First molecular detection of porcine circovirus type 3 in dogs in China

Soluble expression and immunogenicity analysis of capsid proteins of porcine circoviruses types 2, 3, and 4

Porcine circoviruses (PCVs) contain four types: PCV1, PCV2, PCV3, and PCV4, all of which can infect pigs. Among them, PCV1 is non-pathogenic, and PCV2 can cause porcine circovirus diseases (PCVD) or porcine circovirus-associated diseases (PCVAD). Although the pathogenicity of PCV3 and PCV4 is still controversial, increasing evidence shows that PCV3 and PCV4 can cause PCV-related disease. However, mixed infection of PCV2, PCV3, and PCV4 with other pathogens often occurs in large-scale pig breeding, bringing severe economic losses to the global pig industry. In this study, the soluble recombinant proteins of PCV2, PCV3, and PCV4 Cap were expressed by the prokaryotic expression system and biotinylated to combine with the Streptavidin magnetic beads, followed by immunogenicity evaluation of the recombinant proteins. Furthermore, we also assessed the efficacy and immunogenicity of trivalent recombinant proteins conjugated with different adjuvants in mice. The results showed that the highly effective anti-PCV serum was successfully prepared, and the recombinant proteins conjugated with different adjuvants produced various degrees of humoral and cellular immunity in mice. Three recombinant proteins are effective immunogens, and the trivalent proteins coupled with the aluminum adjuvant or GM-CSF-CpG for two-dose immunization can stimulate prominent humoral and cellular immunity against PCVs in vivo. The soluble recombinant proteins are the most promising candidate for developing a trivalent vaccine against PCVs (PCV2, PCV3, and PCV4) infection simultaneously.

Recombinant expression and characterization of Canine circovirus capsid protein for diagnosis

Canine circovirus (CanineCV) is a contagious virus that causes severe gastroenteritis, diarrhea, respiratory disease, and vasculitis, often resulting in fatality among infected dogs. In this study, a recombinant Capsid protein (rCap) of CanineCV was expressed in the Escherichia coli (E. coli) Rosetta (DE3) pLysS host cell, followed by affinity purification, and then analyzed by SDS-PAGE, revealing a molecular weight of approximately 31 kDa. The antigenicity of the CanineCV rCap protein was confirmed through recognition by a rabbit anti-CanineCV rCap protein polyclonal antibody (PoAb). Additionally, the reactivity and specificity of this PoAb were assessed using indirect enzyme-linked immunosorbent assay (ELISA) and Western blot analysis before applying in an immunohistochemistry (IHC), namely, immunoperoxidase detection. The immunoperoxidase assay using rabbit anti-CanineCV rCap protein PoAb demonstrated that the CanineCV Cap protein was predominantly located in immune cells, especially lymphocytes and macrophages, within the spleen, lung, tracheobronchial lymph nodes, small intestine, and kidney. Similarly, the Cap protein was also found in pneumocytes in the lung and renal tubular epithelial cells in the kidney. These findings reflected the biological activity and cell tropism of the virus. Therefore, the recombinant Cap protein and its PoAb could be used for the development of a valuable diagnostic tool for CanineCV detection.

First report on identification and genomic analysis of a novel porcine circovirus (porcine circovirus 4) in cats

Porcine circovirus type 4 (PCV4) is an emerging circovirus, which has been detected in domestic pigs across various provinces in China and Korea. In this study, we aimed to investigate whether cats are susceptible to PCV4. For this purpose, we collected 116 cat samples from animal hospitals in Sichuan Province, China, between 2021 and 2022. Using a SYBR Green-based real-time PCR assay, we detected PCV4 in 5 out of the 116 clinical samples, indicating a positive rate of 4.31% (5/116) and confirming the presence of PCV4 in cats from Sichuan Province, China. Moreover, we successfully sequenced and analyzed the complete genome of one PCV4 strain (SCGA-Cat) along with 60 reference sequences deposited in the GenBank database. SCGA-Cat exhibited high nucleotide homology (98.2-99.0%) with PCV4 strains from other species, including dogs, pigs, dairy cows, and fur animals. Notably, the SCGA-Cat strain from cats clustered closely with a PCV4 strain derived from a pig collected in Fujian Province, China. To the best of our knowledge, this study represents the first report on the molecular detection of PCV4 in cats worldwide, which prompted us to understand the genetic diversity and cross-species transmission of the ongoing PCV4 cases. However, further investigations are needed to explore the association between PCV4 infection and clinical syndromes in cats.

Canine circovirus: An emerging or an endemic undiagnosed enteritis virus?

Canine Circovirus (CanineCV) belongs to the family Circoviridae. It is an emerging virus described for the first time in 2011; since then, it has been detected in different countries and can be defined as worldwide distribution virus. CanineCV infects domestic and wild canids and is mainly related to hemorrhagic enteritis in canines. However, it has been identified in fecal samples from apparently healthy animals, where in most cases it is found in coinfection with other viral agents such as the canine parvovirus type-2 (CPV). The estimated prevalence/frequency of CanineCV has been variable in the populations and countries where it has been evaluated, reaching from 1 to 30%, and there are still many concepts to define the epidemiological characteristics of the virus. The molecular characterization and phylo-evolutive analyses that allow to postulate the wild origin and intercontinental distribution of the virus. This review focuses on the importance on continuing research and establish surveillance systems for this emerging virus.

The first dog-origin porcine circovirus type 4 complete genomic sequence have high homology with that of pig-derived strains

Introduction: Porcine circovirus 4 (PCV4) was discovered in 2019 and then proved to be pathogenic to piglets. Nevertheless, few studies were currently available about PCV4 infection in species other than pigs and there is no information about the prevalence of PCV4 in dogs. Methods: To fill this gap, 264 dog samples were collected from animal hospitals in the Southwest of China from 2021 to 2022 and screened for PCV4. Moreover, the complete genome of one PCV4 strain (SCABTC-Dog2022) were obtained successfully and shared a high identity (97.9-99.0%) with other PCV4 strains derived from pigs, dairy cows, raccoon dogs and foxes. The SCABTC-Dog2022 were analyzed together with 51 reference sequences. Results and Discussion: The detected results showed a low percentage of PCV-4 DNA (1.14%, 3/264), indicating that PCV4 could be identified in dogs in southwest China. Phylogenetic tree showed that SCABTC-Dog2022 strain derived from dog were clustered in a closed relative and geographically coherent branch with other PCV4 strains collected from four provinces (Sichuan, Fujian, Hunan and Inner Mongolia) of China. To our knowledge, it is the first detection of PCV4 in dogs globally. The association between PCV4 status and clinical syndromes in dogs deserves additional investigations.

Cross-species transmission of an emerging porcine circovirus (PCV4): First molecular detection and retrospective investigation in dairy cows

Porcine circovirus 4 (PCV4), a novel porcine circovirus identified in pigs, has recently been proved to be pathogenic to piglets. However, little is known about its cross-species transmission, and demonstration of PCV4 in dairy cows is lacking. To explore whether the PCV4 genome exists in dairy cows, 1170 fecal samples were collected from dairy farms in 7 cities in Henan Province of China during 2012-2021, and screened by qPCR for the presence of PCVs (PCV2-PCV4). The detection results showed that the positive rate of PCV4 in dairy cows was 2.22 % (26/1170), but all fecal samples were negative for PCV2 and PCV3. Three full-length and five partial genomes of PCV4 strains were acquired, of which two PCV4 strains (NY2012-DC and XC2013-DC) were achieved from 2012 and 2013, indicating that PCV4 has been circulating in dairy cows in Henan Province of China for at least 10 years. The three PCV4 strains sequenced in this study shared high identity (97.5-99.5 %) with reference strains at the genome level. In phylogenetic analysis, three genotypes (PCV4a, PCV4b and PCV4c) were temporarily confirmed by analyzing 44 strains, and one amino acid variation in Rep (V239L) and three amino acid variations in Cap (N27S, R28G and M212L) were considered as a conserved genotype specific molecular marker. Analyzed from three perspectives (cross-time, cross-species and transboundary), the high nucleotide homology of PCV4 strains indicated the PCV4 evolutionary rate might be slow. Overall, this study was the first to report the detection of PCV4 in dairy cows and conducted a long-term retrospective investigation of PCV4 in Henan Province of China, which has important implications for understanding the genetic diversity and cross-species transmission of the ongoing PCV4 cases.

Expression and immunogenicity analysis of the capsid proteins of porcine circovirus types 2 to 4

Porcine circovirus (PCV) comprises four types, PCV1, PCV2, PCV3, and PCV4, which belong to the Circovirus genus of the family Circoviridae. PCV1 is nonpathogenic, whereas PCV2, PCV3, and PCV4 can infect pigs and cause disease. However, due to a lack of experimental evidence, whether vaccines based on PCV capsid (Cap) can induce cross-reactivity against PCVs remains controversial. In this study, recombinant truncated capsids (rCaps) of PCV2, PCV3, and PCV4 were highly and efficiently expressed and purified, followed by the development and evaluation of antibodies against PCVs. The results showed that monovalent and trivalent antigens based on the recombinant Caps had adequate immunogenicity to stimulate specific antibodies against the corresponding protein and virus. Furthermore, antisera prepared from the recombinant Caps also cross-reacted with different PCVs. Therefore, recombinant proteins can be used as candidate antigens to develop vaccines and ELISA diagnostic kits. In addition, the antibodies prepared in this study are promising candidates for the simultaneous prevention and treatment of PCVs in the clinic.

Reconstruction of the Evolutionary Origin, Phylodynamics, and Phylogeography of the Porcine Circovirus Type 3

Porcine circovirus type 3 (PCV3) is a newly identified virus associated with porcine dermatitis and nephropathy syndrome (PDNS) and multisystemic inflammatory responses in pigs. Recent studies suggests that PCV3 originated from bat circoviruses; however, the origin time, mode of spread, and geographic distribution of PCV3 remain unclear. In this study, the evolutionary origin, phylodynamics, and phylogeography of PCV3 were reconstructed based on the available complete genome sequences. PCV3 showed a closer relationship with bird circovirus than with bat circovirus, but their common ancestor was bat circovirus, indicating that birds may be intermediate hosts for the spread of circoviruses in pigs. Using the BEAST and phylogenetic analyses, three different clades of PCV3 (PCV3a, PCV3b, and PCV3c) were identified, with PCV3a being the most prevalent PCV3 clade. Further studies indicated that the earliest origin of PCV3 can be traced back to 1907.53–1923.44, with a substitution rate of 3.104 × 10^–4 to 6.8524 × 10^–4 substitution/site/year. A phylogeographic analysis highlighted Malaysia as the earliest location of the original PCV3, which migrated to Asia, America, and Europe. Overall, this study provides novel insights into the evolutionary origin, spread mode, and geographic distribution of PCV3, which will facilitate the prevention and control of PCV3 epidemics in the future.

Prevalence of Porcine Circoviruses in Slaughterhouses in Central Shanxi Province, China

Background

Porcine circovirus disease is currently the greatest threat to pig farming. Four main porcine circovirus genotypes are circulating worldwide.

Objective

The study aimed to assess the prevalence of porcine circovirus genotypes in the central part of Shanxi province.

Methods

We investigated the prevalence of porcine circovirus type 2 (PCV2), porcine circovirus type 3 (PCV3), and porcine circovirus type 4 (PCV4). Porcine circoviruses were analyzed by polymerase chain reaction (PCR) in the lung tissues of 180 pigs from 7 slaughterhouses in central Shanxi, China.

Results

The prevalence of PCV2, PCV3, and PCV4 were 56.8, 80, and 9.4%, respectively, and the negative rate was 10% for all three pathogens. The co-infection with PCV2 + PCV3, PCV2 + PCV4, PCV3 + PCV4, and PCV2 + PCV3 + PCV4 were 47.2, 7.4, 7.4, and 5.6%, respectively. Among PCV4-positive samples, the positive rate of PCV4 + PCV2 was 52.9% (9/17), whereas that of PCV4 + PCV3 was 100% (17/17). On the other hand, PCV2 and PCV3 were detected in 57.1% (93/163) and in 78.5% (128/163) of PCV4-negative samples, respectively. Phylogenetic analysis demonstrated that PCV2, PCV3, and PCV4 were not in the same clade and were distant from each other.

Conclusion

The high positive rates of PCV3, PCV2 + PCV3, and PCV3 + PCV4 suggest that PCV3 may play a decisive role in PCV2 and PCV4 infections. Therefore, further control of PCV3 is needed to reduce the spread of the virus.

Porcine Circoviruses and Herpesviruses Are Prevalent in an Austrian Game Population

During the annual hunt in a privately owned Austrian game population in fall 2019 and 2020, 64 red deer (Cervus elaphus), 5 fallow deer (Dama dama), 6 mouflon (Ovis gmelini musimon), and 95 wild boars (Sus scrofa) were shot and sampled for PCR testing. Pools of spleen, lung, and tonsillar swabs were screened for specific nucleic acids of porcine circoviruses. Wild ruminants were additionally tested for herpesviruses and pestiviruses, and wild boars were screened for pseudorabies virus (PrV) and porcine lymphotropic herpesviruses (PLHV-1-3). PCV2 was detectable in 5% (3 of 64) of red deer and 75% (71 of 95) of wild boar samples. In addition, 24 wild boar samples (25%) but none of the ruminants tested positive for PCV3 specific nucleic acids. Herpesviruses were detected in 15 (20%) ruminant samples. Sequence analyses showed the closest relationships to fallow deer herpesvirus and elk gammaherpesvirus. In wild boars, PLHV-1 was detectable in 10 (11%), PLHV-2 in 44 (46%), and PLHV-3 in 66 (69%) of animals, including 36 double and 3 triple infections. No pestiviruses were detectable in any ruminant samples, and all wild boar samples were negative in PrV-PCR. Our data demonstrate a high prevalence of PCV2 and PLHVs in an Austrian game population, confirm the presence of PCV3 in Austrian wild boars, and indicate a low risk of spillover of notifiable animal diseases into the domestic animal population.

Novel Porcine Circoviruses in View of Lessons Learned from Porcine Circovirus Type 2-Epidemiology and Threat to Pigs and Other Species

Porcine circovirus type 2 (PCV2) plays a key role in PCV2-associated disease (PCVAD) etiology and has yielded significant losses in the pig husbandry in the last 20 years. However, the impact of two recently described species of porcine circoviruses, PCV3 and PCV4, on the pork industry remains unknown. The presence of PCV3 has been associated with several clinical presentations in pigs. Reproductive failure and multisystemic inflammation have been reported most consistently. The clinical symptoms, anatomopathological changes and interaction with other pathogens during PCV3 infection in pigs indicate that PCV3 might be pathogenic for these animals and can cause economic losses in the swine industry similar to PCV2, which makes PCV3 worth including in the differential list as a cause of clinical disorders in reproductive swine herds. Moreover, subsequent studies indicate interspecies transmission and worldwide spreading of PCV3. To date, research related to PCV3 and PCV4 vaccine design is at early stage, and numerous aspects regarding immune response and virus characteristics remain unknown.

The construction and immunogenicity analyses of a recombinant pseudorabies virus with porcine circovirus type 3 capsid protein co-expression

Porcine circovirus-associated diseases (PCVADs) and pseudorabies (PR) are highly contagious and economically significant diseases of swine in China. Porcine circovirus type 3 (PCV3) is an emerging swine pathogen of PCVAD. Currently, no PCV3 vaccine is commercially available, and the epidemic caused by it is still spreading worldwide. In this study, we used the PRV variant strain HNX as the parental virus to construct recombinant PRV with TK/gE gene deletion and capsid (Cap) protein co-expression, named HNX-ΔTK/ΔgE-ORF2. The results revealed that PCV3 Cap protein can be detected in HNX-ΔTK/ΔgE-ORF2-infected PK-15 cells by both western blotting and immunofluorescence assays. Vaccination with HNX-ΔTK/ΔgE-ORF2 did not cause pruritus, ruffled fur, systemic infection, or inflammation (without high expression of interleukin-6 (IL-6) and granulocyte colony-stimulating factor (G-CSF) in plasma). Furthermore, HNX-ΔTK/ΔgE-ORF2 immunization induced an anti-Cap specific antibody, activated a PRV-specific cellular immune response, and provided 100 % protection to mice against the challenge of the virulent HNX strain. Thus, HNX-ΔTK/ΔgE-ORF2 appears to be a promising vaccine candidate against PRV and PCV3 for the control of the PRV variant and PCV3.

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.

First detection and phylogenetic analysis of porcine circovirus 3 in female donkeys with reproductive disorders

Background

PCV3 is a pathogen associated with porcine dermatitis and nephropathy syndrome (PDNS)-like clinical signs, reproductive failure, and cardiac and multiorgan inflammation, which was newly identified in 2016 in sows in USA. Recently, PCV3 has also been identified from several non-porcine species like (cattle, dog, wild boar, deer, mice and ticks). However, PCV3 infection in donkey is not well established. Since 2019, 300 blood samples were collected from female donkey, which was characterized by abortion and sterility, in Liaocheng city of China.

Results

In the present study, an investigation of PCV3 in donkey blood samples was undertaken employing by real time PCR. Positive rates of PCV3 in donkeys reach to 21.0 %. In addition, one full-length PCV3 genome sequence was obtained, and it had a highest identity with porcine circovirus 3 PCV3/CN/Nanjing2017 strain and is clustered to PCV3a genotype based on ORF2 sequences.

Conclusions

This is the first report of detection of PCV3 from female donkeys presenting reproductive failure in large-scale donkey farms, China. In addition, the PCV3 strain identified in this study shared the closest relationship with those from porcine, suggesting that PCV3 may be transmitted from pigs to donkeys. Totally, PCV3 infection in donkey should be concerned although the association between it and reproductive failure are not better understood.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-021-03013-6.

Detection and molecular characterization of two canine circovirus genotypes co-circulating in Vietnam

Background

Canine circovirus is reported in dogs in many countries, including the USA, China and Thailand. It has been detected in healthy dogs and dogs with diarrhea, hemorrhagic gastroenteritis, and vasculitis. It comprises five genotypes and is frequently found as a coinfection with canine parvovirus-2 (CPV-2).

Aim

To characterize canine circovirus genotypes co-circulating with CPV-2 in Vietnam.

Method

PCR assessment of 81 CPV-2-positive fecal samples from Vietnamese diarrheic dogs up to seven months of age for other viral enteric pathogens, including canine bocavirus, canine adenovirus, paramyxovirus, canine coronavirus, porcine circovirus-3 and canine circovirus. In addition, eight selected full genome sequences of Vietnamese canine circovirus were analyzed and used for phylogeny.

Results

In total 19.8% of samples were found to be positive for canine circovirus. Phylogeny revealed that the Vietnamese canine circovirus strains were clustered in two different genotypes (genotype-1 and -3). The genetic diversity among Vietnamese canine circovirus was 86.0–87.2%. The nucleotide discrepancy among both genotypes altered the deduced amino acid sequence in 14 and ten residues of the replicase and capsid proteins, respectively. Genetic recombination analysis revealed that the Vietnamese canine circovirus-6 strain has the American and Chinese canine circovirus as its major and minor parents, respectively. Only a single dog revealed triple detections of CPV-2c, Canine circovirus and canine adenovirus (1.2%).

Conclusion

The co-circulation of two different genotypes of canine circovirus and CPV-2c in dogs in Vietnam has been illustrated.

Clinical relevance

The mortality rate with CPV-2 only (22%) doubled in dogs with canine circovirus and CPV-2 co-infection.

Development of an indirect immunofluorescence assay for PCV3 antibody detection based on capsid protein

Porcine circovirus type 3 (PCV3) is a novel porcine circovirus associated with porcine dermatitis and nephritis syndrome (PDNS), reproductive failure, and multisystemic inflammation. Capsid protein (Cap) encoded by PCV3 ORF2 gene has been identified as an immunogenic protein. Currently, there is no immunofluorescence assay (IFA) available for serological diagnosis. Here, the N-terminal 33 amino acids of Cap protein were predicted to serve as a PCV3 nuclear localization signal (NLS). Two types of recombinant plasmids were constructed for recombinant protein expression in Sf9 cells by using a baculovirus expression system: plasmid rvBac-Pc for full-length Cap protein expression and rvBac-Sc for Cap protein expression with a honeybee melittin signal peptide in place of the predicted NLS sequence. Expression of the nuclear localization sequences was further analyzed by IFA. Strong and specific fluorescence signals were observed in the nucleus of rvBac-Pc-transfected cells and in the cytoplasm of rvBac-Sc-transfected cells. No cross-reactivity was observed with porcine circovirus type 2, porcine pseudorabies virus, classical swine fever virus, or porcine reproductive and respiratory syndrome virus. In summary, we developed two fluorescence detection modes for Cap protein that can be used to detect PCV3 antibodies. This method is suitable  for the diagnosis and epidemiological investigation of PCV3. This study provides a reliable detection method for monitoring PCV3 antibody level in pigs in the future.

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.

Circovirus in Blood of a Febrile Horse with Hepatitis

Circoviruses infect vertebrates where they can result in a wide range of disease signs or in asymptomatic infections. Using viral metagenomics we analyzed a pool of five sera from four healthy and one sick horse. Sequences from parvovirus-H, equus anellovirus, and distantly related to mammalian circoviruses were recognized. PCR identified the circovirus reads as originating from a pregnant mare with fever and hepatitis. That horse's serum was also positive by real time PCR for equine parvovirus H and negative for the flavivirus equine hepacivirus. The complete circular genome of equine circovirus 1 strain Charaf (EqCV1-Charaf) was completed using PCR and Sanger sequencing. EqCV1 replicase showed 73-74% identity to those of their closest relatives, pig circoviruses 1/2, and elk circovirus. The closest capsid proteins were from the same ungulate circoviruses with 62-63% identity. The overall nucleotide identity of 72% to its closest relative indicates that EqCV1 is a new species in the Circovirus genus, the first reported in genus Equus. Whether EqCV1 alone or in co-infections can result in disease and its prevalence in different equine populations will require further studies now facilitated using EqCV1's genome sequence.

Detection and genetic characterization of porcine circovirus 4 (PCV4) in Guangxi, China

Porcine circovirus type 4 (PCV4), a novel circovirus, was identified in pigs with serious symptoms, including porcine dermatitis and nephropathy syndrome (PDNS)-like signs, in China in 2019. This study investigated the prevalence and genome diversity of PCV4 in pigs from Guangxi Province, China, between 2015 and 2019. Thirteen of 257 (5.1%) samples were positive for PCV4, 9 of these (69.2%) PCV4-positive samples were coinfected with PCV2 or PCV3, and one PCV4-positive sample was coinfected with both PCV2 and PCV3. Three complete PCV4 genomes shared 36.9-73.8% nucleotide similarity with other representative circovirus genomes. Phylogenetic analysis indicated that PCV4 was most closely related to bat-associated circovirus and mink circovirus. In summary, this is the first epidemiological investigation and evolutionary analysis of PCV4 in Guangxi Province, China, and the results provide insight into the molecular epidemiology of PCV4.

High repetitive arginine in the anterior of PCV3 capsid protein is a severe obstacle for its expression in E. coli

Porcine circovirus type 3 (PCV3) is a novel circovirus identified in sows with PDNS-like clinical signs and reproductive failure. The capsid protein (CAP) of PCV3 is expected to be an effective vaccine candidate. Here, we expressed the original capsid protein, truncated capsid protein without anterior highly repetitive arginine (ΔCAP) and their codon-optimized counterparts in E. coli. These results showed that lots of repeated arginine could severely lower the expression of PCV3 capsid protein in E. coli. At the same time, the recombined truncated PCV3 capsid protein forms typic virions. The efficient expression of capsid protein is expected to serve the development of PCV3 vaccines and other studies of PCV3 capsid protein.

Porcine Circovirus Type 3 in Pig Farms Experiencing Diarrhea in Jiangxi, China: Prevalence, Genome Sequence and Pathogenicity

Simple Summary

Porcine circovirus 3 (PCV3) is a new species of PCV that was associated with porcine dermatitis and nephropathy syndrome (PDNS), respiratory disease, cardiac and multisystem inflammation in nursery and finishing pigs, and reproductive failure problems, including abortion, mummified fetuses, and stillbirth in sows. To date, the reports on the PCV3 present in diarrhea pigs are limited and the genetic characteristics of PCV3 from diarrheal pigs and pathogenicity on pigs were inconsistent. This study aimed to investigate the prevalence of PCV3 in pigs with/without diarrhea, to analyze the genome sequence of PCV3 from diarrheal pigs, and to inquire into the associated pathogenicity of PCV3 to piglets experimentally infected with PCV3-positive intestinal contents. The results demonstrated that PCV3 was widely circulating in diarrheal suckling and weaned piglets. Clinical signs, gross lesions, and histological changes were observed in suckling piglets inoculated with PCV3. The complete genome of a PCV3a strain was determined and two mutations (V24A and K27R) were present when compared with PCV3b strains. The findings of this study increase the knowledge of the epidemiology, viral genetics, pathogenicity, and pathogenesis of PCV3.

Abstract

Porcine circovirus 3 (PCV3) infections have been reported in different clinical presentations. However, the prevalence and pathogenicity of PCV3 associated with diarrhea in piglets have been limited. Herein, we present an investigation and genome analyses of PCV3 in piglets experiencing diarrhea, and observed clinical signs, gross lesions, and histological changes in pigs negative for all known pathogens associated with diarrhea but positive for PCV3 alone. Among the feces (n = 141) tested, 16.31% (23/141) were positive for PCV3. Of which, 27.28% (15/55) and 14.29% (5/35) were present in diarrheal samples from suckling and weaned piglets, respectively. Moderate to severe atrophic villi was confined in duodenum, jejunum, and ileum, and significantly decreased average heights of villi, and the depths of crypt were observed in PCV3-infected piglets. The complete genome of a representative strain of PCV3, designated as JX/CH/2018, was determined. Multialignment analysis indicated that JX/CH/2018 had 97.7–99.7% nucleotide identity at the complete genome level, and 97.2–100% at the amino acid level of the capsid protein when compared with reference PCV3 strains. Phylogenetic analysis showed that the PCV3 strain identified in this study belonged to PCV3a lineage. The present study demonstrated that PCV3 is a common virus in diarrheal suckling and weaned piglets.

First detection and full genomic analysis of Canine Circovirus in CPV-2 infected dogs in Colombia, South America

Canine Circovirus (CanineCV) is an emerging virus which since its first report in USA in 2012, it has been described worldwide. It was the second mammalian circovirus species identified in dogs and its role in canine enteritis is still being uncertain as much as its association in disease with the Canine Parvovirus-2 (CPV-2). Here, we aim to confirm for the first time the presence of CanineCV in Colombia and to develop phylogenetic evolutive analyses of CanineCV in CPV-2 positive animals. DNA from samples were extracted and PCR, full genome sequencing and phylogenetic analysis was performed to detect and characterize CanineCV. From a total of 30 CPV-2 positive samples, 16.6% (n = 5) were positives for CanineCV. Sequencing analysis of Colombian CanineCV wild-type strains displayed high identity to each other (99.5–99.7% nt; 99.7% aa). The full genome phylogenetic analysis confirmed that worldwide reported CanineCV strains were separated into four distinct genotypes in addition to a European origin of the South American CanineCV strains. This study demonstrated the importance of continue surveillance of emerging viruses in canine populations and confirm for the first time the circulation and origin of CanineCV in Colombia.

Lack of Evidence on the Susceptibility of Ticks and Wild Rodent Species to PCV3 Infection

Porcine circovirus 3 (PCV3) is an emerging virus, first detected in 2016 and widespread in the swine industry. Although not considered a primary pathogen, PCV3 is potentially linked to several clinical conditions that threaten swine farming. Wild boars are considered the main reservoir species for PCV3 infection in the wild, but recent detection in roe deer, chamois and associated ticks has complicated our understanding of its epidemiology. Much emphasis has been placed on ticks, as competent vectors, and wild rodents, which typically feed immature tick stages. The aim of this study was to clarify whether wild rodent species and associated ticks are susceptible to PCV3 infection and involved in its spread. Wild small mammals' serum samples and hosted ticks were, therefore, collected from areas where no wild boars were present and tested by PCR, targeting the PCV3 rep gene. A total of 90 yellow-necked mice (Apodemus flavicollis), two wood mice (A. sylvaticus), 26 bank voles (Myodes glareolus) and 262 Ixodes spp. ticks were investigated. PCV3 DNA was not detected in serum or in tick samples. These findings support the hypothesis that the investigated species do not have an actual role as PCV3 reservoirs. Further studies would be necessary to state whether these species, or others that we did not test, are involved in PCV3 infection spread-in particular when susceptible species share the same habitat.

First molecular detection and complete sequence analysis of porcine circovirus type 3 (PCV3) in Peninsular Malaysia

Porcine circovirus type 3 (PCV3) is a newly emerging virus in the swine industry, first reported recently in 2016. PCV3 assembles into a 2000 bp circular genome; slightly larger than PCV1 (1758-1760 bp), PCV2 (1766-1769 bp) and PCV4 (1770 bp). Apart from being associated with porcine dermatitis and nephropathy syndrome (PDNS), PCV3 has been isolated from pigs with clinical signs of reproductive failures, myocarditis, porcine respiratory disease complex (PRDC) and neurologic disease. Given that PCV3 is increasingly reported in countries including Thailand and U.S. with whom Malaysia shares trade and geographical relationship; and that PCV3 is associated with several clinical presentations that affect productivity, there is a need to study the presence and molecular characteristics of PCV3 in Malaysian swine farms. Twenty-four commercial swine farms, three abattoirs and retail shops in Peninsular Malaysia were sampled using convenience sampling method. A total of 281 samples from 141 pigs, including 49 lung archive samples were tested for PCV3 by conventional PCR. Twenty-eight lung samples from wild boar population in Peninsular Malaysia were also included. Nucleotide sequences were analyzed for maximum likelihood phylogeny relationship and pairwise distances. Results revealed that PCV3 is present in Peninsular Malaysia at a molecular prevalence of 17.02%, with inguinal lymph nodes and lungs showing the highest molecular detection rates of 81.82% and 71.43% respectively. Despite wide reports of PCV3 in healthy animals and wild boars, no positive samples were detected in clinically healthy finishers and wild boar population of this study. PCV3 strain A1 and A2 were present in Malaysia, and Malaysian PCV3 strains were found to be phylogenetically related to Spanish, U.S. and Mexico strains.

Dynamic Alterations of Gut Microbiota in Porcine Circovirus Type 3-Infected Piglets

Porcine circovirus type 3 (PCV3) is a novel porcine circovirus species associated with several diseases such as porcine dermatitis and nephropathy syndrome (PDNS)-like clinical signs, reproductive failure, cardiac pathologies, and multisystemic inflammation in piglets and sows. Currently, many studies have focused on the interaction between microbiota composition and disease progression. However, dynamic changes in the composition of the gut microbiota following PCV3 infection are still unknown. In this study, alterations in gut microbiota in PCV3-inoculated and sham-inoculated piglets were analyzed at various time points [7, 14, 21, and 28 days post-inoculation (dpi)] using the Illumina MiSeq platform. Using principal coordinate analysis, obvious structural segregations were observed in bacterial diversity and richness between PCV3- and sham-inoculated piglets, as well as at the four different time points. The abundance of gut microbiota exhibited a remarkable time-related decrease in Clostridium_sensu_stricto_1 in PCV3-inoculated piglets. In addition, significant differences were observed in functional classification based on cluster of orthologous groups assignment, between PCV3- and sham-inoculated piglets. Our findings demonstrated that PCV3 infection caused dynamic changes in the gut microbiota community. Therefore, regulating gut microbiota community may be an effective approach for preventing PCV3 infection.

Investigation on porcine circovirus type 3 in serum of farrowing sows with stillbirths

Since its first identification in 2016, porcine circovirus 3 (PCV3) has been detected in healthy and/or diseased swine in many countries worldwide. In a previous study by our group, PCV3 was detected in sera of sows which had at least one stillborn piglet in the last parturition. As such, it became important to investigate if the presence of PCV3 in sows' sera could be associated to the occurrence of stillbirths. With that aim, the frequency of PCV3 infections and viral DNA loads in sows' sera was investigated through a real-time quantitative PCR in 89 serum samples of just farrowed sows with or without stillbirths. PCV3 genomes were identified in most samples, with genome loads ranging between less than 10 to 200,000 copies per mL of serum. No significant differences were observed either in the frequency of infection or PCV3 viral loads in sows with or without stillbirths. Thus, no association could be established between PCV3 infection of sows at farrowing and stillbirths' occurrence.

Porcine circoviruses: current status, knowledge gaps and challenges

Circoviruses (CV) include some of the smallest viruses known. They were named after their circularly arranged single-stranded DNA genome with a gene encoding a conserved replicase protein on the sense strand. Circoviruses are widely distributed in mammals, fish, avian species and even insects. In pigs, four different CVs have been identified and named with consecutive numbers based on the order of their discovery: Porcine circovirus 1 (PCV1), Porcine circovirus 2 (PCV2), Porcine circovirus 3 (PCV3) and most recently Porcine circovirus 4 (PCV4). PCVs are ubiquitous in global pig populations and uninfected herds are rarely found. It is generally accepted that PCV1 is non-pathogenic. In contrast, PCV2 is considered an important, economically challenging pathogen on a global scale with comprehensive vaccination schemes in place. The role of PCV3 is still controversial several years after its discovery. Propagation of PCV3 appears to be challenging and only one successful experimental infection model has been published to date. Similarly to PCV2, PCV3 is widespread and found in many pigs regardless of their health history, including high health herds. PCV4 has only recently been discovered and further information on this virus is required to understand its potential impact. This review summarizes current knowledge on CVs in pigs and aims to contrast and compare known facts on PCVs.

Fine mapping of linear B cell epitopes on capsid protein of porcine circovirus 3

Porcine circovirus type 3 (PCV3) is an emerging swine pathogen associated with acute porcine dermatitis and nephropathy syndrome (PDNS)-like clinical signs, reproductive failure, and multisystemic inflammation. Current evidence shows that PCV3 is spread worldwide, and its high incidence may pose a threat to the global pig industry. Capsid (Cap) protein is the sole structural protein which plays an important role in inducing protective immunity against PCV3 infection. In this study, monoclonal antibodies (mAbs) against Cap protein of PCV3 were produced by the hybridoma technique. Subsequently, 12 serial overlapping peptides (P1 to P12) spanning the entire region of Cap were synthesized to determine the B cell epitope regions using the mAbs. Results from dot-blot and peptide ELISA identified that P3, P9, and P10 were the major B cell antigenic regions. Fine mapping by shorter N- and C-terminal truncated peptides confirmed that the motifs ⁵⁷NKPWH⁶¹, ¹⁴⁰KHSRYFT¹⁴⁶, and ¹⁶¹QSLFFF¹⁶⁶ were linear B cell epitopes, which were highly conserved among different PCV3 strains. Interestingly, we found that the motif ¹⁴⁰KHSRYFT¹⁴⁶ was highly conserved in all reported types of PCVs (i.e., PCV1, PCV2, PCV3, and PCV4), except for the substitution (Y → K → R) of the first residue. This is the first research to identify B cell epitopes of PCV3 Cap, and these findings may lead to a better understanding of the antibody-antigen interaction and provide some guidance for PCV3 vaccine design.Key points• The recombinant Cap protein of PCV3 was expressed and purified in soluble form. • PCV3 Cap-specific mAbs prepared in this study had no cross-reactivity with PCV1/PCV2 Cap. • This is the first report of three conserved linear B cell epitopes on PCV3 Cap. • The minimal residues of the epitopes were 57-61 aa, 140-146 aa, and 161-166 aa.

Genetic Characterization of Porcine Circovirus 3 Strains Circulating in Sardinian Pigs and Wild Boars

Porcine circovirus 3 (PCV3) is a recently discovered member of the Circoviridae family. So far, its presence has been reported in North America, Asia, South America, and Europe. In this study, blood and tissue samples from 189 Sardinian suids (34 domestic pigs, 115 feral free ranging pigs, and 39 wild boars) were used to genetically characterize the PCV3 strains from Sardinia. PCV3 infection in the animals was confirmed by real time PCR. The detection rate in the three groups analyzed was l7.64% in domestic pigs, 77.39% in free ranging pigs, and 61.54% in wild boars. Moreover, our results showed that co-infection of PCV3 with other viruses is quite a common occurrence. Molecular characterization of Sardinian PCV3 strains was performed by sequencing 6 complete genomes and 12 complete cap genes. Our results revealed that there is a high similarity between our strains and those identified in different countries, confirming the genetic stability of PCV3 regardless of geographical origin. Haplotype network analysis revealed the presence of 6 whole genomes or 12 unique ORF2 haplotypes and a nonsynonymous mutation in ORF2 that leads to an R14K amino acid substitution. Phylogenetic analysis of whole genome and ORF2 was also conducted. The Sardinian strains were allocated in three different clusters of phylogenetic trees of both complete genome and ORF2. With this study, we have provided a snapshot of PCV3 circulation in Sardinia. Our findings might help to achieve a deeper understanding of this emerging porcine virus.

Genotyping Porcine Circovirus 3 (PCV-3) Nowadays: Does It Make Sense?

The discovery of a globally distributed porcine circovirus (Porcine circovirus 3; PCV-3) has led to intense research activity and the production of a large amount of molecular data. Different research groups have proposed several, not always concordant, genotypes for this virus. While such categories could aid an easier interpretation of PCV-3 molecular epidemiology, any classification, to be useful in practical settings, must be univocal and of help in the understanding of underlying biological features and epidemiology. Based on these premises, the possibility of defining PCV-3 genotypes was evaluated on the broadest available dataset of PCV-3 complete genome (n = 357) and open reading frame 2 (ORF2, n = 653) sequences. Genetic distance and phylogenetic clustering were selected as the main objective criteria. Additional factors, including the number of within-cluster sequences, host and geographic clustering, concordance between different genomic regions, and analysis method were also taken in account to generate a classification that could be effectively applied in research and diagnostic settings. A maximum within-genotype genetic distance of 3% at the complete genome and 6% at the ORF2 levels, bootstrap support higher than 90%, and concordance between analysis methods allowed us to clearly define two clades which could be potentially defined as genotypes. Further subdivision was not suggested due to the absence of a meaningful association between PCV-3 and its biological/epidemiological features. Nevertheless, since one of the clades included two strains only, thus far we formally propose the definition of only one PCV-3 genotype (PCV-3a). The established criteria will allow us to automatically recognize other genotypes when more strain sequences are characterized.

Detection and genetic characterization of porcine circovirus 3 (PCV3) in pigs in India

Porcine circovirus type 3 (PCV3), a novel circovirus, has been reported recently from major swine growing countries globally, and the virus is associated with diseases like porcine dermatitis, nephropathy syndrome and reproductive failure. This report describes the identification of PCV3 associated with reproductive failure in sows and piglet mortality and circulation of the virus in healthy pigs in India. The pathological changes in various tissues from stillborn piglet and characterization of the virus genomes were reported. The genome sequences of Indian PCV3 strains showed 91.4%-99.8% nucleotide identity with other sequences of PCV3 strains circulating worldwide. The phylogenetic analysis showed clustering of Indian strains into a separate group with the isolate from USA (MN/2016) under PCV3a genotype. The results confirmed the circulation of PCV3 in Indian pigs and its association with clinical cases. This study speculates emergence of PCV3 as an important pig pathogen in the country, which warrants the thorough investigation on PCV3 epidemiology, pathogenesis and to implement the control measures.

Metagenomics revealing new virus species in farm and pet animals and aquaculture

Viral metagenomics is slowly taking over the traditional and widely used molecular techniques for the investigation of pathogenic viruses responsible for illness and inflicting great economic burden on the farm animal industry. Owing to the continued improvements in sequencing technologies and the dramatic reduction of per base costs of sequencing the use of next generation sequencing have been key factors in this progress. Discoveries linked to viral metagenomics are expected to be beneficial to the field of veterinary medicine starting from the development of better diagnostic assays to the design of new subunit vaccines with minimal investments. With these achievements the research has taken a giant leap even toward the better healthcare of animals and, as a result, the animal sector could be growing at an unprecedented pace.

ITRAQ-based quantitative proteomics reveals the first proteome profiles of piglets infected with porcine circovirus type 3

Porcine circovirus type 3 (PCV3) infection induces porcine dermatitis and nephropathy syndrome, reproductive failure, and multisystemic inflammatory lesions in piglets and sows. To better understand the host responses to PCV3 infection, isobaric tags for relative and absolute quantification (iTRAQ) labeling combined with LC-MS/MS analysis was used for quantitative determination of differentially regulated cellular proteins in the lungs of specific-pathogen-free piglets after 4 weeks of PCV3 infection. Totally, 3429 proteins were detected in three independent mass spectrometry analyses, of which 242 differential cellular proteins were significantly regulated, consisting of 100 upregulated proteins and 142 downregulated proteins in PCV3-infected group relative to control group. Bioinformatics analysis revealed that these higher or lower abundant proteins involved primarily metabolic processes, innate immune response, MHC-I and MHC-II components, and phagosome pathways. Ten genes encoding differentially regulated proteins were selected for investigation via real-time RT-PCR. The expression levels of six representative proteins, OAS1, Mx1, ISG15, IFIT3, SOD2, and HSP60, were further confirmed by Western blotting and immunohistochemistry. This study attempted for the first time to investigate the protein profile of PCV3-infected piglets using iTRAQ technology; our findings provide valuable information to better understand the mechanisms underlying the host responses to PCV3 infection in piglets. SIGNIFICANCE: Our study identified differentially abundant proteins related to a variety of potential signaling pathways in the lungs of PCV3-infected piglets. These findings provide valuable information to better understand the mechanisms of host responses to PCV3 infection.

First detection and genomic characterization of porcine circovirus 3 in mosquitoes from pig farms in China

The porcine circovirus type 3 (PCV3) becomes an important causative agent of swine disease since its discovery in 2016. PCV3 infection exhibits a wide range of clinical syndromes causing substantial economic losses in swine industry. Previous studies have reported the detection of numerous known viruses including circovirus in mosquitoes. However, the transmission of PCV3 in field-caught mosquitoes remains largely unknown. This study aims to detect PCV3 infection in mosquitoes and analyze its genomic characteristics. Here, we performed a PCR to detect the PCV3 in 269 mosquito samples collected from pig farms located in Heilongjiang, Jilin, and Yunnan provinces. The proportion of PCV3-positive mosquitoes was 32.0 % (86/269), ranging from 21.4%-42.5% at farm level, which may imply that mosquito serves as a route of transmission for PCV3. To determine the possible origin of PCV3 in mosquitoes, 80 pig serum samples were collected from the pig farms where mosquito sampling was also performed. The proportion of PCV3-positive farms ranged from 15.0%-30.0 % in which infection of positive pigs positively correlated with mosquitoes carrying the virus. Additionally, we sequenced the entire genome of 6 strains of PCV3 in mosquitoes and 2 strains of PCV3 in pigs. Sequence analysis indicated a 100 % nucleotide similarity between mosquito and pig viral isolates that were all collected from similar farms. Phylogenetic analysis showed that PCV3 could be divided into two clades, PCV3a and PCV3b, and the PCV3 strains isolated in mosquitoes were distributed on the two clades. Our results demonstrate that mosquitoes may serve as a potential transmission vector in the life-cycle of PCV3, revealing possible transmission routes of PCV3.

Reservoirs of Porcine Circoviruses: A Mini Review

Porcine circovirus (PCV) is one of the smallest known DNA viruses in mammals. At present, PCVs are divided into three species, PCV1, PCV2, and PCV3. PCV1 and PCV2 were found in the 1970s and the 1990s, respectively, whereas PCV3 was discovered recently in 2016. PCV1 does not cause diseases in pigs. However, PCV3, similar to PCV2, is reported to be associated with several swine diseases, including porcine dermatitis and nephropathy syndrome (PDNS) and reproductive failure. PCVs are very common in domestic pigs as well as wild boars. However, PCVs have been occasionally isolated from non-porcine animals, including ruminants (such as cattle, goats, wild chamois, and roe deers), rodents (such as NMRI mice, BALB/c mice, Black C57 mice, ICR mice, Mus musculus, and Rattus rattus), canines (such as dogs, minks, foxes, and raccoon dogs), insects (such as flies, mosquitoes, and ticks), and shellfish. Moreover, PCVs are frequently reported in biological products, including human vaccines, animal vaccines, porcine-derived commercial pepsin products, and many cell lines. PCVs are also abundant in the environment, including water samples and air samples. Interestingly, PCV1 and/or PCV2 antibody or antigen has also been detected in sera, stool samples and respiratory swab samples of human, revealing zoonotic potential of PCVs. Thus, PCVs inhabit many types of reservoirs. In this review, we summarize the reservoirs of PCVs, and this information would be helpful in understanding the natural circulating status and possible cross-species transmission of PCVs.

An epidemiological investigation of porcine circovirus 3 infection in dogs in the Guangxi Province from 2015 to 2017, China

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This study was the first seroprevalence and genetic investigation of PCV3 in dogs in the Guangxi province, China.

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This work is the first in the world to obtain the complete genome of dog PCV3.

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These PCV3 strains from the Guangxi province help to determine that PCV3 from dog origin and pig origin are from different branches.

Porcine circovirus type 3 (PCV3) is an emerging circovirus species associated with several diseases. The study aimed to investigate the frequency of porcine circovirus 3 (PCV3) and its coinfection with canine parvovirus type 2 (CPV-2) in dogs in the Guangxi province from 2015 to 2017, China, and to examine the genome diversity of PCV3. Using polymerase chain reaction (PCR) amplification and sequencing, 96 of 406 (23.6%)samples were positive for PCV3, 38 out of 406 (9.4%) samples were coinfected with both PCV3 and CPV-2. The CPV-positive rate was significantly higher in the PCV3-positive samples than in the non-PCV3 samples, and the difference was extremely significant (P < 0.01). The complete genome (n=4) and ten capsid genes (n=10) of PCV3 were sequenced. Multiple sequence alignment results showed that these sequences shared 98.5–100% nucleotide similarity with the reference genome sequence and 97.5–100% nucleotide similarity with the reference capsid gene sequence. PCV3 was classified into two different genotypes, according to phylogenetic analysis based on the whole genome. These strains were clustered in PCV3a, showing a close relationship with PCV3-US/SD2016. Surprisingly, we separately analyzed these PCV3 strains from the Guangxi province and found that the dog and pig PCV3 are from different branches. In summary, this was the first seroprevalence and genetic investigation of PCV3 in dogs in the Guangxi province, China, and the first complete genome PCV3 from dogs obtained in the world. The results provide insights into the epidemiology and pathogenesis of this important virus.

Recent progress on porcine circovirus type 3

Porcine circovirus 3 (PCV3) is a newly identified virus that belongs to the genus Circovirus in the family Circoviridae. Since the first identification of PCV3 in domestic swine in 2016 in the USA, exciting progress on PCV3 has emphasized the importance of the virus. The aim of this review is to present recent advances in the molecular characteristics, epidemiology, and pathogenesis of PCV3. The virus spreads widely throughout almost all tissues of pig and wild boar in various countries, with a gradual increase of the infection. PCV3 is a pathogen associated with porcine dermatitis and nephropathy syndrome (PDNS)-like clinical signs, reproductive failure, and cardiac and multiorgan inflammation. Furthermore, PCV3 has been detected in other animals and ticks, suggesting that PCV3 possesses cross-species transmission abilities and has an unexpectedly broad distribution and circulation in the wild, where these animals may serve as potential reservoirs for PCV3 and pose a threat to the swine industry or even to humans. Moreover, several detection methods, which can specifically detect PCV3 or differentiate PCV3 from the other viruses, are also reviewed. The present review provides updated knowledge on PCV3-related research. Identification of the prevailing strain of PCV3 and its reservoirs is essential for researchers to understand PCV3 infections and PCV3-related diseases.

Insights into the genetic and host adaptability of emerging porcine circovirus 3

Porcine circovirus 3 (PCV3) was found to be associated with reproductive disease in pigs, and since its first identification in the United States, it subsequently spread worldwide, especially in China, where it might pose a potential threat to the porcine industry. However, no exhaustive analysis was performed to understand its evolution in the prospect of codon usage pattern. Here, we performed a deep codon usage analysis of PCV3. PCV3 sequences were classified into two clades: PCV3a and PCV3b, confirmed by principal component analysis. Additionally, the degree of codon usage bias of PCV3 was slightly low as inferred from the analysis of the effective number of codons. The codon usage pattern was mainly affected by natural selection, but there was a co-effect of mutation pressure and dinucleotide frequency. Moreover, based on similarity index analysis, codon adaptation index analysis and relative codon deoptimization index analysis, we found that PCV3 might pose a potential risk to public health though with unknow pathogenicity. In conclusion, this work reinforces the systematic understanding of the evolution of PCV3, which was reflected by the codon usage patterns and fitness of this novel emergent virus.

A wild circulation: High presence of Porcine circovirus 3 in different mammalian wild hosts and ticks

Porcine circovirus 3 (PCV-3) has emerged as a potential threat for swine industry, being consistently reported in the presence of several clinical signs all around the world. Recently, its presence in wild boar has been demonstrated at high prevalence. This evidence is surprising since the lower density of wild populations might not be expected to sustain such efficient viral transmission. Porcine circoviruses were proven to exhibit a certain plasticity in the host tropism and were detected in unrelated species, like mice, dogs and ruminants. However, if this scenario applies also to wild animals remains to be established. Therefore, this study aimed to investigate the presence of PCV-3 in wild ungulates other than wild boar and in related hematophagous ectoparasites. One hundred and nine animals were sampled from different hilly and mountain areas of Friuli Venezia Giulia, including 9 chamois (Rupicapra rupicapra), 17 red deer (Cervus elaphus), 4 mouflons (Ovis musimon), 50 roe deer (Capreolus capreolus) and 29 wild boars (Sus scrofa). Additionally, host-matched ectoparasites were collected when present. Porcine circovirus 3 was diagnosed using molecular techniques and sequencing. This study results confirmed the high PCV-3 occurrence in wild boar and reported for the first time its presence, at low prevalence, in chamois and roe deer. Moreover, two ticks (Ixodes ricinus), one of which non-engorged, collected from PCV-3 negative roe deer, tested PCV-3 positive. The genetic characterization of some of the strains collected from non-swine hosts allowed to prove that, albeit clearly part of PCV-3 species, they were genetically unique, demonstrating the absence of among-samples contamination and thus confirming the actual presence of PCV-3 genome in these new hosts. Therefore, this study highlights an unexpected broad PCV-3 distribution and circulation in the wild, rising further questions on porcine circoviruses infectious cycle, epidemiology and origin, which will deserve additional investigations.

Construction, expression and antiviral activity analysis of recombinant adenovirus expressing human IFITM3 in vitro

Interferon-inducible transmembrane protein 3 (IFITM3) inhibits the replication of multiple pathogenic viruses by blocking their entry. In this study, we constructed a shuttle plasmid, harboring human IFITM3. Thereafter, recombinant adenovirus rAd5-IFITM3 was obtained by co-transfection of the linearized viral backbone vector pAd5 and the shuttle plasmid. The results showed that human IFITM3 did not affect the assembly and morphogenesis of progeny adenovirus. Human IFITM3 can be expressed in both A549 and MDCK cells in a time dependent manner. Furthermore, cells infected with rAd5-IFITM3 at a multiplicity of infection (MOI) of 100 for 24 h were challenged with avian influenza virus (AIV) H5N1 at an MOI of 1 for 6, 12 and 24 h. Rates of H5N1 infection in rAd5-IFITM3 cells were significantly decreased at 24 h post-infection (hpi), in a time dependent manner, compared with that of wild type wtAd5-infected cells. The expressions of viral genes were significantly inhibited at transcriptional and translational levels at 6 and 12 hpi. These results suggest that IFITM3 can suppress H5N1 replication in the early stage of the infection, which may be used as a promise agent against H5N1 infection in vivo.

Development and application of a baculovirus-expressed capsid protein-based indirect ELISA for detection of porcine circovirus 3 IgG antibodies

BACKGROUND

Porcine circovirus type 3 (PCV3), recently widely isolated from pigs with various clinical conditions, is likely globally epidemic. However, development of serological diagnosis for PCV3 in pigs is ongoing. Our objectives were to: 1) establish an indirect ELISA, using PCV3 capsid protein (Cap) prepared by Baculovirus Expression Vector System (BEVS) as a high-quality coating antigen for detection of PCV3-associated antibodies in serum samples; and 2) use this ELISA to conduct a serological survey for PCV3 in various regions of Hunan province, China.

RESULTS

The PCV3 positive rate to the ELISA assay (total of 190 serum samples) was higher in sows with reproductive failure compared to healthy sows (34/85, 40.0% versus 30/105, 28.6%), with similar results using qPCR assays. Further, in an additional 1038 serum samples collected from January 2016 to May 2018 in various regions of Hunan province and tested with this established ELISA, 20 to 84% were positive for PCV3 (according to region of sera collection), with high PCV3 seroprevalence (> 50%) in herds in Changde, Hengyang and Yueyang. Moreover, among serum samples from herds in Shaoyang and Changde, PCV3 seroprevalence was higher in sows than in other classes of pigs (i.e., suckling piglets, nursery pigs, gilts, growing-finishing pigs and boars).

CONCLUSIONS

We developed a full-length PCV3 Cap-based ELISA using a eukaryotic expression system with excellent potential to elucidate PCV3 epidemiology. Based on this assay, PCV3 has been circulating in Hunan province. PCV3 prevalence was lower in healthy sows than in those with reproductive failure. Further studies are warranted to identify the PCV3 responsible for high seroprevalence in sows and determine pathogenesis of PCV3 in sows with reproductive failure.

Co-Infection of Swine with Porcine Circovirus Type 2 and Other Swine Viruses

Porcine circovirus 2 (PCV2) is the etiological agent that causes porcine circovirus diseases and porcine circovirus-associated diseases (PCVD/PCVAD), which are present in every major swine-producing country in the world. PCV2 infections may downregulate the host immune system and enhance the infection and replication of other pathogens. However, the exact mechanisms of PCVD/PCVAD are currently unknown. To date, many studies have reported that several cofactors, such as other swine viruses or bacteria, vaccination failure, and stress or crowding, in combination with PCV2, lead to PCVD/PCVAD. Among these cofactors, co-infection of PCV2 with other viruses, such as porcine reproductive and respiratory syndrome virus, porcine parvovirus, swine influenza virus and classical swine fever virus have been widely studied for decades. In this review, we focus on the current state of knowledge regarding swine co-infection with different PCV2 genotypes or strains, as well as with PCV2 and other swine viruses.

An epidemiological investigation of porcine circovirus 3 infection in cattle in Shandong province, China

Background

Porcine circovirus type 3 (PCV3) is a single-stranded, closed circular DNA virus, which causes porcine dermatitis and nephropathy syndrome (PDNS), multisystemic inflammation, and reproductive failure. The present study aimed to investigate the seroprevalence of PCV3 in cattle (Bos taurus) in Shandong province, China, and examine its genome diversity.

Results

PCR amplification and sequencing showed that 74 of 213 bovine samples (34.7%) were positive for PCV3. Among them, the capsid gene (n = 12) and the complete genome (n = 4) were sequenced. These sequences had high identities to the reference capsid gene (98.0–100%) and the complete genome (97.5–99.8%). The PCV3 strains were classified into two different genotypes (PCV3a and PCV3b), according to phylogenetic analysis based on the complete genome and capsid gene sequences. Specifically, the bovine-origin strains in this study were grouped into PCV3a, showing a close relationship with PCV3-US/SD2016 (American strain; GenBank: KX966193.1). Notably, a comparison of the inferred amino acid sequences revealed a mutation from D124 to Y124.

Conclusion

This was the first seroprevalence and genetic investigation of PCV3 in cattle in Shandong province, China. The results could provide insights into the epidemiology and pathogenesis of this important virus.

Current Knowledge on Porcine circovirus 3 (PCV-3): A Novel Virus With a Yet Unknown Impact on the Swine Industry

Porcine circovirus 3 (PCV-3) is a recently described virus belonging to the family Circoviridae. It represents the third member of genus Circovirus able to infect swine, together with PCV-1, considered non-pathogenic, and PCV-2, one of the most economically relevant viruses for the swine worldwide industry. PCV-3 was originally found by metagenomics analyses in 2015 in tissues of pigs suffering from porcine dermatitis and nephropathy syndrome, reproductive failure, myocarditis and multisystemic inflammation. The lack of other common pathogens as potential infectious agents of these conditions prompted the suspicion that PCV-3 might etiologically be involved in disease occurrence. Subsequently, viral genome was detected in apparently healthy pigs, and retrospective studies indicated that PCV-3 was already present in pigs by early 1990s. In fact, current evidence suggests that PCV-3 is a rather widespread virus worldwide. Recently, the virus DNA has also been found in wild boar, expanding the scope of infection susceptibility among the Suidae family; also, the potential reservoir role of this species for the domestic pig has been proposed. Phylogenetic studies with available PCV-3 partial and complete sequences from around the world have revealed high nucleotide identity (>96%), although two main groups and several subclusters have been described as well. Moreover, it has been proposed the existence of a most common ancestor dated around 50 years ago. Taking into account the economic importance and the well-known effects of PCV-2 on the swine industry, a new member of the same family like PCV-3 should not be neglected. Studies on epidemiology, pathogenesis, immunity and diagnosis are guaranteed in the next few years. Therefore, the present review will update the current knowledge and future trends of research on PCV-3.

Structure-Based Design of Porcine Circovirus Type 2 Chimeric VLPs (cVLPs) Displays Foreign Peptides on the Capsid Surface

Although porcine circovirus-like particles can function as a vector to carry foreign peptides into host cells, displaying foreign peptides on the surface of virus-like particles (VLPs) remains challenging. In this study, a plateau, consisting of the middle portion of Loop CD (MP-Lcd) from two neighboring subunits of PCV2 capsid protein (Cap), was identified as an ideal site to insert various foreign peptides or epitopes and display them on the surface of PCV2 VLPs. One of the goals of this work is to determine if the surface pattern of this plateau can be altered without compromising the neutralizing activity against PCV2 infections. Therefore, biological roles of MP-Lcd regarding VLPs assembly, cell entry, and antigenicity were investigated to determine whether this was a universal site for insertion of foreign functional peptides. Three-dimensional (3D) structure simulations and mutation assays revealed MP-Lcd was dispensable for PCV2 Cap assembly into VLPs and their entry into host cells. Notably, substitution of MP-Lcd with a foreign peptide, caused surface pattern changes around two-fold axes of PCV2 VLPs based on 3D structure simulation, but was not detrimental to VLPs assembly and cell entry. Moreover, this substitution had no adverse effect on eliciting neutralizing antibodies (NAbs) against PCV2 infection in pigs. In conclusion, MP-Lcd of the PCV2 Cap was a promising site to accommodate and display foreign epitopes or functional peptides on the surface of PCV2 VLPs. Furthermore, chimeric VLPs (cVLPs) would have potential as bivalent or multivalent vaccines and carriers to deliver functional peptides to target cells.

Retrospective study of porcine circovirus 3 infection in China

PCV3 is an emerging swine virus associated with porcine dermatitis and nephropathy syndrome (PDNS), reproductive failure, respiratory diseases and systematic inflammation. Although first identified in 2015, the earliest case has been traced back to 2009 in the United States. In China, PCV3 infection was first detected in 2015, but little information has been available about its occurrence and prevalence there before 2015. In this study, 200 porcine clinical samples collected from 20 provinces, five autonomous regions and four municipalities between 1990 and 1999 were analysed for PCV3 infection by PCR. Results showed that 6.5% of the porcine samples collected from eight provinces and one autonomous region were PCV3 positive, with the earliest cases occurring in 1996. Nucleotide sequence analysis showed that PCV3 strains obtained in this study shared 96.6%-99.7% and 97.1%-99.4% sequence identity at the ORF2 gene and genome levels with all available reference strains from China and other countries, indicating the high genetic stability of PCV3 over the past 20 years.