A novel avian virus with trisegmented double-stranded RNA and further observations on previously described similar viruses with bisegmented genome

Picobirnaviruses in animals: a review

Picobirnaviruses (PBVs) are small non enveloped viruses with bi-segmented ds RNA. They have been observed in a wide variety of vertebrates, including mammals and birds with or without diarrhoea, as well as in sewage samples since its discovery (1988). The source of the viruses is uncertain. True hosts of PBVs and their role as primary pathogens or secondary opportunistic agents or innocuous viruses in the gut remains alien. The mechanisms by which they play a role in pathogenicity are still unclear based on the fact that they can be found in both symptomatic and asymptomatic cases. There is a need to determine their tropism since they have not only been associated with viral gastroenteritis but also been reported in the respiratory tracts of pigs. As zoonotic agents with diverse hosts, the importance of epidemiological and surveillance studies cannot be overstated. The segmented genome of PBV might pose a serious public health issue because of the possibility of continuous genetic reassortment. Aware of the growing attention being given to emerging RNA viruses, we reviewed the current knowledge on PBVs and described the current status of PBVs in animals.

Epidemiologic Status of Picobirnavirus in India, A Less Explored Viral Disease

Since the unexpected discovery of picobirnaviruses (PBV) in 1988, they have been reported in many animals including mammals and birds, which comprises both terrestrial and marine species. Due to their divergent characteristics to other viral taxa they are classified into a new family Picobirnaviridae. Although their pathogenicity and role in causing diarrhea still remains a question since they have been discovered in symptomatic and asymptomatic cases both. Recent studies employing state-of-art molecular tools have described their presence in various clinical samples, like stool samples from different mammals and birds, respiratory tracts of pigs and humans, sewage water, different foods, etc. Furthermore, their epidemiological status from different parts of the world in different hosts has also increased. Due to their diverse host and irregular host pattern their role in causing diarrhea remains alien. The heterogeneity nature can be ascribed to segmented genome of PBV, which renders them prone to continuous reassortment. Studies have been hampered on PBVs due to their non-adaptability to cell culture system. Here, we describe the molecular epidemiological data on PBVs in India and discusses the overall status of surveillance studies carried out till date in India.

Prevalence and complete genome characterization of turkey picobirnaviruses

The "light turkey syndrome" (LTS), in which birds weigh less than their standard breed character at the marketing time, is believed to be a consequence of viral enteritis at an early age (3-5 weeks) from which the birds never fully recover. In a previously published study, we collected fecal pools from 2, 3, 5 and 8 week old turkey poults (80 pools from LTS farms and 40 from non-LTS farms) and examined them for the presence of astro-, rota-, reo-, and coronaviruses. To determine the presence of additional enteric viruses, we analyzed a fecal pool by Illumina sequencing and found picobirnavirus (PBV). Segments 1 and 2 of this virus shared 45.8%aa and 60.9-64.5%aa identity with genogroup I of human PBV, respectively. Primers based on RNA-dependent RNA polymerase and capsid genes were designed for detection and molecular characterization of PBVs in the 120 fecal pools described above. From LTS farms, 39 of 80 (48.8%) pools were PBV positive while 23 of 40 (57.5%) were positive from non-LTS farms. The phylogenetic analysis of 15 randomly selected strains divided them into four subgroups within genogroup I (subgroups 1A-D). Nine strains were in subgroup IA showing 69.9-76.4%nt identity with human PBV GI strainVS111 from the Netherlands. Strains in subgroup IB (n=2) had 91.4-91.7%nt identity with chicken PBV GI strain AVE 42v1 from Brazil. Two strains in subgroup IC had 72.3-74.2%nt identity with chicken PBV strain AVE 71v3 from Brazil. In subgroup ID, two strains showed 72.4-81.8%nt identity with chicken PBV GI strain AVE 57v2 from Brazil. Subgroup IC and ID were the most divergent. Five of the 15 strains were typed using capsid gene primers. They showed 32.6-33.4%nt and 39.5-41.3%aa identity with VS10 human PBV strain. These results indicate co-circulation of divergent strains of PBVs among Minnesota turkeys.

Epidemiology, phylogeny, and evolution of emerging enteric Picobirnaviruses of animal origin and their relationship to human strains

Picobirnavirus (PBV) which has been included in the list of viruses causing enteric infection in animals is highly versatile because of its broad host range and genetic diversity. PBVs are among the most recent and emerging small, nonenveloped viruses with a bisegmented double-stranded RNA genome, classified under a new family “Picobirnaviridae.” PBVs have also been detected from respiratory tract of pigs, but needs further close investigation for their inhabitant behavior. Though, accretion of genomic data of PBVs from different mammalian species resolved some of the ambiguity, quite a few questions and hypotheses regarding pathogenesis, persistence location, and evolution of PBVs remain unreciprocated. Evolutionary analysis reveals association of PBVs with partitiviruses especially fungi partitiviruses. Although, PBVs may have an ambiguous clinical implication, they do pose a potential public health concern in humans and control of PBVs mainly relies on nonvaccinal approach. Based upon the published data, from 1988 to date, generated from animal PBVs across the globe, this review provides information and discussion with respect to genetic analysis as well as evolution of PBVs of animal origin in relation to human strains.

Molecular and phylogenetic analysis of a novel turkey-origin picobirnavirus

A previous metagenomic analysis of the turkey gut RNA virus community identified novel enteric viruses that may play roles in poultry enteric diseases or in performance problems noted in the field. As part of the molecular characterization of these novel enteric viruses, a reverse transcriptase-PCR diagnostic assay was developed, targeting a novel turkey-origin picobirnavirus (PBV) initially identified in a pooled intestinal sample from turkey poults in North Carolina. Little detailed molecular information exists regarding the family Picobirnaviridae, particularly for the PBVs that have been described in avian species. This diagnostic assay targets the turkey PBV RNA-dependent RNA polymerase gene and produces an 1135-bp amplicon. This assay was validated using in vitro transcribed RNA and was tested using archived enteric samples collected from turkey flocks in the southeastern United States. Further, a phylogenetic analysis suggests the turkey PBV is unique because it does not group closely with the recognized PBV genogroups circulating in mammalian hosts.

Animal picobirnavirus

Picobirnavirus (PBV) is a small, non-enveloped, bisegmented double-stranded RNA (dsRNA) virus of vertebrate hosts. The name 'Picobirnavirus' derives from the prefix 'pico' (latin for 'small') in reference to the small virion size, plus the prefix 'bi' (latin for 'two') and the word 'RNA' to indicate the nature of the viral genome. The serendipitous discovery of PBV dates back to 1988 from Brazil, when human fecal samples collected during the acute gastroenteritis outbreaks were subjected for routine rotavirus surveillance by polyacrylamide gel electrophoresis (PAGE) and silver straining (S/S). The PAGE gels after silver staining showed a typical 'two RNA band' pattern, and it was identified as Picobirnavirus. Likewise, the feces of wild black-footed pigmy rice rats (Oryzomys nigripes) subjected for PAGE assay by the same research group in Brazil reported the presence of PBV (Pereira et al., J Gen Virol 69:2749-2754, 1988). PBVs have been detected in faeces of humans and wide range of animal species with or without diarrhoea, worldwide. The probable role of PBV as either a 'primary diarrhoeal agent' in 'immunocompetent children'; or a 'potential pathogen' in 'immunocompromised individuals' or an 'innocuous virus' in the intestine remains elusive and needs to be investigated despite the numerous reports of the presence of PBV in fecal samples of various species of domestic mammals, wild animals, birds and snakes; our current knowledge of their biology, etiology, pathogenicity or their transmission characteristics remains subtle. This review aims to analyse the veterinary and zoonotic aspects of animal Picobirnavirus infections since its discovery.

Genogroup I avian picobirnavirus detected in Brazilian broiler chickens: a molecular epidemiology study

Picobirnavirus (PBV) belongs to the family Picobirnaviridae. Picobirnaviruses contain a bisegmented dsRNA genome that is non-enveloped. A total of 85 pooled faecal samples were collected from the poultry of 37 farms from the Metropolitan Mesoregion of Belém (MMB), Pará state, Brazil. The viral RNA from each sample was analysed by PAGE and reverse transcriptase PCR (RT-PCR). For each county affected, at least one positive sample was selected, cloned and sequenced. The samples showed a positivity of 15.3 % (13/85) by PAGE and 49.4 % (42/85) by RT-PCR. Sequencing of these strains demonstrated a considerable RdRp gene heterogeneity that ranged from 56.1 to 100 % at the nucleotide level compared with prototypes of different species and water sewage, and from 50.3 to 100 % among themselves. Avian picobirnavirus (AvPBV) was detected in MMB broiler farms and showed a heterogeneous relationship with the prototypes used. This report includes what is believed to be the first gene sequencing of AvPBV in Brazilian broiler chickens.

Simian genogroup I picobirnaviruses: prevalence, genetic diversity, and zoonotic potential

We previously reported the first detection of simian picobirnaviruses (PBVs) by polyacrylamide gel electrophoresis in fecal specimens of two monkeys with diarrhea in China. We now report the detection of genogroup I PBVs in 48% (44/92) of the fecal specimens by reverse transcriptase PCR (RT-PCR) and amplicon sequencing using primers specific for the RNA-dependent RNA polymerase (RDRP) gene. Molecular characterization of these 44 strains demonstrated both sequence conservation and diversity among simian PBVs and among simian, porcine, and human PBVs. We further determined full-length sequences of segment 2 of the two simian PBV strains, monkey/CHN-14/2002 and monkey/CHN-49/2002, and demonstrated 52.5% to 54.2% nucleotide sequence similarity to the corresponding gene of the bovine strain RUBV and the prototype human strain 1-CHN-97 of genogroup I PBVs and an even lower similarity (38.4%) to segment 2 of the prototype human genogroup II strain 4-GA-91. Further studies are needed to investigate the epidemiology and pathogenesis of PBVs in animals and humans.

Picobirnavirus infections: viral persistence and zoonotic potential

Picobirnaviruses (PBVs) are small, non-enveloped, bisegmented double-stranded RNA genomic viruses of vertebrate hosts. Since their discovery in the late 1980s in clinical specimens from outbreaks of acute gastroenteritis in children, significant efforts have been made to investigate the role of PBV in diarrheic diseases. PBV has been detected in sporadic episodes of diarrhea as sole pathogen or coinfection as well as in outbreaks of acute gastroenteritis and in immunocompromised patients with diarrhea. However, PBV is frequently detected in non-diarrheic healthy hosts, and prolonged shedding has been observed in some individuals. Of interest, similar patterns of PBV infection have also been observed in pigs and other animal hosts. The increasing amount of PBV sequence data gathered from molecular epidemiological studies has evidenced a great sequence diversity of PBVs in various hosts and environmental samples. Importantly, evidence has been found for genetic relatedness between human and animal PBV strains, suggesting extant crossing points in the ecology and evolution of heterologous PBV strains. At present, no cell culture and animal model exists for PBVs. Well-structured epidemiological studies are still the only alternative to demonstrate the potential etiological role of PBVs in acute gastroenteritis or other diseases. This review aims to analyze the public health aspects of PBV infection, especially its possible association with zoonosis.

The picobirnavirus: an integrated view on its biology, epidemiology and pathogenic potential

Picobirnaviruses (PBV) are a group of small, nonenveloped viruses with bi-segmented dsRNA genomes. The large genomic segment encodes for the capsid protein while the small segment encodes for the RNA-dependent RNA polymerase. PBV are widely distributed and have been detected in the feces of a large variety of vertebrate species, including farm and captive animals and also in humans. Their etiological role as a cause of diarrhea remains elusive. Still, compelling evidence indicates that PBV may be opportunistic pathogens associated with diarrhea in immunocompromised individuals. The partial molecular characterization of human and animal strains revealed that PBVs are highly variable, and at least two distinct genogroups have been recognized. In addition, the possibility of interspecies transmission has been suggested. This article examines the molecular epidemiology and the biology of PBV and highlights the major challenges in the field.

Metagenomic analysis of the turkey gut RNA virus community

Viral enteric disease is an ongoing economic burden to poultry producers worldwide, and despite considerable research, no single virus has emerged as a likely causative agent and target for prevention and control efforts. Historically, electron microscopy has been used to identify suspect viruses, with many small, round viruses eluding classification based solely on morphology. National and regional surveys using molecular diagnostics have revealed that suspect viruses continuously circulate in United States poultry, with many viruses appearing concomitantly and in healthy birds. High-throughput nucleic acid pyrosequencing is a powerful diagnostic technology capable of determining the full genomic repertoire present in a complex environmental sample. We utilized the Roche/454 Life Sciences GS-FLX platform to compile an RNA virus metagenome from turkey flocks experiencing enteric disease. This approach yielded numerous sequences homologous to viruses in the BLAST nr protein database, many of which have not been described in turkeys. Our analysis of this turkey gut RNA metagenome focuses in particular on the turkey-origin members of the Picornavirales, the Caliciviridae, and the turkey Picobirnaviruses.

Picobirnavirus causes persistent infection in pigs

A study aimed to further understand the biology of porcine picobirnaviruses (PBV) was conducted between November 2003 and January 2008, on a farm located in the outskirts of Córdoba City, Argentina. PBV prevalence was examined by polyacrylamide gel electrophoresis and silver staining (PAGE S/S) on a total of 265 samples collected from pigs divided into four groups, according to age and physiological status. PBV detection rate was highest in the group of sows sampled within the lactogenic period (38.02%; p<0.05), followed by pregnant sows (15.09%), piglets aged 2-5 months of age (18.42%) and adult (> or =50 weeks) male pigs (0%). In addition, 103 samples collected in 3 follow-up studies were analyzed by PAGE S/S and reverse transcription followed by PCR (RT-PCR). Two of these studies followed female pigs from weaning up to slaughter and a third one from weaning up to 4 pregnancy periods. The results provide evidence that PBV establishes a persistent infection in the host with periods of silence intermingled with periods of low and high viral excretion. High PBV excretion levels were detected by PAGE S/S and were conditioned by age (primary infection) and host physiological status. Low PBV excretion levels were detected by RT-PCR throughout the entire study period. Sequence analysis of selected amplicons indicated that the virus excreted through the follow-up study was the same. These results suggest that porcine PBV is maintained in nature by transmission from infected asymptomatic individuals to susceptible ones.

Nomenclature proposal for picobirnavirus

Picobirnaviruses have been identified in the feces of a broad range of hosts by several international research groups. Because there is no standard nomenclature for these viruses, we propose a clear and unique name for each strain.

Molecular characterization of full-length genomic segment 2 of a bovine picobirnavirus (PBV) strain: evidence for high genetic diversity with genogroup I PBVs

We report here the molecular characterization of a bovine genogroup I picobirnavirus strain RUBV-P detected from a 1-month-old diarrhoeic calf in eastern India. Sequence comparisons and phylogenetic analysis of a short stretch of gene segment 2 of RUBV-P revealed low nucleotide identities (51.2-64.9%) with and distant genetic relatedness to other genogroup I picobirnaviruses. The complete gene segment 2 sequence of RUBV-P was obtained by the single primer amplification method with modifications. Gene segment 2 of RUBV-P was 1758 bp long, encoded a predicted protein of 554 aa and exhibited low nucleotide (58.1-58.8%) and amino acid (51.3-55.4%) identities with genogroup I human strains Hy005102 and 1-CHN-97. The 5'- and 3'-end nucleotide sequences, and the three motifs of RNA-dependent RNA polymerases of double-stranded RNA viruses, were conserved among these strains. Our findings suggested that bovine strain RUBV-P might be distinct from genogroup I picobirnaviruses of humans and other animals.

Molecular characterization of porcine picobirnaviruses and development of a specific reverse transcription-PCR assay

The molecular characterization of partial- length genomic segment 2 of porcine picobirnavirus (PBV) strains and the development of a specific reverse transcription-PCR (RT-PCR) assay for detection of virus in feces are reported. Phylogenetic analysis indicated that the studied porcine isolates were more closely related (>85% identity) to human PBV belonging to genogroup I than to the other porcine PBV described so far. Analysis by RT-PCR and polyacrylamide gel electrophoresis of fecal samples collected in Venezuela and Argentina showed that PBV circulate at high frequencies in piglets.

Picobirnavirus (PBV) natural hosts in captivity and virus excretion pattern in infected animals

A picobirnavirus (PBV) analysis was carried out by polyacrylamide gel electrophoresis of 513 stool samples obtained from 150 animal species collected from the Córdoba city zoo. The purpose of the present study was to determine susceptible species for PBV infection, the viral excretion pattern in infected animals, and the potential association with PBV diarrheic illness. Our findings suggest that PBVs are widespread in animals and could have a similar excretion behavior to that previously detected in infected humans. No disease association with PBV infection could be demonstrated. Thus, infected animals could be persistently infected asymptomatic carriers and could serve as reservoirs of infection.

[Picobirnavirus]

Picobirnavirus is named after the small birnavirus which contains two double-stranded RNA segments as a genome. However, their properties are quite different to each other. Although the virus has been detected mainly from the stools of gastroenteritis patients and several mammals and birds, the pathogenicity of the virus has not been established. Characterizations of the virus are hampered due to the lack in the system for multiplication of the virus in cultured cells or experimental animals. Recently, complete nucleotide sequences of two RNA segments of a human picobirnavirus detected in Thailand were determined.

Complete nucleotide sequences of two RNA segments of human picobirnavirus

Picobirnaviruses are unclassified, non-enveloped, spherical, small viruses with a genome comprising two double-stranded RNA segments. Only incomplete sequence data on picobirnaviruses are available so far. By cloning involving single primer amplification, full-length cDNAs were prepared corresponding to RNA segments 1 and 2 of a picobirnavirus (strain Hy005102) isolated from a stool specimen from an infant with acute non-bacterial gastroenteritis in Thailand, and the complete nucleotide sequences were determined. RNA segments 1 and 2 are 2,525 and 1,745 base pairs in length, respectively. RNA segment 1 encodes two open reading frames (ORFs) of 224 and 552 amino acids, and RNA segment 2 codes for a single ORF of 534 amino acids. On comparison with a part of the nucleotide sequences of the RNA segment, 2 of the other published picobirnavirus strains, the Thai strain was found to be related most closely to one of the US strains.

Molecular diversity of partial-length genomic segment 2 of human picobirnavirus

OBJECTIVES

This study was carried out in order to evaluate the efficacy of the recently developed picobirnavirus (PBV) sets of primers and to establish the phylogenetic relationships of Argentine strains with PBV strains isolated in China and the USA.

METHODS

Thirteen fecal specimens tested as positive for PBV by polyacrylamide gel electrophoresis were analyzed by reverse transcription-polymerase chain reaction assays using primers target to the genomic segments 2 of PBV strains isolated in China and the USA. The amplicons were sequenced and analyzed.

RESULTS

Primers derived from the China strain produced amplicons in only 4 of the 13 specimens (30.76%). No sample was revealed as positive with the primers derived from the US strain. DNA sequencing of polymerase chain reaction products differed in nucleic acid and amino acid sequences by 13.9-42.28% and 18.1-51.1%, respectively. Despite this strain diversity, three domains of conserved nucleotide sequences as well as the amino acid motif D-S-D typical of RNA-dependent RNA polymerase gene of double-strand RNA viruses were identified. Comparatively, these conserved regions were also identified in homologous PBV strains from the USA and China. Phylogenetic analysis showed no time or geographic clustering.

CONCLUSIONS

These findings provide evidence that PBV may represent an emerging heterogeneous group of viruses.

Other viruses causing gastroenteritis

Besides the viruses producing the majority of human viral gastroenteritis, other viruses infect more rarely but are sometimes able to cause epidemics. In particular, they cause chronic infection in the immunocompromised. Some of these viruses discussed in this chapter are toroviruses, picobirnaviruses, enteroviruses, human immunodeficiency virus (HIV), herpesviruses, and coronaviruses. Toroviruses make up a genus of the Coronaviridae family. They are a well-described cause of diarrhea in calves and horses but may also infect sheep, goats, and pigs. Picobirnaviruses are related to members of the Birnaviridae family. They are found in the feces of HIV-infected patients with diarrhea more frequently than in HIV-infected patients without diarrhea, but a virus-specific immune response was not measurable. The genus Enterovirus is of the Picornaviridae family. All enteroviruses infect man via the gastrointestinal tract where they have their first site of replication, probably in lymphoid tissues of the pharynx and gut. HIV, the causative agent of the acquired immunodeficiency syndrome (AIDS), is a member of the Lentivirus genus of the Retroviridae family. Cytomegalovirus (CMV) and herpes simplex viruses, members of the Herpesviridae family, are found as the cause of colitis and esophagitis, mainly in HIV-infected patients. Coronavirus is another genus of the Coronaviridae family. Coronaviruses infect the respiratory and gastrointestinal tracts. They are a recognized cause of the common cold in man.

Cloning of human picobirnavirus genomic segments and development of an RT-PCR detection assay

Nearly full-length genomic segments 2 and a partial-length genomic segment 1 of human picobirnavirus were cloned and sequenced. The clones were derived from viruses obtained from human immunodeficiency virus (HIV)-infected patients in Atlanta, Georgia (strains 3-GA-91 and 4-GA-91) and a nonHIV-infected person from China (strain 1-CHN-97). The picobirnavirus genomic segments lacked sequence similarities with other viral sequences in GenBank and EMBL. Comparison of genomic segment 1 from a human and a rabbit picobirnavirus identified a region of 127 nucleotides with 54.7% identity. The genomic segments 2 of the 4-GA-91 and 1-CHN-97 strains had 41.4% nucleic acid identity and 30.0% amino acid similarity and contained amino acid motifs typical of RNA-dependent RNA polymerase genes. Reverse transcription-PCR detection assays were developed with primers targeted to the genomic segments 2 of strains 4-GA-91 or 1-CHN-97. Picobirnaviruses related to the China strain were the predominant viruses detected in stool samples from people in four countries on three continents. Picobirnaviruses were detected in samples from two outbreaks of gastroenteritis in long-term elder care facilities but were not determined to be the primary pathogen. Our findings support the view that picobirnaviruses constitute a distinct family of viruses.

Identification of picobirnavirus, viruses with bisegmented double stranded RNA, in rabbit faeces

Picobirnaviruses are a novel group of viruses recently found in the faeces of several species of vertebrates. Examination by polyacrylamide gel electrophoresis of rabbit faecal samples collected in one animal facility revealed the viruses in 23 (11 per cent) of 211 samples. Further analysis by electron microscopy and caesium chloride isopycnic centrifugation confirmed the presence of picobirnaviruses in the samples. The oral inoculation of three newly weaned rabbits with purified viruses resulted in the excretion of a virus with an electropherotype similar to the inoculum, by two of the three inoculated animals. Maximal viral shedding was detected 13 days after inoculation. No sign of diarrhoea was observed either in the inoculated animals or in the virus excreting animals surveyed. No antibody activity could be detected in the paired serum samples taken from the inoculated animals.

Detection and characterisation of bisegmented double-stranded RNA viruses (picobirnaviruses) in human faecal specimens

The prevalence of picobirnaviruses (PBVs) in human stools was investigated by polyacrylamide gel electrophoresis (PAGE) analysis of 832 faecal specimens collected between 1982 and 1993 from patients in various clinical groups. Similar prevalences (9-13%) were detected in patients with or without gastroenteritis and throughout the age range of 3 to > 65 years. Two methods for the extraction of nucleic acid, a phenol/chloroform method and a guanidinium thiocynate (GTC)/silica method, were compared. Detection of PBVs by PAGE was three times more sensitive following RNA extraction by the GTC/silica method. Characterisation of three strains was carried out. Segment sizes ranged from 1.625 to 1.95 kilo base pairs (Kbp) and 2.2 to 2.5 Kbp for the fast and slow migrating bands, respectively. The nuclic acid was shown to be double-stranded RNA (dsRNA) by nuclease digestion. PBV-like particles were detected by electron microscopy in two PAGE-positive stools. Virion diameters ranged from 35 to 41 nm and a buoyant density of 1.38-1.4 g/ml in caesium chloride (CsCl) was demonstrated. These findings suggest that PBVs are widespread in humans in the United Kingdom. However, no disease association could be demonstrated.

Identification of viruses with bi- and trisegmented double-stranded RNA genome in faeces of children with gastroenteritis

Polyacrylamide gel electrophoresis of nucleic acid extracted from faecal samples of diarrhoeic children revealed the presence of group A rotavirus in 50 (23.4%) samples and group C rotavirus in 1 (0.5%) sample out of 214 tested. One other sample showed the presence of three bands (with apparent length of 2.92, 2.37 and 1.32 kbp) which by enzymatic digestion analysis, were shown to consist of double-stranded RNA (dsRNA). The sample was shown by electron microscopy to contain virus particles with a diameter of 32-34 nm. On the basis of morphology and genomic characteristics, this virus closely resembles a virus hitherto described only in chickens by Leite et al. in 1990 and tentatively named "picotrirnavirus". From the same group of 214, one sample containing a "picobirnavirus" was also identified. Thus, small icosahedral viruses with either a bior trisegmented dsRNA genome appear to infect humans. However, their pathogenic potential remains to be established.

Identification in porcine faeces of a novel virus with a bisegmented double stranded RNA genome

Polyacrylamide gel electrophoresis of nucleic acids extracted from porcine faecal samples revealed in several samples the presence of two discrete bands. The bands were resistant to digestion with of DNase I and RNase T1, but not with RNase A in low salt conditions, indicating that they consisted of double stranded (ds) RNA. The two bands from different samples varied in sizes, in a range between 2.4-2.6 kbp and 1.7-1.9 kbp for the slow and fast moving band respectively. The bands cosedimented in CsCl gradients at an average density of 1.415 g/ml with icosahedral virus particles of a diameter of 34 nm and a triangulation number equal to 3. Aggregates of virus, which appeared to be immunocomplexes, were seen in one sample. From 244 faecal samples collected in one farm, 27 (11.1%) were found to contain the characteristic dsRNA pattern, with a higher prevalence in samples from animals 15 to 35 days old. The agent was equally distributed among samples from diarrhoeic or non-diarrhoeic animals. These results confirm the circulation among pigs of a novel virus, possibly of vertebrates, with a bisegmented double stranded RNA genome, similar to viruses previously described in humans, wild rats, guinea pigs, pigs, and chickens, for which the name "picobirnavirus" has been proposed.