A novel posavirus-related single-stranded RNA virus from fish (Cyprinus carpio)

Diversity of Picorna-Like Viruses in the Teltow Canal, Berlin, Germany

The viromes of freshwater bodies are underexplored. The Picornavirales order, with 371 acknowledged species, is one of the most expansive and diverse groups of eukaryotic RNA viruses. In this study, we add 513 picorna-like viruses to the assemblage of more than 2000 unassigned picorna-like viruses. Our set of the aquatic Picornavirales virome of the Teltow Canal in Berlin, Germany, consists of 239 complete and 274 partial genomes. This urban freshwater body is characterized by the predominance of marna-like viruses (30.8%) and dicistro-like viruses (19.1%), whereas picornaviruses, iflaviruses, solinvi-like viruses, polycipi-like viruses, and nora-like viruses are considerably less prevalent. Caliciviruses and secoviruses were absent in our sample. Although presenting characteristic domains of Picornavirales, more than 100 viruses (20.8%) could not be assigned to any of the 9 Picornavirales families. Thirty-three viruses of the Marnaviridae-mostly locarna-like viruses-exhibit a monocistronic genome layout. Besides a wealth of novel virus sequences, viruses with peculiar features are reported. Among these is a clade of untypeable marna-like viruses with dicistronic genomes, but with the capsid protein-encoding open reading frame located at the 5' part of their RNA. A virus with a similar genome layout but clustering with dicistroviruses was also observed. We further detected monocistronic viruses with a polymerase gene related to aparaviruses. The detection of Aichi virus and five novel posa-like viruses indicates a slight burden in municipal wastewater.

Virome analysis of New Zealand's bats reveals cross-species viral transmission among the Coronaviridae

The lesser short-tailed bat (Mystacina tuberculata) and the long-tailed bat (Chalinolobus tuberculatus) are Aotearoa New Zealand's only native extant terrestrial mammals and are believed to have migrated from Australia. Long-tailed bats arrived in New Zealand an estimated two million years ago and are closely related to other Australian bat species. Lesser short-tailed bats, in contrast, are the only extant species within the Mystacinidae and are estimated to have been living in isolation in New Zealand for the past 16-18 million years. Throughout this period of isolation, lesser short-tailed bats have become one of the most terrestrial bats in the world. Through a metatranscriptomic analysis of guano samples from eight locations across New Zealand, we aimed to characterise the viromes of New Zealand's bats and determine whether viruses have jumped between these species over the past two million years. High viral richness was observed among long-tailed bats with viruses spanning seven different viral families. In contrast, no bat-specific viruses were identified in lesser short-tailed bats. Both bat species harboured an abundance of likely dietary- and environment-associated viruses. We also identified alphacoronaviruses in long-tailed bat guano that had previously been identified in lesser short-tailed bats, suggesting that these viruses had jumped the species barrier after long-tailed bats migrated to New Zealand. Of note, an alphacoronavirus species discovered here possessed a complete genome of only 22,416 nucleotides with entire deletions or truncations of several non-structural proteins, thereby representing what may be the shortest genome within the Coronaviridae identified to date. Overall, this study has revealed a diverse range of novel viruses harboured by New Zealand's only native terrestrial mammals, in turn expanding our understanding of bat viral dynamics and evolution globally.

Genome of a husavirus from Southern Brazil

New viruses of the Picornavirales order have been discovered with the increase in the number of sequences obtained by high-throughput sequencing, as well as human stool-associated RNA virus (husavirus [HuV]), found in human stool samples. However, there is much to be clarified about HuV. Its cellular host, evolutionary history, and other biological characteristics are still unknown. Therefore, samples collected from human beings and environmental samples in a watershed in Southern Brazil were processed for the metagenomic library. Upon metagenomic analysis, we identified a HuV (husavirus LMM_67754 OP019707) genome with 8,846 bp, which was reported for the first time in Southern Brazil. The new genome presents only 37% of nucleotide identity with Brazilian strains and more than 90% with genomes from China, Vietnam, Venezuela, and the Netherlands. The HuV phylogeny presents significant differences among genomes, probably because multiple introductions of the virus may have occurred. Many questions still need to be answered about HuV. Therefore, more sequences and studies on this virus are necessary to improve the comprehension of the unknown origin of Picornavirales.

Enhanced Arbovirus Surveillance with High-Throughput Metatranscriptomic Processing of Field-Collected Mosquitoes

Surveillance programs are essential for the prevention and control of mosquito-borne arboviruses that cause serious human and animal diseases. Viral metatranscriptomic sequencing can enhance surveillance by enabling untargeted, high-throughput arbovirus detection. We used metatranscriptomic sequencing to screen field-collected mosquitoes for arboviruses to better understand how metatranscriptomics can be utilised in routine surveillance. Following a significant flood event in 2016, more than 56,000 mosquitoes were collected over seven weeks from field traps set up in Victoria, Australia. The traps were split into samples of 1000 mosquitoes or less and sequenced on the Illumina HiSeq. Five arboviruses relevant to public health (Ross River virus, Sindbis virus, Trubanaman virus, Umatilla virus, and Wongorr virus) were detected a total of 33 times in the metatranscriptomic data, with 94% confirmed using reverse transcription quantitative PCR (RT-qPCR). Analysis of metatranscriptomic cytochrome oxidase I (COI) sequences enabled the detection of 12 mosquito and two biting midge species. Screening of the same traps by an established public health arbovirus surveillance program corroborated the metatranscriptomic arbovirus and mosquito species detections. Assembly of genome sequences from the metatranscriptomic data also led to the detection of 51 insect-specific viruses, both known and previously undescribed, and allowed phylogenetic comparison to past strains. We have demonstrated how metatranscriptomics can enhance surveillance by enabling untargeted arbovirus detection, providing genomic epidemiological data, and simultaneously identifying vector species from large, unsorted mosquito traps.

Multiple clades of Husavirus in South America revealed by next generation sequencing

Husavirus (HuV) is an unclassified virus of the order Picornavirales that has already been identified worldwide in various locations. The genetic, epidemiological, and pathogenic characteristics are, however, little understood. In children with acute gastroenteritis, this study used next-generation sequencing to recognize unknown sources of viruses. In particular, 251 fecal samples obtained from individuals were sequenced in southern, northeastern, and northern Brazil. all samples were also analyzed using culture methods and parasitological tests to classify other enteric pathogens such as bacteria, parasites, and viruses. 1.9% of the samples tested positive for HuV, for a total of 5 positive children, with a mean age of 2 year, with three males and two females. Detailed molecular characterization of full genomes showed that Brazilian HuVs’ nucleotide divergence is less than 11%. The genetic gap between Brazilian sequences and the closest HuV reported previously, on the other hand, is 18%. The study showed that Brazilian sequences are closely related to the HuV defined in Viet Nam in 2013, further characterization based on phylogenetics. At least two divergent clades of HuV in South America were also seen in the phylogenetic study.

Characterization of a novel picornavirus isolated from moribund aquacultured clownfish

Over the last decade, a number of USA aquaculture facilities have experienced periodic mortality events of unknown aetiology in their clownfish (Amphiprion ocellaris). Clinical signs of affected individuals included lethargy, altered body coloration, reduced body condition, tachypnea, and abnormal positioning in the water column. Samples from outbreaks were processed for routine parasitological, bacteriological, and virological diagnostic testing, but no consistent parasitic or bacterial infections were observed. Histopathological evaluation revealed individual cell necrosis and mononuclear cell inflammation in the branchial cavity, pharynx, oesophagus and/or stomach of four examined clownfish, and large basophilic inclusions within the pharyngeal mucosal epithelium of one fish. Homogenates from pooled external and internal tissues from these outbreaks were inoculated onto striped snakehead (SSN-1) cells for virus isolation and cytopathic effects were observed, resulting in monolayer lysis in the initial inoculation and upon repassage. Transmission electron microscopy of infected SSN-1 cells revealed small round particles (mean diameter=20.0-21.7 nm) within the cytoplasm, consistent with the ultrastructure of a picornavirus. Full-genome sequencing of the purified virus revealed a novel picornavirus most closely related to the bluegill picornavirus and other members of the genus Limnipivirus. Additionally, pairwise protein alignments between the clownfish picornavirus (CFPV) and other known members of the genus Limnipivirus yielded results in accordance with the current International Committee on Taxonomy of Viruses criteria for members of the same genus. Thus, CFPV represents a proposed new limnipivirus species. Future experimental challenge studies are needed to determine the role of CFPV in disease.

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.

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.

Phylogenetic analysis of novel posaviruses detected in feces of Japanese pigs with posaviruses and posa-like viruses of vertebrates and invertebrates

Posaviruses and posa-like viruses are unclassified viruses with sequence similarity to viruses of the order Picornavirales. They have been reported in various vertebrates and invertebrates. We identified 11 posavirus-like sequences in porcine feces and performed phylogenic analysis. Previously reported Japanese posaviruses and those identified in this study clustered with posavirus 1, 4, and 7 and husavirus 1, while five viruses branched into three independent lineages, tentatively named posavirus 10, 11, and 12. Interestingly, posaviruses, except for posavirus 8 and 9, husaviruses, and rasaviruses, formed a cluster consisting of viruses only from pigs, humans, and rats, while posavirus 8 and 9, fisavirus, and basaviruses clustered with posa-like viruses from invertebrates.

Genome Characterization, Prevalence, and Transmission Mode of a Novel Picornavirus Associated with the Threespine Stickleback Fish (Gasterosteus aculeatus)

The complete genome sequence of an RNA virus was assembled from RNA sequencing of virus particles purified from threespine stickleback intestine tissue samples. This new virus is most closely related to the Eel picornavirus and can be assigned to the genus Potamipivirus in the family Picornaviridae Its unique genetic properties are enough to establish a new species, dubbed the Threespine Stickleback picornavirus (TSPV). Due to their broad geographic distribution throughout the Northern Hemisphere and parallel adaptation to freshwater, threespine sticklebacks have become a model in evolutionary ecology. Further analysis using diagnostic PCRs revealed that TSPV is highly prevalent in both anadromous and freshwater populations of threespine sticklebacks, infects almost all fish tissues, and is transmitted vertically to offspring obtained from in vitro fertilization in laboratory settings. Finally, TSPV was found in Sequence Reads Archives of transcriptome of Gasterosteus aculeatus, further demonstrating its wide distribution and unsought prevalence in samples. It is thus necessary to test the impact of TSPV on the biology of threespine sticklebacks, as this widespread virus could interfere with the behavioral, physiological, or immunological studies that employ this fish as a model system.IMPORTANCE The threespine stickleback species complex is an important model system in ecological and evolutionary studies because of the large number of isolated divergent populations that are experimentally tractable. For similar reasons, its coevolution with the cestode parasite Schistocephalus solidus, its interaction with gut microbes, and the evolution of its immune system are of growing interest. Herein we describe the discovery of an RNA virus that infects both freshwater and anadromous populations of sticklebacks. We show that the virus is transmitted vertically in laboratory settings and found it in Sequence Reads Archives, suggesting that experiments using sticklebacks were conducted in the presence of the virus. This discovery can serve as a reminder that the presence of viruses in wild-caught animals is possible, even when animals appear healthy. Regarding threespine sticklebacks, the impact of Threespine Stickleback picornavirus (TSPV) on the fish biology should be investigated further to ensure that it does not interfere with experimental results.

Complex virome in feces from Amerindian children in isolated Amazonian villages

The number of viruses circulating in small isolated human populations may be reduced by viral extinctions and rare introductions. Here we used viral metagenomics to characterize the eukaryotic virome in feces from healthy children from a large urban center and from three Amerindian villages with minimal outside contact. Numerous human enteric viruses, mainly from the Picornaviridae and Caliciviridae families, were sequenced from each of the sites. Multiple children from the same villages shed closely related viruses reflecting frequent transmission clusters. Feces of isolated villagers also contained multiple viral genomes of unknown cellular origin from the Picornavirales order and CRESS-DNA group and higher levels of nematode and protozoan DNA. Despite cultural and geographic isolation, the diversity of enteric human viruses was therefore not reduced in these Amazonian villages. Frequent viral introductions and/or increased susceptibility to enteric infections may account for the complex fecal virome of Amerindian children in isolated villages.

Enteric virome of Ethiopian children participating in a clean water intervention trial

BACKGROUND

The enteric viruses shed by different populations can be influenced by multiple factors including access to clean drinking water. We describe here the eukaryotic viral genomes in the feces of Ethiopian children participating in a clean water intervention trial.

METHODOLOGY/PRINCIPAL FINDINGS

Fecal samples from 269 children with a mean age of 2.7 years were collected from 14 villages in the Amhara region of Ethiopia, half of which received a new hand-dug water well. Feces from these villages were then analyzed in 29 sample pools using viral metagenomics. A total of 127 different viruses belonging to 3 RNA and 3 DNA viral families were detected. Picornaviridae family sequence reads were the most commonly found, originating from 14 enterovirus and 6 parechovirus genotypes plus multiple members of four other picornavirus genera (cosaviruses, saliviruses, kobuviruses, and hepatoviruses). Picornaviruses with nearly identical capsid VP1 were detected in different pools reflecting recent spread of these viral strains. Next in read frequencies and positive pools were sequences from the Caliciviridae family including noroviruses GI and GII and sapoviruses. DNA viruses from multiple genera of the Parvoviridae family were detected (bocaviruses 1-4, bufavirus 3, and dependoparvoviruses), together with four species of adenoviruses and common anelloviruses shedding. RNA in the order Picornavirales and CRESS-DNA viral genomes, possibly originating from intestinal parasites or dietary sources, were also characterized. No significant difference was observed between the number of mammalian viruses shed from children from villages with and without a new water well.

CONCLUSIONS

We describe an approach to estimate the efficacy of potentially virus transmission-reducing interventions and the first complete (DNA and RNA viruses) description of the enteric viromes of East African children. A wide diversity of human enteric viruses was found in both intervention and control groups. Mammalian enteric virome diversity was not reduced in children from villages with a new water well. This population-based sampling also provides a baseline of the enteric viruses present in Northern Ethiopia against which to compare future viromes.

Detection of novel RNA viruses from free-living gorillas, Republic of the Congo: genetic diversity of picobirnaviruses

Most of the emerging infectious diseases reported so far originated in wildlife. Therefore, virological surveillance of animals and particularly great apes is of great interest to establish the repertory of viruses associated with healthy hosts. This will further help to identify the emergence of new viruses and predict the possibility of interspecies transmission. In this study, we performed shotgun viral metagenomics on stool samples collected from seventeen free-living wild gorillas from the Republic of the Congo. The analysis revealed the presence of novel RNA viruses (picobirnaviruses, partitivirus, and Picornavirales (posa-like and dicistrovirus-like viruses)). Among these, picobirnavirus-related sequences were abundantly covered in the stools. Based on genetic variations both in capsid and RdRp proteins of picobirnaviruses, at least 96 variants were identified and most of them were novel. Among the 96, 22 variants had a nearly complete genome or segment. A comprehensive sequence analysis identified a potential new genogroup/genetic cluster and the presence of a short linear amino acid motif (ExxRxNxxxE) in a hypothetical protein. The sequence analysis of posa-like virus and dicistrovirus showed that these two viruses were novel members in the respective viral families. In conclusion, the identification of novel RNA viruses and their genetic diversity increases our knowledge about viruses that are associated with stools of wild gorillas and contributes to the initiatives in the search for potential emerging zoonotic viruses.

A decade of RNA virus metagenomics is (not) enough

It is hard to overemphasize the role that metagenomics has had on our recent understanding of RNA virus diversity. Metagenomics in the 21st century has brought with it an explosion in the number of RNA virus species, genera, and families far exceeding that following the discovery of the microscope in the 18th century for eukaryotic life or culture media in the 19th century for bacteriology or the 20th century for virology. When the definition of success in organism discovery is measured by sequence diversity and evolutionary distance, RNA viruses win. This review explores the history of RNA virus metagenomics, reasons for the successes so far in RNA virus metagenomics, and methodological concerns. In addition, the review briefly covers clinical metagenomics and environmental metagenomics and highlights some of the critical accomplishments that have defined the fast pace of RNA virus discoveries in recent years. Slightly more than a decade in, the field is exhausted from its discoveries but knows that there is yet even more out there to be found.

Detection and complete genome characteristics of Posavirus 1 from pigs in China

Porcine stool-associated RNA virus 1 (Posavirus 1) is a novel member of picornaviruses and first identified from fecal samples of 30-day-old pigs with diarrhea in USA in 2011. To evaluate the existence of Posavirus 1 in swine herds, 118 clinical samples from diarrheal pigs and 31 fecal swabs from healthy pigs were collected and detected by reverse transcription-polymerase chain reaction (RT-PCR) using Posavirus 1-specific primers. Only five fecal samples from diarrheal pigs on two swine farms were positive for Posavirus 1. The complete genome sequences [excluding poly (A) tail] of two representative isolates SDQD-25 and HBTS-11 are determined and consist of 9840 and 9819 nucleotides in length, and encode one putative polyprotein of 3070 and 2952 amino acids, respectively. They share 90.3% homology with each other and 81.3-95.4% homologies with American Posavirus 1 isolates or strains at the nucleotide sequence level. The phylogenetic analysis based on the entire genomes of reference picornavirus strains or isolates showed SDQD-25, HBTS-11 cluster together with American Posavirus 1 isolates or strains, yet are clearly distant from the other picornaviruses. The complete genome sequences of Chinese Posavirus 1 isolates will enrich the information of Posavirus 1 sequence database and further expedite posavirus research on the genetic diversity, epidemiology, and evolution in China.

Characterization of Posa and Posa-like virus genomes in fecal samples from humans, pigs, rats, and bats collected from a single location in Vietnam

Porcine stool-associated RNA virus (posavirus), and Human stool-associated RNA virus (husavirus) are viruses in the order Picornavirales recently described in porcine and human fecal samples. The tentative group (Posa and Posa-like viruses: PPLVs) also includes fish stool-associated RNA virus (fisavirus) as well as members detected in insects (Drosophila subobscura and Anopheles sinensis) and parasites (Ascaris suum). As part of an agnostic deep sequencing survey of animal and human viruses in Vietnam, we detected three husaviruses in human fecal samples, two of which share 97–98% amino acid identity to Dutch husavirus strains and one highly divergent husavirus with only 25% amino acid identity to known husaviruses. In addition, the current study found forty-seven complete posavirus genomes from pigs, ten novel rat stool-associated RNA virus genomes (tentatively named rasavirus), and sixteen novel bat stool-associated RNA virus genomes (tentatively named basavirus). The five expected Picornavirales protein domains (helicase, 3C-protease, RNA-dependent RNA polymerase, and two Picornavirus capsid domain) were found to be encoded by all PPLV genomes. In addition, a nucleotide composition analysis revealed that the PPLVs shared compositional properties with arthropod viruses and predicted non-mammalian hosts for all PPLV lineages. The study adds seventy-six genomes to the twenty-nine PPLV genomes currently available and greatly extends our sequence knowledge of this group of viruses within the Picornavirales order.

Virome comparisons in wild-diseased and healthy captive giant pandas

BACKGROUND

The giant panda (Ailuropoda melanoleuca) is a vulnerable mammal herbivore living wild in central China. Viral infections have become a potential threat to the health of these endangered animals, but limited information related to these infections is available.

METHODS

Using a viral metagenomic approach, we surveyed viruses in the feces, nasopharyngeal secretions, blood, and different tissues from a wild giant panda that died from an unknown disease, a healthy wild giant panda, and 46 healthy captive animals.

RESULTS

The previously uncharacterized complete or near complete genomes of four viruses from three genera in Papillomaviridae family, six viruses in a proposed new Picornaviridae genus (Aimelvirus), two unclassified viruses related to posaviruses in Picornavirales order, 19 anelloviruses in four different clades of Anelloviridae family, four putative circoviruses, and 15 viruses belonging to the recently described Genomoviridae family were sequenced. Reflecting the diet of giant pandas, numerous insect virus sequences related to the families Iflaviridae, Dicistroviridae, Iridoviridae, Baculoviridae, Polydnaviridae, and subfamily Densovirinae and plant viruses sequences related to the families Tombusviridae, Partitiviridae, Secoviridae, Geminiviridae, Luteoviridae, Virgaviridae, and Rhabdoviridae; genus Umbravirus, Alphaflexiviridae, and Phycodnaviridae were also detected in fecal samples. A small number of insect virus sequences were also detected in the nasopharyngeal secretions of healthy giant pandas and lung tissues from the dead wild giant panda. Although the viral families present in the sick giant panda were also detected in the healthy ones, a higher proportion of papillomaviruses, picornaviruses, and anelloviruses reads were detected in the diseased panda.

CONCLUSION

This viral survey increases our understanding of eukaryotic viruses in giant pandas and provides a baseline for comparison to viruses detected in future infectious disease outbreaks. The similar viral families detected in sick and healthy giant pandas indicate that these viruses result in commensal infections in most immuno-competent animals.

Highly diverse population of Picornaviridae and other members of the Picornavirales, in Cameroonian fruit bats

BACKGROUND

The order Picornavirales represents a diverse group of positive-stranded RNA viruses with small non-enveloped icosahedral virions. Recently, bats have been identified as an important reservoir of several highly pathogenic human viruses. Since many members of the Picornaviridae family cause a wide range of diseases in humans and animals, this study aimed to characterize members of the order Picornavirales in fruit bat populations located in the Southwest region of Cameroon. These bat populations are frequently in close contact with humans due to hunting, selling and eating practices, which provides ample opportunity for interspecies transmissions.

RESULTS

Fecal samples from 87 fruit bats (Eidolon helvum and Epomophorus gambianus), were combined into 25 pools and analyzed using viral metagenomics. In total, Picornavirales reads were found in 19 pools, and (near) complete genomes of 11 picorna-like viruses were obtained from 7 of these pools. The picorna-like viruses possessed varied genomic organizations (monocistronic or dicistronic), and arrangements of gene cassettes. Some of the viruses belonged to established families, including the Picornaviridae, whereas others clustered distantly from known viruses and most likely represent novel genera and families. Phylogenetic and nucleotide composition analyses suggested that mammals were the likely host species of bat sapelovirus, bat kunsagivirus and bat crohivirus, whereas the remaining viruses (named bat iflavirus, bat posalivirus, bat fisalivirus, bat cripavirus, bat felisavirus, bat dicibavirus and bat badiciviruses 1 and 2) were most likely diet-derived.

CONCLUSION

The existence of a vast genetic variability of picorna-like viruses in fruit bats may increase the probability of spillover infections to humans especially when humans and bats have direct contact as the case in this study site. However, further screening for these viruses in humans will fully indicate their zoonotic potential.

Current Advances on Virus Discovery and Diagnostic Role of Viral Metagenomics in Aquatic Organisms

The global expansion of the aquaculture industry has brought with it a corresponding increase of novel viruses infecting different aquatic organisms. These emerging viral pathogens have proved to be a challenge to the use of traditional cell-cultures and immunoassays for identification of new viruses especially in situations where the novel viruses are unculturable and no antibodies exist for their identification. Viral metagenomics has the potential to identify novel viruses without prior knowledge of their genomic sequence data and may provide a solution for the study of unculturable viruses. This review provides a synopsis on the contribution of viral metagenomics to the discovery of viruses infecting different aquatic organisms as well as its potential role in viral diagnostics. High throughput Next Generation sequencing (NGS) and library construction used in metagenomic projects have simplified the task of generating complete viral genomes unlike the challenge faced in traditional methods that use multiple primers targeted at different segments and VPs to generate the entire genome of a novel virus. In terms of diagnostics, studies carried out this far show that viral metagenomics has the potential to serve as a multifaceted tool able to study and identify etiological agents of single infections, co-infections, tissue tropism, profiling viral infections of different aquatic organisms, epidemiological monitoring of disease prevalence, evolutionary phylogenetic analyses, and the study of genomic diversity in quasispecies viruses. With sequencing technologies and bioinformatics analytical tools becoming cheaper and easier, we anticipate that metagenomics will soon become a routine tool for the discovery, study, and identification of novel pathogens including viruses to enable timely disease control for emerging diseases in aquaculture.

First characterization of viruses from freshwater snails of the genus Biomphalaria, the intermediate host of the parasite Schistosoma mansoni

We report the genome sequence and organization of five viruses infecting snails of both Biomphalaria glabrata and Biomphalaria pfeifferi, which are vectors of the intestinal schistosomiasis. Four viruses presented a polyadenylated positive single strand RNA genome encoding one or two large open reading frames (ORFs) flanked by untranslated region. Conserved protein motifs typical of the picorna-like virus superfamily were identified in these viruses but they all presented different genome organization. Phylogenetic analysis confirmed their assignment to this superfamily. The partially characterized fifth virus presented sequence similarity for Totiviridae, a family of non-polyadenylated double-strand RNA viruses. Virus distribution and relative abundance between the five strains of Biomphalaria originating from different geographical areas was determined. Our results provide valuable information of new viruses from Biomphalaria and pave the way for future studies dedicated to their impact on snail fitness and Biomphalaria/Schistosoma interactions.

Identification of further diversity among posaviruses

Recently, there have been reports of new members of posavirus-like viruses in the order Picornavirales. In this study, using a metagenomics approach, 11 posavirus-like sequences (>7,000 nucleotides) were detected in 155 porcine fecal samples. Phylogenetic analysis revealed that the newly identified virus sequences, together with other posavirus-like viruses, form distinct clusters within the order Picornavirales, composed of eight genogroups and unassigned sequences based on amino acid sequences of the helicase and RNA-dependent RNA polymerase regions, with <40 % and <50 % sequence identity, respectively. We propose further classifications of highly diverse posavirus populations based on newly identified sequences from Japanese pig feces.

A novel genus in the order Picornavirales detected in human stool

Recently, four new viruses belonging to an unassigned family within the order Picornavirales were identified in excrements of healthy carp (fisavirus) and pigs (posavirus 1, 2 and 3). We report the detection and characterization of a fifth virus present in human faeces. The virus, named human stool-associated RNA virus (husavirus), contains a single ORF encoding a putative 2993 AA polyprotein, with a Hel-Pro-Pol replication block, typical for the Picornavirales. Phylogenetic analysis revealed that the closest relative to husavirus is posavirus 1, and together they cluster with fisavirus, posavirus 2 and 3 and a roundworm (Ascaris suum) derived virus. Husavirus was detected in eight human stool samples collected in 1984 (n52), 1985 (n54), 1995 (n51) and 2014 (n51). From three strains of husavirus from 1984 and 1985 the full genome sequence was determined, showing less than 5% intraspecies variation in the nucleotide composition. The host of this virus remains to be determined.

Highly diverse posaviruses in swine faeces are aquatic in origin

Posaviruses are a group of highly divergent viruses identified in swine faeces that are distantly related to other members of the order Picornavirales. Eighteen posavirus genomes were assembled from 10 out of 25 (40 %) faecal-swab pools collected from healthy adult swine. Phylogenetic analysis of the conserved RNA-dependent RNA polymerase (Pol) domain found that posaviruses form a large, highly diverse, monophyletic clade, which includes similar viruses identified in human (husavirus) and fish (fisavirus) faeces or intestinal contents, respectively. Quantitative reverse transcription PCR analysis of water samples collected from commercial swine barns identified four out of 19 (21 %) samples were positive using a 5'-nuclease assay targeting the Pol region of posavirus 1. ICPD (immunoprecipitation coupled to PCR detection) assays to explore serological evidence of posavirus infection found only a single positive sample, suggesting posaviruses do not commonly infect swine, and together these results suggests a likely aquatic host.

Identification of a novel Picornavirales virus distantly related to posavirus in swine feces

De novo assembly of metagenomic sequencing reads from feces from a clinically normal pig identified two approximately 9 kb contigs which each consisted of a single large open reading frame. While one contig encoded a predicted 2990 amino acid protein with 83 % identity to the recently described posavirus 1, the other contig encoded a predicted 2942 amino acid protein with only 25 % identity limited to the genomic region encoding the RNA-dependent RNA polymerase (RdRp) of posavirus 2. Besides RdRp, search of the conserved domain database identified domains associated with picornavirus capsid proteins but failed to identify picornaviral helicase and proteinase domains. In addition, a domain representing a family of Mycoplasma and Ureaplasma immunoglobulin-blocking virulence proteins was identified near the 5'-terminus. Phylogenetic analysis found a distant relationship between this novel virus, provisionally named posavirus 3, to the unclassified posaviruses and fisavirus which are proposed to represent different genera in a novel family of the Picornavirales.