Characterization of a complete genome of a circular single-stranded DNA virus from porcine stools in Korea

A variety of highly divergent eukaryotic ssDNA viruses in sera of pigs

Over the last decade, viral metagenomics has been established as a non-targeted approach for identifying viruses in stock animals, including pigs. This has led to the identification of a vast diversity of small circular ssDNA viruses. The present study focuses on the investigation of eukaryotic circular Rep-encoding single-stranded (CRESS) DNA viral genomes present in serum of commercially reared pigs from southern Brazil. Several CRESS DNA viral genomes were detected, including representatives of the families Smacoviridae (n=5), Genomoviridae (n=3), Redondoviridae (n=1), Nenyaviridae (n=1) and other yet unclassified genomes (n=9), plus a circular DNA molecule, which probably belongs to the phylum Cressdnaviricota. A novel genus within the family Smacoviridae, tentatively named 'Suismacovirus', comprising 21 potential new species, is proposed. Although the reported genomes were recovered from pigs with clinical signs of respiratory disease, further studies should examine their potential role as pathogens. Nonetheless, these findings highlight the diversity of circular ssDNA viruses in serum of domestic pigs, expand the knowledge on CRESS DNA viruses' genetic diversity and distribution and contribute to the global picture of the virome of commercially reared pigs.

A 2021 taxonomy update for the family Smacoviridae

The family Smacoviridae (order Cremevirales, class Arfiviricetes, phylum Cressdnaviricota) is comprised of viruses with small circular single-stranded DNA genomes of ~2.3-3 kb in length that have primarily been identified in fecal sample of various animals. Smacovirus genomes carry two genes in ambisense orientation encoding a capsid protein and a rolling-circle replication initiation protein, respectively. We have revised the taxonomy of the family by assigning 138 new genomic sequences deposited in GenBank to already established taxa as well as 41 new species and six new genera. Furthermore, we have adopted binomial species nomenclature, conforming to the "Genus + freeform epithet" format for all 84 species from 12 genera. The updated Smacoviridae taxonomy presented in this article has been ratified by the International Committee on Taxonomy of Viruses (ICTV).

Genomic Diversity of CRESS DNA Viruses in the Eukaryotic Virome of Swine Feces

Replication-associated protein (Rep)-encoding single-stranded DNA (CRESS DNA) viruses are a diverse group of viruses, and their persistence in the environment has been studied for over a decade. However, the persistence of CRESS DNA viruses in herds of domestic animals has, in some cases, serious economic consequence. In this study, we describe the diversity of CRESS DNA viruses identified during the metagenomics analysis of fecal samples collected from a single swine herd with apparently healthy animals. A total of nine genome sequences were assembled and classified into two different groups (CRESSV1 and CRESSV2) of the Cirlivirales order (Cressdnaviricota phylum). The novel CRESS DNA viral sequences shared 85.8–96.8% and 38.1–94.3% amino acid sequence identities for the Rep and putative capsid protein sequences compared to their respective counterparts with extant GenBank record. Data presented here show evidence for simultaneous infection of swine herds with multiple novel CRESS DNA viruses, including po-circo-like viruses and fur seal feces-associated circular DNA viruses. Given that viral genomes with similar sequence and structure have been detected in swine fecal viromes from independent studies, investigation of the association between presence of CRESS DNA viruses and swine health conditions seems to be justified.

Torque teno virus from Korean domestic swine farms, 2017-2018

Background

Torque teno viruses (TTVs) have been detected worldwide, from a wide range of animals. Up to date, few studies focused on the prevalence of TTVs in general and swine torque teno viruses (TTSuVs) in particular in Korean swine farms.

Objective

This study aimed to investigate the appearance of TTSuVs and TTVs in sick pigs during the 2017–2018 period.

Materials and Methods

Molecular‐based method using TTSuV1‐, TTSuV2‐ and TTV3‐specific primers was used to screen for the viruses from either sera or pooled internal organs of sick pigs. For genetic characterization, genomic sequences of TTVs were sequenced by a primer walking method. Several bioinformatic tools have been utilized to investigate the genomic organization and genetic relationship of TTVs.

Results

Two years of prevalence survey reveal that the prevalence of TTSuV2 is about twice that of TTSuV1. Furthermore, we identified TTV of genogroup 3 in swine pooled organ samples. The genome of two strains, M265_Korea_2017 and N119_Korea_2018, are 3,817 bp in size; M265_2017 has three open reading frames (ORFs); and N119_2018 strain has four ORFs. The complete genome nucleotide sequencing of the two strains shows 98.4% homology, and the phylogenetic analysis of Open reading frame (ORF)1 indicates that the strains are located close to TUPB strain subgroup C of genogroup 3.

Conclusion

Our study provided the information of TTSuVs prevalence in swine farms in Korea and highlighted the presence of TTV genogroup 3 strains in pigs.

New genotype classification and molecular characterization of canine and feline parvoviruses

Background

Canine parvovirus (CPV) and feline panleukopenia (FPV) cause severe intestinal disease and leukopenia.

Objectives

In Korea, there have been a few studies on Korean FPV and CPV-2 strains. We attempted to investigate several genetic properties of FPV and CPV-2.

Methods

Several FPV and CPV sequences from around world were analyzed by Bayesian phylo-geographical analysis.

Results

The parvoviruses strains were newly classified into FPV, CPV 2-I, CPV 2-II, and CPV 2-III genotypes. In the strains isolated in this study, Gigucheon, Rara and Jun belong to the FPV, while Rachi strain belong to CPV 2-III. With respect to CPV type 2, the new genotypes are inconsistent with the previous genotype classifications (CPV-2a, -2b, and -2c). The root of CPV-I strains were inferred to be originated from a USA strain, while the CPV-II and III were derived from Italy strains that originated in the USA. Based on VP2 protein analysis, CPV 2-I included CPV-2a-like isolates only, as differentiated by the change in residue S297A/N. Almost CPV-2a isolates were classified into CPV 2-III, and a large portion of CPV-2c isolates was classified into CPV 2-II. Two residue substitutions F267Y and Y324I of the VP2 protein were characterized in the isolates of CPV 2-III only.

Conclusions

We provided an updated insight on FPV and CPV-2 genotypes by molecular-based and our findings demonstrate the genetic characterization according to the new genotypes.

Genotyping of PCV3 based on reassembled viral gene sequences

Porcine circovirus type 3 (PCV3) has been reported in many countries such as USA, China, Korea and many European countries during 2015–2018. The six PCV3 strains named IH, SJ, N5, N10, N13 and N62 were detected out of 220 samples by PCR methods while the prevalence our study was conducted in 2017 to 2018. The six detected strains were hard to genotype with reference viruses due to their diverse phylogenetic relationship. PCV3 capsid, ORF3 and replicase protein coding genes were reassembled at the nucleotide sequence level, then 16 new reassembled PCV3 sequences were generated. Based on the maximum likelihood mapping analysis of 303 PCV3 sequences a model with a combination of replicase, ORF3 and capsid protein coding genes was selected as the most appropriate target for genotyping, which provided the best support for the clade classification into three genotypes and several subtypes (genotype 1, genotype 2; subtype: a and b, genotype 3; subtype a, b, c, d, e, f, g, h). This study, the IH_Korea_2017 and N62_Korea_2018 strains belong to genogroup 3 (subtype a) the SJ_Korea_2017 strain genogroup 3 (subtype g) and the N5, N10, N13 Korea_ 2018 strains genogroup 3 (subtype f), respectively. In conclusion, this study may provide insights to classification of PCV3 genotypes around the world.

PCR-based detection and genetic characterization of porcine parvoviruses in South Korea in 2018

Background

with the advantage of sequencing technology, many novel porcine parvoviruses (PPV) rather than PPV1 has been reported. This study ultilized specific PCR- based method and gene- based analysis to study the presence and genetic diversity of porcine parvoviruses in South Korea in 2018.

Results

The present study was conducted in 2018 and found PPV1 and PPV7 in nine out of 151 field samples (organs and semen) by the PCR method. Among these, the complete genome sequences of five strains (N2, N91, N108, N133, and N141) were recovered. Phylogenic analysis revealed that the strains N2, N91, and N108 belong to the PPV1 genotype, while N133 and N141 belong to PPV7 genotype. The PPV7 strains collected in this study had deletion mutations in the VP2 gene but differed from that of PPV7 strains collected in 2017. Among the PPV1 strains, the amino acid variations in the B cell epitopes of the VP2 protein were observed between three Korean PPV1 field strains (N2, N91, and N108) and the reference PPV1 strains. Those substitutions resulted in six out of 12 predicted epitopes having significant differences in antigenic index compared to the other PPV1 strains.

Conclusions

This study confirmed the presence of different genotypes of porcine parvoviruses in South Korea. The PPVs circulating in South Korea were phylogenetically classified as PPV1 and PPV7 genotypes. Three Korean PPV1 strains collected in 2018 were predicted to have antigenic alteration in VP2 compared to several reference strains of PPV1.

Viral DNA genomes in sera of farrowing sows with or without stillbirths

A study was conducted to investigate the serum virome of sows with and without stillbirths after farrowing. Sera from sows with at least one stillbirth or with normal litters were collected immediately after farrowing. Viral DNA was extracted from serum pools and submitted to high throughput sequencing. No differences in the proportion of virus-related reads were found in both groups (p > 0.05). A variety of viral DNA genomes were identified, mostly representative of three viral families: Anelloviridae, Circoviridae and Smacoviridae. Besides, a number of novel unclassified circular Rep-encoding single stranded DNA (CRESS DNA) viruses were also identified. These findings suggest that the presence of such viral genomes in sows’ sera bears no correlation with stillbirths’ occurrence; it seems likely that these constitute part of the normal serum microbiome of sows at farrowing.

Molecular-based investigation and genetic characterization of porcine stool-associated RNA virus (posavirus) lineages 1 to 3 in pigs in South Korea from 2017 to 2019

Recent results on the detection and genetic characterization of stool-associated RNA viruses from different species have increased the knowledge about the extreme genetic diversity of picornaviruses. This study aimed to investigate the presence of unclassified porcine stool-associated RNA viruses (posaviruses) in South Korea and to elucidate the molecular evolution of the viruses. By RT-PCR, posaviruses 1 and 3 were exclusively found in fecal samples and consistently detected in three consecutive years in six of eight provinces, with 148/697 (21.2%) and 33/84 (39.3%) positive samples and farms, respectively. Every age group but the older age groups (finisher, sow) had significantly higher positive rates of posavirus 1 than posavirus 3. An analysis of the RNA-dependent RNA polymerase sequences by likelihood mapping and maximum-likelihood-based phylogenetic analysis revealed that stool-associated RNA viruses formed four supergroups that were well separated from all recognized families of the order Picornavirales. Five genomes of Korean posaviruses generated in this study were phylogenetically grouped with posavirus 1 and posavirus 3 and were predicted to have the typical genome organization of picornaviruses.

Eukaryotic Circular Rep-Encoding Single-Stranded DNA (CRESS DNA) Viruses: Ubiquitous Viruses With Small Genomes and a Diverse Host Range

While single-stranded DNA (ssDNA) was once thought to be a relatively rare genomic architecture for viruses, modern metagenomics sequencing has revealed circular ssDNA viruses in most environments and in association with diverse hosts. In particular, circular ssDNA viruses encoding a homologous replication-associated protein (Rep) have been identified in the majority of eukaryotic supergroups, generating interest in the ecological effects and evolutionary history of circular Rep-encoding ssDNA viruses (CRESS DNA) viruses. This review surveys the explosion of sequence diversity and expansion of eukaryotic CRESS DNA taxonomic groups over the last decade, highlights similarities between the well-studied geminiviruses and circoviruses with newly identified groups known only through their genome sequences, discusses the ecology and evolution of eukaryotic CRESS DNA viruses, and speculates on future research horizons.

Smacoviridae: a new family of animal-associated single-stranded DNA viruses

Smacoviruses have small (∼2.3-2.9 kb), circular single-stranded DNA genomes encoding rolling circle replication-associated proteins (Rep) and unique capsid proteins. Although smacoviruses are prevalent in faecal matter of various vertebrates, including humans, none of these viruses have been cultured thus far. Smacoviruses display ∼45% genome-wide sequence diversity, which is very similar to that found within other families of circular Rep-encoding single-stranded (CRESS) DNA viruses, including members of the families Geminiviridae (46% diversity) and Genomoviridae (47% diversity). Here, we announce the creation of a new family Smacoviridae and describe a sequence-based taxonomic framework which was used to classify 83 smacovirus genomes into 43 species within six new genera, Bovismacovirus (n=3), Cosmacovirus (n=1), Dragsmacovirus (n=1), Drosmacovirus (n=3), Huchismacovirus (n=7), and Porprismacovirus (n=28). As in the case of genomoviruses, the species demarcation is based on the genome-wide pairwise identity, whereas genera are established based on the Rep amino acid sequence identity coupled with strong phylogenetic support. A similar sequence-based taxonomic framework should guide the classification of an astonishing diversity of other uncultured and currently unclassified CRESS DNA viruses discovered by metagenomic approaches.

Complete Genome Sequences of Porcine Deltacoronavirus Strains DH1/2016 and DH2/2016 Isolated in South Korea

Two porcine deltacoronavirus (PDCoV) strains, named DH1/2016 and DH2/2016, were isolated from feces of piglets which had severe watery diarrhea symptoms. A comparison of the complete genome sequences suggested that the DH1/2016 and DH2/2016 strains are highly homologous to each other and to PDCoVs isolated in early 2014 from the United States.

Circular replication-associated protein encoding DNA viruses identified in the faecal matter of various animals in New Zealand

In recent years, innovations in molecular techniques and sequencing technologies have resulted in a rapid expansion in the number of known viral sequences, in particular those with circular replication-associated protein (Rep)-encoding single-stranded (CRESS) DNA genomes. CRESS DNA viruses are present in the virome of many ecosystems and are known to infect a wide range of organisms. A large number of the recently identified CRESS DNA viruses cannot be classified into any known viral families, indicating that the current view of CRESS DNA viral sequence space is greatly underestimated. Animal faecal matter has proven to be a particularly useful source for sampling CRESS DNA viruses in an ecosystem, as it is cost-effective and non-invasive. In this study a viral metagenomic approach was used to explore the diversity of CRESS DNA viruses present in the faeces of domesticated and wild animals in New Zealand. Thirty-eight complete CRESS DNA viral genomes and two circular molecules (that may be defective molecules or single components of multicomponent genomes) were identified from forty-nine individual animal faecal samples. Based on shared genome organisations and sequence similarities, eighteen of the isolates were classified as gemycircularviruses and twelve isolates were classified as smacoviruses. The remaining eight isolates lack significant sequence similarity with any members of known CRESS DNA virus groups. This research adds significantly to our knowledge of CRESS DNA viral diversity in New Zealand, emphasising the prevalence of CRESS DNA viruses in nature, and reinforcing the suggestion that a large proportion of CRESS DNA viruses are yet to be identified.