Risk factors for the spread of African Swine Fever in China: A systematic review of Chinese-language literature

Embedding research and enquiry in Australian DVM curriculum

Research and enquiry (R&E) is an integral part of veterinary training. It is a foundation of evidence-based practice. In the University of Sydney Doctor of Veterinary Medicine degree R&E culminates in a cap-stone experience in Year 3: a 'professionally focused project', a student-driven and academic supported individual research project. The project provides an authentic experience within a veterinary discipline. Students work with an academic advisor who provides guidance for developing and achieving meaningful educational and professional goals. Successful advising depends upon a shared understanding of, and commitment to, the advising process by students, advisors and the university. The R&E mission can be broadly defined as - veterinarians recognise that evidence-based approach to practice, which is based on the scientific method, leads to the generation of new knowledge that underpins the veterinary medical profession.

The role of vehicle movement in swine disease dissemination: Novel method accounting for pathogen stability and vehicle cleaning effectiveness uncertainties

Several propagation routes drive animal disease dissemination, and among these routes, contaminated vehicles traveling between farms have been associated with indirect disease transmission. In this study, we used near-real-time vehicle movement data and vehicle cleaning efficacy to reconstruct the between-farm dissemination of the African swine fever virus (ASFV). We collected one year of Global Positioning System data of 823 vehicles transporting feed, pigs, and people to 6363 swine production farms in two regions in the U.S. Without cleaning, vehicles connected up to 2157 farms in region one and 437 farms in region two. Individually, in region one vehicles transporting feed connected 2151 farms, pigs to farms 2089 farms, pigs to market 1507 farms, undefined vehicles 1760 farm, and personnel three farms. The simulation results indicated that the contact networks were reduced the most for crew transport vehicles with a 66% reduction, followed by vehicles carrying pigs to market and farms, with reductions of 43% and 26%, respectively, when 100% cleaning efficacy was achieved. The results of this study showed that even when vehicle cleaning and disinfection are 100% effective, vehicles are still connected to numerous farms. This emphasizes the importance of better understanding transmission risks posed by vehicles to the swine industry and regulatory agencies.

Development of a novel sensitive single-tube nested PCR assay for the detection of African swine fever virus

African swine fever (ASF) is a highly fatal and contagious viral disease caused by African swine fever virus (ASFV). It has caused significant economic losses to the swine industry and poses a serious threat to food security worldwide. Diagnostic tests with high sensitivity are essential for the effective management of ASF. Here, we describe a single-tube nested PCR (STN-PCR) assay for the detection of ASFV in which two consecutive amplification steps are carried out within a single tube. Two pairs of primers (outer and inner) were designed to target the p72 gene of ASFV. The primer concentrations, annealing temperatures, and number of amplification cycles were optimized to ensure the consecutive utilization of outer and inner primer pairs during amplification while minimizing the likelihood of amplicon contamination. In comparison with two conventional endpoint PCR assays (one of which is recommended by the World Organization for Animal Health), the newly developed STN-PCR assay demonstrated a 100-fold improvement in the limit of detection (LOD), detecting 100 copies of ASFV genomic DNA, whereas the endpoint PCR assays could detect no fewer than 10,000 copies. The clinical performance of the STN-PCR assay was validated using 95 tissue samples suspected of being positive for ASFV, and the assay showed 100% specificity. A Cohen's kappa value of 0.91 indicated perfect agreement between the assays. This new STN-PCR assay is a potentially valuable tool that will facilitate the control of ASF.

A porcine kidney-derived clonal cell line with clear genetic annotation is highly susceptible to African swine fever virus

African Swine Fever virus (ASFV), the causative agent of African swine fever, is a highly lethal hemorrhagic virus affecting domestic pigs and wild boars. The primary target cells for ASFV infection are porcine alveolar macrophages (PAMs), which are difficult to obtain and maintain in vitro, and less subjective to genetic editing. To overcome these issues and facilitate ASFV research, we obtained a subclonal cell line PK1-C5 by subcloning LLC-PK1 cells that support stable ASFV proliferation. This consequential cell line exhibited high ASFV infection levels and similar viral growth characteristics to PAMs, while also allowing high-efficiency genomic editing through transfection or lentivirus transduction of Cas9. Taken together, our study provided a valuable tool for research aspects including ASFV-host interactions, pathogenicity, and vaccine development.

A triplex crystal digital PCR for the detection of genotypes I and II African swine fever virus

African swine fever (ASF) is a highly contagious and lethal viral disease that causes severe hemorrhagic fever in pigs. It keeps spreading around the world, posing a severe socioeconomic risk and endangering biodiversity and domestic food security. ASF first outbroke in China in 2018, and has spread to most provinces nationwide. Genotypes I and II ASF virus (ASFV) as the etiological pathogens have been found in China. In this study, three pairs of specific primers and probes targeting the ASFV B646L gene, F1055L gene, and E183L gene were designed to detect universal, genotype I, and genotype II strains, respectively. A triplex crystal digital PCR (cdPCR) was established on the basis of optimizing various reaction conditions. The assay demonstrated remarkably sensitive with low limits of detection (LODs) of 5.120, 4.218, 4.588 copies/reaction for B646L, F1055L, and E183L gene, respectively; excellent repeatability with 1.24-2.01% intra-assay coefficients of variation (CVs) and 1.32-2.53% inter-assay CVs; good specificity for only detection of genotypes I and II ASFV, without cross-reactivity with PCV2, PRV, SIV, PRRSV, PEDV, FMDV, and CSFV. The triplex cdPCR was used to test 1,275 clinical samples from Guangxi province of China, and the positivity rates were 5.05, 3.22, and 1.02% for genotype I, genotype II, and co-infection of genotypes I and II, respectively. These 1,275 clinical samples were also detected using a reported reference triplex real-time quantitative PCR (qPCR), and the agreements of detection results between these two methods were more than 98.98%. In conclusion, the developed triplex cdPCR could be used as a rapid, sensitive, and accurate method to detect and differentiate genotypes I and II strains of ASFV.

Epidemiological investigation of ASF outbreaks in Kerala (India): detection, source tracing and economic implications

This study investigates suspected African swine fever (ASF) outbreaks in two villages of Kannur district in Kerala, India, with the aim of identifying the causative agent and its genotype, the source of infection, and estimating the economic losses due to the outbreaks. Clinically, the disease was acute with high mortality, while gross pathology was characterized by widespread haemorrhages in various organs, especially the spleen, which was dark, enlarged and had friable cut surfaces with diffuse haemorrhages. Notably, histopathological examination revealed multifocal, diffuse haemorrhages in the splenic parenchyma and lymphoid depletion accompanied by lymphoid cell necrosis. The clinico-pathological observations were suggestive of ASF, which was confirmed by PCR. The source of outbreak was identified as swill and it was a likely point source infection as revealed by epidemic curve analysis. The phylogenetic analysis of p72 gene identified the ASFV in the current outbreak as genotype-II and IGR II variant consistent with ASFVs detected in India thus far. However, the sequence analysis of the Central Variable Region (CVR) of the B602L gene showed that the ASFVs circulating in Kerala (South India) formed a separate clade along with those found in Mizoram (North East India), while ASFVs circulating in Arunachal Pradesh and Assam states of India grouped in to different clade. This study represents the first investigation of ASF outbreak in South India, establishing the genetic relatedness of the ASFV circulating in this region with that in other parts of the country. The study also underscores the utility of the CVR of the B602L gene in genetically characterizing highly similar Genotype II ASFVs to understand the spread of ASF within the country.

Rhein suppresses African swine fever virus replication in vitro via activating the caspase-dependent mitochondrial apoptosis pathway

African swine fever (ASF) is a virulent infectious diseases of pigs caused by the African swine fever virus (ASFV) that can spread widely and cause high fatality rates. Currently, there is no effective way to treat the disease, and there is no effective vaccine to prevent it. Rhein, an anthraquinone compound extracted from many traditional Chinese medicines, exhibits anti-inflammatory, anti-tumor, and anti-viral activities. However, the anti-viral effects of rhein on ASFV remain unclear. Therefore, this study aimed to investigate the anti-ASFV activity of rhein in porcine alveolar macrophages (PAMs) and the underlying mechanisms. In this study, we confirmed that rhein inhibits ASFV replication significantly in a dose-dependent manner in vitro. Moreover, rhein could alter the susceptibility of PAMs to ASFV and promoted the production of superoxide in the mitochondria, which induced the loss of mitochondrial membrane potential, leading to the activation of caspase-9, caspase-3, and apoptosis. Mito-TEMPO, a mitochondria-targeted antioxidant, blocked rhein-induced mitochondrial superoxide generation and loss of mitochondrial membrane potential, prevented caspase-9 and caspase-3 activation, alleviated apoptosis, and suppressed the anti-ASFV activity of rhein. Altogether, our results suggested that rhein could play an anti-ASFV role by inducing apoptosis through the activation of the caspase-dependent mitochondrial apoptotic pathway and may provide a novel compound for developing anti-ASFV drugs.

Resumption of production operations during the silent disposal period of African swine fever outbreaks: a case study

BACKGROUND

Batch production, a widely implemented production model in large-scale pig farms, was characterized by its long-term duration, cost-effectiveness, and efficiency. Nevertheless, the recent occurrence of African swine fever (ASF) outbreaks in China has necessitated the implementation of discreet mating operations within this model, leading to disruptions in production cycles and substantial indirect losses.

CASE PRESENTATION

This study implemented a novel operational procedure, which involved the division of risk areas for zone management and allowed mating operations, in 12 farms experiencing ASF outbreaks. Another 12 farms were used as a control group, employing the old procedure. Subsequently, the prognoses of both the old and new procedures were calculated and analyzed. The findings indicate that the new method resulted in an enhanced retention rate and reduced non-productive days (NPD), without impacting the positive detection rate and disposal time. Consequently, this approach significantly mitigated economic losses (p < 0.05).

CONCLUSION

The efficacy of the novel procedure in mitigating the indirect economic losses stemming from ASF outbreaks, through the reduction of NPD while maintaining retention rates and disposition days, has been substantiated. This methodology has demonstrated feasibility in extensive pig farming operations and exhibits promise for broader application.

What can we learn from the five-year African swine fever epidemic in Asia?

Today's global swine industry is exposed to the unprecedented threat of African swine fever (ASF). Asia, the site of the most recent epidemics, could serve as a huge viral reservoir for the rest of the world given the severity of the damage, the huge swine industry, and the high volume of trade with other countries around the world. As the majority of ASF notifications in Asia today originate from pig farms, the movement of live pigs and associated pork products are considered critical control points for disease management. Particularly, small-scale or backyard farms with low biosecurity levels are considered major risk factors. Meanwhile, wild boars account for most notified cases in some countries and regions, which makes the epidemiological scenario different from that in other Asian countries. As such, the current epidemic situation and higher risk factors differ widely between these countries. A variety of studies on ASF control have been conducted and many valuable insights have been obtained in Asia; nevertheless, the overall picture of the epidemic is still unclear. The purpose of this review is to provide an accurate picture of the epidemic situation across Asia, focusing on each subregion to comprehensively explain the disease outbreak. The knowledge gained from the ASF epidemics experienced in Asia over the past 5 years would be useful for disease control in areas that are already infected, such as Europe, as well as for non-affected areas to address preventive measures. To this end, the review includes two aspects: a descriptive analytical review based on publicly available databases showing overall epidemic trends, and an individualized review at the subregional level based on the available literature.

Factors Affecting the Spread, Diagnosis, and Control of African Swine Fever in the Philippines

African Swine Fever (ASF) is a highly contagious disease that threatens the swine industry globally. Since its introduction into the Philippines in 2019, ASF has spread extensively in both commercial and backyard farms. Here, using a mix of qualitative and quantitative methods, including conjoint and SWOT analyses, world café discussions, and multivariable regression models, the most important factors that influence the spread, diagnosis, and control of ASF in the Philippines were identified. Research findings suggest that swill or contaminated feed, inadequate biosecurity protocols, and movement of personnel were the top risk factors favoring ASF spread among farms in general. For commercial farms, contaminated vehicles and personnel were also important, whereas for backyard farms, the introduction of new pigs, environmental contamination, and poor feeding quality were relevant risk factors. Notable clinical signs of ASF in pigs include reduced feed intake, huddled behavior, and reluctance to stand. This study highlights the need for timely reporting, trust-building initiatives, and enhanced biosecurity measures to effectively manage ASF outbreaks in the country. Results here contribute to the knowledge of factors affecting ASF spread in the Philippines and can help design prevention and control measures in ASF-infected countries while enhancing preparedness in countries free from the disease.

The live pig supply chain as reported by farmers in selected districts affected by African swine fever in Uganda, June and July 2022

Introduction

Uganda is a pork-producing country in East Africa. The African swine fever virus (ASFV) has had a devastating impact on the country's pig industry. The movements of pigs and pork are a major pathway of spreading ASFV. This study was done to describe the live pig supply chain within and through districts that are impacted by African swine fever (ASF) in Uganda.

Methods

A pig farmer survey in districts known to have ASFV was done using a semi-structured questionnaire available in English and two local languages. In total, 99 farmers were interviewed across five districts. Farmers were conveniently and purposively selected by local government veterinary officials. An online key informant survey was also used to validate farmer responses.

Results

Most farmers interviewed in all districts reported to source and sell most of their pigs from within their district the farm was in, although there was variation by district and pig type. In relation to pig type, 89.7% of farmers sourced sows, 80.0% sourced boars, and 96.4% sourced weaned pigs from the district where the farm was located. As for sales, 91.3% of farmers sold sows, 92.7% sold boars, 91.9% sold weaned pigs, and 92.2% sold market pigs in the district where the farm was located. There was also variation to whom pigs were sold and sourced by pig type.

Conclusion

This information is useful when planning the scale and focus of disease control programs based on animal movement. This study revealed that pig disease control programs can be targeted to smaller regions. Furthermore, there is a need for farmers and pig traders to be educated on and adhere to veterinary regulations of animal movement and good biosecurity practices to reduce disease spread when purchasing and selling pigs from known ASFV infected areas.

Risk Assessment and Response Strategy for Pig Epidemics in China

Strengthening the analysis and risk assessment of the pig epidemic will help to better prevent and mitigate epidemic risks and promote the high-quality development of the pig industry. Based on a systematic understanding of live pig epidemics, a risk assessment index system was constructed, and the spatial and temporal variation characteristics of pig epidemics in China were explored by the entropy method. In recent years, the overall trend in pig epidemics over time first increased and then decreased; in space, the acceleration of the spread of epidemics across the country weakened. China still faces challenges, including many types and a wide range of diseases, large total livestock breeding and weak epidemic prevention and control capacity, and a large risk of introduced foreign animal epidemics. The spatial and temporal variations in the pig epidemic risk were obvious; one high-risk area, two medium-high-risk areas and 10 medium-risk areas have been found in recent years, during which time, the epidemic risk was highest in Beijing, Hainan, Liaoning, Tibet and Zhejiang. However, there were significant differences in the regional distribution of the risk level of pig epidemics in different years. To further build a secure "defense system" for the high-quality development of the pig industry, it is recommended to improve the monitoring and early warning system of pig epidemic risk, perfect the pig epidemic prevention and control system, and strengthen the regional collaboration mechanism of epidemic prevention and control.

Evaluation of African Swine Fever Virus E111R Gene on Viral Replication and Porcine Virulence

African swine fever (ASF) is an acute infectious disease of domestic pigs and wild boars caused by the African swine fever virus (ASFV), with up to a 100% case fatality rate. The development of a vaccine for ASFV is hampered by the fact that the function of many genes in the ASFV genome still needs to be discovered. In this study, the previously unreported E111R gene was analyzed and identified as an early-expressed gene that is highly conserved across the different genotypes of ASFV. To further explore the function of the E111R gene, a recombinant strain, SY18ΔE111R, was constructed by deleting the E111R gene of the lethal ASFV SY18 strain. In vitro, the replication kinetics of SY18ΔE111R with deletion of the E111R gene were consistent with those of the parental strain. In vivo, high-dose SY18ΔE111R (105.0 TCID50), administered intramuscularly to pigs, caused the same clinical signs and viremia as the parental strain (102.0 TCID50), with all pigs dying on days 8–11. After being infected with a low dose of SY18ΔE111R (102.0 TCID50) intramuscularly, pigs showed a later onset of disease and 60% mortality, changing from acute to subacute infection. In summary, deletion of the E111R gene has a negligible effect on the lethality of ASFV and does not affect the viruses’ ability to replicate, suggesting that E111R could not be the priority target of ASFV live-attenuated vaccine candidates.

Comparison of Genotype II African Swine Fever Virus Strain SY18 Challenge Models

African swine fever (ASF) is a viral haemorrhagic disease found in domestic and wild boars caused by the African swine fever virus (ASFV). A highly virulent strain was used to evaluate the efficacy of newly developed vaccine candidates. The ASFV strain SY18 was isolated from the first ASF case in China and is virulent in pigs of all ages. To evaluate the pathogenesis of ASFV SY18 following intraoral (IO) and intranasal (IN) infections, a challenge trial was conducted in landrace pigs, with intramuscular (IM) injection as a control. The results showed that the incubation period of IN administration with 40–1000 50 % tissue culture infective dose (TCID50) was 5–8 days, which was not significantly different from that of IM inoculation with 200 TCID50. A significantly longer incubation period, 11–15 days, was observed in IO administration with 40–5000 TCID50. Clinical features were similar among all infected animals. Symptoms, including high fever (≥40.5 °C), anorexia, depression, and recumbency, were observed. No significant differences were detected in the duration of viral shedding during fever. There was no significant difference in disease outcome, and all animals succumbed to death. This trial showed that IN and IO infections could be used for the efficacy evaluation of an ASF vaccine. The IO infection model, similar to that of natural infection, is highly recommended, especially for the primary screening of candidate vaccine strains or vaccines with relatively weak immune efficacy, such as live vector vaccines and subunit vaccines.

Intradermal needle-free injection prevents African Swine Fever transmission, while intramuscular needle injection does not

Shared needles are a possible iatrogenic and hematogenous inanimate vector of African Swine Fever virus (ASFV) in farm conditions. To evaluate that possible transmission, sixty, 4-week-old pigs were procured from an ASF free herd free. Upon arrival, pigs were randomly divided into two sets. Set 1 served as seeder pigs, and were randomly allocated to 4 groups. The other pigs were divided into 8 groups, and served as sentinels. Seeder pigs were oronasally challenged with ASFV at high (10⁸ copy numbers/mL), moderate (10⁶ copy numbers/mL) or low (10¹ copy numbers/mL) challenge titer, except a subgroup that remained unchallenged (negative control). At 7 days post challenge (peak viremia), all four seeder groups were intradermally and intramuscularly (IM) injected with a vaccine adjuvant (Diluvac Forte, MSD Animal Health, The Netherlands) using a needle-free device (IDAL 3G, MSD Animal Health, The Netherlands) and conventional needles, respectively. The same needle or needle-free device was then used to inject the same volume of adjuvant into set 2 (n = 48) pigs. All pigs were observed for clinical disease daily and assayed for the presence of ASFV DNA by quantitative PCR. All seeder groups developed viremia (except the control pigs). ASFV viremia was detected in all sentinel groups injected via the intramuscular route. Transmission rate from the IM route via conventional needles was positively correlated with virus titer in blood circulation of seeders. Sentinels intramuscularly exposed to needles from high titer challenged seeders displayed more severe and acute clinical disease compared to that of exposed to low titer challenged seeders. No viremia nor clinical signs were observed in the sentinel groups injected via the intradermal route. This study confirmed the hematogenous transmission of ASFV between pigs through needle-sharing.

Expounding the role of tick in Africa swine fever virus transmission and seeking effective prevention measures: A review

African swine fever (ASF), a highly contagious, deadly infectious disease, has caused huge economic losses to animal husbandry with a 100% mortality rate of the most acute and acute infection, which is listed as a legally reported animal disease by the World Organization for Animal Health (OIE). African swine fever virus (ASFV) is the causative agent of ASF, which is the only member of the Asfarviridae family. Ornithodoros soft ticks play an important role in ASFV transmission by active biological or mechanical transmission or by passive transport or ingestion, particularly in Africa, Europe, and the United States. First, this review summarized recent reports on (1) tick species capable of transmitting ASFV, (2) the importance of ticks in the transmission and epidemiological cycle of ASFV, and (3) the ASFV strains of tick transmission, to provide a detailed description of tick-borne ASFV. Second, the dynamics of tick infection with ASFV and the tick-induced immune suppression were further elaborated to explain how ticks spread ASFV. Third, the development of the anti-tick vaccine was summarized, and the prospect of the anti-tick vaccine was recapitulated. Then, the marked attenuated vaccine, ASFV-G-ΔI177L, was compared with those of the anti-tick vaccine to represent potential therapeutic or strategies to combat ASF.

Porcine respiratory disease complex: Dynamics of polymicrobial infections and management strategies after the introduction of the African swine fever

A few decades ago, porcine respiratory disease complex (PRDC) exerted a major economic impact on the global swine industry, particularly due to the adoption of intensive farming by the latter during the 1980's. Since then, the emerging of porcine reproductive and respiratory syndrome virus (PRRSV) and of porcine circovirus type 2 (PCV2) as major immunosuppressive viruses led to an interaction with other endemic pathogens (e.g., Mycoplasma hyopneumoniae, Actinobacillus pleuropneumoniae, Streptococcus suis, etc.) in swine farms, thereby exacerbating the endemic clinical diseases. We herein, review and discuss various dynamic polymicrobial infections among selected swine pathogens. Traditional biosecurity management strategies through multisite production, parity segregation, batch production, the adoption of all-in all-out production systems, specific vaccination and medication protocols for the prevention and control (or even eradication) of swine diseases are also recommended. After the introduction of the African swine fever (ASF), particularly in Asian countries, new normal management strategies minimizing pig contact by employing automatic feeding systems, artificial intelligence, and robotic farming and reducing the numbers of vaccines are suggested. Re-emergence of existing swine pathogens such as PRRSV or PCV2, or elimination of some pathogens may occur after the ASF-induced depopulation. ASF-associated repopulating strategies are, therefore, essential for the establishment of food security. The "repopulate swine farm" policy and the strict biosecurity management (without the use of ASF vaccines) are, herein, discussed for the sustainable management of small-to-medium pig farms, as these happen to be the most potential sources of an ASF re-occurrence. Finally, the ASF disruption has caused the swine industry to rapidly transform itself. Artificial intelligence and smart farming have gained tremendous attention as promising tools capable of resolving challenges in intensive swine farming and enhancing the farms' productivity and efficiency without compromising the strict biosecurity required during the ongoing ASF era.