity is not comparable to the IPT. It is essential to have a better understanding of the antigenic properties of ASFV p30 to improve p30‐based serologic tests. In this study, we developed a panel of 21 monoclonal antibodies (mAbs) against ASFV p30. With 14 out of the 21 mAbs, we defined 4 antigenic regions that contain at least 4 linear epitopes. Nine of the 14 mAbs mapped to antigenic regions 3 and 4 reacted with p30 in all serologic methods tested in this study, such as indirect immunofluorescence assay (IFA), ELISA and Western blot. The antigenic regions 3 and 4 are highly conserved and immunodominant in host antibody response. These mAbs and the defined p30 antigenic regions 3 and 4 provide valuable tools for the development and improvement of ASF serologic assays.     

Understanding African Swine Fever infection dynamics in Sardinia using a spatially explicit transmission model in domestic pig farms

African swine fever virus (ASFV ) has been endemic in Sardinia since 1978, resulting in severe losses for local pig producers and creating important problems for the island's veterinary authorities. This study used a spatially explicit stochastic transmission model followed by two regression models to investigate the dynamics of ASFV spread amongst domestic pig farms, to identify geographic areas at highest risk and determine the role of different susceptible pig populations (registered domestic pigs, non‐registered domestic pigs [brado ] and wild boar) in ASF occurrence. We simulated transmission within and between farms using an adapted version of the previously described model known as Be‐FAST . Results from the model revealed a generally low diffusion of ASF in Sardinia, with only 24% of the simulations resulting in disease spread, and for each simulated outbreak on average only four farms and 66 pigs were affected. Overall, local spread (indirect transmission between farms within a 2 km radius through fomites) was the most common route of transmission, being responsible for 98.6% of secondary cases. The risk of ASF occurrence for each domestic pig farm was estimated from the spread model results and integrated in two regression models together with available data for brado and wild boar populations. There was a significant association between the density of all three populations (domestic pigs, brado , and wild boar) and ASF occurrence in Sardinia. The most significant risk factors were the high densities of brado (OR = 2.2) and wild boar (OR = 2.1). The results of both analyses demonstrated that ASF epidemiology and infection dynamics in Sardinia create a complex and multifactorial disease situation, where all susceptible populations play an important role. To stop ASF transmission in Sardinia, three main factors (improving biosecurity on domestic pig farms, eliminating brado practices and better management of wild boars) need to be addressed.     

The evolution of African swine fever virus in Sardinia (1978–2014) as revealed by whole‐genome sequencing and comparative analysis

African swine fever (ASF) is a highly contagious and lethal viral disease of pigs and wild boars, which is enzootic in many African countries and on the Italian island of Sardinia, where it has been present since 1978. Previous genetic analyses of Sardinian ASF virus (ASFV) isolates have revealed that they all belong to p72 genotype I, with only minor sequence variations. However, these studies examined only a few selected genes. To distinguish between these closely related isolates and better investigate ASFV evolution in Sardinia, we sequenced the complete genomes of 12 Sardinian ASFV isolates collected between 1978 and 2012, and compared them with 47/Ss/2008 and 26544/OG10. Most of the observed changes occurred in a time‐dependent manner; however, their biological significance remains unclear. As a whole, our results demonstrate the remarkable genetic stability of these strains, supporting a single‐source introduction of the virus.     

First Detection of Antibodies Against African Swine Fever Virus in Faeces Samples

African swine fever (ASF) is a viral, highly lethal haemorrhagic disease of swine with no available vaccine or effective treatment. Introduction of ASF into a country triggers immediate restriction measures that cause significant economic losses and threatens spread to neighbouring countries. Wild boar populations have been recently assigned an essential role in the spread of African swine fever virus (ASFV) to European countries. Therefore, effective surveillance and monitoring of wild boar populations is required, but sampling wild boar is logistically challenging and expensive. This study assessed the feasibility of detecting antibodies against ASFV in faeces for later implementation in surveillance and control programmes. Two groups of pigs were experimentally infected with an attenuated ASFV isolate Ken05, and blood, oral fluid and faecal samples were tested for the presence of viral DNA using quantitative real‐time polymerase chain reaction (qPCR) to monitor infection progress. Faecal samples were analysed using two indirect enzyme‐linked immunosorbent assays (ELISAs) based on semipurified viral protein (vp) 72 or purified recombinant vp30 expressed in mammalian cells. Faecal samples from 9 of 10 pigs with non‐haemorrhagic diarrhoea tested positive for antibodies against ASFV using the two ELISA tests that showed a positive correlation. The serum sample results from the two indirect ELISAs were compared against results from the reference ELISA technique and the immunoperoxidase test. Our findings indicate the feasibility of faecal sampling for detecting anti‐ASFV antibodies, which may provide a practical non‐invasive alternative for sampling wild boar populations. In conclusion, the application of these ELISA tests to faecal field samples could be particularly useful to screen for the presence of ASF in field conditions.