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.

African Swine Fever Diagnosis in Africa: Challenges and Opportunities

The global spread of African swine fever (ASF) in recent decades has led to the need for technological advances in sampling and diagnostic techniques. The impetus for these has been the need to enable sampling by lay persons and to obtain at least a preliminary diagnosis in the field for early control measures to be put in place before final laboratory confirmation. In rural Africa, rapid diagnosis is hampered by challenges that include lack of infrastructure as well as human and financial resources. Lack of animal health personnel, access to affordable means to transport field samples to a laboratory, and lack of laboratories with the capacity to make the diagnosis result in severe under-reporting of ASF, especially in endemic areas. This review summarizes the challenges identified in gap analyses relevant to low- and middle-income countries, with a focus on Africa, and explore the opportunities provided by recent research to improve field diagnosis and quality of diagnostic samples used. Sampling techniques include invasive sampling techniques requiring trained personnel and non-invasive sampling requiring minimal training, sampling of decomposed carcass material, and preservation of samples in situations where cold chain maintenance cannot be guaranteed. Availability and efficacy of point-of-care (POC) tests for ASF has improved considerably in recent years and their application, as well as advantages and limitations, are discussed. The adequacy of existing laboratory diagnostic capacity is evaluated and opportunities for networking amongst reference and other laboratories offering diagnostic services are discussed. Maintaining laboratory diagnostic efficiency in the absence of samples during periods of quiescence is another issue that requires attention, and the role of improved laboratory networking is emphasized. Early diagnosis of ASF is key to managing the disease spread. Therefore, the establishment of the Africa Chapter of the Global African Swine Fever Research Alliance (GARA) increases opportunities for collaboration and networking among the veterinary diagnostic laboratories in the region.

Overview of Modern Commercial Kits for Laboratory Diagnosis of African Swine Fever and Swine Influenza A Viruses

Rapid and early detection of infectious diseases in pigs is important, especially for the implementation of control measures in suspected cases of African swine fever (ASF), as an effective and safe vaccine is not yet available in most of the affected countries. Additionally, analysis for swine influenza is of significance due to its high morbidity rate (up to 100%) despite a lower mortality rate compared to ASF. The wide distribution of swine influenza A virus (SwIAV) across various countries, the emergence of constantly new recombinant strains, and the danger of human infection underscore the need for rapid and accurate diagnosis. Several diagnostic approaches and commercial methods should be applied depending on the scenario, type of sample and the objective of the studies being implemented. At the early diagnosis of an outbreak, virus genome detection using a variety of PCR assays proves to be the most sensitive and specific technique. As the disease evolves, serology gains diagnostic value, as specific antibodies appear later in the course of the disease (after 7-10 days post-infection (DPI) for ASF and between 10-21 DPI for SwIAV). The ongoing development of commercial kits with enhanced sensitivity and specificity is evident. This review aims to analyse recent advances and current commercial kits utilised for the diagnosis of ASF and SwIAV.

Natural co-infection of pigs with African swine fever virus and porcine reproductive and respiratory syndrome virus in India

Porcine reproductive and respiratory syndrome (PRRS) and African swine fever (ASF) are economically important diseases of pigs throughout the world. During an outbreak, all age groups of animals except piglets < 1 month of age were affected with symptoms of high fever, cutaneous hemorrhages, vomition with blood, diarrhea, poor appetite, ataxia, and death. The outbreak was confirmed by the detection of the N gene of the porcine reproductive and respiratory syndrome virus (PRRSV) and the VP72 gene of the African swine fever virus (ASFV) by PCR in representative blood samples from affected pigs followed by Sanger sequencing. Mixed infection was also confirmed by simultaneous detection of both the viruses using multiplex PCR. Phylogenetic analysis of both the viruses revealed that the outbreak was related to ASFV and PRRSV strains from China which were also closely related to the PRRSV and ASFV strains from the recent outbreak from India. The study confirmed the involvement of genotype II of ASFV and genotype 2 of PRRSV in the present outbreak. Interestingly, PRRSV associated with the present outbreak was characterized as a highly pathogenic PRRSV. Therefore, the present study indicates the possibility of future waves or further outbreaks of these diseases (PRRS and ASF) in this region. This is the first report of ASFV and PRRSV co-infection in pigs from India.

Emergent Molecular Techniques Applied to the Detection of Porcine Viruses

Molecular diagnostic tests have evolved very rapidly in the field of human health, especially with the arrival of the recent pandemic caused by the SARS-CoV-2 virus. However, the animal sector is constantly neglected, even though accurate detection by molecular tools could represent economic advantages by preventing the spread of viruses. In this regard, the swine industry is of great interest. The main viruses that affect the swine industry are described in this review, including African swine fever virus (ASFV), porcine reproductive and respiratory syndrome virus (PRRSV), porcine epidemic diarrhea virus (PEDV), and porcine circovirus (PCV), which have been effectively detected by different molecular tools in recent times. Here, we describe the rationale of molecular techniques such as multiplex PCR, isothermal methods (LAMP, NASBA, RPA, and PSR) and novel methods such as CRISPR-Cas and microfluidics platforms. Successful molecular diagnostic developments are presented by highlighting their most important findings. Finally, we describe the barriers that hinder the large-scale development of affordable, accessible, rapid, and easy-to-use molecular diagnostic tests. The evolution of diagnostic techniques is critical to prevent the spread of viruses and the development of viral reservoirs in the swine industry that impact the possible development of future pandemics and the world economy.

Development of a TaqMan-Probe-Based Multiplex Real-Time PCR for the Simultaneous Detection of African Swine Fever Virus, Porcine Circovirus 2, and Pseudorabies Virus in East China from 2020 to 2022

African swine fever virus (ASFV), porcine circovirus 2 (PCV2), and pseudorabies virus (PRV) are important DNA viruses that cause reproductive disorders in sows, which result in huge losses in pig husbandry, especially in China. The multiplex qPCR assay could be utilized as a simultaneous diagnostic tool for field-based surveillance and the control of ASFV, PCV2, and PRV. Based on the conserved regions on the p72 gene of ASFV, the Cap gene of PCV2, the gE gene of PRV, and the porcine endogenous β-Actin gene, the appropriate primers and probes for a multiplex TaqMan real-time PCR test effective at concurrently detecting three DNA viruses were developed. The approach demonstrated high specificity and no cross-reactivity with major pathogens related to swine reproductive diseases. In addition, its sensitivity was great, with a detection limit of 10¹ copies/L of each pathogen, and its repeatability was excellent, with intra- and inter-group variability coefficients of <2%. Applying this assay to detect 383 field specimens collected from 2020 to 2022, the survey data displayed that the ASFV, PCV2, and PRV single infection rates were 22.45%, 28.46%, and 2.87%, respectively. The mixed infection rates of ASFV + PCV2, ASFV + PRV, PCV2 + PRV, and ASFV + PCV2 + PRV were 5.22%, 0.26%, 1.83%, and 0.26%, respectively. Overall, the assay established in this study provides an effective tool for quickly distinguishing the viruses causing sow reproductive disorders, suggesting its huge clinical application value in the diagnosis of swine diseases.

A Multiplex Crystal Digital PCR for Detection of African Swine Fever Virus, Classical Swine Fever Virus, and Porcine Reproductive and Respiratory Syndrome Virus

African swine fever (ASF), classical swine fever (CSF), and porcine reproductive and respiratory syndrome (PRRS) are highly infectious diseases of domestic pigs and wild boars. The co-infections of ASF virus (ASFV), CSF virus (CSFV), and PRRS virus (PRRSV) have been reported in different pig farms. Early differential detection and diagnosis of ASFV, CSFV, and PRRSV in the clinical samples is very important for the effective prevention and control of these diseases. A multiplex crystal digital PCR (dPCR) was developed for differential detection of ASFV, CSFV, and PRRSV in this study, targeting p72, 5' untranslated region (UTR), and ORF7 genes, respectively. The different reaction conditions were optimized, and the specificity, sensitivity, and repeatability of the assay were evaluated. The results showed that the multiplex crystal dPCR was able to accurately and differentially detect ASFV, CSFV, and PRRSV with a limit of detection of 4.69 × 10⁻¹ copies/μl, respectively, and could not detect other porcine viruses, i.e., foot-and-mouth disease virus (FMDV), Senecavirus A (SVA), atypical porcine pestivirus (APPV), pseudorabies virus (PRV), porcine circovirus type 2 (PCV2), and porcine parvovirus (PPV). The assay showed excellent repeatability and reproducibility, with coefficients of variation (CV) of the intra- and inter-assay from 0.09 to 1.40%, and from 0.64 to 2.26%, respectively. The 289 clinical samples from different pig herds in Guangxi province, China, were tested by the multiplex crystal dPCR and a reference multiplex real-time quantitative RT-PCR (qRT-PCR) established previously in our laboratory. The positive rates of ASFV, CSFV, and PRRSV were 30.10, 13.49, and 22.49% by the multiplex crystal dPCR, and 24.57, 8.65, and 18.34% by the multiplex qRT-PCR, with coincidence rates of 94.66, 95.16, and 95.84%, respectively. The results indicated that the established multiplex crystal dPCR was a specific, sensitive, and accurate method for the detection and quantification of ASFV, CSFV, and PRRSV. This is the first report on the multiplex dPCR for detecting ASFV, CSFV, and PRRSV.

Development of a Multiplex RT-PCR Assay for Simultaneous Detection of Four Potential Zoonotic Swine RNA Viruses

Swine viruses like porcine sapovirus (SaV), porcine encephalomyocarditis virus (EMCV), porcine rotavirus A (RVA) and porcine astroviruses (AstV) are potentially zoonotic viruses or suspected of potential zoonosis. These viruses have been detected in pigs with or without clinical signs and often occur as coinfections. Despite the potential public health risks, no assay for detecting them all at once has been developed. Hence, in this study, a multiplex RT-PCR (mRT-PCR) assay was developed for the simultaneous detection of SaV, EMCV, RVA and AstV from swine fecal samples. The PCR parameters were optimized using specific primers for each target virus. The assay’s sensitivity, specificity, reproducibility, and application to field samples have been evaluated. Using a pool of plasmids containing the respective viral target fragments as a template, the developed mRT-PCR successfully detected 2.5 × 10³ copies of each target virus. The assay’s specificity was tested using six other swine viruses as a template and did not show any cross-reactivity. A total of 280 field samples were tested with the developed mRT-PCR assay. Positive rates for SaV, EMCV, RVA, and AstV were found to be 24.6% (69/280), 5% (14/280), 4.3% (12/280), and 17.5% (49/280), respectively. Compared to performing separate assays for each virus, this mRT-PCR assay is a simple, rapid, and cost-effective method for detecting mixed or single infections of SaV, EMCV, RVA, and AstV.

Real-Time Detection of LAMP Products of African Swine Fever Virus Using Fluorescence and Surface Plasmon Resonance Method

African swine fever (ASF) is a swine disease with a very high fatality rate caused by a complex double-stranded DNA virus. The fluorescence PCR detection method is widely used for virus nucleic acid detection. Surface plasmon resonance (SPR) is a label-free and real-time detection method, unlike the fluorescence PCR detection method. In this research, we detected the loop-mediated isothermal amplification (LAMP) products of the African swine fever virus by using the SPR and fluorescence methods separately and simultaneously. By comparing the positive and negative control results, we found that the SPR response unit is completely different before and after the LAMP process. In addition, the fluorescence results on a chip showed that with an increase in the concentration of the sample, the cycle threshold (CT) value decreased, which is consistent with commercial instruments. Both the decline rate of the SPR response unit and the CT value of the fluorescence realized were used to distinguish the positive control from the negative control and water, which indicates that the SPR method can be combined with fluorescence to detect LAMP products. This research provides a label-free and simple method for detecting LAMP products.

Development of a multiplex qRT-PCR assay for detection of African swine fever virus, classical swine fever virus and porcine reproductive and respiratory syndrome virus

BACKGROUND

African swine fever virus (ASFV), classical swine fever virus (CSFV), and porcine reproductive and respiratory syndrome virus (PRRSV) are still prevalent in many regions of China. Co-infections make it difficult to distinguish their clinical symptoms and pathological changes. Therefore, a rapid and specific method is needed for the differential detection of these pathogens.

OBJECTIVES

The aim of this study was to develop a multiplex real-time quantitative reverse transcription polymerase chain reaction (multiplex qRT-PCR) for the simultaneous differential detection of ASFV, CSFV, and PRRSV.

METHODS

Three pairs of primers and TaqMan probes targeting the ASFV p72 gene, CSFV 5' untranslated region, and PRRSV ORF7 gene were designed. After optimizing the reaction conditions, including the annealing temperature, primer concentration, and probe concentration, multiplex qRT-PCR for simultaneous and differential detection of ASFV, CSFV, and PRRSV was developed. Subsequently, 1,143 clinical samples were detected to verify the practicality of the assay.

RESULTS

The multiplex qRT-PCR assay could specifically and simultaneously detect the ASFV, CSFV, and PRRSV with a detection limit of 1.78 × 10⁰ copies for the ASFV, CSFV, and PRRSV, but could not amplify the other major porcine viruses, such as pseudorabies virus, porcine circovirus type 1 (PCV1), PCV2, PCV3, foot-and-mouth disease virus, porcine parvovirus, atypical porcine pestivirus, and Senecavirus A. The assay had good repeatability with coefficients of variation of intra- and inter-assay of less than 1.2%. Finally, the assay was used to detect 1,143 clinical samples to evaluate its practicality in the field. The positive rates of ASFV, CSFV, and PRRSV were 25.63%, 9.36%, and 17.50%, respectively. The co-infection rates of ASFV+CSFV, ASFV+PRRSV, CSFV+PRRSV, and ASFV+CSFV+PRRSV were 2.45%, 2.36%, 1.57%, and 0.17%, respectively.

CONCLUSIONS

The multiplex qRT-PCR developed in this study could provide a rapid, sensitive, specific diagnostic tool for the simultaneous and differential detection of ASFV, CSFV, and PRRSV.

Development of Diagnostic Tests Provides Technical Support for the Control of African Swine Fever

African swine fever is a highly contagious global disease caused by the African swine fever virus. Since African swine fever (ASF) was introduced to Georgia in 2007, it has spread to many Eurasian countries at an extremely fast speed. It has recently spread to China and other major pig-producing countries in southeast Asia, threatening global pork production and food security. As there is no available vaccine at present, prevention and control must be carried out based on early detection and strict biosecurity measures. Early detection should be based on the rapid identification of the disease on the spot, followed by laboratory diagnosis, which is essential for disease control. In this review, we introduced the prevalence, transmission routes, eradication control strategies, and diagnostic methods of ASF. We reviewed the various methods of diagnosing ASF, focusing on their technical characteristics and clinical test results. Finally, we give some prospects for improving the diagnosis strategy in the future.

Inhibition of African Swine Fever Virus Replication by Porcine Type I and Type II Interferons

Interferons (IFNs) are proteins produced by a variety of cells during the process of virus infection. It can activate the transcription of multiple functional genes in cells, regulate the synergistic effect of multiple signaling pathways, and mediate a variety of biological functions such as antiviral activity and immune regulation. The symptoms of hosts infected with African swine fever virus (ASFV) depend on the combined interaction between viruses and the host. However, it is unclear whether IFNs can be used as an emergency preventive treatment for ASFV. This study focused on the use of recombinant porcine IFNs, produced by Escherichia coli, to inhibit the replication of ASFV. The activity of IFN against ASFV was detected using primary alveolar macrophages at different doses through immunofluorescence assays and quantitative real-time PCR. We found that both 1000 and 100 U/mL doses significantly inhibited the replication of ASFV. Meanwhile, we found that IFNs could significantly trigger the production of a variety of IFN-induced genes (IFIT1, IFITM3, Mx-1, OASL, ISG15, PKR, GBP1, Viperin, BST2, IRF-1, and CXCL10) and MHC molecules, which play key roles in resistance to virus infection. Peripheral blood samples were also obtained from surviving pigs treated with IFNs, and the viral load was determined. Consistent with in vitro tests, low-dose (10⁵ U/kg) recombinant porcine IFNs (PoIFN-α and PoIFN-γ) significantly reduced viral load compared to that with high-dose (10⁶ U/kg) treatment. Our results suggest that recombinant porcine IFNs have high antiviral activity against ASFV, providing a new strategy for the prevention of African swine fever.

Rapid, Unbiased PRRSV Strain Detection Using MinION Direct RNA Sequencing and Bioinformatics Tools

Prompt detection and effective control of porcine reproductive and respiratory syndrome virus (PRRSV) during outbreaks is important given its immense adverse impact on the swine industry. However, the diagnostic process can be challenging due to the high genetic diversity and high mutation rate of PRRSV. A diagnostic method that can provide more detailed genetic information about pathogens is urgently needed. In this study, we evaluated the ability of Oxford Nanopore MinION direct RNA sequencing to generate a PRRSV whole genome sequence and detect and discriminate virus at the strain-level. A nearly full length PRRSV genome was successfully generated from raw sequence reads, achieving an accuracy of 96% after consensus genome generation. Direct RNA sequencing reliably detected the PRRSV strain present with an accuracy of 99.9% using as few as 5 raw sequencing reads and successfully differentiated multiple co-infecting strains present in a sample. In addition, PRRSV strain information was obtained from clinical samples containing 10⁴ to 10⁶ viral copies or more within 6 hours of sequencing. Overall, direct viral RNA sequencing followed by bioinformatic analysis proves to be a promising approach for identification of the viral strain or strains involved in clinical infections, allowing for more precise prevention and control strategies during PRRSV outbreaks.

Establishment of a multiplex RT-PCR assay for identification of atmospheric virus contamination in pig farms

Spread of pathogens in pig farms not only causes transfection of diseases to other pigs or even farmers working in the farms, but also induces pollution to the living atmospheric environment of the residents around the farm. Therefore, it is necessary to establish a rapid and simple monitoring method. In this study, full genome sequences of common viruses were analyzed in pig farms, in combination with the design of primers, optimization of the reaction parameters, so as to establish a multiplex RT-PCR assay for the identification of classical swine fever virus (CSFV), Japanese encephalitis virus (JEV), porcine reproductive and respiratory syndrome virus (PRRSV), porcine circovirus Type 2 (PCV-2), porcine pseudorabies virus (PRV) and porcine parvovirus virus (PPV), which are common in pig farms. This method has a minimal detectable concentration of 10^-3 ng/μL, which is highly specific. Furthermore, multiplex RT-PCR was applied to examine air samples from 4 pig farms located in different cities of China. The results were in line with those obtained by single PCR. Therefore, this study can be expected to provide essential technique support for the early warning mechanism as well as disease prevention and control system against the major viruses.

African swine fever (ASF) diagnosis, an essential tool in the epidemiological investigation

Since there is no vaccine available, prevention, control, and eradication of African swine fever (ASF) is based on the implementation of appropriated surveillance and strict sanitary measures. Success of surveillance activities depends on the availability of the most appropriate diagnostic tests. Although a number of good validated ASF diagnostic techniques are available, the interpretation of the ASF diagnostic results can be complex. The reasons lie in the complexity of the epidemiology with different scenarios, as well as in the characteristics of the viruses circulating giving rise to a wide range of clinical forms of ASF. This review provides guidance for an accurate interpretation of ASF diagnostic results linked to the different clinical presentations ranging from per-acute to chronic disease, including apparently asymptomatic infections.

Interferon as a Mucosal Adjuvant for an Influenza Vaccine in Pigs

Interferon, a natural protein that is produced by a variety of cells during viral infection, activates the transcription of multiple functional genes in cells, regulates synergy among various signaling pathways, and mediates many biological functions such as antiviral activity, immune regulation, and cell growth. However, clinical research on interferon in livestock is lacking. In this study, recombinant porcine interferon (PoIFNα) was used as an adjuvant, in combination with inactivated influenza virus, to vaccinate 6-week-old pigs via nasal infusion. The transcription of target genes was then monitored and the functions of PoIFNα were determined with respect to the activation of mucosal immunity. We found that a combination of low-dose PoIFNα and inactivated influenza virus could significantly up-regulate the expression of immunoregulatory cytokines such as IL-2, IL-18, IFN-γ, IL-6, and IL-10 by real-time PCR, suggesting the induction of a strong mucosal innate immune response after administration. In addition, low-dose PoIFNα can significant enhancing the transcription of genes encoding homing factors including CCR9 and CCR10 (P < 0.001), thereby resulting in the induction of higher levels of HA-specific antibodies (P < 0.05), which can be determined by ELISA and IFA. Post-immunization challenges with H1N1 virus demonstrated that PoIFNα, combined with inactivated influenza virus, could alleviate clinical signs in pigs during the early stages of viral infection. These studies reveal low-dose PoIFNα as a potential mucosal adjuvant for influenza virus in pigs.

A multiplex RT-PCR assay for rapid and simultaneous detection of four RNA viruses in swine

A multiplex reverse transcription polymerase chain rection (mRT-PCR) was developed for simultaneous detection of four RNA viruses in swine. The conserved target sequences directed to classical swine fever virus (CSFV), porcine reproductive and respiratory syndrome virus (PRRSV), porcine epidemic diarrhea virus (PEDV) and transmissible gastroenteritis coronavirus (TGEV) were selected based on alignments of genomic sequences and then specific primers were designed. The mRT-PCR assay was developed and evaluated for its specificity and sensitivity. The expected product from the single viral template was amplified by mRT-PCR and no spurious PCR amplification occurred from the genomic RNA or DNA of other pathogens. For single virus or different combinations of two viruses the detection limit of mRT-PCR was consistent with a single RT-PCR wtith 1 × 10³ copies. For different combinations of the three viruses or four viruses, sensitivity of PEDV detection partially decreased. All of positive clinical specimens by the mRT-PCR were identically confirmed using Taqman RT-qPCR. Therefore, the mRT-PCR is a useful tool for epidemiological studies and laboratory diagnosis of single virus and/or mixed infections in swine.

Duplex nested-PCR for detection of small ruminant lentiviruses

Small ruminant lentiviruses (SRLV) have high genetic variability which results in different viral strains around the world. This create a challenge to design sensible primers for molecular diagnosis in different regions. This work proposes a protocol of duplex nested-PCR for the precise diagnosis of SRLV. The technique was designed and tested with the control strains CAEV Co and MVV 1514. Then, field strains were submitted to the same protocol of duplex nested-PCR. Blood samples of sheep and goats were tested with AGID and nested PCR with specific primers for pol, gag and LTR. The AGID results showed low detection capacity of positive animals, while the nested PCR demonstrated a greater capacity of virus detection. Results demonstrated that LTR-PCR was more efficient in detecting positive sheep samples, whereas gag-PCR allowed a good detection of samples of positive goats and positive sheep. In addition, pol-PCR was more efficient with goat samples than for sheep. Duplex nested PCR performed with standard virus samples and field strains demonstrated that the technique is more efficient for the detection of multiple pro-viral DNA sequences. This study demonstrated a successful duplex nested PCR assay allowing a more accurate diagnosis of SRLV.

The emergence of porcine circovirus 2 infections in the Northeastern part of India: A retrospective study from 2011 to 2017

Porcine circovirus (PCV) infection has emerged as an alarming threat to the pig population of India, especially in the Northeastern region (NER) over the last 10 years. The present study is a comprehensive report of the seroepidemiology of PCV2 and its incidences in the pig population from organized and unorganized farms of the entire NER of India from 2011 to 2017. A total of 5697 serum samples were screened by ELISA and the mean positivity of PCV2 antibodies in suspected sera was 31.27%. A total of 22 confirmed cases of PCV2 infection were recorded during the years 2014-2017. Seroprevalence of PCV2 infection in sows causing reproductive disorders in NER suggested its higher incidence in organized farms (65.7%) as compared to unorganized farms (17.6%). A detailed pathological and histopathological examination of the tissue samples collected from the affected animals indicated the presence of PCV2. Molecular characterization and phylogenetic analysis of four PCV2 isolates depicted the circulation of PCV2d genotype in the states of Meghalaya and Assam.

Rapid diagnosis of human adenovirus B, C and E in the respiratory tract using multiplex quantitative polymerase chain reaction

Human adenovirus (HAdV) is increasingly recognized as a major cause of human respiratory tract viral infections. Its outbreaks and epidemics in various populations resulted in considerable morbidity and mortality. Therefore, a rapid and specific assay for HAdV in clinical samples is of crucial importance to diagnosing HAdV infections. The present study aimed to develop and evaluate a multiplex quantitative polymerase chain reaction (qPCR) assay for the rapid detection and accurate quantification of HAdV B, C and E. The lower limit of detection for this assay was two genomic copies per reaction, and quantitative linearity ranged from 2 to 2×10⁶ copies per reaction of the input viral DNA. Furthermore, 3,160 throat swab samples that tested HAdV negative by the immunofluorescence assay were collected and retested using the multiplex qPCR assay. The results showed that 2,906 samples were HAdV negative and the other 254 samples were HAdV positive. The HAdV species identified included B (184 samples), C (51 samples), and E (39 samples). Among the three HAdV species, HAdV B and E were detected from 8 samples, and HAdV C and E were detected from other 12 samples. The overall results demonstrated that the sensitivity and specificity of the proposed assay were 100% (254/254) and 99.6% (2894/2906), respectively. From the perspective of routine clinical diagnosis, this assay represented a rapid (≤1.5 h) and economic strategy, and had the potential to be used for the rapid and accurate diagnosis of human respiratory infections caused by HAdV B, C and E.

Simultaneous detection of multiple pathogens by multiplex PCR coupled with DNA biochip hybridization

Traditional serological enzyme-linked immunosorbent assay (ELISA) is routinely used to monitor pathogens during quarantine in most animal facilities to prevent possible infection. However, the ELISA platform is a single-target assay, and screening all targeted pathogens is time-consuming and laborious. In this study, to increase sensitivity and to reduce diagnosis time for high-throughput processes, multiplex PCR and DNA biochip techniques were combined to develop a multi-pathogen diagnostic method for use instead of routine ELISA. Eight primer sets were designed for multiplex PCR to detect genes from seven targeted bacterial and viral pathogens. DNA-DNA hybridization was conducted on a biochip following the multiple PCR analysis. Using this method, a total of 24 clinical samples were tested, and the result showed that not only single infection but also co-infection by multi-pathogens can be detected. In conclusion, multiplex PCR coupled with a DNA biochip is an efficient method for detecting multi-pathogens in a reaction. This platform is a useful tool for quarantine services and disease prevention in animal facilities.

Assessment of listing and categorisation of animal diseases within the framework of the Animal Health Law (Regulation (EU) No 2016/429): porcine reproductive and respiratory syndrome (PRRS)

Porcine reproductive and respiratory syndrome (PRRS) has been assessed according to the criteria of the Animal Health Law (AHL), in particular criteria of Article 7 on disease profile and impacts, Article 5 on the eligibility of PRRS to be listed, Article 9 for the categorisation of PRRS according to disease prevention and control rules as in Annex IV and Article 8 on the list of animal species related to PRRS. The assessment has been performed following a methodology composed of information collection and compilation, expert judgement on each criterion at individual and, if no consensus was reached before, also at collective level. The output is composed of the categorical answer, and for the questions where no consensus was reached, the different supporting views are reported. Details on the methodology used for this assessment are explained in a separate opinion. According to the assessment performed, PRRS can be considered eligible to be listed for Union intervention as laid down in Article 5(3) of the AHL. The disease would comply with the criteria as in Sections 4 and 5 of Annex IV of the AHL, for the application of the disease prevention and control rules referred to in points (d) and (e) of Article 9(1). The animal species to be listed for PRRS according to Article 8(3) criteria are domestic pigs and wild boar.

Development of cross-priming amplification for direct detection of the African Swine Fever Virus, in pig and wild boar blood and sera samples

African swine fever (ASF) is considered a major threat to the production of pigs worldwide. The ASF aetiological agent, ASFV, is the sole member of the Asfivirus genus, belonging to the Asfarviridae family. An effective ASF vaccine is not currently available, thus the only measures of ASF spread control include, reliable and fast diagnosis. Officially approved, diagnostic methods include, virus isolation, serological assays, including enzyme-linked immunosorbent assay and immunoperoxidase assay (IPT) and different modifications of the polymerase chain reaction (PCR). This paper describes the first development and application of a cross-priming amplification method (CPA) for the direct detection of genetic ASFV material, in blood and sera from pigs and wild boars. This method is specific only to ASFV DNA. The study showed that CPA had equal sensitivity, in comparison to the official, universal probe library (UPL) real-time PCR and reached 7·2 copies of standard plasmid DNA, containing a p72 gene fragment. This method was capable of detecting ASFV DNA in all examined blood samples, originating from pigs; n = 10 and wild boars; n = 76. The obtained results were also confirmed by the officially approved, real-time PCR. The developed CPA might be further used by local and county veterinary officers, hunters or pig farmers, for preliminary ASF diagnosis.

SIGNIFICANCE AND IMPACT OF THE STUDY

The spread of the African swine fever virus (ASFV) among infected pigs and wild boars, is currently one of the most important facets of virus transmission in eastern Europe. Cross-priming amplification (CPA) has been developed, for fast and direct development of genetic ASFV material in the blood and sera of infected pigs and wild boars. It has been shown that CPA is a rapid, sensitive and specific isothermal method for the detection of ASFV DNA, in directly collected blood or sera from pigs and wild boars.