Co-infection status of novel parvovirus's (PPV2 to 4) with porcine circovirus 2 in porcine respiratory disease complex and porcine circovirus-associated disease from 1997 to 2012

Coinfection with bacterial pathogens and genetic modification of PRRSV-2 for suppression of NF-κB and attenuation of proinflammatory responses

Porcine reproductive and respiratory syndrome virus (PRRSV) infects pulmonary alveolar macrophages and induces inflammation in the respiratory system. In swine farms, coinfection with PRRSV and bacterial pathogens is common and can result in clinically complicated outcomes, including porcine respiratory disease complex. Coinfection can cause excessive expressions of proinflammatory mediators and may lead to cytokine-storm-like syndrome. An immunological hallmark of PRRSV-2 is the bidirectional regulation of NF-κB with the nucleocapsid (N) protein identified as the NF-κB activator. We generated an NF-κB-silencing mutant PRRSV-2 by mutating the N gene to block its binding to PIAS1 [protein inhibitor of activated STAT-1 (signal transducer and activator of transcription 1)]. PIAS1 functions as an NF-κB repressor, and thus, the PIAS1-binding modified N-mutant PRRSV-2 became NF-κB activation-resistant in its phenotype. During coinfection of pigs with PRRSV-2 and Streptococcus suis, the N-mutant PRRSV-2 decreased the expression of proinflammatory cytokines and showed clinical attenuation. This review describes the coinfection of pigs with various pathogens, the generation of mutant PRRSV for NF-κB suppression, inflammatory profiles during bacterial coinfection, and the potential application of these findings to designing a new vaccine candidate for PRRSV-2.

Development and application of a blocking ELISA method based on Cap protein for detecting antibodies against porcine circovirus 2

Porcine circovirus type 2 (PCV2) serves as the key pathogen linked to porcine circovirus-associated disease, representing a considerable risk to the worldwide swine industry. A blocking enzyme-linked immunosorbent assay (ELISA) was established to identify antibodies specifically targeting PCV2, employing recombinant Cap protein as the antigen and a monoclonal antibody against PCV2 Cap protein as the detector antibody. Utilizing receiver operating characteristic curve analysis, a cutoff value of 33.8% was determined to distinguish between positive and negative serum samples. The sensitivity and specificity of this blocking ELISA method were reported at 94.7% and 96.1%, respectively. Notably, this approach exclusively identified antibodies for PCV2, showing no cross-reactivity with antibodies related to African swine fever virus (ASFV), Porcine epidemic diarrhea virus (PEDV), Porcine pseudorabies virus (PRV), and porcine reproductive and respiratory syndrome virus. Both intra-assay and inter-assay coefficients of variation were less than 10%. In a comparison involving 402 porcine serum samples, the agreement rate with a commercial indirect ELISA kit reached 98.76%, with a kappa value of 0.888, reflecting high concordance between the two testing methods. This study showcases the blocking ELISA method as an efficient and standardized approach for serological monitoring of PCV2 in swine populations and for assessing seroconversion in vaccinated pigs.

IMPORTANCE

Porcine circovirus type 2 (PCV2) has become recognized as a pathogen of significant economic concern within the swine industry. PCV2 mainly affects the immune systems of pigs, leading to a reduction in lymphocytes and resulting in immune suppression in the affected animals. Co-infection with other porcine pathogens can enhance PCV2 infection and exacerbate porcine circovirus disease. Currently, the kits available for detecting PCV2 antibodies primarily employ indirect enzyme-linked immunosorbent assay (ELISA); however, this method is prone to false positives. In contrast, the blocking ELISA method offers enhanced specificity and provides a more straightforward interpretation of results. Previous studies utilizing blocking ELISA for PCV2 antibody detection have depended on plates coated with purified PCV2 virus, a process that is both technically challenging and time-consuming. Consequently, there is a pressing need to develop a new blocking ELISA method that is more efficient to detect antibodies against PCV2.

Distribution and phylogenetic analysis of porcine parvoviruses in the wild boar population of Russia

BACKGROUND

Porcine parvoviruses (PPVs) are widespread worldwide in the swine population. PPV1 is a significant infectious agent in pig production, causing porcine reproductive failure. The pathogenic potential of novel PPVs has been poorly studied. Since wild boars are a reservoir for PPVs, the aim of this study was to investigate their prevalence and genetic diversity in the wild boar population. Tissue samples (spleen, lungs, and lymph nodes) collected from 108 wild boars from three regions of Russia during 2021-2024 were analyzed.

RESULTS

PPV1-7 were found in wild boar populations in Russia, and the most abundant species were PPV7 (59.3%) and PPV3 (49.1%). The research did not reveal any significant relationship between the gender and age of the animals and the prevalence of PPVs. A comparison between the detection rates of PPVs and PCV2/PCV3 revealed the random nature of coinfections. For phylogenetic analysis, complete VP1/VP2 gene sequences of 17 PPV1 isolates were obtained. Most of them belonged to the 27a-like group. Two isolates were in the same cluster as the highly virulent Kresse strain. Isolate BelWB57 had amino acid substitutions that were specific to both the Kresse and 27a-like strains, but it was not classified in either group. Additionally, three sequences for PPV2, PPV3, and PPV7, and one sequence for PPV5 and PPV6 VP1/VP2 genes were obtained. PPV2, PPV3, and PPV7 isolates demonstrated distribution across various clusters with strains from domestic pigs and wild boars from different countries. PPV6 isolate was included in the same clade as the Russian isolate from a domestic pig, whereas PPV5 did not enter any clade with representatives from our country.

CONCLUSIONS

This is the first work devoted to the study of the PPV1-7 prevalence, as well as the genetic characteristics of isolates circulating among wild boars in various regions of Russia. Our data showed that PPV1-7 is widespread in wild boar populations. Phylogenetic analysis of PPV1 demonstrates a significant prevalence of 27a-like isolates.

Detection of porcine parvovirus 2 in pigs in North Kerala, India

Porcine parvovirus 2 (PPV2) is one the viruses that has been reported to be associated with respiratory ailments in pigs. In North Kerala, there has been an increase in the cases of respiratory diseases in pigs. The prevalence of porcine circovirus 2 (PCV2) and porcine reproductive and respiratory syndrome virus (PRRSV) that are associated with respiratory disease in pigs has been established in Kerala. However, no study has been carried out on PPV2 in the state. This paper reports the results of a pioneer study carried out to detect and characterize PPV2 associated with cases of respiratory ailments in pigs in North Kerala. A total of 54 samples were tested for the presence of PPV2 by NS1 and VP1 gene-based polymerase chain reaction (PCR). Of the samples tested, 3 (5.56%) were found to be positive for the virus. In two samples, coinfection of PPV2 and PCV2 was observed. On phylogenetic analysis of the VP1 gene of the virus, it was revealed that the virus was similar to PPV2 viruses detected in Croatia, Hungary and Romania. The results of the study indicate that PPV2 is present in pigs of North Kerala and that its prevalence is low. Since the virus is capable of inducing significant pathological changes in the lungs, and due to the possibility of coinfection with other viruses inducing respiratory ailments, measures are to be taken to control the spread of the virus in pigs in Kerala.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13337-025-00909-x.

Comparative Prevalence Estimation and Phylogenetic Analysis of Novel Porcine Parvoviruses (PPV2-7) in Hungarian Pig Herds

To date, seven novel parvoviruses have been identified in pigs and designated as porcine parvovirus 2-7 (PPV2-7). The presence of these emerging viruses has been reported in several countries around the world, although their pathogenic role and clinical and economical relevance are largely unknown. Here, we report the estimated prevalence and genetic diversity of novel PPV2-7 in Hungarian pig herds and the detection of these viruses in two Slovakian pig farms. For the comparative prevalence estimation, 2505 serum samples from different age groups, 218 oral fluid samples, and 111 processing fluid samples were collected from 26 large-scale Hungarian farms according to a systematic, cross-sectional sampling protocol. All samples were tested by real-time quantitative polymerase chain reaction (qPCR), and the presence of at least one PPV was detected in 24 of the 26 (92%) Hungarian and both Slovakian farms, suggesting high levels of subclinical circulation in most herds. The estimated PPV2-7 prevalence in Hungary varied from 50% to 89%, with PPV4 being the least and PPV2 being the most prevalent virus. The highest detection rates were observed in oral fluid samples, indicating that this sample type is most suitable for screening PPVs, but all viruses were also detected in serum samples and processing fluids. All novel PPVs were most frequently detected in the serum samples of weaned pigs and fatteners, with slightly higher viral burden in the younger age groups. These results may suggest an age-related susceptibility, which could play a significant role in the epidemiology of these viruses, impacting herd health and productivity.

Molecular Epidemiology and Phyloevolutionary Analysis of Porcine Parvoviruses (PPV1 through PPV7) Detected in Replacement Gilts from Colombia

Eight porcine parvovirus (PPV) species, designated as PPV1 through PPV8, have been identified in swine. Despite their similarities, knowledge about their distribution and genetic differences remains limited, resulting in a gap in the genetic classification of these viruses. In this study, we conducted a comprehensive analysis using PPV1 to PPV7 genome sequences from Colombia and others available in the GenBank database to propose a classification scheme for all PPVs. Sera from 234 gilts aged 180 to 200 days were collected from 40 herds in Colombia. Individual detection of each PPV (PPV1 through PPV7) was performed using end-point PCR. Complete nucleotide (nt) sequencing was performed on the PPV1 viral protein (VP), and near-complete genome (NCG) sequencing was carried out for novel porcine parvoviruses (nPPVs) (PPV2 through PPV7). Phylogenetic analyses were conducted by comparing PPV1-VP sequences to 94 available sequences and nPPVs with 565 NCG, 846 nPPV-VP, and 667 nPPV-nonstructural protein (NS) sequences. Bayesian phylogenetic analysis was used to estimate substitution rates and the time to the most recent common ancestor for each PPV. The highest prevalence was detected for PPV3 (40.1%), followed by PPV5 (20.5%), PPV6 (17%), PPV1 (14.5%), PPV2 (9.8%), PPV4 (4.2%), and PPV7 (1.3%). Notably, all tested sera were negative for PPV8 genomes. An analysis of the PPV1-VP sequences revealed two main clades (PPV1-I and PPV1-II), with the sequences recovered in this study grouped in the PPV1-II clade. Comparative analysis showed significant genetic distances for PPV2 to PPV7 at the NCG (>6.5%), NS (>6.3%), and VP (>7.5%) regions, particularly when compared to equivalent regions of PPV genomes recovered worldwide. This study highlights the endemic circulation of nPPVs in Colombian pig herds, specifically among gilts. Additionally, it contributes to the phylogenetic classification and evolutionary studies of these viruses. The proposed method aims to categorize and divide subtypes based on current knowledge and the genomes available in databanks.

The first report of porcine parvovirus 8 (PPV8) on the American continent is associated with pigs in Colombia with porcine respiratory disease

Seven novel porcine parvoviruses (PPV2 to PPV8) have been discovered in the last two decades. The last one reported was PPV8 in China in 2022, which was proposed to be a member of the genus Protoparvovirus. Here, we report the first detection of PPV8 outside China - in two provinces from Colombia. Six out of 146 (4.1%) pigs showing porcine respiratory disease (PRD) tested positive for PPV8. Sequencing and phylogenetic analysis of two Colombian PPV8 isolates (GenBank database accession numbers PP335559 and PP335560) showed them to be members of the genus Protoparvovirus. Furthermore, PPV8 was detected in coinfections with porcine circovirus type 2 (PCV2) and porcine reproductive and respiratory syndrome virus (PRRSV), which are associated with PRD.

First Report of Porcine Parvovirus 8 in Europe: Widespread Detection and Genetic Characterization on Commercial Pig Farms in Hungary and Slovakia

Porcine parvovirus 8 (PPV8), a novel virus in the Parvoviridae family, was first identified in 2022 in lung samples of domestic pigs from China. Retrospective analyses showed that it had been circulating in China since 1998, but no other countries had reported its presence so far. A recent study conducted in South America did not detect any PPV8-positive samples in that region. Here, we report the detection of PPV8 in Hungarian and Slovakian pig farms and the estimated prevalence of the virus in Hungary. Altogether, 2230 serum, 233 oral fluid, and 115 processing fluid samples were systematically collected from 23 Hungarian and 2 Slovakian pig farms between 2020 and 2023. A real-time quantitative PCR method was developed to detect the viral genome. Our results revealed the presence of PPV8 on 65% of the Hungarian farms and both Slovakian farms included in our study, marking its first detection in Europe. Oral fluid samples showed the highest positivity rates, reaching up to 100% in some herds. The viral genome was successfully detected in serum and processing fluid samples too, but with significantly lower prevalence rates of 4% and 5%, respectively. Genetic analysis of 11 partial VP2 sequences demonstrated high similarity to the original Chinese strain but with unique amino acid mutations, suggesting possible local evolution of the virus. Our study presents the first scientific evidence of PPV8 infection outside of China and offers a comprehensive assessment of its prevalence in the Hungarian pig population. Further research is required to understand its potential impact on swine health.

First Report of Porcine Parvovirus 2 (PPV2) in Pigs from Colombia Associated with Porcine Reproductive Failure (PRF) and Porcine Respiratory Disease Complex (PRDC)

Pigs are affected by various parvoviruses (PPVs); eight have been reported to date (PPV1-PPV8). Porcine parvovirus 1 is considered a primary agent of porcine reproductive failure (PRF), while it is unknown whether other PPVs impact porcine health. Recently, the presence of PPV2 has been confirmed in the lung, either as a single agent or in the form of coinfection with other respiratory; therefore, it has been proposed as a potential participant in the porcine respiratory disease complex (PRDC). In the present study, the presence of PPV2 alone and coinfection with other viruses (PCV2, PCV3, and PRRSV) was evaluated in lung samples obtained from pigs with respiratory signs (respiratory group: RG) (n = 146) and stillborn lungs (stillborn group: SG) (n = 19) from 82 farms in the five regions with the highest swine production in Colombia. The overall PPV2 prevalence was 37.6% (62/165), with the highest proportion mainly detected in grow-finisher pigs (62.5%), while its herd prevalence was 51.2% (42/82). The most prevalent virus was PRRSV in both groups, while PPV2 alone was found only in the RG group. The most common dual coinfection in the RG and SG was PCV2/PRRSV (17.8% and 10.5%), while the most frequent coinfections involving PPV2 in the RG were PPV2/PCV2 (7.5%) and PPV2/PRRSV (4%) and PPV2/PCV2 (5.3%) in the SG. The most common triple coinfection was PPV2/PCV2/PRRSV at 15% in the RG and 21% in the SG, while quadruple coinfection PVV2/PCV2/PCV3/PRRSV was detected only in the RG (5.5%). Histopathological evaluation of 21 PPV2-positive lungs showed variable degrees of histiocytic or lymphohistiocytic interstitial pneumonia (9%) in the RG, while no significant changes were observed in SG; in addition, neutrophilic bronchopneumonia was observed in 73.7% if cases evaluated. In situ hybridization-RNAScope® confirmed the presence of PPV2 within pulmonary lesions in 2/19 RG pigs, while no in situ detection was observed in the SG pigs. The phylogenetic evaluation of seven PPV2 sequences detected in Colombia was compared with another 102 reported sequences, indicating that the Colombian strains are located in clade 2. Our results confirm the presence of PPV2 in pigs with PRDC alone and pigs coinfected with PCV2, PCV3, and PRRSV. Likewise, its presence alone or in coinfection in stillbirths suggests that PPV2 is also involved in PRF.

Development and application of a TaqMan-probe-based multiplex real-time PCR assay for simultaneous detection of porcine circovirus 2, 3, and 4 in Guangdong province of China

Porcine circoviruses disease (PCVD), caused by porcine circovirus (PCVs), is an important swine disease characterized by porcine dermatitis, nephrotic syndrome and reproductive disorders in sows. However, diseases caused by PCV2, PCV3, or PCV4 are difficult to distinguish, so a simple, rapid, accurate and high-throughput diagnostic and identification method is urgently needed to differentiate these three types. In this study, specific primers and probes were designed based on the conserved region sequences of the Rep gene of PCV2, and the Cap gene of PCV3 and PCV4. A multiplex qPCR assay was developed and optimized that the limit of detection concentration could reach as low as 3.8 copies/μL, with all correlation coefficients (R2) exceeding 0.999. Furthermore, the method showed no cross-reaction with other crucial porcine viral pathogens, and both intra-repeatability and inter-reproducibility coefficients of variation were below 2%. The assay was applied to the detection of 738 pig samples collected from 2020 to 2021 in Guangdong Province, China. This revealed positive infection rates of 65.18% for PCV2, 29.27% for PCV3, and 0% for PCV4, with a PCV2/PCV3 co-infection rate of 23.17%. Subsequently, complete genome sequences of 17 PCV2 and 4 PCV3 strains were obtained from the above positive samples and pre-preserved positive circovirus samples. Nucleotide sequence analysis revealed that the 17 PCV2 strains shared 96.7-100% complete nucleotide identity, with 6 strains being PCV2b and 11 strains being PCV2d; the 4 PCV3 strains shared 98.9-99.4% complete nucleotide identity, with 2 strains being PCV3a-1 and 2 strains being PCV3b. This research provides a reliable tool for rapid PCVs identification and detection. Molecular epidemiological investigation of PCVs in pigs in Guangdong Province will help us to understand PCV2 and PCV3 epidemiological characteristics and evolutionary trends.

Infection and Coinfection of Porcine-Selected Viruses (PPV1 to PPV8, PCV2 to PCV4, and PRRSV) in Gilts and Their Associations with Reproductive Performance

Seven novel porcine parvoviruses (nPPVs) (PPV2 through PPV8) have been described, although their pathogenicity and possible effects on porcine reproductive failure (PRF) are undefined. In this study, these nPPVs were assessed in gilts from Colombia; their coinfections with PPV1, PCV2, PCV3, PCV4, and PRRSV and an association between the nPPVs and the reproductive performance parameters (RPPs) in sows were determined. For this, 234 serum samples were collected from healthy gilts from 40 herds in five Colombian regions, and the viruses were detected via real-time PCR. The results confirmed the circulation of PPV2 through PPV7 in Colombia, with PPV3 (40%), PPV5 (20%), and PPV6 (17%) being the most frequent. Additionally, no PCV4 or PPV8 was detected. PPV2 to PPV7 were detected in concurrence with each other and with the primary PRF viruses, and these coinfections varied from double to sextuple coinfections. Additionally, the association between nPPVs and PRF primary viruses was statistically significant for the presence of PPV6 in PCV3-positive (p < 0.01) and PPV5 in PPRSV-positive (p < 0.05) gilts; conversely, there was a significant presence of PPV3 in both PCV2-negative (p < 0.01) and PRRSV-negative (p < 0.05) gilts. Regarding the RPPs, the crude association between virus detection (positive or negative) and a high or low RPP was only statistically significant for PCV3 and the farrowing rate (FR), indicating that the crude odds of a low FR were 94% lower in herds with PCV3-positive gilts. This finding means that the detection of PCV3 in gilts (PCV3-positive by PCR) is associated with a higher FR in the farm or that these farms (with positive gilts) have lower odds (OR 0.06, p-value 0.0043) of a low FR. Additionally, a low FR tended to be associated with the detection of PPV4 and PPV5 (p-value < 0.20). This study is important for establishing the possible participation of nPPVs in PRF.

Natural compound Sanggenon C inhibits porcine reproductive and respiratory syndrome virus replication in piglets

Porcine reproductive and respiratory syndrome virus is one of the main pathogens threatening the global pig industry, and there is still a lack of effective therapeutic drugs. Sanggenon C is a flavanone Diels-Alder adduct compound extracted from the root bark of the mulberry genus, which has blood pressure-reducing, anti-atherosclerotic, anti-oxidative, and anti-inflammatory effects. In our previous study, Sanggenon C was confirmed to significantly inhibit PRRSV replication in vitro. However, its antiviral potential to inhibit PRRSV infection in vivo has not been evaluated in piglets. Here, the antiviral effect of Sanggenon C was evaluated in PRRSV-challenged piglets based on assessments of rectal temperature, viral load, pathological changes of lung tissue and secretion of inflammatory cytokines. The results showed that Sanggenon C treatment relieved the clinical symptoms, reduced the viral loads in the lungs and bloods, alleviated the pathological damage of lung tissue, decreased the secretion of inflammatory cytokines, and shorten the excretion time of virus from the oral and nasal secretions and feces of piglets after PRRSV infection. The results indicated that Sanggenon C is a promising anti-PRRSV drug, which provides a new strategy for the prevention and control of PRRS in clinical practice.

Molecular basis for the different PCV2 susceptibility of T-lymphoblasts in Landrace and Piétrain pigs

Clinically, Landrace pigs are more susceptible to porcine circovirus-associated diseases (PCVADs) than Piétrain pigs. We previously found that porcine circovirus type 2 (PCV2) can infect T-lymphoblasts. The present study examined the replication kinetics of six PCV2 strains in the lymphoblasts of Landrace and Piétrain pigs. The results showed that T-lymphoblasts from Landrace pigs are much more susceptible to PCV2 infection than those from Piétrain pigs. In addition, PCV2 replication was strain-dependent. PCV2 binding to T-lymphoblasts was partially mediated by chondroitin sulfate (CS) and dermatan sulfate (DS). Phosphacan, an effective internalization mediator in monocytes that contains several CS chains, was also demonstrated to be involved in PCV2 internalization. Viral binding and internalization were not different between the two breeds, however, the subsequent step, the disassembly was. Although inhibition of serine proteases blocked PCV2 replication in both Landrace and Piétrain pigs, this only occurred at a neutral pH in Piétrain pigs, whereas this occurred also at a low pH in Landrace. This suggested that more proteases can cleave PCV2 in Landrace lymphoblasts than in Piétrain lymphoblasts, explaining the better replication. Through co-localization studies of viral particles with endo-lysosomal markers, and quantitative analysis of organelle sizes during viral internalization, it was observed that PCV2 may exhibit a higher propensity for viral escape from late endosomes in Landrace pigs (smaller) compared to Piétrain pigs. These results provide new understandings of the different PCV2 susceptibility in Landrace and Piétrain pigs.

Molecular Survey on Porcine Parvoviruses (PPV1-7) and Their Association with Major Pathogens in Reproductive Failure Outbreaks in Northern Italy

Successful reproductive performance is key to farm competitiveness in the global marketplace. Porcine parvovirus 1 (PPV1) has been identified as a major cause of reproductive failure, and since 2001 new species of porcine parvoviruses, namely PPV2-7, have been identified, although their role is not yet fully understood yet. The present study aimed to investigate PPVs' presence in reproductive failure outbreaks occurring in 124 farms of northern Italy. Fetuses were collected from 338 sows between 2019 and 2021 and tested for PPVs by real-time PCR-based assays and for other viruses responsible for reproductive disease. At least one PPV species was detected in 59.7% (74/124) of the tested farms. In order, PPV1, PPV5, PPV6, PPV7 and PPV4 were the most frequently detected species, whereas fewer detections were registered for PPV2 and PPV3. Overall, the new PPV2-7 species were detected in 26.6% (90/338) of the cases, both alone or in co-infections: PCV-2 (7.1%, 24/338), PCV-3 (8.2%, 28/338), and PRRSV-1 (6.2%, 21/338) were frequently identified in association with PPVs. Single PPVs detections or co-infections with other agents commonly responsible for reproductive failure should encourage future studies investigating their biological, clinical, and epidemiological role, for a better preparedness for potential emerging challenges in intensive pig production.

The Novel Porcine Parvoviruses: Current State of Knowledge and Their Possible Implications in Clinical Syndromes in Pigs

Parvoviruses (PVs) affect various animal species causing different diseases. To date, eight different porcine parvoviruses (PPV1 through PPV8) are recognized in the swine population, all of which are distributed among subfamilies and genera of the Parvoviridae family. PPV1 is the oldest and is recognized as the primary agent of SMEDI, while the rest of the PPVs (PPV2 through PPV8) are called novel PPVs (nPPVs). The pathogenesis of nPPVs is still undefined, and whether these viruses are putative disease agents is unknown. Structurally, the PPVs are very similar; the differences occur mainly at the level of their genomes (ssDNA), where there is variation in the number and location of the coding genes. Additionally, it is considered that the genome of PVs has mutation rates similar to those of ssRNA viruses, that is, in the order of 10-5-10-4 nucleotide/substitution/year. These mutations manifest mainly in the VP protein, constituting the viral capsid, affecting virulence, tropism, and viral antigenicity. For nPPVs, mutation rates have already been established that are similar to those already described; however, within this group of viruses, the highest mutation rate has been reported for PPV7. In addition to the mutations, recombinations are also reported, mainly in PPV2, PPV3, and PPV7; these have been found between strains of domestic pigs and wild boars and in a more significant proportion in VP sequences. Regarding affinity for cell types, nPPVs have been detected with variable prevalence in different types of organs and tissues; this has led to the suggestion that they have a broad tropism, although proportionally more have been found in lung and lymphoid tissue such as spleen, tonsils, and lymph nodes. Regarding their epidemiology, nPPVs are present on all continents (except PPV8, only in Asia), and within pig farms, the highest prevalences detecting viral genomes have been seen in the fattener and finishing groups. The relationship between nPPVs and clinical manifestations has been complicated to establish. However, there is already some evidence that establishes associations. One of them is PPV2 with porcine respiratory disease complex (PRDC), where causality tests (PCR, ISH, and histopathology) lead to proposing the PPV2 virus as a possible agent involved in this syndrome. With the other nPPVs, there is still no clear association with any pathology. These have been detected in different systems (respiratory, reproductive, gastrointestinal, urinary, and nervous), and there is still insufficient evidence to classify them as disease-causing agents. In this regard, nPPVs (except PPV8) have been found to cause porcine reproductive failure (PRF), with the most prevalent being PPV4, PPV6, and PPV7. In the case of PRDC, nPPVs have also been detected, with PPV2 having the highest viral loads in the lungs of affected pigs. Regarding coinfections, nPPVs have been detected in concurrence in healthy and sick pigs, with primary PRDC and PRF viruses such as PCV2, PCV3, and PRRSV. The effect of these coinfections is not apparent; it is unknown whether they favor the replication of the primary agents, the severity of the clinical manifestations, or have no effect. The most significant limitation in the study of nPPVs is that their isolation has been impossible; therefore, there are no studies on their pathogenesis both in vitro and in vivo. For all of the above, it is necessary to propose basic and applied research on nPPVs to establish if they are putative disease agents, establish their effect on coinfections, and measure their impact on swine production.

The Synergic Role of Emerging and Endemic Swine Virus in the Porcine Respiratory Disease Complex: Pathological and Biomolecular Analysis

Porcine respiratory disease complex (PRDC) represents a significant threat to the swine industry, causing economic losses in pigs worldwide. Recently, beyond the endemic viruses PRRSV and PCV2, emerging viruses such as TTSuV, PCV3, and PPV2, have been associated with PRDC, but their role remains unclear. This study investigates the presence of PCV2 and PRRSV and emerging viruses (PCV3, TTSuV, and PPV2) in the lungs of swine belonging to different age groups by histopathology and real-time PCR. The prevalent lung lesion was interstitial pneumonia with increased severity in post-weaning pigs. PRRSV was detected in 33% of piglets' lungs and in 20% of adults and post-weaning pigs with high Ct, while PCV2 was found in 100% of adult pigs, 33% of post-weaning pigs, and 22% of piglets, with low Ct in post-weaning pigs. PCV3 was present in all categories and coexisted with other viruses. TTSuV was detected in all swine in combination with other viruses, possibly influencing the disease dynamics, while PPV2 was detected in 100% of adults' and 90% of piglets' lungs. The detection of TTSuV, PCV3, and PPV2 in affected pigs prioritizes the need for comprehensive approaches in implementing appropriate control measures and minimizing economic losses associated with PRDC.

Secondary Highly Pathogenic Porcine Reproductive and Respiratory Syndrome Virus (HP-PRRSV2) Infection Augments Inflammatory Responses, Clinical Outcomes, and Pathogen Load in Glaesserella-parasuis-Infected Piglets

Glaesserella parasuis (Gps), Gram-negative bacteria, are a universal respiratory-disease-causing pathogen in swine that colonize the upper respiratory tract. Highly Pathogenic Porcine Reproductive and Respiratory Syndrome Virus (HP-PRRSV2HP-PRRSV2) and Gps coinfections are epidemics in China, but little is known about the influence of concurrent coinfection on disease severity and inflammatory responses. Herein, we studied the effects of secondary HP-PRRS infection on clinical symptoms, pathological changes, pathogen load, and inflammatory response of Gps coinfection in the upper respiratory tract of piglets. All coinfected piglets (HP-PRRSV2 + Gps) displayed fever and severe lesions in the lungs, while fever was present in only a few animals with a single infection (HP-PRRSV2 or Gps). Additionally, HP-PRRSV2 and Gps loading in nasal swabs and blood and lung tissue samples was significantly increased in the coinfected group. Necropsy data showed that coinfected piglets suffered from severe lung damage and had significantly higher antibody titers of HP-PRRSV2 or Gps than single-infected piglets. Moreover, the serum and lung concentrations of inflammatory cytokines (TNF-α, IL-1β, IL-6, and IL-8) were also significantly higher in coinfected piglets than in those infected with HP-PRRSV2 or Gps alone. In conclusion, our results show that HP-PRRSV2 promotes the shedding and replication of Gps, and their coinfection in the upper respiratory tract aggravates the clinical symptoms and inflammatory responses, causing lung damage. Therefore, in the unavoidable situation of Gps infection in piglets, necessary measures must be made to prevent and control secondary infection with HP-PRRSV2, which can save huge economic losses to the pork industry.

Development of a TaqMan-Probe-Based Multiplex Real-Time PCR for the Simultaneous Detection of Porcine Circovirus 2, 3, and 4 in East China from 2020 to 2022

Porcine circovirus disease (PCVD) caused by porcine circovirus (PCV) is an important swine disease that is characterized by porcine dermatitis, nephropathy syndrome, and reproductive disorders in sows. However, disease caused by PCV2, PCV3, or PCV4 is hard to distinguish, so a rapid and sensitive detection method is urgently needed to differentiate these three types. In this study, four pairs of specific primers and the corresponding probes for PCV 2, -3, and -4, and porcine endogenous gene β-Actin as the positive internal reference index, were designed to establish a TaqMan multiplex real-time PCR (qPCR) assay for the simultaneous differential diagnosis of different types of viruses. The results showed that this assay has good specificity and no cross-reactivity with other important porcine viral pathogens. Furthermore, it has high sensitivity, with a detection limit of 101 copies/μL, and good reproducibility, with intra- and inter-group coefficients of variation below 2%. Subsequently, 535 clinical samples of suspected sow reproductive disorders collected from Shandong, Zhejiang, Anhui, and Jiangsu provinces from 2020 to 2022 were analyzed using the established assay. The results showed that the individual positive rates of PCV2, PCV3, and PCV4 were 31.03%, 30.09%, and 30.84%, respectively; the mixed infection rates of PCV2 and PCV3, PCV2 and PCV4, and PCV3 and PCV4 were 31.03%, 30.09%, and 30.84%, respectively; the mixed infection rate of PCV2, PCV3, and PCV4 was 28.22%. This indicated that this assay provides a convenient tool for the rapid detection and differentiation of PCV2, PCV3, and PCV4 in pig farms in East China. Our findings highlight that there are different types of porcine circovirus infection in pig farms in East China, which makes pig disease prevention and control difficult.

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.

TGF-β from the Porcine Intestinal Cell Line IPEC-J2 Induced by Porcine Circovirus 2 Increases the Frequency of Treg Cells via the Activation of ERK (in CD4+ T Cells) and NF-κB (in IPEC-J2)

Porcine circovirus 2 (PCV2) causes immunosuppression. Piglets infected with PCV2 can develop enteritis. Given that the gut is the largest immune organ, however, the response of the gut's immune system to PCV2 is still unclear. Here, IPEC-J2 cells with different treatments were co-cultured with PBMC or CD4⁺ T cells (Transwell). Flow cytometry and Western blotting revealed that PCV2-infected IPEC-J2 increased the frequency of CD4⁺ T cells among piglets' peripheral blood mononuclear cells (PBMCs) and caused CD4⁺ T cells to undergo a transformation into Foxp3⁺ regulatory T cells (Treg cells) via activating CD4⁺ T ERK. Cytokines production and an inhibitor assay showed that the induction of Tregs by PCV2-infected IPEC-J2 was dependent on TGF-β induced by PCV2 in IPEC-J2, which was associated with the activation of NF-κB. Taken together, PCV2-infected IPEC-J2 activated NF-κB to stimulate the synthesis of TGF-β, which enhanced the differentiation of CD4⁺ T cells into Treg cells through the activation of ERK in CD4⁺ T cells. This information sheds light on PCV2's function in the intestinal immune system and suggests a potential immunosuppressive mechanism for PCV2 infection.

Self-Assembly of Porcine Parvovirus Virus-like Particles and Their Application in Serological Assay

Porcine parvovirus (PPV) is widely prevalent in pig farms. PPV is closely related to porcine respiratory disease complex (PRDC) and porcine circovirus disease (PCVD), which seriously threatens the healthy development of the pig industry. Although commercial antibody detection kits are available, they are expensive and unsuitable for large-scale clinical practice. Here, a soluble VP2 protein of PPV is efficiently expressed in the E. coli expression system. The VP2 protein can be self-assembled into virus-like particles (VLPs) in vitro. After multiple steps of chromatography purification, PPV-VLPs with a purity of about 95% were obtained. An indirect, enzyme-linked immunosorbent assay (I-ELISA), comparable to a commercial PPV kit, was developed based on the purified PPV-VLPs and was used to detect 487 clinical pig serum samples. The results showed that the I-ELISA is a simple, cost-effective, and efficient method for the diagnosis of clinical pig serum and plasma samples. In summary, high-purity, tag-free PPV-VLPs were prepared, and the established VLP-based I-ELISA is of great significance for the sero-monitoring of antibodies against PPV.

A Systematic Investigation Unveils High Coinfection Status of Porcine Parvovirus Types 1 through 7 in China from 2016 to 2020

Porcine parvovirus genotype 1 (PPV1) causes reproductive disorder in swine and is prevalent in China. Recently, six new genotypes of PPVs (PPV2 through PPV7) have also been detected in Chinese swine herds. However, the coinfection status of all these seven genotypes of PPVs (PPV1-7) in China was not clarified yet. In this study, we developed a panel of PPV1–7 PCR assays with satisfied specificity, sensitivity and reproducibility and then applied to the detection of PPV1–7 in 435 clinical samples collected from eight provinces of China in 2016–2020. A total of 55.40% samples (241 out of 435) were PPV positive, while PPV2 and PPV3 (both 22.53%) belonging to the genus of Tetraparvovirus were the most prevalent genotypes. Noticeably, PPV1–7 strains were more prevalent in nursery and finishing pigs than in suckling pigs. In addition, coinfection could be detected in all eight provinces and 27.36% (119/435) samples were coinfected with two to five genotypes of PPVs. Meanwhile, the coinfection of PPVs with PCV2 was 22.30% (97/435). Twenty complete genomes of representative PPV1–7 were determined, and phylogenetic analysis confirmed the genotyping results by sequence comparisons and PCR assays. Remarkably, the PPV7 HBTZ20180519-152 strain from domestic pig was recombined from parental JX15-like and JX38-like isolates from wild boars. Selective pressure analysis based on VP2 sequences of PPV1–7 showed that they were predominantly under negative selection, while few positive selection sites could be detected in VP2 of PPV7. Overall, this systematic investigation unveils high prevalence and coinfection of PPV1–7 in China from 2016 to 2020.

IMPORTANCE Porcine parvoviruses (PPVs) are prevalent in China associating with reproductive failure in swine. The coinfection of seven genotypes of PPVs (PPV1-7) might have synergistic effects on PPV1 associated SMEDI syndrome. However, the coinfection status of PPV1–7 in China is not clear yet. This study showed that PPV1–7 strains are highly prevalent (55.40%) in China and mainly in nursery and finishing pigs in recent years. In addition, the coinfections of different genotypes of PPVs (27.36%) and PPVs with PCV2 (22.30%) are common. Geographic analysis indicated that different genotypes of PPVs are widely cocirculating in China. Intriguingly, a PPV7 strain from the domestic pig was detected as a recombinant from two wild boar isolates. Selective pressure analyses showed that PPV1–7 are mainly under purifying selection. Our findings provide the first systematic investigation on the prevalence, coinfection, and evolution of PPV1 through PPV7 in Chinese swineherds from 2016 to 2020.

Advanced Research in Porcine Reproductive and Respiratory Syndrome Virus Co-infection With Other Pathogens in Swine

The porcine reproductive and respiratory syndrome virus (PRRSV) is the pathogen causing epidemics of porcine reproductive and respiratory syndrome (PRRS), and is present in every major swine-farming country in the world. Previous studies have demonstrated that PRRSV infection leads to a range of consequences, such as persistent infection, secondary infection, and co-infection, and is common among pigs in the field. In recent years, coinfection of PRRSV and other porcine pathogens has occurred often, making it more difficult to define and diagnose PRRSV-related diseases. The study of coinfections may be extremely suitable for the current prevention and control in the field. However, there is a limited understanding of coinfection. Therefore, in this review, we have focused on the epidemiology of PRRSV coinfection with other pathogens in swine, both in vivo and in vitro.

Porcine Parvovirus 2 Is Predominantly Associated With Macrophages in Porcine Respiratory Disease Complex

Porcine respiratory disease complex (PRDC) is a significant source of morbidity and mortality, manifested by pneumonia of multiple etiologies, where a variety of pathogens and environment and management practices play a role in the disease. Porcine reproductive and respiratory syndrome virus (PRRSV), influenza A virus (IAV), and porcine circovirus 2 (PCV2) are well-established pathogens in PRDC. Porcine parvovirus 2 (PPV2) has been identified in both healthy and clinically diseased pigs at a high prevalence worldwide. Despite widespread circulation, the significance of PPV2 infection in PRDC and its association with other co-infections are unclear. Here, PPV2 was detected in the lung tissue in 39 of 100 (39%) PRDC-affected pigs by quantitative polymerase chain reaction (qPCR). Using in situ hybridization (ISH) in conjunction with tissue microarrays (TMA), PPV2 infection was localized in alveolar macrophages and other cells in the lungs with interstitial pneumonia in 28 of 99 (28.2%) samples. Viral load tended to correlate with the number of macrophages in the lungs. Assessment of the frequency, viral titers, and tissue distributions showed no association between infection of PPV2 and other major viral respiratory pathogens. In one-third of the PPV2-positive samples by qPCR, no other known viruses were identified by metagenomic sequencing. The genome sequences of PPV2 were 99.7% identical to the reference genomes. Although intensive intranuclear and intracytoplasmic signals of PPV2 were mainly detected in alveolar macrophages by ISH, no obvious virus replication was noted in in vitro cell culture. Together, these results suggest that PPV2 is associated, but may not be the sole causative agent, with PRDC, warranting the control and prevention of this underdiagnosed virus.