Development of a Novel Indirect ELISA for the Serological Diagnosis of African Swine Fever Using p11.5 Protein as a Target Antigen

Detection of African swine fever virus antibodies using p11.5 and p14.5 protein-based indirect ELISA

African swine fever (ASF), which is caused by the African swine fever virus (ASFV). There are currently no effective vaccines or therapies for ASF; rapid diagnosis has become an important way to control the disease. The p11.5 and p14.5 proteins are structural proteins of ASFV that have immunogenicity and potential as diagnostic antigens. In this study, p11.5 and p14.5 proteins were used as diagnostic antigens in an indirect ELISA examine to detect ASFV antibodies. The p11.5 and p14.5-iELISA methods showed no cross-reaction with other swine virus positive sera. The lowest detection limit of positive serum was 1: 6400, and the coefficients of variation (CV) of intra - and inter-assay were less than 7%. By comparing 71 serum samples, the coincidence rate of p11.5 and p14.5-iELISA with commercial ELISA kits was 91.55%. Taken together, these results showed that there is a reliable method of detecting ASFV antibodies in clinical pig serum.

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.

The antibodies against the A137R protein drive antibody-dependent enhancement of African swine fever virus infection in porcine alveolar macrophages

African swine fever virus (ASFV) is the causative agent of African swine fever (ASF), a highly contagious disease that can kill up to 100% of domestic pigs and wild boars. It has been shown that the pigs inoculated with some ASF vaccine candidates display more severe clinical signs and die earlier than do pigs not immunized. We hypothesize that antibody-dependent enhancement (ADE) of ASFV infection may be caused by the presence of some unidentified antibodies. In this study, we found that the ASFV-encoded structural protein A137R (pA137R) can be recognized by the anti-ASFV positive sera, indicating that the anti-pA137R antibodies are induced in the ASFV-infected pigs. Interestingly, our results demonstrated that the anti-pA137R antibodies produced in rabbits or pigs enhanced viral replication of different ASFV strains in primary porcine alveolar macrophages (PAMs), the target cells of ASFV. Mechanistic investigations revealed that anti-pA137R antibodies were able to promote the attachment of ASFV to PAMs and two types of Fc gamma receptors (FcγRs), FcγRII and FcγRIII, mediated the ADE of ASFV infection. Taken together, anti-pA137R antibodies are able to drive ASFV ADE in PAMs. These findings shed new light on the roles of anti-ASFV antibodies and have implications for the pathophysiology of the disease and the development of ASF vaccines.

Classical swine fever: Unveiling the complexity through a multifaceted approach

Classical swine fever (CSF), sometimes referred to as hog cholera, is a highly contagious, virally based, systemic illness that affects both domestic and wild pigs. The virus known as classical swine fever virus (CSFV) is a member of the Flaviviridae family, specifically the genus Pestivirus. This disease is thought to be endemic in many Asian countries that produce pork as well as in several countries in Central and South America, the Caribbean, and elsewhere. As previously indicated, depending on the virulence of the virus strain involved and several host circumstances, clinical indications of CSFV infection can vary greatly, ranging from abrupt fatality to an occult course. CSF diagnosis can be made by serological detection, antigen, RNA, and isolation. CSF's highly varied symptoms and post-mortem pathology resemble those of African swine fever (ASF). ASF, the kind of CSFV, the pig's age, and its susceptibility all affect the clinical symptoms. Pigs that contract CSFV, a highly infectious and economically significant virus. The great economic significance of the swine business makes the CSFV a potential bioterrorism threat. Live attenuated CSF vaccinations have been around for many years and are quite safe and effective. Controlling epidemics in CSFV-free zones requires quick action. Pigs that are impacted must be slaughtered, and the carcasses must be buried or burned.

Towards Safe African Swine Fever Vaccines: The A137R Gene as a Tool to Reduce Virulence and a Promising Serological DIVA Marker Candidate

African swine fever (ASF) is an emerging disease caused by the African swine fever virus (ASFV), which is a great threat to the swine industry worldwide. Currently registered vaccines that have demonstrated protection against the homologous ASFV strains are live attenuated vaccines based on recombinant ASFV strains with the deletions of virulence-associated genes. In this study, we evaluated the deletion of the A137R gene in the ASFV virulent Stavropol_01/08 strain isolated in Russia in 2008. Our animal experiment results demonstrated that the deletion of the A137R gene did not lead to the full attenuation of this strain, and increasing the dose of the A137R-deletion mutant during infection led to the death of 87.5% of the infected animals. In this report, we also demonstrated that immunofluorescence (IFA) and Western blotting assays based on the recombinant p11.5 protein can be used to detect antibodies in animals infected with the attenuated ASFV variants of several genotypes/serotypes. Both assays were specific to ASFV p11.5 protein and showed negative results when examining the sera of the non-infected animals or those infected with the A137R-deletion mutant. Therefore, we propose to use the p11.5 protein along with other previously proposed ASFV proteins, such as CD2v, as negative antigenic DIVA markers for an attenuated ASF vaccine.

Establishment of an ELISA Based on a Recombinant Antigenic Protein Containing Multiple Prominent Epitopes for Detection of African Swine Fever Virus Antibodies

African swine fever virus (ASFV) poses a significant threat to the global pig industry, necessitating accurate and efficient diagnostic methods for its infection. Previous studies have often focused on a limited number of epitopes from a few proteins for detecting antibodies against ASFV. Therefore, the current study aimed to use multiple B-cell epitopes in developing an indirect Enzyme-Linked Immunosorbent Assay (ELISA) for enhanced detection of ASFV antibodies. For the expression of recombinant protein, k3 derived from 27 multiple peptides of 11 ASFV proteins, such as p72, pA104R, pB602L, p12, p14.5, p49, pE248R, p30, p54, pp62, and pp220, was used. To confirm the expression of the recombinant protein, we used the Western blotting analysis. The purified recombinant K3 protein served as the antigen in our study, and we employed the indirect ELISA technique to detect anti-ASFV antibodies. The present finding showed that there was no cross-reactivity with antibodies targeting Foot-and-mouth disease virus (FMDV), Porcine circovirus type 2 (PCV2), Pseudorabies virus (PRV), Porcine reproductive and respiratory syndrome virus (PRRSV), and Classical swine fever virus (CSFV). Moreover, the current finding was sensitive enough to find anti-ASFV in serum samples that had been diluted up to 32 times. The test (k3-iELISA) showed diagnostic specificity and sensitivity of 98.41% and 97.40%, respectively. Moreover, during the present investigation, we compared the Ingenasa kit and the k3-iELISA to test clinical pig serum, and the results revealed that there was 99.00% agreement between the two tests, showing good detection capability of the k3-iELISA method. Hence, the current finding showed that the ELISA kit we developed can be used for the rapid detection of ASFV antibodies and used as an alternative during serological investigation of ASF in endemic areas.

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.

A Robust Quadruple Protein-Based Indirect ELISA for Detection of Antibodies to African Swine Fever Virus in Pigs

African swine fever (ASF) emerged in domestic pigs and wild boars in China in 2018 and rapidly spread to neighboring Asian countries. Currently, no effective vaccine or diagnostic tests are available to prevent its spread. We developed a robust quadruple recombinant-protein-based indirect enzyme-linked immunosorbent assay (QrP-iELISA) using four antigenic proteins (CD2v, CAP80, p54, and p22) to detect ASF virus (ASFV) antibodies and compared it with a commercial kit (IDvet) using ASFV-positive and -negative serum samples. The maximum positive/negative value was 24.033 at a single antigen concentration of 0.25 μg/mL and quadruple ASFV antigen combination of 1 μg/mL at a 1:100 serum dilution. Among 70 ASFV-positive samples, 65, 67, 65, 70, 70, and 14 were positive above the cut-offs of 0.121, 0.121, 0.183, 0.065, 0.201, and 0.122, for CD2v, CAP80, p54, p22-iELISA, QrP-iELISA, and IDvet, respectively, with sensitivities of 92.9%, 95.7%, 92.9%, 100%, 100%, and 20%, respectively, all with 100% specificity. The antibody responses in QrP-iELISA and IDvet were similar in pigs infected with ASFV I. QrP-iELISA was more sensitive than IDvet for early antibody detection in pigs infected with ASFV II. These data provide a foundation for developing advanced ASF antibody detection kits critical for ASF surveillance and control.

Generation and characterization of a monoclonal antibody against an African swine fever virus protein encoded by the A137R gene

The ongoing African swine fever (ASF) pandemic continues to have a major impact on global pork production and trade. Since ASF cannot be distinguished from other swine hemorrhagic fevers clinically, ASF-specific laboratory diagnosis is critical. Thus ASF virus (ASFV)-specific monoclonal antibodies (mAbs) are critical for the development of laboratory diagnostics. In this study, we report one ASFV-specific mAb, F88ASF-55, that was generated and characterized. This mAb recognizes the ASFV A137R-encoded protein (pA137R). Epitope mapping results revealed a highly conserved linear epitope recognized by this mAb, corresponding to amino acids 111-125 of pA137R. We explored the potential use of this mAb in diagnostic applications. Using F88ASF-55 as the detection antibody, six ASFV strains were detected in an enzyme-linked immunosorbent assay (ELISA) with low background. In immunohistochemistry (IHC) assays, this mAb specifically recognized ASFV antigens in the submandibular lymph nodes of animals experimentally infected with different ASFV strains. Although not all ASFV genotypes were tested in this study, based on the conserved ASFV epitope targeted by F88ASF-55, it has the potential to detect multiple ASFV genotypes. In conclusion, this newly generated ASFV pA137R-specific mAb has potential value in ASF diagnostic tool development. It can be used in ELISA, IHC, and possibly-immunochromatographic strip assays for ASFV detection. It also suggests that pA137R may be a good target for diagnostic assays to detect ASFV infection.