Development of a fluorescent probe hydrolysis-insulated isothermal PCR for rapid and sensitive on-site detection of African swine fever virus

Development of Real-Time and Lateral Flow Dipstick Recombinase Polymerase Amplification Assays for the Rapid Field Diagnosis of MGF-505R Gene-Deleted Mutants of African Swine Fever Virus

Pigs are susceptible to the deadly infectious disease known as African swine fever (ASF), which is brought on by the African swine fever virus (ASFV). As such, prompt and precise disease detection is essential. Deletion of the virulence-related genes MGF-505/360 and EP402R generated from the virulent genotype II virus significantly reduces its virulence, and animal tests using one of the recombinant viruses show great lethality and transmissibility in pigs. The isothermal technique known as recombinase polymerase amplification (RPA) is perfect for rapid in-field detection. To accurately identify ASFV MGF-505R gene-deleted mutants and assess the complex infection situation of ASF, RPA assays in conjunction with real-time fluorescent detection (real-time RPA assay) and lateral flow dipstick (RPA-LFD assay) were created. These innovative methods allow for the direct detection of ASFV from pigs, offering in-field pathogen detection, timely disease management, and satisfying animal quarantine requirements. The specific primers and probes were designed against conserved regions of ASFV B646L and MGF-505R genes. Using recombinant plasmid DNA containing ASFV MGF-505R gene-deleted mutants as a template, the sensitivity of both ASF real-time RPA and ASF RPA-LFD assays were demonstrated to be 10 copies per reaction within 20 min at 37 °C. Neither assay had cross-reactions with CSFV, PRRSV, PPV, PRV, ot PCV2, common viruses seen in pigs, indicating that these methods were highly specific for ASFV. The evaluation of the performance of ASFV real-time RPA and ASFV RPA-LFD assays with clinical samples (n = 453) demonstrated their ability to specifically detect ASFV or MGF-505R gene-deleted mutants in samples of pig feces, ham, fresh pork, and blood. Both assays exhibited the same diagnostic rate as the WOAH-recommended real-time fluorescence PCR, highlighting their reliability and validity. These assays offer a simple, cost-effective, rapid, and sensitive method for on-site identification of ASFV MGF-505R gene-deleted mutants. As a promising alternative to real-time PCR, they have the potential to significantly enhance the prevention and control of ASF in field settings.

Advances in the diagnostic techniques of African swine fever

African swine fever (ASF) is a highly contagious disease of pigs caused by African swine fever virus, which poses a huge threat to the global swine industry and is therefore listed as a notifiable disease by the World Organization for Animal Health. Due to the global lack of safe and efficacious vaccines and therapeutic drugs, early diagnosis of cases, whether on-site or laboratory, are crucial for the prevention and control of ASF. Therefore, rapid and reliable diagnosis and detection have become the main means to combat ASF. In this paper, various diagnostic techniques developed globally for ASF diagnosis, including etiological, molecular biological and serological diagnostic techniques, as well as conventional and novel diagnostic techniques, were comprehensively reviewed, and the main advantages and disadvantages of currently commonly used diagnostic techniques were introduced. It is expected that this paper will provide references for selecting appropriate ASF diagnostic techniques in different application scenarios, and also provide directions for the development of innovative diagnostic techniques for ASF in the future.

Development of two novel on-site detection visualization methods for murine hepatitis virus based on the multienzyme isothermal rapid amplification

Murine hepatitis virus (MHV) infection is one of the most prevalent types of mice infection in laboratory. MHV could cause death in mice and even interfere with the results in animal experiments. Herein, we developed two isothermal approaches based on the Multienzyme Isothermal Rapid Amplification (MIRA), for rapid detection of MHV in conserved M gene. We designed and screened several pairs of primers and probes and the isothermal fluorescence detector was applied for the exonuclease Ⅲ reverse transcription MIRA (exo-RT-MIRA) assay. To further simplify the workflow, the portable fluorescence visualization instrument, also as a palm-sized handheld system, was used for the naked-eye exo-RT-MIRA assay. The amplification temperature and time were optimized. The assay could be processed well at 42 °C 20 min for the exo-RT-MIRA and the naked-eye exo-RT-MIRA assay. The limit of detection (LoD) of the exo-RT-MIRA assay was 43.4 copies/μL. The LoD of the naked-eye exo-RT-MIRA assay was 68.2 copies/μL. No nonspecific amplifications were observed in the two assays. A total of 107 specimens were examined by qPCR and two assays developed. The experimental results statistical analysis demonstrated that the exo-RT-MIRA assay with the qPCR yielded sufficient agreement with a kappa value of 1.000 (p < 0.0001). The results also exhibited a good agreement (kappa value, 0.961) (p < 0.0001) between the naked-eye exo-RT-MIRA assay and the qPCR assay. In our study, the exo-RT-MIRA assay and the naked-eye exo-RT-MIRA assay presented the possibility of new methods in MHV point-of-testing diagnosis.

Current detection methods of African swine fever virus

African swine fever (ASF), caused by the African swine fever virus (ASFV), is a highly contagious and notifiable animal disease in domestic pigs and wild boars, as designated by the World Organization for Animal Health (WOAH). The effective diagnosis of ASF holds great importance in promptly controlling its spread due to its increasing prevalence and the continuous emergence of variant strains. This paper offers a comprehensive review of the most common and up-to-date methods established for various genes/proteins associated with ASFV. The discussed methods primarily focus on the detection of viral genomes or particles, as well as the detection of ASFV associated antibodies. It is anticipated that this paper will serve as a reference for choosing appropriate diagnostic methods in diverse application scenarios, while also provide direction for the development of innovative technologies in the future.

Airborne transmission of common swine viruses

The transmission of viral aerosols poses a vulnerable aspect in the biosecurity measures aimed at preventing and controlling swine virus in pig production. Consequently, comprehending and mitigating the spread of aerosols holds paramount significance for the overall well-being of pig populations. This paper offers a comprehensive review of transmission characteristics, influential factors and preventive strategies of common swine viral aerosols. Firstly, certain viruses such as foot-and-mouth disease virus (FMDV), porcine reproductive and respiratory syndrome virus (PRRSV), influenza A viruses (IAV), porcine epidemic diarrhea virus (PEDV) and pseudorabies virus (PRV) have the potential to be transmitted over long distances (exceeding 150 m) through aerosols, thereby posing a substantial risk primarily to inter-farm transmission. Additionally, other viruses like classical swine fever virus (CSFV) and African swine fever virus (ASFV) can be transmitted over short distances (ranging from 0 to 150 m) through aerosols, posing a threat primarily to intra-farm transmission. Secondly, various significant factors, including aerosol particle sizes, viral strains, the host sensitivity to viruses, weather conditions, geographical conditions, as well as environmental conditions, exert a considerable influence on the transmission of viral aerosols. Researches on these factors serve as a foundation for the development of strategies to combat viral aerosol transmission in pig farms. Finally, we propose several preventive and control strategies that can be implemented in pig farms, primarily encompassing the implementation of early warning models, viral aerosol detection, and air pretreatment. This comprehensive review aims to provide a valuable reference for the formulation of efficient measures targeted at mitigating the transmission of viral aerosols among swine populations.

Advanced Strategies for Developing Vaccines and Diagnostic Tools for African Swine Fever

African swine fever (ASF) is one of the most lethal infectious diseases affecting domestic pigs and wild boars of all ages. Over a span of 100 years, ASF has continued to spread over continents and adversely affects the global pig industry. To date, no vaccine or treatment has been approved. The complex genome structure and diverse variants facilitate the immune evasion of the ASF virus (ASFV). Recently, advanced technologies have been used to design various potential vaccine candidates and effective diagnostic tools. This review updates vaccine platforms that are currently being used worldwide, with a focus on genetically modified live attenuated vaccines, including an understanding of their potential efficacy and limitations of safety and stability. Furthermore, advanced ASFV detection technologies are presented that discuss and incorporate the challenges that remain to be addressed for conventional detection methods. We also highlight a nano-bio-based system that enhances sensitivity and specificity. A combination of prophylactic vaccines and point-of-care diagnostics can help effectively control the spread of ASFV.

Development of a Duplex Insulated Isothermal PCR Assay for Rapid On-Site Detection and Differentiation of Genotypes 1 and 2 of African Swine Fever Virus

Genotype II African swine fever virus (ASFV) has been plaguing Asian pig industry since 2018. Recently, genotype I ASFV was reported for the first time in China. Since there is no commercial vaccine available against ASFV, early onsite detection and quick culling procedures are commonly used by many countries all over the world. It is important that the above two genotypes of ASFV could be quickly differentiated during onsite detection at the same time. In this study, we established a sensitive and simple Fluorescent Probe Hydrolysis-Insulated isothermal PCR (iiPCR) that can detect and differentiate two genotypes of ASFV within 40 minutes. The positive or negative results of tested samples were displayed on the screen of the device automatically after PCR amplification was complete. The detection limit of the iiPCR was tested to be 20 copies for both genotype I and genotype II ASFVs. There was no cross-reactivity with other swine viruses by using the established iiPCR. Fifty-eight ASFV positive samples confirmed by National ASF Reference Laboratory were subjected to the established duplex iiPCR for genotype differentiation. The results showed that all these ASFV-positive samples belong to genotype II. At last, we found serum samples could be directly used as the templates for iiPCR without comprising sensitivity and specificity. Therefore, the duplex iiPCR established in study provide a useful tool for ASFV onsite detection and genotype differentiation.