Expression of the putative ORF1 capsid protein of Torque teno sus virus 2 (TTSuV2) and development of Western blot and ELISA serodiagnostic assays: correlation between TTSuV2 viral load and IgG antibody level in pigs

Trans-replicase helper activity of porcine circoviruses promotes the synergistic replication of torque teno virus

While the primary pathogenic potential of torque teno viruses (TTVs) is yet to be defined, TTVs are often co-detected with other pathogens and are suspected of exacerbating clinical disease in coinfections. Swine TTVs (TTSuVs) enhance clinical signs of porcine circovirus type 2 (PCV2) in a gnotobiotic pig model. However, the mechanisms involved are unknown. In this study, we observed that co-culture of TTSuV1 and PCV1, and specifically supplementing TTSuV1 cultures with the PCV replicase protein in trans consistently resulted in higher levels of replication of TTSuV1 when compared to TTSuV1 cultured alone. Therefore, the hypothesis that the PCV replicase (rep) protein has trans-replicase helper activity for TTSuV1 was examined. Based on EMSA and reporter gene assays, it was determined that the PCV1 rep directly interacted with the TTSuV1 UTR. The TTSuV1 rep trans-complemented a PCV rep null mutant virus, indicating that the TTSuV1 and PCV1 replicase proteins supported the replication of both viruses. In mice, the administration of plasmids encoding the PCV1 rep and a TTSuV1 infectious clone resulted in the production of higher TTSuV1 genome copies in dually exposed mice when compared to singly exposed mice. Higher sero-conversion and lymphoid hyperplasia were also observed in the dually exposed experimental mice. Thus, this study provides evidence for trans-replicase activity of PCVs and TTVs as a novel mechanism of explaining enhanced viral replication in coinfections involving both viruses.

High-throughput sequencing of the porcine antibody repertoire with or without PEDV infection: A proof-of-concept study

A host's adaptive immune system can protect against a wide variety of pathogens by producing diverse antibodies. The antibody repertoire is so vast that traditional low-throughput methods cannot fully sequence it. In this study, we developed a high-throughput sequencing (HTS) method for antibody repertoire assessment in swine, and tested it with or without porcine epidemic diarrhea virus (PEDV) infection. We isolated peripheral blood mononuclear cells from normal or PEDV-seropositive pigs and applied multiplex PCR to amplify the porcine B cell receptor heavy chain library, followed by HTS using the Illumina Miseq system to obtain full sequence information. The results from sequence analysis demonstrated that in normal conditions, several V gene segments were preferentially used, with IGHV1-4 and IGHV1S2 being the two most frequent. The IGHV usage in PEDV-seropositive pigs was not exactly the same as that of PEDV-seronegative pigs, with an increased usage of IGHV1-6. Our study provides an effective approach to comprehensively understand the overall porcine antibody repertoire, as well as to monitor broad antibody responses to viral challenge in pigs.

Torque teno viruses in health and disease

Torque teno viruses (TTVs) are small, ubiquitous, viruses with a highly diverse, single-stranded, negative sense DNA genome and wide host range. They are detected at high rates in both healthy and diseased individuals and are considered a significant part of the mammalian virome. Similar to human TTVs, swine TTVs (TTSuVs) are epidemiologically linked to several coinfections including porcine circovirus types 2 and 3 and the porcine reproductive and respiratory disease syndrome virus. Experimental infection of gnotobiotic pigs with TTSuVs resulted in lesions in multiple organs and exacerbation of coinfections, making TTSuVs the only members of the Anelloviridae family with experimental evidence for pathogenicity. However, due to the lack of reliable cell culture and animal models, mechanistic studies on viral immunity and pathogenesis are limited. The objective of this review is to summarize the current status of knowledge regarding the biology, detection, pathogenesis and public health significance of TTSuVs, while identifying gaps in knowledge which limit the field.

Characterization of a novel bat-HKU2-like swine enteric alphacoronavirus (SeACoV) infection in cultured cells and development of a SeACoV infectious clone

Swine enteric alphacoronavirus (SeACoV), also known as swine acute diarrhea syndrome coronavirus (SADS-CoV), belongs to the species Rhinolophus bat coronavirus HKU2. Herein, we report on the primary characterization of SeACoV in vitro. Four antibodies against the SeACoV spike, membrane, nucleocapsid and nonstructural protein 3 capable of reacting with viral antigens in SeACoV-infected Vero cells were generated. We established a DNA-launched SeACoV infectious clone based on the cell adapted passage-10 virus and rescued the recombinant virus with a unique genetic marker in cultured cells. Six subgenomic mRNAs containing the leader-body junction sites, including a bicistronic mRNA encoding the accessory NS7a and NS7b genes, were experimentally identified in SeACoV-infected cells. Cellular ultrastructural changes induced by SeACoV infection were visualized by electron microscopy. The availability of the SeACoV infectious clone and a panel of antibodies against different viral proteins will facilitate further studies on understanding the molecular mechanisms of SeACoV replication and pathogenesis.

Specific recombinant proteins of porcine epidemic diarrhea virus are immunogenic, revealing their potential use as diagnostic markers

Given the highly contagious and acute nature of porcine epidemic diarrhea (PED), especially in piglets, there is an urgent need for the development of rapid and sensitive diagnostic assays. The diagnostic potentials of specific porcine epidemic diarrhea virus (PEDV) accessory and nonstructural proteins, if any, have not yet been investigated. In order to determine and compare which of the viral proteins may be useful as diagnostic antigens, whole virus (WV) particles and a panel of structural and nonstructural PEDV proteins [spike subunit 1 (S1), the C-terminal part of ORF3 (ORF3C), envelope (E), nonstructural protein 1 (Nsp1), Nsp2, Ac (acidic domain of Nsp3), and ADRP (ADP-ribose-1-monophosphatase domain of Nsp3), expressed individually in bacterial and/or mammalian cells] were tested for reactivity with sera from PEDV-infected pigs by ELISA and/or western blot analysis. According to western blots, serum antibody interactions with the S1 protein were relatively more sensitive and specific than ORF3C, E and Ac. Furthermore, a total of 851 serum samples from diarrheal pigs of different ages were analyzed by ELISA, with most showing immune-reactivity towards the WV, S1, ORF3C, and E proteins. The earliest IgG antibody response was observed in the one-week-old piglets, with similar antibody ontogeny and patterns of seroconversion for S1, ORF3C, E, and WV antigens. In addition, the pattern of neutralizing antibody was more similar to that of IgA in weaning piglets after PEDV infection. Collectively, these data provide more reliable information on the host immune response to different viral proteins, which will be useful for development of novel serological assays and for design of vaccines that better stimulate protective immunity.

Molecular characterization of the ORF2 of Torque teno sus virus 1a and Torque teno sus virus 1b detected in cases of postweaning multisystemic wasting syndrome in Mexico

Worldwide Torque teno sus virus (TTSuV, genus Iotatorquevirus) species have been regarded as possible agents associated with porcine circovirus-associated disease. Iotatorquevirus species possess high genomic variability, suggesting that diverse genotypes are widely geographically distributed. In this study, we validated the genomic variability of Iotaroquevirus species in pigs with postweaned multisystemic wasting syndrome. Genomic DNA from nine TTSuV1a-positive tissues and 15 TTSuV1b-positive tissues was used to amplify the complete ORF2 of each species by nested PCR to perform a molecular characterization. It was found that Mexican TTSuV1a sequences belong to genotype B, sharing phylogenetic origin, high nucleic acid and amino acid sequence similarity and dominant epitope conformation with commercially linked countries, such as the United States, Canada and China, whereas the Mexican TTSuV1b sequences belong to genotype A, being more divergent among each other and displaying low nucleotide identity with worldwide genotype A sequences. In both Iotatorquevirus species, a PTPase-like signature motif was identified in the predicted amino acid sequence, being more conserved for Mexican TTSuV1b sequences than for Mexican TTSuV1a sequences, in which several substitutions were observed. These changes may influence the conformation of dominant epitopes as different arrays were determined among TTSuV1a genotypes. ORF2 variability may account for pathogenic differences by modifying viral replication and immune response, as depicted for human TTV.

Identification of a peptide derived from the heptad repeat 2 region of the porcine epidemic diarrhea virus (PEDV) spike glycoprotein that is capable of suppressing PEDV entry and inducing neutralizing antibodies

Heptad repeat (HR) regions are highly conserved motifs located in the glycoproteins of enveloped viruses that form a six-helix bundle structure and is important in the process of virus fusion. Peptides derived from the HR regions of some viruses have also been shown to inhibit viral entry. Porcine epidemic diarrhea virus (PEDV) was predicted to have HR regions (HR1 and HR2) in the spike glycoprotein S2 subunit. Based on this analysis, six peptides derived from HR1 and HR2 were selected, expressed in Escherichia coli, purified, and characterized. Three peptides (HR2M, HR2L and HR2P) were identified as potential competitive inhibitors in PEDV in vitro infection assays, with the HR2P peptide representing the most potent inhibitor. Further study indicated that immunization of HR2P in mice elicited antibodies capable of neutralizing PEDV infection in vitro. These results demonstrate that the HR2P peptide and anti-HR2P antibody can serve as a tool for dissecting the fusion mechanism of PEDV, guiding the search for potent inhibitors with therapeutic value against PEDV infection.

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Six peptides derived from heptad repeat (HR) 1 and 2 regions of PEDV S glycoprotein were expressed and characterized.

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Three peptides (HR2M, HR2L and HR2P) exhibited antiviral activity in vitro.

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Immunization of the HR2P peptide in mice elicited antibodies capable of neutralizing PEDV infection in vitro.

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HR2P peptide can serve as a potential antiviral drug against PEDV infection.

Genetic and pathogenic characterization of a novel reassortant mammalian orthoreovirus 3 (MRV3) from a diarrheic piglet and seroepidemiological survey of MRV3 in diarrheic pigs from east China

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A novel reassortant mammalian orthoreovirus 3 (MRV3), designated MRV-ZJ2013, was isolated from diarrheic piglets.

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Genomic and phylogenetic analysis shows that MRV-ZJ2013 may have originated from reassortments among mink, bat, and pig MRVs.

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Experimental infection study showed that MRV-ZJ2013 had low, if any, pathogenesis in newborn piglets.

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A seroepidemiological survey of MRV3 revealed a high seroprevalence (77%) from diarrheic pigs of different ages in east China.

Mammalian orthoreoviruses (MRVs), which cause gastrointestinal and respiratory illness, have been isolated from a wide variety of mammalian species including bats, minks, pigs and humans. Here we report the isolation and genetic and pathogenic characterization of a novel MRV type 3 (MRV3), named MRV-ZJ2013, from the diarrheic feces of piglets in Zhejiang province, China. Genomic and phylogenetic analysis shows that MRV-ZJ2013 may have originated from reassortments among mink, bat, and pig MRVs, suggesting the hypothesis that interspecies transmission has occurred in pig herds. Neonatal piglets infected with MRV-ZJ2013 displayed mild clinical signs such as poor appetite and soft feces, but vomiting and diarrhea were not observed. Fecal virus shedding was detected only in three out of six piglets, each for one- or two-day post-infection. In contrast, piglets inoculated with a virulent porcine epidemic diarrhea virus (PEDV) strain as the control group had severe signs characterized by acute vomiting and watery diarrhea. These findings suggest that the virulence of MRV-ZJ2013, if any, was likely not significant compared to that of PEDV. A seroepidemiological survey of MRV by means of an indirect enzyme-linked immune-sorbent assay (ELISA) based on a recombinant MRV3 capsid protein sigma1 as antigen revealed a high seroprevalence (77%) in 1037 samples from diarrheic pigs of different ages from 24 herds in seven provinces of east China between 2015 and 2016, indicating that MRV3 is endemic in pig herds in China, and may contribute collectively to enteric disease along with other porcine pathogens.

Retrospective study of the relationship of Torque teno sus virus 1a and Torque teno sus virus 1b with porcine circovirus associated disease

Genus Iotatorquevirus consists of 2 species, Torque teno sus virus 1a and Torque teno sus virus 1b, which are ubiquitous in swine populations, and are widely reported in association with porcine circovirus associated disease (PCVAD). To evaluate the relationship with PCVAD, 100 formalin-fixed paraffin-embedded tissue samples were used to detect both Iotatorquevirus species by nested PCR and sequencing. Sixty-eight PCVAD cases were selected as well as 32 porcine circovirus type 2 (PCV2) non-affected cases. Overall, 33 of the 100 cases were positive for Torque teno sus virus 1a and 8 of 100 were positive for Torque teno sus virus 1b. Only 24 of 68 (35%) PCVAD cases were positive for Torque teno sus virus 1a; 39% (9/23) of post-weaning multisystemic wasting syndrome, and 33% (15/45) of PCV2-associated reproductive failure cases. Among PCV2 non-affected cases, 28% were positive for Torque teno sus virus 1a and 6% were positive for Torque teno sus virus 1b. Torque teno sus virus 1b was not detected in PCV2-associated reproductive failure cases. Regardless of the PCV2-status, a lower frequency of both Iotatorquevirus species was found than depicted in other reports and there was no statistical relationship with PCVAD (χ 2 < 0.01). Given the worldwide genomic variability of Iotatorquevirus species, it is feasible that species prevalent in Mexico share a lower nucleotide sequence identity, leading to different pathogenic potential.

Molecular characterization of pigeon torque teno virus (PTTV) in Jiangsu province

The torque teno virus (TTV) is a recently discovered DNA virus that has been detected in many different hosts, including humans, livestock and poultry. To date, there is no report of pigeon TTV (PTTV) from anywhere in the world. To investigate the distribution of PTTV in pigeons from the eastern Chinese province of Jiangsu and characterize their genomes, we employed PCR to detect PTTV in 144 samples collected from 6 pigeon plants in Jiangsu province, amplify complete genomes from representative samples and analyze genetic characteristics using bioinformatics. The results demonstrated that 71.5% (103/144) of samples were PTTV positive. The rate of sequence homology among the six PTTV complete genomes obtained from Jiangsu province ranged from 99.7% to 100%. Phylogenetic analysis suggested that PTTV genomes had a high degree of genetic similarity and were similar to chicken anemia virus that also had poultry as a host. Although with the same host, PTTV shared distant relationship with PiCV in both complete genome, Rep and Cap genes. The results of this study provided evidence that PTTV could be detected in Chinese pigeons at a high level, the evolutionary process of complete genome, Rep and Cap genes of Anelloviridae family had obvious divergence.

Identification of heterologous Torque Teno Viruses in humans and swine

Torque Teno Viruses (TTVs) are ubiquitous viruses which are highly prevalent in several mammalian species. Human TTV’s are epidemiologically associated with several human disease conditions such as respiratory illnesses, auto-immune disorders and hepatitis. Recently it was found that swine TTV’s (TTSuVs) can act as primary pathogens. The common occurrence of TTVs as environmental contaminants and the increasing interest in the use of swine organs for xenotransplantation lend importance to the question of whether TTV’s can cross-infect across species. In this study, we examined human and swine sera by swine or human TTV-specific PCRs, to determine whether swine TTVs (TTSuV) DNA can be detected in humans and vice versa. Surprisingly, both human and TTSuV DNA were present in a majority of the samples tested. Transfection of human PBMC’s with TTSuV1 genomic DNA resulted in productive viral infection which was sustained for the three serial passages tested. Lymphoproliferative responses in infected human PBMCs were diminished when compared to the controls. Furthermore, mild to moderate antibody responses against the TTSuV1 ORF2 protein was detected in 16 of the 40 human sera by ELISA. Therefore, these study findings provide initial and fundamental evidence for possible cross-species transmission of TTVs.

Lack of strong anti-viral immune gene stimulation in Torque Teno Sus Virus1 infected macrophage cells

While recent findings suggest that swine TTVs (TTSuVs) can act as primary or co-infecting pathogens, very little is known about viral immunity. To determine whether TTSuVs downregulate key host immune responses to facilitate their own survival, a swine macrophage cell line, 3D4/31, was used to over-express recombinant TTSuV1 viral particles or the ORF3 protein. Immune gene expression profiles were assessed by a quantitative PCR panel consisting of 22 immune genes, in cell samples collected at 6, 12, 24 and 48h post-transfection. Despite the upregulation of IFN-β and TLR9, interferon stimulated innate genes and pro-inflammatory genes were not upregulated in virally infected cells. The adaptive immune genes, IL-4 and IL-13, were significantly downregulated at 6h post-transfection. The ORF3 protein did not appear do not have a major immuno-suppressive effect, nor did it stimulate anti-viral immunity. Data from this study warrants further investigation into the mechanisms of TTV related immuno-pathogenesis.

Immune gene expression in swine macrophages expressing the Torque Teno Sus Virus1 (TTSuV1) ORF-1 and 2 proteins

Torque Teno viruses (TTVs) are small DNA viruses which are ubiquitous in nature. Recent reports indicate that swine torque teno viruses (TTSuVs) can act as primary pathogens or play a role in exacerbating co-infections. However, very little is known about the TTSuV host-viral interaction or how they so successfully establish chronic infections in the host. To determine whether the major viral proteins can modulate host immunity, recombinant TTSuV1 ORF1 and 2 proteins were expressed in a swine macrophage cell line (3D4/31). The differential expression of a panel of innate, adaptive, regulatory and inflammatory immune genes was studied by quantitative PCR; using cDNA samples collected at 6, 12, 24 and 48h post-transfection. The ORF1 protein induced an early anti-viral response. However, at 6h post-transfection it also upregulated IL-10, PD-1 and SOCS-1, the suppressors of T cell mediated immunity. An ensuing diminishment of the early protective response was noted. The TTSuV1 ORF2 protein suppressed IFN-β and IL-13 responses but did not significantly influence anti-viral immunity otherwise. These findings indicate that the TTSuV1 ORF1 protein plays a significant but dual role in viral immunity.

Functional characterization of a new promoter isolated from torque teno sus virus 1

Torque teno sus virus 1 (TTSuV1) has a non-enveloped, single-stranded, negative-sense circular DNA genome, and it is widely distributed in pigs. Open reading frame 1 (ORF1) of TTSuV1 can be transcribed into mRNA and then translated into protein; however, its promoter has not yet been identified. We used a dual-luciferase reporter system, involving pGL3-Basic and pRL-TK, to identify the promoter of TTSuV1 ORF1. Our results revealed that the sequence between nucleotides 196 and 525 promoted the transcription of the firefly luciferase gene. The core sequence of the promoter was between nucleotides 250 and 400. A comparison of the identified TTSuV1 ORF1 promoter with that from cytomegalovirus (CMV) suggested that the two promoters were similar in strength. Our findings provide new information regarding the molecular biology of TTSuV1 and have revealed a new promoter that can be used in plasmids for numerous applications.

Development of an indirect ELISA assay for the detection of IgG antibodies against the ORF1 of Torque teno sus viruses 1 and 2 in conventional pigs

Torque teno sus viruses (TTSuV, family Anelloviridae) cause long lasting and persistent infection in pigs under subclinical scenarios, and are potentially linked to several economically important swine diseases. Currently, little is known about swine immune response against TTSuV infections. In this study, an ELISA assay was developed based on the ORF1-A recombinant protein of two known TTSuVs, namely TTSuV1 (genus Iotatorquevirus) and TTSuV2 (genus Kappatorquevirus). The assay was used to study the development of the humoral immune response against TTSuV1 and TTSuV2 in longitudinally sampled clinically healthy pigs and their dams. Anti ORF1-A IgG was found in serum of pigs and sows for both TTSuVs. From 15 sows, 15 (100%) and 13 (83%) had anti ORF1-A IgG against TTSuV1 and TTSuV2, respectively. Pig sero-prevalences at the first sampling (4 weeks of age) were 65% (24/37) and 5% (2/37) for TTSuV1 and TTSuV2, respectively. For TTSuV1, the highest anti ORF1-A IgG prevalence was observed at weeks 21 and 25, with 68% (25/37) sero-positive pigs. Quantitative PCR (qPCR) results at week 21 revealed that 26 out of 32 (81%) pigs were positive for TTSuV1. In the case of TTSuV2, the highest anti ORF1-A IgG prevalence was observed at week 21, with 84% (31/37) pigs being sero-positive. At the same week, 92% (34/37) of pigs were qPCR positive. In summary, anti ORF1-A IgGs were detected in both sows and piglets at different ages, indicating that these animals could mount a humoral immune response against both TTSuVs. However, the high percentage of viremic pigs in presence of anti ORF1-A IgG suggests that these antibodies are not able to remove TTSuVs from circulation.

Analysis of TTSuV1b antibody in porcine serum and its correlation with four antibodies against common viral infectious diseases

Background

The purpose of the present study was to evaluate the correlation between Torque teno sus virus 1b (TTSuV1b) infection and other viral infections or vaccine immunization in conventional pigs.

Methods

With overexpressed and purified viral protein TTSuV1b as antigen, an indirect enzyme-linked immunosorbent assay (ELISA) method for detecting TTSuV1b antibody was established, which demonstrated great specificity and reproducibility. Porcine serum samples (n = 212) were tested using ELISA. Meanwhile, the antibodies against Classical Swine Fever Virus (CSFV), Pseudorabies Virus (PRV), Porcine Reproductive and Respiratory Syndrome Virus (PRRSV), and Porcine Circovirus 2 (PCV2) were also examined using the commercial kits.

Results

Statistical analysis indicated that the level of anti-TTSuV1b antibody was positively correlated with the level of anti-PCV2 antibody in a lesser extent; the level of antibodies against TTSuV1b or PCV2 were significantly lower in porcine serum with low level of TTSuV1b virus, implicating the potential consistency and synchronization in the mechanism of TTSuV1b and PCV2 infection. Whereas, antibodies against PRRSV or CSFV showed no statistical significance on comparison with anti-TTSuV1b antibody, implicating that in conventional pigs, the antibody level for PRRSV and CSFV were not significantly influenced by TTSuV1b infection.

Conclusion

In conclusion, examination of anti-TTSuV1b antibody in porcine serum with the presently established ELISA method would serve as a supplementary approach for etiological investigation, and the combined statistical analysis of the antibodies against four other viruses might help to further understand the TTSuV1b infection as well as its pathogenicity.

Development of a Serological Assay for the Sea Lion (Zalophus californianus) Anellovirus, ZcAV

New diseases in marine animals are emerging at an increasing rate, yet methodological limitations hinder characterization of viral infections. Viral metagenomics is an effective method for identifying novel viruses in diseased animals; however, determining virus pathogenesis remains a challenge. A novel anellovirus (Zalophus californianus anellovirus, ZcAV) was recently reported in the lungs of captive California sea lions involved in a mortality event. ZcAV was not detected by PCR in the blood of these animals, creating the inability to assess the prevalence of ZcAV in live sea lions. This study developed an enzyme-linked immunosorbent assay (ELISA) to detect antibodies to ZcAV in sea lion serum. To assess ZcAV prevalence, paired serum and lung samples (n = 96) from wild sea lions that stranded along the California coast were tested through ELISA and PCR, respectively. Over 50% of the samples tested positive for ZcAV by ELISA (34%), PCR (29%), or both (11%) assays. ZcAV is prevalent in stranded wild sea lion populations and results suggest that PCR assays alone may grossly underestimate ZcAV exposure. This ELISA provides a tool for testing live sea lions for ZcAV exposure and is valuable for subsequent studies evaluating the potential pathogenicity of this anellovirus.

Identification of novel anelloviruses with broad diversity in UK rodents

Anelloviruses are a family of small circular ssDNA viruses with a vast genetic diversity. Human infections with the prototype anellovirus, torque teno virus (TTV), are ubiquitous and related viruses have been described in a number of other mammalian hosts. Despite over 15 years of investigation, there is still little known about the pathogenesis and possible disease associations of anellovirus infections, arising in part due to the lack of a robust cell culture system for viral replication or tractable small-animal model. We report the identification of diverse anelloviruses in several species of wild rodents. The viruses are highly prevalent in wood mice (Apodemus sylvaticus) and field voles (Microtus agrestis), detectable at a low frequency in bank voles (Myodes glareolus), but absent from house mice (Mus musculus). The viruses identified have a genomic organization consistent with other anelloviruses, but form two clear phylogenetic groups that are as distinct from each other as from defined genera.

Development and validation of a 4-plex antibody assay for simultaneous detection of IgG antibodies against Torque teno sus virus 1 (TTSuV1), TTSuV2, and porcine reproductive and respiratory syndrome virus types 1 and 2

A fluorescent microbead-based immunoassay (FMIA) for simultaneous detection of IgG antibodies against Torque teno sus virus 1 (TTSuV1), TTSuV2, porcine reproductive and respiratory syndrome virus type 1 (PRRSV-1) and PRRSV-2 was developed. Serum samples were obtained over time from 20 pigs. Twelve of 20 were exposed to TTSuV2 on day 0, 20/20 were vaccinated with a PRRSV-2 vaccine on day 35, and 20/20 were exposed to PRRSV-2 on day 63. Anti-TTSuV antibodies were detected in 30% of the pigs on day 0, and 90% by day 35. All PRRSV-2 vaccinated pigs had detectable anti-PRRSV-2 IgG 21 days after vaccination. Field samples from 17 farms were also tested. The seroprevalence of both PRRSV and TTSuV increased with age. Comparison of the PRRSV-2 FMIA to an ELISA revealed good correlation in young pigs but a high rate of false positives in older pigs. Cross-reaction between PRRSV types was a problem.

Torque teno sus virus (TTSuV) infection at different stages of pig production cycle

Torque teno sus virus (TTSuV) infection is present in pig herds worldwide. It has been demonstrated that TTSuV might increase the severity of other important viral diseases with economic and public health impacts. At present, there is no information on the age distribution of pigs infected with TTSuV in Brazilian herds. This study evaluated the frequency of TTSuV infection in pigs at different stages of production. Fecal samples (n=190) from pigs at 1 to 24 weeks of age and from breeders at 6 farrow-to-weaning (up to 8 weeks of age) and 9 grower-to-finish (9 weeks of age onwards) farms in the western region of Paraná state, Brazil, were evaluated by PCR. Fragments of the 5' UTRs of TTSuV1 and/or TTSuVk2 DNAs were identified in 126 (66.3%) of the fecal samples. Significant differences were found with the percentages of positive samples for TTSuV1, TTSuVk2, and mixed infections by both genera between and within the different pig production stages. Fecal samples from the grower-to-finish farms had TTSuV detection rates (90.1%; 64/71) that were significantly (p<0.05) higher than those from the farrow-to-weaning farms (52.1%; 62/119). TTSuV detection was significantly (p<0.05) more frequent in finisher pigs than in the animals from the other stages. The UTR nucleotide sequences in this study presented higher similarities to strains from Norway (96%, TTSuV1), and Argentina and China (97.1%, TTSuVk2). These results suggest that TTSuV infection has spread to pigs of all production stages and that the viral infection rate increases with the age of the animals. In the western region of Paraná state, Brazil, TTSuV1 and TTSuVk2-induced infections were more frequently observed in suckling piglets and finisher pigs, respectively. Phylogenetic analysis pointed out the possibility of different strains of TTSuV1 and TTSuVk2 circulating in pig herds of Brazil.

Three new emerging subgroups of Torque teno sus viruses (TTSuVs) and co-infection of TTSuVs with porcine circovirus type 2 in China

Background

Torque teno sus viruses (TTSuVs) are non-enveloped viruses and have single-stranded, negative sense circular DNA genomes and are widely distributed in pigs. But till now, the prevalence of TTSuVs with porcine circovirus type 2 (PCV2) in pig herds of China is not very clear; and the genetic variation among different TTSuVs isolate is very large and need to divide the subgroups. In this study, the co-infection with TTSuVs and porcine circovrius (PCV) in the pig population of China was investigated and the subgroups of all TTSuVs genomes in Genbank were divided.

Results

Results showed that the rate of co-infection with TTSuV1 and TTSuV2 reached 75% in PCV2-positive samples. Also Two TTSuV1 and four TTSuV2 isolates genome sequences were obtained, and the similarity of all TTSuV1 and TTSuV2 genomic sequences in GenBank were compared. Phylogenetic trees indicated that both the TTSuV1 and TTSuV2 sequences could be divided into four genotypes. Interestingly, the sub-genotypes TTSuV1d, TTSuV2c and TTSuV2d exist only in the pig population of China.

Conclusions

This study demonstrates that co-infection with TTSuVs and PCVs is very common in the pig population of China, in which the viruses maybe contribute to clinical diseases cooperatively. In addition, three new subgroups of TTSuVs emerged in China for the first time and a high level of variation among different isolates of TTSuV1 and TTSuV2 was indicated by their genetic diversity.

Preliminary epitope mapping of Torque teno sus virus 1 and 2 putative capsid protein and serological detection of infection in pigs

The aim of this work is to identify antigenic regions within the ORF1 protein of Torque teno sus virus 1 (TTSuV1) and Torque teno virus sus 2 (TTSuV2) that could be used as antigens to detect virus-specific antibodies following infection in pigs. Protein sequences of TTSuV ORF1 genes were analysed to predict linear antigenic epitopes. Synthesized peptides were analysed for serological reactivity with swine sera. Such an antigenic region was identified at the C terminus of the ORF1 protein of both viruses and showed serological reactivity with 78 % (TTSuV1) and 88 % (TTSuV2) of swine sera. An ELISA with an immunodominant peptide as antigen was used to examine the sera of piglets, aged 4–20 weeks, and adults. Results indicated that TTSuV1- and TTSuV2-specific antibodies were detectable at 4 weeks. Antibody titres increased from week 10 and peaked at week 20. A relatively high antibody titre persisted to adulthood.

Exploratory study of Torque teno sus viruses in pulmonary inflammatory lesions in pigs

The pathogenic role of Torque teno sus viruses 1 (TTSuV1) and 2 (TTSuV2), and their capacity to induce lesions are controversial. TTSuVs have been linked to porcine circovirus diseases (PCVDs) and described as cause of mild respiratory lesions in gnotobiotic pigs; moreover, an increased TTSuV prevalence has been found in porcine respiratory disease complex (PRDC) affected pigs. In the present study, TTSuV1 and TTSuV2 loads and their prevalence were evaluated in formalin-fixed, paraffin-embedded (FFPE) lung samples displaying different types of inflammatory lesions. Such measurements were made by means of a real time quantitative PCR technique to detect these viruses. The technique was optimised for its use on FFPE tissues comparing results with frozen lung tissues. Selection criteria included negativity against porcine circovirus type 2 (PCV2), porcine reproductive and respiratory syndrome virus (PRRSV), Aujeszky's disease virus (ADV) and swine influenza virus (SIV). Results from the present study demonstrated that both TTSuVs were present in lung. However, TTSuV2 had higher viral load and prevalence in all the studied groups when compared to TTSuV1. TTSuV2 mean load was also higher in lungs with viral background (interstitial pneumonia and broncho-interstitial pneumonia) when compared to normal lungs or to those with bacterial background (catarrhal-purulent bronchopneumonia, fibrinous pleuritis and fibrinous-necrotizing pleuropneumonia). This result suggests a possible role of TTSuV2 in the pathogenic mechanism of inflammatory lesions of lungs compatible with viral infection.

Discovery of a novel Torque teno sus virus species: genetic characterization, epidemiological assessment and disease association

The study describes a novel Torque teno sus virus (TTSuV) species, provisionally named Torque teno sus virus k2b (TTSuVk2b), originally found in commercial pig sera by applying the rolling-circle amplification technique. Full-length sequences of TTSuVk2b were obtained, annotated and used in the phylogenetic analyses, which revealed that TTSuVk2b is a novel Anellovirus species within the genus Kappatorquevirus of the family Anelloviridae. Quantitative PCR techniques were developed to determine total TTSuV DNA quantities as well as the prevalence and viral DNA quantities of TTSuV1, TTSuVk2a and TTSuVk2b. The mean total TTSuV load in seven commercial sera was determined at 6.3 log(10) DNA copies ml(-1) of serum, with TTSuVk2b loads being the lowest at 4.5 log(10) DNA copies ml(-1) of serum. Subsequently, prevalence and loads of TTSuVs were determined in pig sera from 17 countries. TTSuVk2b prevalence ranged from 0 to 100 % with viral loads from 3.3 to 4.6 log(10) copies ml(-1) of sera. TTSuVk2a, so far the only species in the genus Kappatorquevirus, has been linked to an economically important swine disease, namely post-weaning multisystemic wasting syndrome (PMWS). Considering the grouping of TTSuVk2b in the same genus as TTSuVk2a, TTSuVk2b prevalence and viral DNA load were determined in PMWS-affected animals and healthy counterparts. This revealed that TTSuVk2a and TTSuVk2b are not only genetically related, but also that their viral loads in serum are elevated in PMWS animals compared with those of healthy pen mates. In summary, the present work describes a novel TTSuV species including its genetic characterization, epidemiological assessment and potential disease association.

Serological profile of torque teno sus virus species 1 (TTSuV1) in pigs and antigenic relationships between two TTSuV1 genotypes (1a and 1b), between two species (TTSuV1 and -2), and between porcine and human anelloviruses

The family Anelloviridae includes human and animal torque teno viruses (TTVs) with extensive genetic diversity. The antigenic diversity among anelloviruses has never been assessed. Using torque teno sus virus (TTSuV) as a model, we describe here the first investigation of the antigenic relationships among different anelloviruses. Using a TTSuV genotype 1a (TTSuV1a) or TTSuV1b enzyme-linked immunosorbent assay (ELISA) based on the respective putative ORF1 capsid antigen and TTSuV1-specific real-time PCR, the combined serological and virological profile of TTSuV1 infection in pigs was determined and compared with that of TTSuV2. TTSuV1 is likely not associated with porcine circovirus-associated disease (PCVAD), because both the viral loads and antibody levels were not different between affected and unaffected pigs and because there was no synergistic effect of concurrent PCV2/TTSuV1 infections. We did observe a higher correlation of IgG antibody levels between anti-TTSuV1a and -TTSuV1b than between anti-TTSuV1a or -1b and anti-TTSuV2 antibodies in these sera, implying potential antigenic cross-reactivity. To confirm this, rabbit antisera against the putative capsid proteins of TTSuV1a, TTSuV1b, or TTSuV2 were generated, and the antigenic relationships among these TTSuVs were analyzed by an ELISA and by an immunofluorescence assay (IFA) using PK-15 cells transfected with one of the three TTSuV ORF1 constructs. The results demonstrate antigenic cross-reactivity between the two genotypes TTSuV1a and TTSuV1b but not between the two species TTSuV1a or -1b and TTSuV2. Furthermore, an anti-genogroup 1 human TTV antiserum did not react with any of the three TTSuV antigens. These results have important implications for an understanding of the diversity of anelloviruses as well as for the classification and vaccine development of TTSuVs.

Torque teno sus virus infection in suckling piglets from Brazilian pig herds

Torque teno sus virus (TTSuV) is responsible for the infection of pig herds around the world. The aim of this study was to analyse the presence of natural infection by both species of TTSuV in suckling piglets from major pig-producing regions of Brazil. Faecal samples (n = 135) from 1 to 3-week-old suckling piglets from the Southern, Southeast and Midwest regions of Brazil were analysed by PCR assay to detect TTSuV1 and 2. TTSuV1 and 2 DNA was identified in 65 (48.1 %) and 23 (17 %) of piglet faecal samples, respectively. Co-infection by both species of TTSuV was detected in 17 (12.6 %) samples. Detection of TTSuV1 was significantly higher than that of TTSuV2 in the three Brazilian regions together (p < 0.05). Based on age of animals, TTSuV1 infection was statistically higher than TTSuV2 in each age group (p < 0.05). For all of the age groups together, no statistical difference was detected in the number of TTSuV1 and 2 positive results (p > 0.05). These findings revealed that TTSuV infection has disseminated in pig herds from different geographic Brazilian regions, and the presence of TTSuV in suckling piglet faecal samples suggested the early infection by the virus and the potential of these animals in spreading the virus.

Rescue of a porcine anellovirus (torque teno sus virus 2) from cloned genomic DNA in pigs

Anelloviruses are a group of single-stranded circular DNA viruses infecting humans and other animal species. Animal models combined with reverse genetic systems of anellovirus have not been developed. We report here the construction and initial characterization of full-length DNA clones of a porcine anellovirus, torque teno sus virus 2 (TTSuV2), in vitro and in vivo. We first demonstrated that five cell lines, including PK-15 cells, are free of TTSuV1 or TTSuV2 contamination, as determined by a real-time PCR and an immunofluorescence assay (IFA) using anti-TTSuV antibodies. Recombinant plasmids harboring monomeric or tandem-dimerized genomic DNA of TTSuV2 from the United States and Germany were constructed. Circular TTSuV2 genomic DNA with or without introduced genetic markers and tandem-dimerized TTSuV2 plasmids were transfected into PK-15 cells, respectively. Splicing of viral mRNAs was identified in transfected cells. Expression of TTSuV2-specific open reading frame 1 (ORF1) in cell nuclei, especially in nucleoli, was detected by IFA. However, evidence of productive TTSuV2 infection was not observed in 12 different cell lines transfected with the TTSuV2 DNA clones. Transfection with circular DNA from a TTSuV2 deletion mutant did not produce ORF1 protein, suggesting that the observed ORF1 expression is driven by TTSuV2 DNA replication in cells. Pigs inoculated with either the tandem-dimerized clones or circular genomic DNA of U.S. TTSuV2 developed viremia, and the introduced genetic markers were retained in viral DNA recovered from the sera of infected pigs. The availability of an infectious DNA clone of TTSuV2 will facilitate future study of porcine anellovirus pathogenesis and biology.

Torque teno sus virus in pigs: an emerging pathogen?

The newly established family Anelloviridae includes a number of viruses infecting humans (Torque teno viruses) and other animal species. The ones infecting domestic swine and wild boar are nowadays named Torque teno sus viruses (TTSuV), which are small circular single-stranded DNA viruses highly prevalent in the pig population. So far, two genetically distinct TTSuV species are infecting swine. Both TTSuVs appear to efficiently spread by vertical and horizontal transmission routes; in fact, foetuses may be infected and the prevalence and viral loads increase by age of the animals. Detailed immunological studies on TTSuVs are still lacking, but it seems that there are no efficient immunological responses limiting viraemia. These viruses are currently receiving more attention due to the latest results on disease association. Torque teno sus viruses have been circulating unnoticed in pigs for a long time, and even considered non-pathogenic by themselves; there is increasing evidence that points to influence the development of some diseases or even affect their outcome. Such link has been mainly established with porcine circovirus diseases.

Emerging and re-emerging swine viruses

In the past two decades or so, a number of viruses have emerged in the global swine population. Some, such as porcine reproductive and respiratory syndrome virus (PRRSV) and porcine circovirus type 2 (PCV2), cause economically important diseases in pigs, whereas others such as porcine torque teno virus (TTV), now known as Torque teno sus virus (TTSuV), porcine bocavirus (PBoV) and related novel parvoviruses, porcine kobuvirus, porcine toroviruses (PToV) and porcine lymphotropic herpesviruses (PLHV), are mostly subclinical in swine herds. Although some emerging swine viruses such as swine hepatitis E virus (swine HEV), porcine endogenous retrovirus (PERV) and porcine sapovirus (porcine SaV) may have a limited clinical implication in swine health, they do pose a potential public health concern in humans due to zoonotic (swine HEV) or potential zoonotic (porcine SaV) and xenozoonotic (PERV, PLHV) risks. Other emerging viruses such as Nipah virus, Bungowannah virus and Menangle virus not only cause diseases in pigs but some also pose important zoonotic threat to humans. This article focuses on emerging and re-emerging swine viruses that have a limited or uncertain clinical and economic impact on pig health. The transmission, epidemiology and pathogenic potential of these viruses are discussed. In addition, the two economically important emerging viruses, PRRSV and PCV2, are also briefly discussed to identify important knowledge gaps.

Histopathological investigation in porcine infected with torque teno sus virus type 2 by inoculation

Background

Porcine torque teno sus virus (TTSuV) is a small icosahedral and non-enveloped virus which contains a single-stranded (ssDNA), circular and negative DNA genome and infects mainly vertebrates and is currently classified into the 'floating' genus Anellovirus of Circoviridae with two species. Viral DNA of both porcine TTSuV species has a high prevalence in both healthy and diseased pigs worldwide and multiple infections of TTSuV with distinct genotypes or subtypes of the same species has been documented in the United States, Europe and Asia. However, there exists no information about histopathological lesions caused by infection with porcine TTSuV2.

Methods

Porcine liver tissue homogenate with 1 ml of 6.91 × 10⁷genomic copies viral loads of porcine TTSuV2 that had positive result for torque teno sus virus type 2 and negative result for torque teno sus virus type 1 and porcine pseudorabies virus type 2 were used to inoculate specific pathogen-free piglets by intramuscular route and humanely killed at 3,7,10,14,17,21 and 24 days post inoculation (dpi), the control pigs were injected intramuscularly with 1 ml of sterile DMEM and humanely killed the end of the study for histopathological examination routinely processed, respectively.

Results

All porcine TTSuV2 inoculated piglets were clinic asymptomatic but developed myocardial fibroklasts and endocardium, interstitial pneumonia, membranous glomerular nephropathy, and modest inflammatory cells infiltration in portal areas in the liver, foci of hemorrhage in some pancreas islet, a tiny amount red blood cells in venule of muscularis mucosae and outer longitudinal muscle, rarely red blood cells in the microvasculation and infiltration of inflammatory cells (lymphocytes and eosinophils) of tonsil and hilar lymph nodes, infiltration of inflammatory lymphocytes and necrosis or degeneration and focal gliosis of lymphocytes in the paracortical zone after inoculation with porcine TTSuV2-containing tissue homogenate.

Conclusions

Analysis of these presentations revealed that porcine TTSuV2 was readily transmitted to TTSuV-negative swine and that infection was associated with characteristic pathologic changes in specific pathogen-free piglets inoculated with porcine TTSuV2. Those results indicated no markedly histopathological changes happened in those parenchymatous organs, especially the digestive system and immune system when the specific pathogen-free pigs were infected with porcine TTSuV2, hence, to some extent, it was not remarkable pathological agent for domestic pigs at least. So, porcine TTSuV2 could be an unrecognized pathogenic viral infectious etiology of swine. This study indicated a directly related description of lesions responsible for TTSuV2 infection in swine.

Concurrent infections are important for expression of porcine circovirus associated disease

Porcine circovirus type 2 (PCV2) is the essential component of porcine circovirus disease (PCVD) as the disease syndrome is referred to in Europe and porcine circovirus associated disease (PCVAD) as it is referred to in North America. Singular PCV2 infection rarely results in clinical disease; however, PCVAD is often accelerated in onset, enhanced in severity and prolonged in duration by concurrent viral or bacterial infections. Due to its effect on the immune system, PCV2 has also been shown to enhance protozoal, metazoal, and fungal infections. Several retrospective or cross-sectional studies have investigated the presence and prevalence of various infectious agents associated with PCVAD under field conditions. Experimental models confirm that PCV2 replication and associated lesions can be enhanced by concurrent infection with other viruses or bacteria. The exact mechanisms by which concurrent pathogens upregulate PCV2 are unknown. Co-infections may promote PCV2 infection by increasing immune host cell replication and accumulation in tissues thereby enhancing targets for PCV2 replication. It has also been proposed that co-infections interfere with PCV2 clearance by alteration of cytokine production and profiles. The outcome of differences in timing of co-infections in PCV2-infected pigs is also likely very important and is an area where more research is needed. Given the current knowledge base, it is important that veterinarians do a thorough diagnostic investigation on herds where PCVAD is a recurrent problem in order to implement the most appropriate and cost effective intervention strategies.