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

African Swine Fever Virus Immunosuppression and Virulence-Related Gene

African swine fever virus (ASFV), a highly contagious pathogen characterized by a complex structure and a variety of immunosuppression proteins, causes hemorrhagic, acute, and aggressive infectious disease that severely injures the pork products and industry. However, there is no effective vaccine or treatment. The main reasons are not only the complex mechanisms that lead to immunosuppression but also the unknown functions of various proteins. This review summarizes the interaction between ASFV and the host immune system, along with the involvement of virulence-related genes and proteins, as well as the corresponding molecular mechanism of immunosuppression of ASFV, encompassing pathways such as cGAS-STING, nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), Janus Kinase (JAK) and JAK Signal Transducers and Activators of Transcription (STAT), apoptosis, and other modulation. The aim is to summarize the dynamic process during ASFV infection and entry into the host cell, provide a rational insight into development of a vaccine, and provide a better clear knowledge of how ASFV impacts the host.

Comparative evaluation of disease dynamics in wild boar and domestic pigs experimentally inoculated intranasally with the European highly virulent African swine fever virus genotype II strain "Armenia 2007"

Since the reintroduction of African swine fever virus (ASFV) in Europe in 2007 and its subsequent spread to Asia, wild boar has played a crucial role in maintaining and disseminating the virus. There are significant gaps in the knowledge regarding infection dynamics and disease pathogenesis in domestic pigs and wild boar, particularly at the early infection stage. We aimed to compare domestic pigs and wild boar infected intranasally to mimic natural infection with one of the original highly virulent genotype II ASFV isolates (Armenia 2007). The study involved euthanising three domestic pigs and three wild boar on days 1, 2, 3, and 5 post-infection, while four domestic pigs and four wild boar were monitored until they reached a humane endpoint. The parameters assessed included clinical signs, macroscopic lesions, viremia levels, tissue viral load, and virus shedding in nasal and rectal swabs from day 1 post-infection. Compared with domestic pigs, wild boar were more susceptible to ASFV, with a shorter incubation period and earlier onset of clinical signs. While wild boar reached a humane endpoint earlier than domestic pigs did, the macroscopic lesions were comparatively less severe. In addition, wild boar had earlier viremia, and the virus was also detected earlier in tissues. The medial retropharyngeal lymph nodes were identified as key portals for ASFV infection in both subspecies. No viral genome was detected in nasal or rectal swabs until shortly before reaching the humane endpoint in both domestic pigs and wild boar, suggesting limited virus shedding in acute infections.

Modelling African swine fever introduction in diverse Australian feral pig populations

African swine fever (ASF) is a viral disease that affects domestic and feral pigs. While not currently present in Australia, ASF outbreaks have been reported nearby in Indonesia, Timor-Leste, and Papua New Guinea. Feral pigs are found in all Australian states and territories and are distributed in a variety of habitats. To investigate the impacts of an ASF introduction event in Australia, we used a stochastic network-based metapopulation feral pig model to simulate ASF outbreaks in different regions of Australia. Outbreak intensity and persistence in feral pig populations was governed by local pig recruitment rates, population size, carcass decay period, and, if applicable, metapopulation topology. In Northern Australia, the carcass decay period was too short for prolonged persistence, while endemic transmission could possibly occur in cooler southern areas. Populations in Macquarie Marshes in New South Wales and in Namadgi National Park in the Australian Capital Territory had the highest rates of persistence. The regions had different modes of transmission that led to long-term persistence. Endemic Macquarie Marshes simulations were characterised by rapid transmission caused by high population density that required a fragmented metapopulation to act as a bottleneck to slow transmission. Endemic simulations in Namadgi, with low density and relatively slow transmission, relied on large, well-connected populations coupled with long carcass decay times. Despite the potential for endemic transmission, both settings required potentially unlikely population sizes and dynamics for prolonged disease survival.

A suitable sampling strategy for the detection of African swine fever virus in living and deceased pigs in the field: a retrospective study

African swine fever (ASF) is a fatal disease that threatens the health status of the swine population and thus can impact the economic outcome of the global pig industry. Monitoring the ASF virus (ASFV) is of utmost concern to prevent and control its distribution. This study aims to identify a suitable sampling strategy for ASFV detection in living and deceased pigs under field conditions. A range of samples, comprising tissues obtained from deceased pigs, as well as serum and tonsil swab samples from live pigs, were gathered and subjected to detection using the qPCR method. The findings revealed that the mandibular lymph nodes demonstrated the highest viral loads among superficial tissues, thereby indicating their potential suitability for detecting ASFV in deceased pigs. Additionally, the correlations between virus loads in various tissues have demonstrated that tonsil swab samples are a viable specimen for monitoring live pigs, given the strong associations observed with other tissues. These findings indicated two dependable sample types for the detection of ASFV: mandibular lymph nodes for deceased pigs and tonsil swabs for live pigs, which supply some references for the development of efficacious preventive measures against ASFV.

Quantitative risk assessment model of the presence of porcine epidemic diarrhea and African swine fever viruses in spray-dried porcine plasma

Introduction

There are no microbiological regulatory limits for viruses in animal feed and feed ingredients.

Methods

A performance objective (PO) was proposed in this study to manufacture a spray-dried porcine plasma (SDPP) batch absent of any infectious viral particles. The PO levels of -7.0, -7.2, and -7.3 log TCID50/g in SDPP were estimated for three batch sizes (10, 15, and 20 tons).

Results and discussion

A baseline survey on the presence of porcine epidemic diarrhea virus (PEDV) in raw porcine plasma revealed a concentration of -1.0 ± 0.6 log TCID50/mL as calculated using a TCID50-qPCR derived standard curve. The mean African swine fever virus (ASFV) concentration in raw plasma was estimated to be 0.6 log HAD50/mL (0.1-1.4, 95% CI) during a pre-clinical scenario (collected from asymptomatic and undetected viremic pigs). Different processing scenarios (baseline: spray-drying + extended storage) and baseline + ultraviolet (UV) radiation were evaluated to meet the PO levels proposed in this study. The baseline and baseline + UV processing scenarios were >95 and 100% effective in achieving the PO for PEDV by using different batch sizes. For the ASFV in SDPP during a pre-clinical scenario, the PO compliance was 100% for all processing scenarios evaluated. Further research is needed to determine the underlying mechanisms of virus inactivation in feed storage to further advance the implementation of feed safety risk management efforts globally.

African swine fever in wild boar: investigating model assumptions and structure

African swine fever (ASF) is a highly virulent viral disease that affects domestic pigs and wild boar. Current ASF transmission in Europe is in part driven by wild boar populations, which act as a disease reservoir. Wild boar are abundant throughout Europe and are highly social animals with complex social organization. Despite the known importance of wild boar in ASF spread and persistence, knowledge gaps remain surrounding wild boar transmission. We developed a wild boar modelling framework to investigate the influence of contact-density functions and wild boar social structure on disease dynamics. The framework included an ordinary differential equation model, a homogeneous stochastic model and various network-based stochastic models that explicitly included wild boar social grouping. We found that power-law functions (transmission∝ density0.5) and frequency-based contact-density functions were best able to reproduce recent Baltic outbreaks; however, power-law function models predicted considerable carcass transmission, while frequency-based models had negligible carcass transmission. Furthermore, increased model heterogeneity caused a decrease in the relative importance of carcass-based transmission. The transmission pathways predicted by each model type affected the efficacy of idealized interventions, which highlights the importance of evaluating model type and structure when modelling systems with significant uncertainties.

Infection of domestic pigs with a genotype II potent strain of ASFV causes cytokine storm and lymphocyte mass reduction

The whole-genome sequence of an African swine fever virus (ASFV) strain (HuB/HH/2019) isolated from Hubei, China, was highly similar to that of the Georgia 2007/1 strain ASFV. After infection with strong strains, domestic pigs show typical symptoms of infection, including fever, depression, reddening of the skin, hemorrhagic swelling of various tissues, and dysfunction. The earliest detoxification occurred in pharyngeal swabs at 4 days post-infection. The viral load in the blood was extremely high, and ASFV was detected in multiple tissues, with the highest viral loads in the spleen and lungs. An imbalance between pro- and anti-inflammatory factors in the serum leads to an excessive inflammatory response in the body. Immune factor expression is suppressed without effectively eliciting an immune defense. Antibodies against p30 were not detected in acutely dead domestic pigs. Sequencing of the peripheral blood mononuclear cell transcriptome revealed elevated transcription of genes associated with immunity, defense, and stress. The massive reduction in lymphocyte counts in the blood collapses the body's immune system. An excessive inflammatory response with a massive reduction in the lymphocyte count may be an important cause of mortality in domestic pigs. These two reasons have inspired researchers to reduce excessive inflammatory responses and stimulate effective immune responses for future vaccine development.

Characterization of an African Swine Fever Virus Field Isolate from Vietnam with Deletions in the Left Variable Multigene Family Region

In this paper, we report the characterization of a genetically modified live-attenuated African swine fever virus (ASFV) field strain isolated from Vietnam. The isolate, ASFV-GUS-Vietnam, belongs to p72 genotype II, has six multi-gene family (MGF) genes deleted, and an Escherichia coli GusA gene (GUS) inserted. When six 6-8-week-old pigs were inoculated with ASFV-GUS-Vietnam oro-nasally (2 × 105 TCID50/pig), they developed viremia, mild fever, lethargy, and inappetence, and shed the virus in their oral and nasal secretions and feces. One of the pigs developed severe clinical signs and was euthanized 12 days post-infection, while the remaining five pigs recovered. When ASFV-GUS-Vietnam was inoculated intramuscularly (2 × 103 TCID50/pig) into four 6-8 weeks old pigs, they also developed viremia, mild fever, lethargy, inappetence, and shed the virus in their oral and nasal secretions and feces. Two contact pigs housed together with the four intramuscularly inoculated pigs, started to develop fever, viremia, loss of appetite, and lethargy 12 days post-contact, confirming horizontal transmission of ASFV-GUS-Vietnam. One of the contact pigs died of ASF on day 23 post-contact, while the other one recovered. The pigs that survived the exposure to ASFV-GUS-Vietnam via the mucosal or parenteral route were fully protected against the highly virulent ASFV Georgia 2007/1 challenge. This study showed that ASFV-GUS-Vietnam field isolate is able to induce complete protection in the majority of the pigs against highly virulent homologous ASFV challenge, but has the potential for horizontal transmission, and can be fatal in some animals. This study highlights the need for proper monitoring and surveillance when ASFV live-attenuated virus-based vaccines are used in the field for ASF control in endemic countries.

Recent progress on gene-deleted live-attenuated African swine fever virus vaccines

African Swine Fever (ASF) is a highly lethal viral disease in swine, with mortality rates approaching 100%. The disease has spread to many swine-producing countries, leading to significant economic losses and adversely impacting global food security. Extensive efforts have been directed toward developing effective ASF vaccines. Among the vaccinology approaches tested to date, live-attenuated virus (LAV) vaccines produced by rational deleting virulence genes from virulent African Swine Fever Virus (ASFV) strains have demonstrated promising safety and efficacy in experimental and field conditions. Many gene-deleted LAV vaccine candidates have been generated in recent years. The virulence genes targeted for deletion from the genome of virulent ASFV strains can be categorized into four groups: Genes implicated in viral genome replication and transcription, genes from the multigene family located at both 5' and 3' termini, genes participating in mediating hemadsorption and putative cellular attachment factors, and novel genes with no known functions. Some promising LAV vaccine candidates are generated by deleting a single viral virulence gene, whereas others are generated by simultaneously deleting multiple genes. This article summarizes the recent progress in developing and characterizing gene-deleted LAV vaccine candidates.

Disease Course of Korean African Swine Fever Virus in Domestic Pigs Exposed Intraorally, Intranasally, Intramuscularly, and by Direct Contact with Infected Pigs

African swine fever (ASF) is a fatal contagious disease affecting swine. The first Korean ASF virus (ASFV) isolate (Korea/Pig/Paju1/2019) was used to compare the disease course of ASFV in pigs inoculated via the four routes. In the challenge experiment, domestic pigs were infected via the intraoral (IO) and intranasal (IN) routes with a 106 50% hemadsorbing dose (HAD50) and an intramuscular (IM) injection of 103 HAD50. In the direct contact (DC) group, five naïve pigs were brought into direct contact with two IM-ASFV-infected pigs. IO-, IN-, and IM-inoculated pigs showed similar disease courses, whereas DC pigs had comparable ASF syndrome after a 7-day latent period. The disease course in the DC route, one of the most common routes of infection, was not significantly different from that in the IO and IN routes. IM and DC groups differed in terms of the severity of fever and hemorrhagic lesions in the lymph nodes and spleen, indicating that the IM route, suitable for early vaccine development trials, is not appropriate for studying the ASFV infection mechanism, including early stage of infection, and IO and IN challenges with a designated dose can be alternatives in trials for assessing ASFV pathogenicity and vaccine efficacy investigations.

Biosecurity measures for the prevention of African swine fever on German pig farms: comparison of farmers' own appraisals and external veterinary experts' evaluations

BACKGROUND

Since its first introduction into the German wild boar population in 2020, African swine fever (ASF) has been spreading slowly from the eastern border westwards and has been introduced into eight domestic pig farms thus far. The European Food Safety Authority has named deficits in farm biosecurity and increased human activity as major risk factors for the introduction of the ASF virus into pig farms. Studies have shown that pig farms in Germany generally have a high level of biosecurity. However, veterinary practitioners and policy-makers have expressed concerns that not all pig farmers are appropriately prepared to deal with the threat of ASF. This study aimed to evaluate the level of biosecurity on pig farms in Lower Saxony and explore the reasons for deficits in the implementation of biosecurity measures. For this purpose, pig farmers were interviewed in open structured face-to-face interviews about their perception of ASF and biosecurity, and the implemented measures on their farms were assessed with a checklist. In the data analysis, the farmers' answers and the results of the biosecurity check were compared to gain further insights into the factors influencing the implementation of biosecurity measures on the farms.

RESULTS

The biosecurity check showed that on most farms, a high level of biosecurity had been implemented. Nevertheless, deficits were found concerning the fences and the delimitation of clean and dirty areas on farm grounds and in the anteroom. Overall, the farmers were well informed about ASF and had a realistic perception of their own biosecurity. They considered the farm layout, financial means and practicality of hygiene measures to be the main barriers to implementing biosecurity measures against ASF. However, the results also suggested that farmers' attitudes and legal regulations were major influencing factors.

CONCLUSION

The results indicated a high level of biosecurity against ASF on most pig farms and a realistic perception of their own biosecurity by the farmers. Current knowledge transfer and information should focus on building upon the farmers' own motivation and expertise and supporting them to put existing knowledge into practice.

Inactivation of highly transmissible livestock and avian viruses including influenza A and Newcastle disease virus for molecular diagnostics

There is a critical need for an inactivation method that completely inactivates pathogens at the time of sample collection while maintaining the nucleic acid quality required for diagnostic PCR testing. This inactivation method is required to alleviate concerns about transmission potential, minimize shipping complications and cost, and enable testing in lower containment laboratories, thereby enhancing disease diagnostics through improved turn-around time. This study evaluated a panel of 10 surrogate viruses that represent highly pathogenic animal diseases. These results showed that a commercial PrimeStore® molecular transport media (PSMTM) completely inactivated all viruses tested by >99.99%, as determined by infectivity and serial passage assays. However, the detection of viral nucleic acid by qRT-PCR was comparable in PSMTM and control-treated conditions. These results were consistent when viruses were evaluated in the presence of biological material such as sera and cloacal swabs to mimic diagnostic sample conditions for non-avian and avian viruses, respectively. The results of this study may be utilized by diagnostic testing laboratories for highly pathogenic agents affecting animal and human populations. These results may be used to revise guidance for select agent diagnostic testing and the shipment of infectious substances.

Molecular contamination of an animal facility during and after African swine fever virus infection

Introduction

The molecular contamination of an animal facility was investigated during and after an infection with highly pathogenic African swine fever virus (ASFV) among domestic pigs. The investigation evaluated the risk of indirect transmission of the disease and indicated points that may facilitate cleaning and disinfection processes.

Material and Methods

Six domestic pigs were infected oronasally with the highly pathogenic Georgia 2007 strain. Environmental samples from the floors, walls, rubber floor mats, feeders, drinkers, high-efficiency particulate-absorbing filter covers and doors were collected 7 days post infection (dpi), 7 days later and 24 h after disinfection of the facility. The samples were investigated by real-time PCR and in vitro assays to find genetic traces of ASFV and infectious virus.

Results

Typical clinical outcomes for ASF (i.e. fever, apathy, recumbency and bloody diarrhoea) were observed, and all animals died or required euthanasia before or at 9 dpi. No infectious virus was found in environmental samples at the sampling time points. Genetic traces of ASFV were found in all locations except the doors. The initial virus load was calculated using real-time PCR threshold cycle values and was the highest at the drain. A statistically significant decrease of virus load over time was found on non-porous surfaces mechanically cleaned by water (the floor and drain).

Conclusion

The gathered data confirmed different routes of virus excretion (oral and nasal, faeces and urine, and aerosol) and showed virus locations and different initial concentrations in the animal facility. Maintaining the facility with mechanical cleaning and using personal protection (gloves) and hand disinfection may efficiently minimise the risk of further virus spread. Together with the results of previously published studies, the present investigations' failure to isolate infectious virus may suggest that if stable environmental conditions are assured, the time needed before the introduction of new herds into previously ASF-affected farm facilities could be shortened and in this way the economic losses caused by the disease outbreak mitigated.

Comparative Analysis of Swine Antibody Responses following Vaccination with Live-Attenuated and Killed African Swine Fever Virus Vaccines

African swine fever virus (ASFV) is circulating in many swine-producing countries, causing significant economic losses. It is observed that pigs experimentally vaccinated with a live-attenuated virus (LAV) but not a killed virus (KV) vaccine develop solid homologous protective immunity. The objective of this study was to comparatively analyze antibody profiles between pigs vaccinated with an LAV vaccine and those vaccinated with a KV vaccine to identify potential markers of vaccine-induced protection. Thirty ASFV seronegative pigs were divided into three groups: Group 1 received a single dose of an experimental LAV, Group 2 received two doses of an experimental KV vaccine, and Group 3 was kept as a non-vaccinated (NV) control. At 42 days post-vaccination, all pigs were challenged with the parental virulent ASFV strain and monitored for 21 days. All pigs vaccinated with the LAV vaccine survived the challenge. In contrast, eight pigs from the KV group and seven pigs from the NV group died within 14 days post-challenge. Serum samples collected on 41 days post-vaccination were analyzed for their reactivity against a panel of 29 viral structural proteins. The sera of pigs from the LAV group exhibited a strong antibody reactivity against various viral structural proteins, while the sera of pigs in the KV group only displayed weak antibody reactivity against the inner envelope (p32, p54, p12). There was a negative correlation between the intensity of antibody reactivity against five ASFV antigens, namely p12, p14, p15, p32, and pD205R, and the viral DNA titers in the blood of animals after the challenge infection. Thus, antibody reactivities against these five antigens warrant further evaluation as potential indicators of vaccine-induced protection.

Increased Presence of Circulating Cell-Free, Fragmented, Host DNA in Pigs Infected with Virulent African Swine Fever Virus

African swine fever virus (ASFV) causes severe hemorrhagic disease in domestic pigs and wild boar, often with high case fatality rates. The virus replicates in the circulating cells of the monocyte-macrophage lineage and within lymphoid tissues. The infection leads to high fever and a variety of clinical signs. In this study, it was observed that ASFV infection in pigs resulted in a >1000-fold increase in the level of circulating cell-free DNA (cfDNA), derived from the nuclei of host cells in the serum. This change occurred in parallel with the increase in circulating ASFV DNA. In addition, elevated levels (about 30-fold higher) of host mitochondrial DNA (mtDNA) were detected in the serum from ASFV-infected pigs. For comparison, the release of the cellular enzyme, lactate dehydrogenase (LDH), a commonly used marker of cellular damage, was also found to be elevated during ASFV infection, but later and less consistently. The sera from pigs infected with classical swine fever virus (CSFV), which causes a clinically similar disease to ASFV, were also tested but, surprisingly, this infection did not result in the release of cfDNA, mtDNA, or LDH. It was concluded that the level of cfDNA in the serum is a sensitive host marker of virulent ASFV infection.

Innate immune escape and adaptive immune evasion of African swine fever virus: A review

African swine fever virus (ASFV) causes hemorrhagic fever in domestic and wild pigs. The continued spread of the virus in Africa, Europe and Asia threatens the global pig industry. The lack of an effective vaccine limits disease control. ASFV has evolved a variety of encoded immune escape proteins and can evade host adaptive immunity, inducing cellular inflammation, autophagy, or apoptosis in host cells. Frequent persistent infections hinder the development of a viral vaccine and impose technical barriers. Currently, knowledge of the virulence-related genes, main pathogenic genes and immunoregulatory mechanism of ASFV is not comprehensive. We explain that ASFV invades the host to regulate its inflammatory response, interferon production, antigen presentation and cellular immunity. Furthermore, we propose potential ideas for ASFV vaccine target design, such as knocking out high-virulence genes in ASFV and performing data mining to identify the main genes that induce antiviral responses. To support a rational strategy for vaccine development, a better understanding of how ASFV interacts with the host and regulates the host's response to infection is needed. We review the current knowledge about ASFV targeting of host innate and adaptive immunity and the mechanisms by which the affected immune pathways are suppressed.

Pathogenicity and Pathological Characteristics of African Swine Fever Virus Strains from Pig Farms in South Korea from 2022 to January 2023

Since the first African swine fever (ASF) outbreak occurred at a pig farm in South Korea in September 2019, as of 31 January 2023, 31 ASF cases have occurred at pig farms, while 2799 ASF virus (ASFV)-infected wild boars have been identified. The circulation of ASFV in wild boar populations poses a high risk of spillover to pig farms in the country. However, information on the changes in the pathogenicity of Korean ASFV strains from wild boars is not available. Investigating the pathogenicity of ASFV strains from pig farms is the only way to predict their alterations. In a previous study, no changes in the pathogenicity of ASFV strains circulating during 2019-2021 were identified through animal experiments. In this study, we chose two ASFV strains with potentially reduced pathogenicity among ten viruses obtained from pig premises from 2022 to January 2023 and estimated their pathogenicities and pathological characteristics. All the inoculated pigs died 8-10 days post-inoculation after showing pyrexia, depression, anorexia, and recumbency together with the common pathological lesions of enlarged hemorrhagic lymph nodes and splenomegaly with infarction. These results support that the pathogenicity among ASFV isolates in South Korea still remained unchanged during the study period.

Epidemiological impacts of attenuated African swine fever virus circulating in wild boar populations

African swine fever virus (ASFV) genotype II has been present in wild boar in the European Union since 2014. Control measures have reduced the incidence of the ASF, but highly virulent as well as attenuated ASFV strains continue to circulate. We present the intraherd epidemiological parameters of low and highly virulent ASFV in wild boar from experimental data, and for the first time, evaluate the impact of attenuated strain circulation through unique deterministic compartmental model simulations under various potential scenarios and hypotheses. Using an estimated PCR infectious threshold of TPCR = 36.4, we obtained several transmission parameters, like an Rx (experimental intraherd R0) value of 4.5. We also introduce two novel epidemiological parameters: infectious power and resistance power, which indicate the ability of animals to transmit the infection and the reduction in infectiousness after successive exposures to varying virulence strains, respectively. The presence of ASFV attenuated strains results in 4-17% of animals either remaining in a carrier state or becoming susceptible again when exposed to highly virulent ASFV for more than two years. The timing between exposures to viruses of different virulence also influences the percentage of animals that die or remain susceptible. The findings of this study can be utilized in epidemiological modelling and provide insight into important risk situations that should be considered for surveillance and future potential ASF vaccination strategies in wild boar.

Unregulated Online Sales are High-Risk Sources of Domestic Swine (Sus scrofa) in Canada: Implications for Invasive Wild Pig and AfricanSwine Fever Risk Preparedness

Free-ranging wild pig (Sus scrofa) populations may cause widespread environmental damage and transmit diseases at the wildlife-livestock interface. For example, African swine fever (ASF) is a highly contagious viral disease of pigs capable of causing catastrophic economic losses. Prevention and preparedness for ASF require understanding wild and domestic pig movements and distribution. We characterized a "grey" swine market and described the risks it poses, contributing to the threats associated with wild pig populations. We monitored www.kijiji.ca, a Canadian internet classified advertising service, for sales of domestic wild boar, pot-bellied pigs, other breeds, and their hybrids across Canada from 28 April to 30 June 2021. Data collected included seller-defined breed, age, sex, number for sale, sexual intactness, presence of identifying tags or tattoos, and the date and location of listings. Advertisement locations were mapped and compared with existing wild pig distributions, identifying areas new populations might be established, and existing populations supplemented or genetically diversified. We identified 151 advertisements on Kijiji: 34% (n=52/151) from Ontario, 29% (n=44/151) from Alberta, 41% (n=62/151) from existing wild pig populations, and 59% (n=89/151) from areas where wild pigs have not yet been identified. We propose requiring the use of individual animal identifiers (tags/tattoos), genetic analysis, and mandatory reporting for all pig sales in Canada to aid in ASF preparedness and to increase regulation and enforcement of the online swine market.

Pathobiological analysis of african swine fever virus contact-exposed pigs and estimation of the basic reproduction number of the virus in Vietnam

BACKGROUND

African swine fever (ASF), caused by African swine fever virus (ASFV), is a fatal disease affecting wild and domestic pigs. Since China reported the first ASF outbreak in August 2018, ASFV has swept over the neighbouring Asian countries. However, studies involving experimental pig-to-pig ASFV transmission in Vietnam are lacking. The main objective of this experimental study was to demonstrate the pathobiological characteristics of ASFV contact-exposed pigs and estimate their basic reproduction number (R₀) in Vietnam. Fifteen pigs were randomly divided into two groups: experimental (n = 10) and negative control (n = 5) groups. One pig in the experimental group was intramuscularly inoculated with ASFV strain from Vietnam in 2020 and housed with the uninoculated pigs during the study period (28 days).

RESULTS

The inoculated pig died 6 days post-inoculation, and the final survival rate was 90.0%. We started observing viremia and excretion of ASFV 10 days post-exposure in contact-exposed pigs. Unlike the surviving and negative control pigs, all necropsied pigs showed severe congestive splenomegaly and moderate-to-severe haemorrhagic lesions in the lymph nodes. The surviving pig presented with mild haemorrhagic lesions in the spleen and kidneys. We used Susceptible-Infectious-Removed models for estimating R₀. The R₀ values for exponential growth (EG) and maximum likelihood (ML) were calculated to be 2.916 and 4.015, respectively. In addition, the transmission rates (β) were estimated to be 0.729 (95% confidence interval [CI]: 0.379-1.765) for EG and 1.004 (95% CI: 0.283-2.450) for ML.

CONCLUSIONS

This study revealed pathobiological and epidemiological information in about pig-to-pig ASFV transmission. Our findings suggested that culling infected herds within a brief period of time may mitigate the spread of ASF outbreaks.

Predicting Suitable Areas for African Swine Fever Outbreaks in Wild Boars in South Korea and Their Implications for Managing High-Risk Pig Farms

African swine fever (ASF) is a highly contagious disease affecting domestic pigs and wild boars, with no effective vaccine or treatment available. In South Korea, extensive measures have been implemented to prevent ASF transmission between wild boars and ASF spillover from wild boars to pig farm sectors, including the search for ASF-infected carcasses in mountainous forests and the installation of fences across wide areas of these forests. To determine the priority search range for infected carcasses and establish pig farm-centered quarantine measures, it is necessary to predict the specific path of ASF outbreaks in wild boars and identify pig farms at high risk of ASF spillover from wild boars. Here, we aimed to predict suitable areas and geographical paths for ASF outbreaks in wild boars using the MaxEnt model and shortest-path betweenness centrality analysis. The analysis identified a high frequency of ASF outbreaks in areas with a suitability value ≥0.4 on the suitability map and in areas within a 1.8 km range from the path on the shortest-path map, indicating these areas were high-risk zones for ASF outbreaks. Among the 5063 pig farms analyzed, 37 were in the high-risk zone on the suitability map, 499 were in the high-risk zone on the shortest-path map, and 9 were in both risk zones. Of the 51 pig farm sectors with a dense distribution of pig farms (kernel density ≥ 8), 25 sectors were in contact with or partially overlapped the high risk zone on the suitability map, 18 sectors were located within the high risk zone on the shortest-path map, and 14 sectors were located within both risk zones. These findings aided in determining the priority range for searches for wild boar carcasses and enabled the establishment of preemptive ASF prevention measures around the pig farming sectors that are at risk of ASF spillover from wild boars.

Evidence of aerosol transmission of African swine fever virus between two piggeries under field conditions: a case study

African swine fever (ASF) is a devastating and economically significant infectious disease that has caused enormous losses in the commercial pig sector in China since 2018. The primary transmission routes of the African swine fever virus (ASFV), the causative agent of ASF, are direct pig-to-pig contact or indirect contact with virus-contaminated objects. While aerosol transmission of ASFV has been previously reported under experimental conditions, no reports have described it under field conditions. In this case study, aerosol-associated samples were collected over a monitoring period of 24 days in an ASFV-positive farm. A complete and clear chain of ASFV transmission through aerosols was observed: pigs in Room A on Day 0-aerosol in Room A on Day 6-dust of air outlets in Room A on Day 9-outdoor aerosols on Day 9-dust of air inlets in Room B on Day 15-aerosols/pigs in Room B on Day 21. Furthermore, a fluorescent powder experiment confirmed the transmission of dust from Room A to Room B. This study represents the first report providing evidence of aerosol transmission of ASFV under field conditions. Further research is needed to study the laws of aerosol transmission in ASFV and develop effective strategies such as air filtration or disinfection to create a low-risk environment with fresh air for pig herds.

Pathology of African Swine Fever in Reproductive Organs of Mature Breeding Boars

African swine fever (ASF) is a severe, globally important disease in domestic and wild pigs. The testing of alternative transmission routes has proven that the ASF virus (ASFV) can be efficiently transmitted to sows via semen from infected boars through artificial insemination. Boars intramuscularly inoculated with the ASFV strain “Estonia 2014” showed grossly and microscopically visible changes in the testis, epididymis, prostate, and vesicular gland. The gross lesions included hemorrhages on the scrotum, testicular membranes, and parenchyma; edema; hydroceles; and proliferations of the tunica vaginalis. Histopathologically, vasculitis and perivasculitis was detected in the testis and epididymis. Subacutely infected animals further revealed a degeneration of the testicular and epididymal tubules, pointing to the destruction of the blood–testis and blood–epididymis barriers upon disease progression. This was confirmed by evidence of semen round cells and sperm abnormalities at later time points after the infection. The histopathology was associated with the presence of viral DNA and the infectious virus, and in a limited amount with viral antigens. In most scenarios, the impact of these changes on the reproductive performance and long-term persistence of the virus is probably negligible due to the culling of the animals. However, under backyard conditions and in wild boar populations, infected males will remain in the population and the long-term fate should be further evaluated.

Pathological Characteristics of Domestic Pigs Orally Infected with the Virus Strain Causing the First Reported African Swine Fever Outbreaks in Vietnam

African swine fever (ASF) is currently Vietnam’s most economically significant swine disease. The first ASF outbreak in Vietnam was reported in February 2019. In this study, VNUA/HY/ASF1 strain isolated from the first ASF outbreak was used to infect 10 eight-week-old pigs orally with 103 HAD50 per animal. The pigs were observed daily for clinical signs, and whole blood samples were collected from each animal for viremia detection. Dead pigs were subjected to full post-mortem analyses. All 10 pigs displayed acute or subacute clinical signs and succumbed to the infection between 10 to 27 (19.8 ± 4.66) days post-inoculation (dpi). The onset of clinical signs started around 4–14 dpi. Viremia was observed in pigs from 6–16 dpi (11.2 ± 3.55). Enlarged, hyperemic, and hemorrhagic lymph nodes, enlarged spleen, pneumonia, and hydropericardium were observed at post-mortem examinations.

Comparison of diaphragm meat juice and muscle swab samples to spleen and spleen swab samples for the detection of African swine fever viral nucleic acid

Use of meat juice and muscle swabs at slaughterhouses may provide an easy-to-collect sample for African swine fever (ASF) surveillance. Meat juice has been experimentally shown to be a reliable sample for the detection of ASF virus (ASFV). We compared the detection of ASFV nucleic acid from diaphragm meat juice, diaphragm muscle swab, spleen, and spleen swabs from pigs with signs of ASFV infection at slaughterhouses around Kampala, Uganda. Pigs with ≥2 clinical or pathology signs at the time of slaughter had a spleen sample, spleen swab, diaphragm muscle sample, and diaphragm muscle swab collected. Meat juice was collected from muscle samples through a freeze-thaw cycle. Each sample was tested individually, and 72 spleen, meat juice, and muscle swab sample pools of 4 negative and 1 positive sample were tested, as well. Standard operating procedures from the USDA-Foreign Animal Disease Diagnostic Laboratory for viral DNA extraction and real-time PCR (rtPCR) were used. Of the 493 pigs evaluated, we classified as positive 357 (72.4%) diaphragm meat juice samples, 218 (44.2%) diaphragm muscle swabs, 247 (50.1%) spleen samples, and 241 (48.9%) spleen swabs. All spleen sample pools were positive (72 of 72; 100%), as were 71 of 72 (98.6%) meat juice pools and 67 of 72 (93.1%) muscle swab pools. Meat juice samples provided a reliable sample type for the detection by rtPCR of ASFV in pigs with natural infections.

Dynamics of Serological and Mucosal Antibody Responses against African Swine Fever Viruses in Experimentally Infected Pigs

African swine fever virus (ASFV) is a lethal swine pathogen, and there is no effective vaccine or treatment available for ASFV infection. Recently, the occurrence of ASFV genotype I and genotype II natural mutants that manifest as subacute, longer-incubation, or persistent infections poses threats to preventing ASFV infection. The dynamics of antibody responses to ASFV are still completely unrevealed, especially the secretion of mucosal antibodies in oral fluid. Here, a systematic analysis was performed of serological and mucosal antibody secretion against 6 ASFV antigens after direct or indirect infection with four different ASFV strains or genotypes, namely, the field virulent genotype II isolate ASFV HLJ/18, the artificially attenuated genotype II strain HLJ/18-7GD, the naturally attenuated genotype II isolate HLJ/HRB1/20, and genotype I isolate SD/DY-I/21. Severe clinical signs of HLJ/18 infection were observed in pigs from 4 days postinoculation. However, no clinical signs were observed in HLJ/18-7GD-infected pigs. The contact pigs cohoused with the pigs intramuscularly infected with the isolate SD/DY-I/21 or HLJ/HRB1/20 only showed chronic clinical signs. Interestingly, the oral fluid sIgA responses to all the selected antigens were significantly stronger and earlier than the serum IgG responses in both HLJ/18- and HLJ/18-7GD-challenged pigs. Although significant fluctuations and individual differences appeared in oral swab sIgA responses in the contact transmission group, they were earlier than the corresponding serological IgG responses. Moreover, according to the comparative analysis of the three infection groups, P54 was proposed to be a dominant target for serological IgG diagnosis, while P30, CD2v, P54, P22, and P10 were more advantageous as mucosal sIgA diagnosis targets. These results highlight the important role of mucosal antibodies in the early diagnosis of ASFV infection and can provide references to screen appropriate targets for ASFV detection.

SWOT analysis of risk factors associated with introduction of African Swine Fever through vehicles returning after export of pigs

Denmark is a major pig exporter and applies a high level of biosecurity, with washing and disinfecting stations for returning livestock vehicles. The introduction of African Swine Fever (ASF) would have significant economic consequences related to loss of export of live pigs and products thereof. In this study, we focused on the role of empty livestock vehicles returning after exports of pigs for the introduction of ASF. Initially, the current components and measures related to export of livestock were described. Next, analyses of strengths, weaknesses, opportunities, and threats (SWOT) were conducted, covering the components and measures identified. Then, export of pigs was described either through assembly centers or directly from farms. Washing and disinfection, as required and undertaken at the designated stations, constitutes the most important among all risk-reducing measures identified. Recommendations are to: (1) ensure the quality of washing and disinfection through staff training; (2) find new, safe, and more efficient disinfectants; (3) ensure the required temperature, and therefore effect, of the disinfectant and water. It was impossible to assess, the influence of export through assembly centers compared to direct transport. However, through SWOT analyses we identified the strengths and weaknesses of the two pathways. Moreover, components/measures with risks of unknown sizes are also discussed, such as vehicles undertaking cabotage and the current vehicle quarantine periods.

Magnetic-bead-based DNA-capture-assisted real-time polymerase chain reaction and recombinase polymerase amplification for the detection of African swine fever virus

African swine fever (ASF) is a deadly disease in swine caused by African swine fever virus (ASFV). The global spread of ASFV has resulted in significant economic losses worldwide. Improved early detection has been the most important first line of defense for preventing ASF outbreaks and for activating control measures. Despite the availability of rapid amplification methods, nucleic acid extraction from specimens still needs to be performed in a laboratory. To facilitate this step, we exploited the strong affinity of biotin-streptavidin binding by functionalizing streptavidin-coated magnetic beads with biotinylated oligonucleotide capture probes to efficiently capture genotype II ASFV DNA directly from crude clinical samples. The captured DNA is suitable for detection using real-time quantitative PCR (qPCR) and recombinase polymerase amplification (RPA). In this study, ASFV DNA was efficiently captured from swine feces, serum, and tissue samples. Both DNA-capture-assisted qPCR and RPA-based detection methods have a limit of detection (LOD) of 10² copies/µl, which is comparable to those of commercially available kits. In addition, an RPA-SYBR Green I method was developed for the immediate visual detection of ASFV DNA, which is time-saving and efficient for resource-limited field settings. In summary, a rapid, versatile, sequence-specific DNA capture method was developed to efficiently capture ASFV DNA from swine clinical samples and subsequent detection by qPCR and RPA, which has the potential to be used for robust screening and surveillance of ASFV and in point-of-care (POC) diagnostics.

A triton X-100 assisted PMAxx-qPCR assay for rapid assessment of infectious African swine fever virus

Introduction

African Swine Fever (ASF) is a highly infectious disease of pigs, caused by African swine fever virus (ASFV). The lack of vaccines and drugs makes strict disinfection practices to be one of the main measurements to curb the transmission of ASF. Therefore, it is important to assess if all viruses are inactivated after disinfection or after long time exposure in their natural conditions. Currently, the infectivity of ASFV is determined by virus isolation and culture in a biosafety level 3 (BSL-3) laboratory. However, BSL-3 laboratories are not readily available, need skilled expertise and may be time consuming.

Methods

In this study, a Triton X-100 assisted PMAxx-qPCR method was developed for rapid assessment of infectious ASFV in samples. PMAxx, an improved version of propidium monoazide (PMA), can covalently cross-link with naked ASFV-DNA or DNA inside inactivated ASFV virions under assistance of 0.1% (v/v) TritonX-100, but not with ASFV-DNA inside live virions. Formation of PMAxx-DNA conjugates prevents PCR amplification, leaving only infectious virions to be detected. Under optimum conditions, the limit of detection of the PMAxx-qPCR assay was 2.32log₁₀HAD₅₀/mL of infectious ASFV. Testing different samples showed that the PMAxx-qPCR assay was effective to evaluate intact ASFV virions after treatment by heat or chemical disinfectants and in simulated samples such as swine tissue homogenate, swine saliva swabs, and environmental swabs. However, whole-blood and saliva need to be diluted before testing because they may inhibit the PCR reaction or the cross-linking of PMAxx with DNA.

Conclusion

The Triton X-100 assisted PMAxx-qPCR assay took less than 3 h from sample to result, offering an easier and faster way for assessing infectious ASFV in samples from places like pig farms and pork markets.

Experimental Infection of Domestic Pigs with African Swine Fever Virus Isolated in 2019 in Mongolia

African swine fever (ASF) is an infectious viral disease caused by African swine fever virus (ASFV), that causes high mortality in domestic swine and wild boar (Sus scrofa). Currently, outbreaks are mitigated through strict quarantine measures and the culling of affected herds, resulting in massive economic losses to the global pork industry. In 2019, an ASFV outbreak was reported in Mongolia, describing a rapidly progressing clinical disease and gross lesions consistent with the acute form of ASF; the virus was identified as a genotype II virus. Due to the limited information on clinical disease and viral dynamics within hosts available from field observations of the Mongolian isolates, we conducted the present study to further evaluate the progression of clinical disease, virulence, and pathology of an ASFV Mongolia/2019 field isolate (ASFV-MNG19), by experimental infection of domestic pigs. Intramuscular inoculation of domestic pigs with ASFV-MNG19 resulted in clinical signs and viremia at 3 days post challenge (DPC). Clinical disease rapidly progressed, resulting in the humane euthanasia of all pigs by 7 DPC. ASFV-MNG19 infected pigs had viremic titers of 10⁸ TCID₅₀/mL by 5 DPC and shed virus in oral secretions late in disease, as determined from oropharyngeal swabs. Whole-genome sequencing confirmed that the ASFV-MNG19 strain used in this study was a genotype II strain highly similar to other regional strains. In conclusion, we demonstrate that ASFV-MNG19 is a virulent genotype II ASFV strain that causes acute ASF in domestic swine.

Comparison of the Virulence of Korean African Swine Fever Isolates from Pig Farms during 2019-2021

African swine fever (ASF) was first reported in South Korea in September 2019, and as of 31 December 2021, a total of 21 cases in domestic pig farms and 1875 ASFV-infected wild boars have been confirmed in the country. With the continued circulation of ASF in wild boars, and subsequent outbreaks in domestic pigs, concerns were raised about the possible changes in virulence occurring among African swine fever viruses (ASFV) circulating in South Korea. In this study, four Korean ASFV strains isolated from domestic pig farms at different time points between 2019 and 2021 were chosen, and used to experimentally infect domestic pigs by intramuscular inoculation to compare their virulence. All challenged pigs died at 4-9 days post-inoculation, with many showing clinical symptoms of fever, depression, loss of appetite, and recumbency. Gross lesions observed at necropsy included enlargement and hemorrhage of the lymph nodes and hydropericardium. The study showed that all four Korean ASFV isolates caused acute forms of illness, which supports the view that virulence among the circulating ASFV isolates in South Korea remained unchanged and highly virulent during this period.

African swine fever virus infection activates inflammatory responses through downregulation of the anti-inflammatory molecule C1QTNF3

African swine fever (ASF) is the most dangerous pig disease, and causes enormous economic losses in the global pig industry. However, the mechanisms of ASF virus (ASFV) infection remains largely unclear. Hence, this study investigated the host response mechanisms to ASFV infection. We analyzed the differentially expressed proteins (DEPs) between serum samples from ASFV-infected and uninfected pigs using quantitative proteomics. Setting the p-value < 0.05 and |log2 (fold change)| > 1.5, we identified 173 DEPs, comprising 57 upregulated and 116 downregulated proteins, which belonged to various biological processes and pathways based on the Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses. The enriched pathways include immune responses, metabolism, and inflammation signaling pathways. Western blot analysis validated the DEPs identified using quantitative proteomics. Furthermore, our proteomics data showed that C1QTNF3 regulated the inflammatory signaling pathway. C1QTNF3 knockdown led to the upregulation of pro-inflammatory factors IL-1β, IL-8, and IL-6, thus inhibiting ASFV replication. These results indicated that C1QTNF3 was critical for ASFV infection. In conclusion, this study revealed the molecular mechanisms underlying the host-ASFV interaction, which may contribute to the development of novel antiviral strategies against ASFV infection in the future.

Thermal inactivation of African swine fever virus in feed ingredients

African swine fever virus (ASFV) causes a fatal infectious disease affecting domestic pigs and wild boars. ASFV is highly stable and easily transmitted by consumption of contaminated swine feed and pork products. Heat treatment of feed ingredients is a means to minimize the risk of contamination through swine feed consumption. The objectives of this study were to determine the thermal inactivation of ASFV in non-animal and animal origin feed ingredients. The rate of thermal inactivation is represented by decimal reduction time (D_T) or time required to reduce ASFV per 1 log at temperature T. The mean D₆₀, D₇₀, D₈₀ and D₈₅ of meat and bone meal (MBM), soybean meal (SBM), and maize grain (MZ) are in the ranges 5.11-6.78, 2.19-3.01, 0.99-2.02, and 0.16-0.99 min, respectively. D_T is used to compare the heat resistance of ASFV in the feed ingredient matrices. The mean D_T of ASFV in MBM, SBM and MZ was not statistically significant, and the heat resistance of ASFV in MBM, SBM, and MZ was not different at 60, 70, 80, or 85 °C. The multiple D_T was used to develop a D_T model to predict D_T at various inactivation temperatures. The D_T models for MBM, SBM, and MZ are log D_T = - [Formula: see text] + 2.69, log D_T = - [Formula: see text] + 2.55, and log D_T = - [Formula: see text] + 4.01. To expand and ease the field applications, a spreadsheet predicting the D_T and the inactivation time (with 95% confidence interval) from these D_T models is available to download.

Modelling and stability analysis of ASFV with swill and the virus in the environment

African swine fever (ASF) is an acute, hemorrhagic and severe infectious disease caused by the African swine fever virus (ASFV), and leads to a serious threat to the pig industry in China. Yet the impact of the virus in the environment and contaminated swill on the ASFV transmission is unclear in China. Then we build the ASFV transmission model with the virus in the environment and swill. We compute the basic reproduction number, and prove that the disease-free equilibrium is globally asymptotically stable when $ R_0 < 1 $ and the unique endemic equilibrium is globally asymptotically stable when $ R_0 > 1 $. Using the public information, parameter values are evaluated. PRCCs and eFAST sensitivity analysis reveal that the release rate of ASFV from asymptomatic and symptomatic infectious pigs and the proportion of pig products from infectious pigs to swill have a significant impact on the ASFV transmission. Our findings suggest that the virus in the environment and contaminated swill contribute to the ASFV transmission. Our results may help animal health to prevent and control the ASFV transmission.

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

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

Non-Invasive Sampling in the Aspect of African Swine Fever Detection—A Risk to Accurate Diagnosis

African swine fever remains one of the most economically important and dangerous diseases of the Suidae family. Until now, neither a safe vaccine nor a treatment against ASF has been available, which is why prevention of the disease involves biosecurity measures and early recognition based on accurate diagnosis. Nowadays, different strategies for ASF detection are discussed to reduce both animal suffering and the costs of ASF surveillance. This article aims to indicate the risk, with regard to non-invasive sampling, for the detection of ASFV. In this study, we analyzed data from three independent animal trials, in the framework of the detection of positive samples in different matrices (blood, sera, oral and rectal swabs) collected from nineteen domestic pigs infected with similar doses but under different scenarios, including different ASFV strains or routes of infection. Genetic material of ASFV was found in all matrices, but detection occurred earlier in the blood samples than in the oral and the rectal swabs. Furthermore, analyses revealed that at relevant sampling timepoints, PCR-positive blood samples were detected more frequently and reached higher percentages (up to 100% during fever) than oral and rectal swabs. Moreover, mean Ct values in blood samples collected from animals infected with virulent strains were significantly lower than in oral and rectal swabs, ensuring a higher probability of ASFV detection. High Ct values and occasional shedding in all tested matrices, in the cases of animals infected by an attenuated ASFV-strain, showed that blood sampling may be necessary to confirm the presence of anti-ASFV antibodies in sera. This study showed that during veterinary surveillance, blood sampling (for both PCR and serological analyses) is essential for the accurate diagnosis of ASF and provides the highest probability of detection of the disease.

Transcriptome profile of spleen tissues from locally-adapted Kenyan pigs (Sus scrofa) experimentally infected with three varying doses of a highly virulent African swine fever virus genotype IX isolate: Ken12/busia.1 (ken-1033)

Background

African swine fever (ASF) is a lethal hemorrhagic disease affecting domestic pigs resulting in up to 100% mortality rates caused by the ASF virus (ASFV). The locally-adapted pigs in South-western Kenya have been reported to be resilient to disease and harsh climatic conditions and tolerate ASF; however, the mechanisms by which this tolerance is sustained remain largely unknown. We evaluated the gene expression patterns in spleen tissues of these locally-adapted pigs in response to varying infective doses of ASFV to elucidate the virus-host interaction dynamics.

Methods

Locally adapted pigs (n = 14) were experimentally infected with a high dose (1x10⁶HAD₅₀), medium dose (1x10⁴HAD₅₀), and low dose (1x10²HAD₅₀) of the highly virulent genotype IX ASFV Ken12/busia.1 (Ken-1033) isolate diluted in PBS and followed through the course of infection for 29 days. The in vivo pig host and ASFV pathogen gene expression in spleen tissues from 10 pigs (including three from each infective group and one uninfected control) were analyzed in a dual-RNASeq fashion. We compared gene expression between three varying doses in the host and pathogen by contrasting experiment groups against the naïve control.

Results

A total of 4954 differentially expressed genes (DEGs) were detected after ASFV Ken12/1 infection, including 3055, 1771, and 128 DEGs in the high, medium, and low doses, respectively. Gene ontology and KEGG pathway analysis showed that the DEGs were enriched for genes involved in the innate immune response, inflammatory response, autophagy, and apoptosis in lethal dose groups. The surviving low dose group suppressed genes in pathways of physiopathological importance. We found a strong association between severe ASF pathogenesis in the high and medium dose groups with upregulation of proinflammatory cytokines and immunomodulation of cytokine expression possibly induced by overproduction of prostaglandin E synthase (4-fold; p < 0.05) or through downregulation of expression of M1-activating receptors, signal transductors, and transcription factors. The host-pathogen interaction resulted in induction of expression of immune-suppressive cytokines (IL-27), inactivation of autophagy and apoptosis through up-regulation of NUPR1 [5.7-fold (high dose) and 5.1-fold (medium dose) [p < 0.05] and IL7R expression. We detected repression of genes involved in MHC class II antigen processing and presentation, such as cathepsins, SLA-DQB1, SLA-DOB, SLA-DMB, SLA-DRA, and SLA-DQA in the medium and high dose groups. Additionally, the host-pathogen interaction activated the CD8⁺ cytotoxicity and neutrophil machinery by increasing the expression of neutrophils/CD8⁺ T effector cell-recruiting chemokines (CCL2, CXCL2, CXCL10, CCL23, CCL4, CXCL8, and CXCL13) in the lethal high and medium dose groups. The recovered pigs infected with ASFV at a low dose significantly repressed the expression of CXCL10, averting induction of T lymphocyte apoptosis and FUNDC1 that suppressed neutrophilia.

Conclusions

We provide the first in vivo gene expression profile data from locally-adapted pigs from south-western Kenya following experimental infection with a highly virulent ASFV genotype IX isolate at varying doses that mimic acute and mild disease. Our study showed that the locally-adapted pigs induced the expression of genes associated with tolerance to infection and repression of genes involved in inflammation at varying levels depending upon the ASFV dose administered.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08754-8.

Experimental Infections of Pigs with African Swine Fever Virus (Genotype II); Studies in Young Animals and Pregnant Sows

African swine fever is an important viral disease of wild and domestic pigs. To gain further knowledge of the properties of the currently circulating African swine fever virus (ASFV), experimental infections of young pigs (approximately 8 weeks of age) and pregnant sows (infected at about 100 days of gestation) with the genotype II ASFV Georgia/2007 were performed. The inoculated young pigs developed typical clinical signs of the disease and the infection was transmitted (usually within 3–4 days) to all of the “in contact” animals that shared the same pen. Furthermore, typical pathogical lesions for ASFV infection were found at necropsy. Inoculation of pregnant sows with the same virus also produced rapid onset of disease from post-infection day three; two of the three sows died suddenly on post-infection day five, while the third was euthanized on the same day for animal welfare reasons. Following necropsy, the presence of ASFV DNA was detected in tonsils, spleen and lymph nodes of some of the fetuses, but the levels of viral DNA were much lower than in these tissues from the sows. Thus, only limited transplacental transmission occurred during the course of this experiment. These studies contribute towards further understanding about the spread of this important viral disease in domestic pigs.

Rapid and sensitive detection of African swine fever virus in pork using recombinase aided amplification combined with QDMs-based test strip

African swine fever virus (ASFV) is the pathogen of African swine fever, a highly contagious and fatal disease of wild boar and domestic pigs. The flow of ASFV through pork products is more concealed, higher risky, and more difficult to prevent and control. Presently, on-site ASFV detection methods in preclinical infected pigs and circulated pork products are lacking. Here, fluorescent test strip-based rapid ASFV detection method in pork was established combined with recombinase aided amplification (RAA) and quantum dot microspheres (QDMs). This method is specific to ASFV with no cross-reactivity to pseudorabies virus (PRV), porcine circovirus type 2 (PCV2), and porcine reproductive and respiratory syndrome virus (PRRSV). The method also showed highly sensitivity with a detection limit of 1 copy for ASFV plasmid templates containing B646L gene and 100 copies/g for DNA extracts from clinical pork samples within a short detection time of less than 25 min. Additionally, the method showed 99.17% consistency with real-time PCR in the ASFV detection of 120 clinical pork samples. Overall, the QDMs-based test strip method provides specific, sensitive, rapid, and simple detection of ASFV in pork, which may contribute to maintain the food safety of pork products, and facilitate ASFV traceability and prevention. Rapid and sensitive detection of African swine fever virus in pork by QDMs based test strip assay.

An Assessment of Diagnostic Assays and Sample Types in the Detection of an Attenuated Genotype 5 African Swine Fever Virus in European Pigs over a 3-Month Period

African swine fever virus causes hemorrhagic disease in swine. Attenuated strains are reported in Africa, Europe, and Asia. Few studies on the diagnostic detection of attenuated ASF viruses are available. Two groups of pigs were inoculated with an attenuated ASFV. Group 2 was also vaccinated with an attenuated porcine reproductive and respiratory syndrome virus vaccine. Commercially available ELISA, as well as extraction and qPCR assays, were used to detect antibodies in serum and oral fluids (OF) and nucleic acid in buccal swabs, tonsillar scrapings, OF, and blood samples collected over 93 days, respectively. After 12 dpi, serum (88.9% to 90.9%) in Group 1 was significantly better for antibody detection than OF (0.7% to 68.4%). Group 1′s overall qPCR detection was highest in blood (48.7%) and OF (44.2%), with the highest detection in blood (85.2%) from 8 to 21 days post inoculation (dpi) and in OF (83.3%) from 1 to 7 dpi. Group 2′s results were not significantly different from Group 1, but detection rates were lower overall. Early detection of attenuated ASFV variants requires active surveillance in apparently healthy animals and is only reliable at the herd level. Likewise, antibody testing will be needed to prove freedom from disease.

Exact Bayesian inference of epidemiological parameters from mortality data: application to African swine fever virus

Pathogens such as African swine fever virus (ASFV) are an increasing threat to global livestock production with implications for economic well-being and food security. Quantification of epidemiological parameters, such as transmission rates and latent and infectious periods, is critical to inform efficient disease control. Parameter estimation for livestock disease systems is often reliant upon transmission experiments, which provide valuable insights in the epidemiology of disease but which may also be unrepresentative of at-risk populations and incur economic and animal welfare costs. Routinely collected mortality data are a potential source of readily available and representative information regarding disease transmission early in outbreaks. We develop methodology to conduct exact Bayesian parameter inference from mortality data using reversible jump Markov chain Monte Carlo incorporating multiple routes of transmission (e.g. within-farm secondary and background transmission from external sources). We use this methodology to infer epidemiological parameters for ASFV using data from outbreaks on nine farms in the Russian Federation. This approach improves inference on transmission rates in comparison with previous methods based on approximate Bayesian computation, allows better estimation of time of introduction and could readily be applied to other outbreaks or pathogens.

Differential antibody responses in sows and finishing pigs naturally infected with African swine fever virus under field conditions

Antibody profile of pigs naturally infected with a virulent African swine fever virus (ASFV) strain under field conditions was studied. Twenty-three serum samples were collected from pigs surviving a natural ASFV infection: 17 samples from finishing pigs (∼7 months old) and 6 samples from sows (between 12 and 36 months old). Additionally, 24 serum samples were collected from ASFV-naïve pigs to serve as negative controls. All sera from ASFV-surviving pigs tested positive while all sera from control pigs tested negative by two different commercial ELISA kits. Antibody reactivity of each serum sample was simultaneously measured against six selected ASFV antigens including p12, p32, p54, pp62, C-type lectin and CD2v. All ASFV-surviving pigs had antibody against p32, p54 and pp62 while 91.3% surviving pigs had antibody against p12. Only small portions of ASFV-surviving pigs exhibited antibodies against C-type lectin (34.8%) and CD2v (26.1%). While antibodies against p12, p32, p54 and pp62 were similarly detected in both finishing pigs and sows, antibodies against C-type lectin and CD2v were mainly detected in sows but not in finishing pigs. These results suggest a differential humoral immune response to ASFV infection in sows and finishing pigs. Further studies are needed to better understand the nature of immune responses to ASFV infection in different pig populations.

Prevention and Control Strategies of African Swine Fever and Progress on Pig Farm Repopulation in China

African swine fever (ASF) is a devastating disease in domestic and wild pigs. Since the first outbreak of ASF in August 2018 in China, the disease has spread throughout the country with an unprecedented speed, causing heavy losses to the pig and related industries. As a result, strategies for managing the disease are urgently needed. This paper summarizes the important aspects of three key elements about African swine fever virus (ASFV) transmission, including the sources of infection, transmission routes, and susceptible animals. It overviews the relevant prevention and control strategies, focusing on the research progress of ASFV vaccines, anti-ASFV drugs, ASFV-resistant pigs, efficient disinfection, and pig farm biosecurity. We then reviewed the key technical points concerning pig farm repopulation, which is critical to the pork industry. We hope to not only provide a theoretical basis but also practical strategies for effective dealing with the ASF epidemic and restoration of pig production.

Dynamics of inter-farm transmission of highly pathogenic avian influenza H5N6 integrating vehicle movements and phylogenetic information

Highly pathogenic avian influenza (HPAI) in poultry holdings commonly spreads through animal trade, and poultry production and health-associated vehicle (PPHaV) movement. To effectively control the spread of disease, it is essential that the contact structure via those movements among farms is thoroughly explored. However, few attempts have been made to scrutinize PPHaV movement compared to poultry trade. Therefore, our study aimed to elucidate the role of PPHaV movement on HPAI transmission. We performed network analysis using PPHaV movement data based on a global positioning system, with phylogenetic information of the isolates during the 2016–2017 HPAI H5N6 epidemic in the Republic of Korea. Moreover, the contribution of PPHaV movement to the spread of HPAI was estimated by Bayesian modeling. The network analysis revealed that there was the relationship between phylogenetic clusters and the contact network via PPHaV movement. Furthermore, the similarity of farm poultry species and the shared integrators between inter-linked infected premises (IPs) were associated with ties within the same phylogenetic clusters. Additionally, PPHaV movement among phylogenetically clustered IPs was estimated to contribute to approximately 30% of HPAI H5N6 infections in IPs on average. This study provides insight into how HPAI spread via PPHaV movement and scientific basis for control strategies.

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

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

Intestinal microbiota disturbance affects the occurrence of African swine fever

Intestinal microbiota not only participates in the digestion and absorption of nutrients, but also plays an important role in regulating host metabolism and health. The current study aimed to explore the intestinal microbiota characteristics in pigs infected with African swine fever. Below the same term, fresh fecal samples of sick and healthy pigs were collected. Primers were designed and PCR was extracted based on the 16S rDNA gene of bacteria by Illumina NovaSeq sequencing platform. The results showed that the bacterial alpha diversity index of healthy pigs was significantly higher than that of sick pigs (p < 0.05). On the phylum taxa, dominant bacteria more than 98.5% in the two groups are composed of Firmicutes, Spirobacteria, and Bacteroides, of which the abundance of Firmicutes and Bacteroidetes decreased and Spiricobacteria increased extremely significant in sick pigs (p < 0.01). On the genus taxa, the relative abundance of Oscillospira, Streptococcus and Roseburia decreased significantly (p < 0.05). Most notably, Treponema performed excellently in distinguishing pigs infected with African swine fever with the abundance increased extremely significantly (p < 0.01). In conclusion, African swine fever could alter the abundance of dominant bacteria in pigs, and Treponema may be one of the important inducers for swine pathogenicity. HighlightsThe bacterial population composition in sick pigs and healthy pigs was basically similar, but the relative abundance of dominant bacteria was significantly difference.ASF could alter the abundance of dominant bacteria in pigs, and Treponema may be one of the important inducers for swine pathogenicity.These results will provide further evidence for the ASF infection in local pig farms and provide reference for their microecological control, which has important practical significance and social value for effective control of ASF, stability of pig production and guarantee of market supply.

Identification of African Swine Fever Virus Transcription within Peripheral Blood Mononuclear Cells of Acutely Infected Pigs

African swine fever virus (ASFV) has become widespread in Europe, Asia and elsewhere, thereby causing extensive economic losses. The viral genome includes nearly 200 genes, but their expression within infected pigs has not been well characterized previously. In this study, four pigs were infected with a genotype II strain (ASFV POL/2015/Podlaskie); blood samples were collected before inoculation and at both 3 and 6 days later. During this period, a range of clinical signs of infection became apparent in the pigs. From the blood, peripheral blood mononuclear cells (PBMCs) were isolated. The transcription of the ASFV genes was determined using RNAseq on poly(A)+ mRNAs isolated from these cells. Only very low levels of virus transcription were detected in the PBMCs at 3 days post-inoculation (dpi) but, at 6 dpi, extensive transcription was apparent. This was co-incident with a large increase in the level of ASFV DNA within these cells. The pattern of the virus gene expression was very reproducible between the individual pigs. Many highly expressed genes have undefined roles. Surprisingly, some genes with key roles in virus replication were expressed at only low levels. As the functions of individual genes are identified, information about their expression becomes important for understanding their contribution to virus biology.

Data-driven dynamical modelling of the transmission of African swine fever in a few places in China

Since the outbreak of African swine fever (ASF) in Shengyang, it has continued spreading in China. In the early stage of the epidemic, multi-point and concentrated outbreaks were mainly in the swill feeding areas. In this paper, we developed compartmental models to investigate the transmission of ASF in several raising units including Guquan, Jinba and Liancheng. Using the data collected from these three infected premises, we calibrated the models to estimate that the average incubation period was between 8 and 11 days, the onset period was about 2-3 days and the basic reproductive number was about 4.83-11.90. We also estimated the infection on the day before culling to be 45.24% (Guquan), 89.20% (Jinba) and 16.35% (Liancheng), respectively. The infection rate of Guquan could reach about 74.8% if culling were postponed by 2 days. We found that the infection was significantly higher than the morbidities (22.11% (Guquan), 49.35% (Jinba) and 12.94% (Liancheng)) calculated by actual statistical data. Besides, we simulated and compared the control effect of stopping transport, disinfecting, stopping swill and culling. Our findings suggest that any single measure was not enough to prevent the spread of ASF on a regional level but the combined measures is the key. Under the current situation, fully culling was recognized as most effective in controlling the epidemic, despite the culling of uninfected pigs.

Dynamic Variations in Infrared Skin Temperature of Weaned Pigs Experimentally Inoculated with the African Swine Fever Virus: A Pilot Study

African swine fever (ASF) is a devastating viral disease in pigs and is therefore economically important for the swine industry. ASF is characterized by a short incubation period and immediate death, making the early identification of ASF-infected pigs essential. This pilot-scale study evaluates whether the infrared thermography (IRT) technique can be used as a diagnostic tool to detect changes in skin temperature (T_sk) during the early stages of disease development in experimentally ASF-infected pigs. Clinical symptoms and rectal temperatures (T_core) were recorded daily, and IRT readings during the experimental ASF infection were analyzed. All infected pigs died at 5–8 days post inoculation (dpi), and the incubation period was approximately 4 dpi. The average T_core increased from 0 dpi (38.9 ± 0.3 °C) to 7 dpi (41.0 ± 0.5 °C) and decreased by 8 dpi (39.8 ± 0 °C). The maximum T_sk of ASF-infected pigs increased from 2 (35.0 °C) to 3 dpi (38.5 °C). The mean maximum T_sk observed from three regions on the skin (ear, inguinal, and neck) significantly increased from 2 to 3 dpi. This study presents a non-contact method for the early detection of ASF in infected pigs using thermal imaging at 3 days after ASF infection.