Real-time PCR to detect and analyze virulent PPV loads in artificially challenged sows and their fetuses

Narrative Review of the Safety of Using Pigs for Xenotransplantation: Characteristics and Diagnostic Methods of Vertical Transmissible Viruses

Amid the deepening imbalance in the supply and demand of allogeneic organs, xenotransplantation can be a practical alternative because it makes an unlimited supply of organs possible. However, to perform xenotransplantation on patients, the source animals to be used must be free from infectious agents. This requires the breeding of animals using assisted reproductive techniques, such as somatic cell nuclear transfer, embryo transfer, and cesarean section, without colostrum derived in designated pathogen-free (DPF) facilities. Most infectious agents can be removed from animals produced via these methods, but several viruses known to pass through the placenta are not easy to remove, even with these methods. Therefore, in this narrative review, we examine the characteristics of several viruses that are important to consider in xenotransplantation due to their ability to cross the placenta, and investigate how these viruses can be detected. This review is intended to help maintain DPF facilities by preventing animals infected with the virus from entering DPF facilities and to help select pigs suitable for xenotransplantation.

Integration of Microfluidics, Photonic Integrated Circuits and Data Acquisition and Analysis Methods in a Single Platform for the Detection of Swine Viral Diseases

Simple Summary

The control of several swine viral diseases relies mainly on evidence-based prevention protocols due to the lack of effective treatments or vaccines. To design these protocols, laboratory investigation of viral infections is critical to confirm their occurrence and determine their epizootiology. However, laboratory confirmation of certain swine viral diseases is a time-consuming and labor-intensive process, requiring scientific personnel with relevant expertise. Point-of-Care (POC) diagnostics are tests and devices that provide clinically relevant information on-site, facilitating decision-makers to swiftly take countermeasures for disease control. In the present study, novel photonic biosensors were integrated into a single, automated POC device that can record and analyze changes in the sensors’ refractive index, allowing the detection of Porcine Parvovirus (PPV) and Porcine Circovirus 2 (PCV-2) in oral fluids within 75 min. The objective of this work was to validate this device using reference and field samples (oral fluids). The system was able to detect PPV and PCV-2 in oral fluid samples satisfactorily. The device can be directly deployed in farms for the fast diagnosis of these diseases, contributing to farm biosecurity.

Abstract

Viral diseases challenge the health and welfare of pigs and undermine the sustainability of swine farms. Their efficient control requires early and reliable diagnosis, highlighting the importance of Point of Care (POC) diagnostics in veterinary practice. The objective of this study was to validate a novel POC system that utilizes Photonic Integrated Circuits (PICs) and microfluidics to detect swine viral pathogens using oral fluids and Porcine Parvovirus (PPV) and Porcine Circovirus 2 (PCV-2) as proofs of concept. The sensitivity and specificity of the device were calculated for both viruses, and Receiver Operating Characteristic (ROC) curves were drawn. PPV had an Area Under Curve (AUC) value of 0.820 (95% CI: 0.760 to 0.880, p < 0.0001), and its optimal efficiency threshold of detection shifts was equal to 4.5 pm (68.6% sensitivity, 77.1% specificity and Limit of Detection (LOD) value 10⁶ viral copies/mL). PCV-2 had an AUC value of 0.742 (95% CI: 0.670 to 0.815, p < 0.0001) and an optimal efficiency threshold of shifts equal to 6.5 pm (69.5% sensitivity, 70.3% specificity and LOD 3.3 × 10⁵ copies/mL). In this work, it was proven that PICs can be exploited for the detection of swine viral diseases. The novel device can be directly deployed on farms as a POC diagnostics tool.

Porcine Circovirus 3 Detection in Aborted Fetuses and Stillborn Piglets from Swine Reproductive Failure Cases

Porcine circovirus 3 (PCV-3) has been widely detected in healthy and diseased pigs; among different pathologic conditions, the strongest evidence of association comes from reproductive disease cases. However, simple viral detection does not imply the causality of the clinical conditions. Detection of PCV-3 within lesions may provide stronger evidence of causality. Thus, this study aimed to assess the frequency of PCV-3 detection in tissues from fetuses/stillborn piglets in cases of reproductive problems in domestic swine, as well as the histopathologic assessment of fetal tissues. Fetuses or stillborn piglets from 53 cases of reproductive failure were collected and analyzed by PCV-3 qPCR. The presence of porcine reproductive and respiratory syndrome virus (PRRSV), porcine circovirus 2 (PCV-2), and porcine parvovirus 1 (PPV1) was also checked. PCV-3 qPCR positive samples with a high viral load were tested by PCV-3 in situ hybridization (ISH), sequenced, and phylogenetically analyzed. PCV-3 DNA was detected in 18/53 (33.9%) reproductive failure cases and in 16 of them PCV-3 was the only pathogen found. PCV-2 DNA was found in 5/53 (9.4%), PRRSV RNA in 4/53 (7.5%) and PPV1 was not detected. Four out of the six PCV-3 qPCR-positive cases with Ct value <30 were positive when tested by ISH. In these samples, PCV-3 was detected within mild histopathologic lesions, such as arteritis and periarteritis in multiple tissues. The present work emphasizes the need to include PCV-3 as a potential causative agent of reproductive failure in swine.

Tropism, pathology, and transmission of equine parvovirus-hepatitis

Equine parvovirus-hepatitis (EqPV-H) has recently been associated with cases of Theiler's disease, a form of fulminant hepatic necrosis in horses. To assess whether EqPV-H is the cause of Theiler's disease, we first demonstrated hepatotropism by PCR on tissues from acutely infected horses. We then experimentally inoculated horses with EqPV-H and 8 of 10 horses developed hepatitis. One horse showed clinical signs of liver failure. The onset of hepatitis was temporally associated with seroconversion and a decline in viremia. Liver histology and in situ hybridization showed lymphocytic infiltrates and necrotic EqPV-H-infected hepatocytes. We next investigated potential modes of transmission. Iatrogenic transmission via allogeneic stem cell therapy for orthopedic injuries was previously suggested in a case series of Theiler's disease, and was demonstrated here for the first time. Vertical transmission and mechanical vectoring by horse fly bites could not be demonstrated in this study, potentially due to limited sample size. We found EqPV-H shedding in oral and nasal secretions, and in feces. Importantly, we could demonstrate EqPV-H transmission via oral inoculation with viremic serum. Together, our findings provide additional information that EqPV-H is the likely cause of Theiler's disease and that transmission of EqPV-H occurs via both iatrogenic and natural routes.

Construction and characterization of the infectious clone of porcine parvovirus carrying genetic marker

Porcine parvovirus (PPV) is one of the major pathogens that bring about reproductive failure of pregnant sows. However, the study of the pathogenesis mechanism is circumscribed due to the lack of efficient genetic manipulation method. Infectious clone is a powerful tool for further studying the genetic mechanisms of PPV. In the present study, the gene fragment (157-4812) of PPV was amplified by PPV China isolate strain as a template, and PPV DNA fragments (1-182) forming Y-structure within in 5' end and (4788-5074) forming U-structure in 3' end were synthesized. And then, the above three fragments were inserted into plasmid pKQLL to congregate a PPV full-length recombinant plasmid by means of In-Fusion cloning technology. After the successful sequencing identification of the recombinant plasmid, the EcoR I restriction site was brought out as a genetic marker by nonsense mutation (A3058 T) to produce plasmid Y-PPV, which was transfected into PK-15 cells for rescue of virus. The rescued viral particles were observed under transmission electron microscopy, and the sequencing analysis showed that Y-PPV could stably carry the genetic marker. It could be seen that Y-PPV has similar replicate capability and pathogenicity as the wild-type parental PPV strain by cellular and animal experiments. These results confirmed that Y-PPV maintain similar biological characteristics with wild-type parental PPV strain. Infectious clone could be a valuable tool for studying the individual genes of PPV and applications in gene deletion or live vector vaccines.

Biology of Porcine Parvovirus (Ungulate parvovirus 1)

Porcine parvovirus (PPV) is among the most important infectious agents causing infertility in pigs. Until recently, it was thought that the virus had low genetic variance, and that prevention of its harmful effect on pig fertility could be well-controlled by vaccination. However, at the beginning of the third millennium, field observations raised concerns about the effectiveness of the available vaccines against newly emerging strains. Subsequent investigations radically changed our view on the evolution and immunology of PPV, revealing that the virus is much more diverse than it was earlier anticipated, and that some of the “new” highly virulent isolates cannot be neutralized effectively by antisera raised against “old” PPV vaccine strains. These findings revitalized PPV research that led to significant advancements in the understanding of early and late viral processes during PPV infection. Our review summarizes the recent results of PPV research and aims to give a comprehensive update on the present understanding of PPV biology.

Review of transmission routes of 24 infectious diseases preventable by biosecurity measures and comparison of the implementation of these measures in pig herds in six European countries

This study aimed to review the transmission routes of important infectious pig diseases and to translate these into biosecurity measures preventing or reducing the transmission between and within pig herds. Furthermore, it aimed to identify the level of implementation of these measures in different European countries and discuss the observed variations to identify potentials for improvement. First, a literature review was performed to show which direct and indirect transmission routes of 24 infectious pig diseases can be prevented through different biosecurity measures. Second, a quantitative analysis was performed using the Biocheck.UGent™, a risk-based scoring system to evaluate biosecurity in pig herds, to obtain an insight into the implementation of these biosecurity measures. The database contained farm-specific biosecurity data from 574 pig farms in Belgium, Denmark, France, Germany, the Netherlands and Sweden, entered between January 2014 and January 2016. Third, a qualitative analysis based on a review of literature and other relevant information resources was performed for every subcategory of internal and external biosecurity in the Biocheck.UGent™ questionnaire. The quantitative analysis indicated that at the level of internal, external and overall biosecurity, Denmark had a significantly distinct profile with higher external biosecurity scores and less variation than the rest of the countries. This is likely due to a widely used specific pathogen-free (SPF) system with extensive focus on biosecurity since 1971 in Denmark. However, the observed pattern may also be attributed to differences in data collection methods. The qualitative analysis identified differences in applied policies, legislation, disease status, pig farm density, farming culture and habits between countries that can be used for shaping country-specific biosecurity advice to attain improved prevention and control of important pig diseases in European pig farms.

Molecular Detection of Pseudorabies Virus (PrV), Porcine Parvovirus (PPV) and Porcine Circovirus 2 (PCV2) in Swine in Republic of Montenegro

The presence of pseudorabies virus (PrV), porcine parvovirus (PPV) and porcine circovirus 2 (PCV2) was examined in sixty samples (spleen and lymph nodes) and thirty samples of sacral ganglia collected from non-vaccinated swine by virus isolation and polymerase chain reaction (PCR). Using PCR method PrV was detected in three samples, PPV in seven samples and six samples were found positive for PCV2. The phylogenetic analysis of the nucleotide sequences of three PrV isolates identified in this study showed high similarity and significant clustering within the PrV genotype I strains such as Kaplan and Bartha isolated from pigs in Hungary, strain Becker isolated in USA and strain Kolchis isolated in Greece. The nucleotide sequences of two PPV isolates showed high level of similarity with the strain Challenge isolated from pigs in UK, strain Kresse isolated in USA and strains 77 and LZ isolated in China. The phylogenetic analysis of the nucleotide sequences of two PCV2 isolates showed high level of similarity and significant clustering within genotype PCV2b strains such as NIVS-3, NIVS-5 and NIVS-6 isolated in Serbia, strain 3959 isolated in Austria, strain PM165 isolated from pigs in Brasil, and strain XT2008 isolated in China. The results of our study present the molecular characterization of PrV, PPV and PCV2 identified in swine in Republic of Montenegro. Besides that, these results confirmed that PCR is a very useful method for rapid detection of these viruses in subclinically infected swine.

A sensitive and specific nanoparticle-assisted PCR assay for rapid detection of porcine parvovirus

A novel nanoparticle-assisted polymerase chain reaction (nanoPCR) assay to detect porcine parvovirus (PPV) is described here. Primers for this assay were designed based on the conserved region of the nonstructural protein 1 (NS1) gene of PPV, which encodes one of the nonstructural proteins. The sensitivity of the PPV nanoPCR assay was measured by using diluted recombinant plasmids in which the PPV NS1 gene had been inserted. The detection limit was 5.6 × 10(1) copies μl(-1) for the PPV nanoPCR assay vs 5.6 × 10(3) copies μl(-1) for conventional PCR assay. The results showed that the sensitivity of PPV nanoPCR assay was 100 times higher than that of conventional PCR assay. The PPV nanoPCR assay produced 142-bp product as expected when amplifying PPV DNA, while produced nothing when amplifying the DNA or cDNA of the following viruses: swine encephalomyocarditis virus, classical swine fever virus, porcine pseudorabies virus, porcine reproductive and respiratory syndrome virus, porcine teschovirus and porcine circovirus type II. PPV was detected in 108 of 109 clinical swine samples from Heilongjiang, Jilin and Henan provinces using the nanoPCR assay, and the results were confirmed by sequencing.

SIGNIFICANCE AND IMPACT OF THE STUDY

Nanoparticle-assisted polymerase chain reaction (nanoPCR) assay is an improved PCR. NanoPCR is highly sensitive and specific because the nanofluids formed in the nanobuffer have high thermal conductivity, which reduces the time required to reach the target temperature. It is more sensitive than conventional PCR, and it could detect the cases earlier than conventional PCR. This report describes the first application of the highly efficient nanoPCR technology for the detection of porcine parvovirus (PPV). The PPV nanoPCR assay will be useful for the detection and study of PPV and will also be applicable to improve the detection of other viruses.

Development of a real-time quantitative PCR for detecting duck hepatitis a virus genotype C

Recently, duck hepatitis A virus genotype C (DHAV-C), a causative agent of duck viral hepatitis, has been responsible for increasing economic losses in the duck industry in China and South Korea. In this study, a real-time PCR assay targeting the 2C gene for detecting DHAV-C was developed. The assay was confirmed to be specific and sensitive, and the minimum detection limit was 3.36 × 10(3) copies per reaction, making this assay suitable for rapid diagnosis of DHAV-C infection from clinical samples. In addition, the dynamics of the viral loads in tissues of specific-pathogen-free (SPF) ducklings infected with DHAV-C were investigated using this method. The DHAV-C could be detected earliest in the liver within 12 h postinfection. Moreover, high viral loads were identified in the heart, liver, spleen, lung, kidney, bursa of Fabricius, thymus, pancreas, brain, and small intestine after 24 h postinfection. Taking the data collectively, the study described in this report is the first to have developed a real-time PCR method for detection of DHAV-C and thus contributes to pathogenicity research.

A multiple SYBR Green I-based real-time PCR system for the simultaneous detection of porcine circovirus type 2, porcine parvovirus, pseudorabies virus and Torque teno sus virus 1 and 2 in pigs

Multiple viral infections are common in pigs under intensive production conditions. All five of the viruses included in this study are associated with multifactorial diseases that cause significant economic losses in swine farming worldwide. The development is described of a novel multiple real-time PCR system based on the use of SYBR Green I that allows the simultaneous detection and differentiation of porcine circovirus 2 (PCV-2), porcine parvovirus (PPV), pseudorabies virus (PRV) and Torque teno sus virus species 1 and 2 (TTSuV1 and TTSuV2) in pigs. The method was able to distinguish between all five viral agents, and tests of other DNA viruses proved the specificity of the system. The multiple real-time PCR system was sensitive, as the limits of detection ranged from 3.65×10(3) to 5.04×10(3) copies of DNA template per reaction. The coefficients of variation were low for both intra-assay and inter-assay variability. In addition, the results of the multiple real-time PCR system tests were 100% consistent with previous results based on specific PCR assay testing of field samples. This method could be a useful tool for epidemiological studies and disease management.

Seroprevalence of porcine reproductive and respiratory syndrome, Aujeszky's disease, and porcine parvovirus in replacement gilts in Thailand

The present study investigated the seroprevalence of porcine reproductive and respiratory syndrome virus, Aujeszky's disease virus (ADV), and porcine parvovirus (PPV) in replacement gilts from selected five swine herds in Thailand. The study consisted of three parts. First, a retrospective data analysis on the seroprevalence of porcine reproductive and respiratory syndrome virus (PRRSV) and ADV glycoprotein I (gI) in gilts, sows, boars, nursery, and fattening pigs in five herds (n = 7,030). Second, a cross-sectional study on seroprevalence of PRRSV, ADV, and PPV (n = 200) in replacement gilts. Last, the seroprevalence of PRRSV, ADV, and PPV in gilts culled due to reproductive failure (n = 166). Across the herds, the seroprevalence of PRRSV and ADV was 79.3% and 5.3%, respectively. The cross-sectional study revealed that 87.5%, 4.0%, and 99.0% of the replacement gilts were infected with PRRSV, ADV, and PPV, respectively. In the gilts culled due to reproductive failure, the seroprevalence of PRRSV, ADV, and PPV was 73.5%, 28.3%, and 86.0%, respectively. Of these culled gilts, 75.5% had been infected with at least two viruses and 18.9% had been infected with all three viruses. It could be concluded that most of the replacement gilts were exposed to PRRSV (84%), PPV (97%), and ADV (4%) before entering the breeding house. PPV was an enzootic disease among the selected herds. The prevalence of ADV was higher in gilts culled due to reproductive disturbance than in the healthy gilts.

Reproductive failure in wild boars associated to porcine parvovirus infection and in vivo and in vitro characterization of the causal isolate

Investigations were made to identify the causal agent of an acute outbreak of abortions in a domesticated herd of wild boar. Only porcine parvovirus (PPV) was isolated from samples of organs from the still-born sucklings and mummified aborted fetuses. The isolated virus hemagglutinated erythrocytes of guinea pig, murine, rat, and chicken. Identity of the virus, designated the BQ strain, was confirmed by the production of a specific cytopathic effect on susceptible cells and by the results from ELISA, PCR, immunofluorescence assay, and electron microscopy. PPV BQ strain was adapted to growth in a swine testicular cell line. When inoculated into healthy sows, PPV BQ caused the same reproductive disorder observed in the affected herd.