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

Comparison of four clinical sample types for detection and investigation of PCV3 prevalence in the pig farrowing room

Porcine circovirus type 3 (PCV3) is a newly described circovirus that has been identified in pig populations across the globe. The virus is associated with multiple diseases including reproductive and systemic diseases. As effective vaccines are lacking, surveillance is crucial for PCV3 control, but there are currently, few side-by-side comparisons of the efficacy of different samples for the detection of PCV3. This study collected four sample types, including colostrum, udder skin wipes, placental umbilical cord blood, and processing fluid from 134 litters in a sow farm from July to September 2021 for PCV3 detection based on quantitative PCR tests. Udder skin wipes showed the highest detection rates (76.9%), while 71.6% of the processing fluid, 49.3% of the placental umbilical cord, and 29.1% of the colostrum samples were positive. Logistic regression analysis suggested that the detection rates of udder skin wipes and processing fluid were similar (odds ratio for processing fluid vs udder skin wipes was 0.76, 95% confidence interval (CI) 0.43-1.32), but the two tests were probably not identifying the same population as infected, as the agreement between the samples was only moderate (Gwet's AC1: 0.65). In this study, we were able to demonstrate that PCV3 was present in the farrowing room throughout the period from birth to weaning using udder skin wipes, although viral load decreased over time. The odds of PCV3 detection in colostrum from 2-parity sows was three times higher (95% CI 1.4-6.8) than that of primiparous sows, while the odds of PCV3 detection in sows with mummified fetuses was 2.7 times higher (95% CI 1.1-6.6) than sows with no mummified fetuses. In conclusion, these results indicate that udder skin wipes have high detection rates in infected animals over the whole period from birth to weaning and would thus be suitable samples for PCV3 surveillance in the farrowing rooms.

Abortion and fetal death in sows

Abortion in sows or the expulsion of foetuses between days 35 and 109 of gestation results in major financial losses. Abortion is the result of maternal failure due to factors interfering with either the endocrine control of pregnancy or causing endometrial damage. In addition, causes of fetal origin, due to infections with a special affinity for the fetus, can also lead to abortion. Many different non-infectious and infectious factors may be involved. Non-infectious risk factors include inappropriate ambient temperature, seasonal effects, different stress factors, and toxic substances. Microorganisms that may cause abortion can be classified as facultative pathogenic and specific pathogenic microorganisms. The first category includes mostly bacteria that are endemic in many pig farms and that are normally harmless commensals. They can cause abortion only in case of decreased immunity or other predisposing factors. Different specific pathogenic microorganisms, especially viruses and bacteria, can cause fetal death and abortion. Some may have a special affinity for the reproductive tract and the foetuses (e.g. Aujeszky's disease virus, parvovirus, Leptospira sp.), while others may cause clinical disease or fever in sows (e.g. swine influenza viruses, Erysipelothrix rhusiopathiae), subsequently leading to abortion. Diagnosis of fetal death and abortion is challenging due to the broad array of processes that may be involved, and the fact that the inciting cause may happen well in advance of the abortion. The diagnostic process should start with a thorough evaluation of the clinical problem and the farm. In case an infectious cause is suspected, proper samples should be collected, preferably from different sows and foetuses, for the detection of specific pathogens. Prevention of abortion mainly relies on the implementation of good management practices, hygiene and biosecurity measures, and for some pathogens also on vaccination.

Chromogenic in situ hybridization technique for detecting porcine circovirus 3 in lung and lymphoid tissues

Background and Aim

Porcine circovirus 3 (PCV3) was recently reported in Malaysian commercial pig population in 2020 by conventional polymerase chain reaction (PCR), revealing a molecular prevalence of 17.02% in the sampled domestic pig population. This study aims to describe a chromogenic in situ hybridization (ISH) technique using digoxigenin (DIG)-labeled cloned PCV3 open reading frame 1 (ORF1) fragment DNA to detect and localize the PCV3 antigen in formalin-fixed, paraffin-embedded lung, and lymphoid tissue specimens.

Materials and Methods

Since PCV3 was mainly detected in lung and lymphoid tissues, we obtained tissue specimens from these organs from the previous Malaysian PCV3 study. Digoxigenin-labeled ISH probes were designed to target a 69 bp region of PCV3 ORF1 spanning from the nucleotide positions (282-350).

Results

Light microscopy analysis revealed that chromogenic staining of PCV3 antigens was visualized within the cytoplasm of pneumocytes and lymphocytes, indicating positive ISH results. The results of molecular detection of PCV3 using PCR and ISH showed a high agreement of 90.91%, including for the negative PCV3 status for all samples.

Conclusion

This study reports a chromogenic ISH technique using DIG-labeled probes targeting PCV3 ORF1 to detect PCV3 antigens in lung and lymphoid tissues. Despite the limited availability of PCV3 antibodies, ISH remains relevant for investigating PCV3 replication and pathogenesis and can be used complementarily with PCR for evaluating the localization of antigens in infected tissues.

Premature farrowing and stillbirths in two organic sow farms due to riboflavin deficiency

BACKGROUND

Riboflavin deficiency can lead to premature farrowing, stillborn piglets, weak-born piglets and neonatal death. Riboflavin (vitamin B2) is considered essential for reproductive function. The longer the period on riboflavin-deficient diets, the more severe the clinical signs become. Litter size as well as body size of piglets can also be considered risk factors that may contribute to the problem.

CASE PRESENTATION

This case report involved two organic farms of 320 (farm A) and 250 sows (farm B). Between 2019 and 2020, premature farrowing with weak-born or stillborn piglets and severe intra-litter mortality, ranging from 60 to 100% were observed. Investigations for infectious causes of reproductive disease, drinking water quality and general feed composition were performed, but showed no significant results. Feed composition was subsequently evaluated more in detail. Riboflavin levels were very low specifically 1.25 mg/kg of diet (3.75 mg/kg of diet is the NRC minimum recommended level). Riboflavin as a vitamin complex supplement (B complex) was administered to sows one month before the farrowing date and this led to a rapid improvement of the problem such that no stillbirth or intra-litter mortality was observed.

CONCLUSIONS

The clinical presentation, the low riboflavin levels in the feed below the recommended levels for gestating sows and the effectiveness of the riboflavin supplementation, led to an ex juvantibus diagnosis of this deficiency condition. This case report highlights that riboflavin deficiency during gestation should be considered in case of premature parturition and stillborn litters.

IDS, Driemeier D. Porcine circovirus type 3: immunohistochemical detection in lesions of naturally affected piglets

This study aimed to evaluate the relationship between porcine circovirus type 3 (PCV3) viral load and histopathological findings in perinatal piglet tissues and to develop an immunohistochemical method for detecting the virus in lesions. The quantitative polymerase chain reaction (qPCR) cycle threshold (Ct) when amplifying PCV3 DNA and the area of perivascular inflammatory infiltrates in different organs [central nervous system (CNS), lung, heart, liver, spleen, and lymph nodes] were compared. To develop an immunohistochemistry technique, rabbit sera were produced against PCV3-capsid protein peptides selected using bioinformatic analyses. The assay was initially implemented using a tissue sample previously tested using qPCR and in situ hybridization to optimize the procedure and reagent dilutions. To evaluate immunohistochemistry performance, tissue samples from another 17 cases were analyzed using standardized parameters. The most common microscopic lesion was multisystemic periarteritis, with associated vasculitis, as the mesenteric vascular plexus is one of the most affected organs. Other tissues, such as the heart, lung, CNS, and skeletal muscle, were also affected. Comparison of the Ct values for different tissues showed no significant difference, except in lymphoid organs (spleen and lymph nodes), which had significantly higher viral loads than the CNS tissues. There was no correlation between Ct values and perivascular inflammatory infiltrates. PCV3 immunohistochemistry revealed granular immunolabeling, mainly in the cytoplasm of cells in the vascular mesenteric plexus, heart, lung, kidney, and spleen.

Detection and Complete Genomic Analysis of Porcine circovirus 3 (PCV3) in Diarrheic Pigs from the Dominican Republic: First Report on PCV3 from the Caribbean Region

The increasing detection of Porcine circovirus 3 (PCV3, family Circoviridae) in clinically ill pigs worldwide has raised concerns on the implications of the virus on porcine health and the pork industry. Although pork production constitutes an important component of the livestock economy and is a major source of animal protein in the Caribbean Islands, there are no reports on PCV3 in pigs from the region so far. In the present study, PCV3 was detected in 21% (21/100) of diarrheic pigs (sampled at three farms) from the Caribbean nation of the Dominican Republic (DR). Although the sample size varied between porcine age groups, the highest PCV3 detection rates (35.3% each, respectively) were observed in piglets and growers. Co-infections with PCV2 and porcine adenovirus were observed in 38.09% and 9.52% of the PCV3 positive samples, respectively. The complete genomes of 11 DR PCV3 strains were analyzed in the present study, revealing a unique deletion (corresponding to nucleotide residue at position 1165 of reference PCV3 sequences) in one of the DR PCV3 sequences. Based on sequence identities and phylogenetic analysis (open reading frame 2 and complete genome sequences), the DR PCV3 strains were assigned to genotype PCV3a, and shared high sequence homologies (>98% identities) between themselves and with those of other PCV3a (Clade-1) strains, corroborating previous observations on the genetic stability of PCV3 worldwide. To our knowledge, this is the first report on the detection and molecular characterization of PCV3 in pigs from the Caribbean region, providing important insights into the expanding global distribution of the virus, even in isolated geographical regions (the Island of Hispaniola). Our findings warrant further investigations on the molecular epidemiology and economic implications of PCV3 in pigs with diarrhea and other clinical conditions across the Caribbean region.

Retrospective assessment of porcine circovirus 3 (PCV-3) in formalin-fixed, paraffin-embedded tissues from pigs affected by different clinical-pathological conditions

BACKGROUND

Porcine circovirus 3 (PCV-3) is a recently discovered pathogen of swine that has been associated with several conditions. However, many questions remain unanswered regarding its infection, especially in terms of pathogenesis and disease impact. The aim of the present study was to retrospectively investigate the presence of PCV-3 genome by real time quantitative PCR (qPCR) and in situ hybridization (ISH) on selected formalin-fixed paraffin-embedded tissues of pigs affected by different clinical conditions and histological lesions.

MATERIALS AND METHODS

Conditions investigated included porcine dermatitis and nephropathy syndrome (PDNS), periweaning failure-to-thrive syndrome (PFTS), congenital tremors type AII, reproductive disorders, and pigs affected by systemic periarteritis/arteritis, myocarditis, or encephalitis. Studied cases (n = 587) were investigated from a diagnostic database (n = 4162) that comprised samples collected within the period 1998-2021. From each condition/lesion, 10 to 12 cases were subsequently selected and tested by qPCR and ISH (72 cases total).

RESULTS

A total of 587 cases fulfilled inclusion criteria of the different studied conditions and were distributed among the seven groups. For the further selected cases, PCV-3 genome was found by qPCR in 12/12 periarteritis, 5/10 reproductive disease, 5/10 PFTS, 3/10 myocarditis, 1/10 encephalitis and 1/10 congenital tremor cases. PCV-3 was not found in any of the PDNS cases assessed. In periarteritis cases, tissues more commonly affected were mesenteric arteries and kidney. Reproductive disease cases associated to PCV-3 genome consistently displayed myocarditis. The lesions and labelling distribution of PFTS cases with presence of PCV-3 genome were comparable to those of the periarteritis group. qPCR and ISH yielded similar results within each studied case and were statistically comparable.

CONCLUSION

Our results suggest that periarteritis is the hallmark lesion of PCV-3-SD, and that mesenteric lymph node and kidney appeared to be the most reliable organs to confirm the presence of PCV-3 genome in cases with periarteritis.

Epidemiological and genetic characteristics of porcine circovirus 3 in 15 provinces and municipalities of China between 2016 and 2020

Porcine circovirus 3 (PCV3) is a newly emerging virus and has been found associated with porcine dermatitis and nephropathy syndrome in pigs. Compared with PCV2, research into PCV3 cap gene sequencing is deficient. To investigate the prevalence and genotype distribution of PCV3, we collected 1291 samples from 211 pig farms throughout 15 provinces and municipalities. 312 out of 1291 samples were tested positive by PCR. We further sequenced and analyzed 164 PCR-positive samples. The majority (61.8%) of isolates we sequenced belong to genotype PCV3c. PCV3c is also the dominant genotype in Hubei, Hunan, Hebei province and Chongqing city. We found 3 sites under positive selection and located in predicted epitope peptide, revealing that the pig’s immunity may be a reason those sites are undergoing highly positive selection.

PCV3-associated reproductive failure in pig herds in Brazil

Porcine circovirus type 3 (PCV3) has been widely detected worldwide in healthy and sick pigs. Recently its association with clinical disease and reproductive failure has been proven through the detection of intralesional viral mRNA in affected pigs. This study aims to describe the occurrence of PCV3-associated reproductive failure (abortions) in sow herds in southern Brazil. Eleven fetuses from five different litters from two herds were analyzed. These herds reported an increase in the rate of late-gestation abortions, stillbirths, and the percentage of mummified piglets. At gross examination, six of the fetuses had large caudally rotated ears and one fetus was mummified. Microscopically, multisystemic vasculitis, lymphocytic interstitial pneumonia, myocarditis, and encephalitis were observed. These six fetuses with gross and histological lesions were positive in qPCR analysis for PCV3, and PCV3 transcription was shown through in situ hybridization (ISH-RNA) within the histologic lesions. Samples from all 11 fetuses tested negative in PCR exam for Porcine Circovirus type 1 and 2, Porcine Reproductive and Respiratory Syndrome, Porcine Parvovirus, and Atypical Porcine Pestivirus. Furthermore, based on the ORF2 analysis, the PCV3a clade was identified. This is the first report of PCV3a-associated reproductive failure in pig herds in South America.

Frequency of porcine circovirus 3 detection and histologic lesions in clinical samples from swine in the United States

Porcine circovirus 3 (PCV3) is widespread in pigs worldwide. Diverse clinical signs and lesions have been associated with PCV3, but the role of PCV3 as a cause of disease in swine remains unclear. We investigated the association of PCV3 with clinical signs and histologic lesions in 730 diagnostic swine cases between February 2016 and January 2018. The cases contained 2,177 samples submitted from 474 sites located in 21 states in the United States. PCR assay results were positive for PCV3 for 577 of 2,177 (27%) samples, 255 of 730 (35%) cases, 181 of 474 (38%) sites, and 17 of 21 (81%) states. We detected PCV3 in 19 of 28 specimen types and in pigs of all ages and clinical presentations, including healthy pigs, with the highest detection rate in adult pigs. PCV3 detection was not associated with respiratory, gastrointestinal, or CNS signs, weight loss, or sudden death. Of 58 types of histologic lesions evaluated, PCV3 detection was associated with myocarditis, cardiac vasculitis, and interstitial pneumonia in growing pigs. A high PCV3 detection rate was observed in aborted fetuses.

High Prevalence of Porcine Circovirus 3 in Hungarian Pig Herds: Results of a Systematic Sampling Protocol

Porcine circovirus type 3 (PCV3) is an emerging pathogen that has been reported worldwide in all ages of healthy and clinically ill pigs. The presence of this virus in Hungary has been confirmed in a commercial farm experiencing reproductive failures, but there were no data on the circulation of PCV3 in the country. Here we report the prevalence and the genetic diversity of PCV3 in Hungarian herds. To estimate the prevalence, 1855 serum samples, 176 oral fluid and 97 processing fluid samples were collected in a systematic, cross-sectional method from 20 large scale swineherds and tested by real-time qPCR. PCV3 was present in at least one type of diagnostic matrix in 19 out of the 20 (95%) pig farms. The highest detection rates were observed in the processing fluid samples (61%), but 41% of the oral fluid and 23% of the serum samples were positive. The virus was found in all age groups, and slightly more adult animals were infected than growing pigs, but the viral burden was lower amongst them. Phylogenetic analysis of nine complete genomes, obtained from either the sampled herds or organ samples of PCV3-positive carcasses, showed high nucleotide identity between the detected sequences, which all belonged to the PCV3a genotype. Our results indicate that PCV3 is widespread in Hungary, but in most cases, the virus seems to circulate subclinically, infecting all age groups and production phases without the presence of apparent clinical disease.

Exploratory Study of the Frequency of Detection and Tissue Distribution of Porcine Circovirus 3 (PCV-3) in Pig Fetuses at Different Gestational Ages

Porcine circovirus 3 (PCV-3) has been associated with several pig diseases. Despite the pathogenicity of this virus has not been completely clarified, reproductive disorders are consistently associated with its infection. The aim of the present work was to analyze the presence of PCV-3 DNA in tissues from pig fetuses from different gestational timepoints. The fetuses were obtained either from farms with no reproductive problems (NRP, n = 249; all of them from the last third of gestation) or from a slaughterhouse (S, n = 51; 49 of the second-third of gestation and 2 from the third one). Tissues collected included brain, heart, lung, kidney, and/or spleen. Overall, the frequency of detection of PCV-3 was significantly higher in fetuses from the last third of the gestation (69/251, 27.5%) when compared to those from the second-third (5/49, 10.2%), although the viral loads were not significantly different. Moreover, the frequency of detection in NRP fetuses (69/249, 27.7%) was significantly higher than in S ones (5/51, 9.8%). Furthermore, PCV-3 DNA was detected in all tissue types analyzed. In conclusion, the present study demonstrates a higher frequency of PCV-3 DNA detection in fetuses from late periods of the gestation and highlights wide organ distributions of the virus in pig fetuses.

Current Understanding of the Pathogenesis of Porcine Circovirus 3

Circoviruses are closed, circular, single-stranded DNA viruses belonging to the family Circoviridae and the genus Circovirus. To date, at least four porcine circoviruses (PCVs) have been recognized, including PCV1 to PCV4, respectively. Similar to PCV2 pathogenesis, PCV3 has been reported worldwide with myriad clinical and pathological presentations such as reproductive disorders, respiratory diseases, diarrhea etc. Current understanding of PCV3 pathogenesis is very limited since the majority of studies were mostly field observations. Interpretation of the results from such studies is not always simple. Various confounding factors affect the clinical appearance and pathological changes of the infected pigs. Recently, several experimental PCV3 infection studies have been reported, providing a better understanding of its pathogenesis. In this review, we focused on novel findings regarding PCV3 pathogenesis from both field observation and experimental infection studies. Possible factors involved in the conflicting results among the experimental infection studies are also discussed. This review article provides important insight into the current knowledge on PCV3 pathogenesis which would aid in prioritizing research in order to fill the knowledge gaps.

Recent Progress on Epidemiology and Pathobiology of Porcine Circovirus 3

The recently discovered porcine circovirus 3 (PCV3) belongs to the Circovirus genus of the Circoviridae family together with the other three PCVs, PCV1, PCV2, and PCV4. As reported, PCV3 can infect pig, wild boar, and several other intermediate hosts, resulting in single or multiple infections in the affected animal. The PCV3 infection can lead to respiratory diseases, digestive disorders, reproductive disorders, multisystemic inflammation, and immune responses. Up to now, PCV3 infection, as well as the disease caused by PCV3, has been reported in many swine farms worldwide with high positive rates, which indicates that the virus may be another important pathogen in the swine industry. Therefore, we reviewed the current progress on epidemiology and pathobiology of PCV3, which may provide the latest knowledge of the virus and PCV3-related diseases.

Multisystemic lymphoplasmacytic inflammation associated with PCV-3 in wasting pigs

Porcine circovirus 3 (PCV-3) has been detected in diseased and healthy pigs of different ages. Several reports have associated the agent with reproductive failure and mummified and stillborn piglets. One report from North America has proposed a consistent potential association with postweaning disorders. Thus, the present case report aimed to describe the histopathological lesions and their association with the presence of PCV-3 genome in postweaning pigs showing growth-retardation and thrown-back ears. All affected animals displayed multi-organic lymphoplasmacytic periarteritis, lymphocytic myocarditis and/or lymphoplasmacytic meningoencephalitis. PCV-3 genetic material was detected by in situ hybridization within the lesions and confirmed by PCV-3 real-time quantitative PCR detection in tissues. This study represents the first report of PCV-3 associated with clinical disease in postweaning pigs in Europe.

Porcine circovirus 3 (PCV-3) as a causal agent of disease in swine and a proposal of PCV-3 associated disease case definition

Porcine circovirus 3 (PCV‐3) was discovered in 2015 using next‐generation sequencing (NGS) methods. Since then, the virus has been detected worldwide in pigs displaying several clinical–pathological outcomes as well as in healthy animals. The objective of this review is to critically discuss the evidence existing so far regarding PCV‐3 as a swine pathogen. In fact, a significant number of publications claim PCV‐3 as a disease causal infectious agent, but very few of them have shown strong evidence of such potential causality. The most convincing proofs of disease association are those that demonstrate a clinical picture linked to multisystemic lymphoplasmacytic to lymphohistiocytic perivascular inflammation and presence of viral nucleic acid within these lesions. Based on these evidence, individual case definitions for PCV‐3‐reproductive disease and PCV‐3‐systemic disease are proposed to standardize diagnostic criteria for PCV‐3‐associated diseases. However, the real frequency of these clinical–pathological conditions linked to the novel virus is unknown, and the most frequent outcome of PCV‐3 infection is likely subclinical based on its worlwide distribution.

What do we know about porcine circovirus 3 (PCV3) diagnosis so far?: A review

Porcine circovirus 3 (PCV3) was first discovered in 2016, almost concomitantly by two groups of researchers in the United States. The novel case was reported in a group of sows with chronic reproductive problems with clinical presentation alike porcine dermatitis and nephropathy syndrome (PDNS), where metagenomic sequencing revealed a genetically divergent porcine circovirus designated PCV3. The discovery of PCV3 in a PDNS case, which used to be considered as part of PCVAD attributed to PCV2 (porcine circovirus 2), has garnered attention and effort in further research of the novel virus. Just when an infectious molecular DNA clone of PCV3 has been developed and successfully used in an in vivo pathogenicity study, yet another novel PCV strain surfaced, designated PCV4 (porcine circovirus 4). So far, PCV3 has been reported in domestic swine population globally at low to moderate prevalence, from almost all sample types including organ tissues, faecal, semen and colostrum samples. PCV3 has been associated with a myriad of clinical presentations, from PDNS to porcine respiratory disease complex (PRDC). This review paper summarizes the studies on PCV3 to date, with focus on diagnosis.