Genetic characterization of a new mammalian reovirus, type 2 Winnipeg (T2W)

Mammalian orthoreoviruses exhibit rare genotype variability in genome constellations

Mammalian orthoreoviruses (reoviruses) are currently classified based on properties of the attachment protein, σ1. Four reovirus serotypes have been identified, three of which are represented by well-studied prototype human reovirus strains. Reoviruses contain ten segments of double-stranded RNA that encode 12 proteins and can reassort during coinfection. To understand the breadth of reovirus genetic diversity and its potential influence on reassortment, the sequence of the entire genome should be considered. While much is known about the prototype strains, a thorough analysis of all ten reovirus genome segment sequences has not previously been conducted. We analyzed phylogenetic relationships and nucleotide sequence conservation for each of the ten segments of more than 60 complete or nearly complete reovirus genome sequences, including those of the prototype strains. Using these relationships, we defined genotypes for each segment, with minimum nucleotide identities of 77-88% for most genotypes that contain several representative sequences. We applied segment genotypes to determine reovirus genome constellations, and we propose implementation of an updated reovirus genome classification system that incorporates genotype information for each segment. For most sequenced reoviruses, segments other than S1, which encodes σ1, cluster into a small number of genotypes and a limited array of genome constellations that do not differ greatly over time or based on animal host. However, a small number of reoviruses, including prototype strain Jones, have constellations in which segment genotypes differ from those of most other sequenced reoviruses. For these reoviruses, there is little evidence of reassortment with the major genotype. Future basic research studies that focus on the most genetically divergent reoviruses may provide new insights into reovirus biology. Analysis of available partial sequences and additional complete reovirus genome sequencing may also reveal reassortment biases, host preferences, or infection outcomes that are based on reovirus genotype.

Isolation and characterization of mammalian orthoreovirus from bats in the United States

Mammalian orthoreovirus (MRV) infects many mammalian species including humans, bats, and domestic animals. To determine the prevalence of MRV in bats in the United States, we screened more than 900 bats of different species collected during 2015-2019 by a real-time reverse-transcription polymerase chain reaction assay; 4.4% bats tested MRV-positive and 13 MRVs were isolated. Sequence and phylogenetic analysis revealed that these isolates belonged to four different strains/genotypes of viruses in Serotypes 1 or 2, which contain genes similar to those of MRVs detected in humans, bats, bovine, and deer. Further characterization showed that these four MRV strains replicated efficiently on human, canine, monkey, ferret, and swine cell lines. The 40/Bat/USA/2018 strain belonging to the Serotype 1 demonstrated the ability to infect and transmit in pigs without prior adaptation. Taken together, this is evidence for different genotypes and serotypes of MRVs circulating in US bats, which can be a mixing vessel of MRVs that may spread to other species, including humans, resulting in cross-species infections.

Isolation and pathogenicity analysis of mink orthoreoviruses

Mammalian orthoreoviruses (MRVs) can infect many mammals including human, and numerous higher virulent MRVs have been reported in recent years. The first mink orthoreovirus was reported in China in 2011. In the present study, three new strains of mammalian orthoreoviruses were isolated from mink and found to be most closely related to human strain MRV2Tou05 and other human strains. Mink experiments demonstrated that the isolated mink reoviruses did not lead to severe pathogenicity. Viruses were eliminated within 2 weeks after infection, but they may cause viral enteritis disease in puppies.

Unexpected Genetic Diversity of Two Novel Swine MRVs in Italy

Mammalian Orthoreoviruses (MRV) are segmented dsRNA viruses in the family Reoviridae. MRVs infect mammals and cause asymptomatic respiratory, gastro-enteric and, rarely, encephalic infections. MRVs are divided into at least three serotypes: MRV1, MRV2 and MRV3. In Europe, swine MRV (swMRV) was first isolated in Austria in 1998 and subsequently reported more than fifteen years later in Italy. In the present study, we characterized two novel reassortant swMRVs identified in one same Italian farm over two years. The two viruses shared the same genetic backbone but showed evidence of reassortment in the S1, S4, M2 segments and were therefore classified into two serotypes: MRV3 in 2016 and MRV2 in 2018. A genetic relation to pig, bat and human MRVs and other unknown sources was identified. A considerable genetic diversity was observed in the Italian MRV3 and MRV2 compared to other available swMRVs. The S1 protein presented unique amino acid signatures in both swMRVs, with unexpected frequencies for MRV2. The remaining genes formed distinct and novel genetic groups that revealed a geographically related evolution of swMRVs in Italy. This is the first report of the complete molecular characterization of novel reassortant swMRVs in Italy and Europe, which suggests a greater genetic diversity of swMRVs never identified before.

Replication and Oncolytic Activity of an Avian Orthoreovirus in Human Hepatocellular Carcinoma Cells

Oncolytic viruses are cancer therapeutics with promising outcomes in pre-clinical and clinical settings. Animal viruses have the possibility to avoid pre-existing immunity in humans, while being safe and immunostimulatory. We isolated an avian orthoreovirus (ARV-PB1), and tested it against a panel of hepatocellular carcinoma cells. We found that ARV-PB1 replicated well and induced strong cytopathic effects. It was determined that one mechanism of cell death was through syncytia formation, resulting in apoptosis and induction of interferon stimulated genes (ISGs). As hepatitis C virus (HCV) is a major cause of hepatocellular carcinoma worldwide, we investigated the effect of ARV-PB1 against cells already infected with this virus. Both HCV replicon-containing and infected cells supported ARV-PB1 replication and underwent cytolysis. Finally, we generated in silico models to compare the structures of human reovirus- and ARV-PB1-derived S1 proteins, which are the primary targets of neutralizing antibodies. Tertiary alignments confirmed that ARV-PB1 differs from its human homolog, suggesting that immunity to human reoviruses would not be a barrier to its use. Therefore, ARV-PB1 can potentially expand the repertoire of oncolytic viruses for treatment of human hepatocellular carcinoma and other malignancies.

High Incidence of Mammalian Orthoreovirus Identified by Environmental Surveillance in Taiwan

Wild poliovirus (WPV) persists in diverse locales worldwide, spreading outward from endemic areas. In response to the international threat of WPV transmission and changes in the national vaccination policy, we established an environmental surveillance system to monitor the circulation of wild and vaccine-related poliovirus in Taiwan. From July 2012 to December 2013, we collected sewage specimens every month from 10 sewage treatment plants located throughout Taiwan. The specimens were concentrated by the two-phase separation method and then inoculated into L20B, RD, and A549 cells for virus isolation. Viral isolates were identified and serotyped by immunofluorescence assay or molecular analysis. A total of 300 sewage samples were collected, and the results showed 163 samples (54.3%) were positive for virus, and 268 isolates were identified. Among these, 75 samples (25%) were positive for enterovirus (EV), but no poliovirus was found. In addition, 92 isolates were identified as enteroviruses and the most common serotypes were coxsackievirus B4, coxsackievirus B3, and coxsackievirus B2. Interestingly, 102 (34%) and 82 (27.3%) specimens were positive for mammalian orthoreovirus (MRV) and adenovirus, respectively. This study confirmed that sewage surveillance can be a useful additional modality for monitoring the possible presence of wild-type or vaccine-derived poliovirus in wastewater, and can indicate the current types of viruses circulating in the population. Furthermore, since MRV was found in children with acute necrotizing encephalopathy and meningitis, the high incidence of MRV detected by environmental surveillance warrants further investigation.

Serological survey of a new type of reovirus in humans in China

To evaluate the presence of a new type of reovirus (designated R4) in humans, we determined the prevalence of specific antibodies using a neutralization assay and ELISA. The sera from 97 healthy people and 219 patients in our hospital with measles, hand-foot-and-mouth disease, liver diseases, and diarrhoea were investigated. Although the study population was limited, our data suggested that R4 is widespread in the human population. A significantly higher level of R4-specific antibody in patients than in healthy people is worthy of consideration, since it poses a risk for aggravation of the extant illness by the reovirus.

Reovirus-associated meningoencephalomyelitis in baboons

Baboon orthoreovirus (BRV) is associated with meningoencephalomyelitis (MEM) among captive baboons. Sporadic cases of suspected BRV-induced MEM have been observed at Southwest National Primate Research Center (SNPRC) for the past 20 years but could not be confirmed due to lack of diagnostic assays. An immunohistochemistry (IHC)-based assay using an antibody against BRV fusion-associated small transmembrane protein p15 and a conventional polymerase chain reaction (PCR)-based assay using primers specific for BRV were developed to detect BRV in archived tissues. Sixty-eight cases of suspected BRV-induced MEM from 1989 through 2010 were tested for BRV, alphavirus, and flavivirus by IHC. Fifty-nine of 68 cases (87%) were positive for BRV by immunohistochemistry; 1 tested positive for flavivirus (but was negative for West Nile virus and St Louis encephalitis virus by real-time PCR), and 1 virus isolation (VI) positive control tested negative for BRV. Sixteen cases (9 BRV-negative and 7 BRV-positive cases, by IHC), along with VI-positive and VI-negative controls, were tested by PCR for BRV. Three (of 9) IHC-negative cases tested positive, and 3 (of 7) IHC-positive cases tested negative by PCR for BRV. Both IHC and PCR assays tested 1 VI-positive control as negative (sensitivity: 75%). This study shows that most cases of viral MEM among baboons at SNPRC are associated with BRV infection, and the BRV should be considered a differential diagnosis for nonsuppurative MEM in baboons.

Identification of Mammalian orthoreovirus type 3 in Italian bats

Summary This study describes the isolation and molecular characterization of Mammalian orthoreovirus (MRV) in microbats. Faecal samples and dead individuals available from rehabilitation centres or collected from known roost sites were virologically tested. In total, 112 carcasses of bats found dead, and 44 faecal samples were analysed. Nineteen viral strains were isolated by in vitro cell culture from faecal and tissue samples of different bat species (Pipistrellus khulii, Tadarida teniotis, Rhinolophus hipposideros and Vespertilio murinus), and they were morphologically identified as reoviruses by negative staining electron microscopy observation. The definitive assignment of all isolates to MRV was confirmed by RT-PCR assays targeting the L1 gene. Through a multiplex RT-PCR assay targeting the S1 gene, we typed 15 of 19 isolates as MRV type 3. Partial L1 (416 bp) and complete S1 (1416 bp) sequences of the isolates were analysed and compared with those of reference strains obtained from GenBank, belonging to the three serotypes. Molecular analysis of the S1 gene revealed that the amino acid residues associated with neurotropism (198-204NLAIRLP, 249I, 350D and 419E) were highly conserved among the Italian bat strains. These results suggest that potentially neurotropic MRV type 3 strains are widespread among Italian bats. Furthermore, the identification of MRV type 3 in bat species such as Pipistrellus Khulii, which is common in urban areas and known for its close contact with humans, underlines the need for vigilance.

Isolation and characterization of three mammalian orthoreoviruses from European bats

In recent years novel human respiratory disease agents have been described in South East Asia and Australia. The causative pathogens were classified as pteropine orthoreoviruses with strong phylogenetic relationship to orthoreoviruses of flying foxes inhabiting these regions. Subsequently, a zoonotic bat-to-human transmission has been assumed. We report the isolation of three novel mammalian orthoreoviruses (MRVs) from European bats, comprising bat-borne orthoreovirus outside of South East Asia and Australia and moreover detected in insectivorous bats (Microchiroptera). MRVs are well known to infect a broad range of mammals including man. Although they are associated with rather mild and clinically unapparent infections in their hosts, there is growing evidence of their ability to also induce more severe illness in dogs and man. In this study, eight out of 120 vespertilionid bats proved to be infected with one out of three novel MRV isolates, with a distinct organ tropism for the intestine. One isolate was analyzed by 454 genome sequencing. The obtained strain T3/Bat/Germany/342/08 had closest phylogenetic relationship to MRV strain T3D/04, isolated from a dog. These novel reoviruses provide a rare chance of gaining insight into possible transmission events and of tracing the evolution of bat viruses.

Novel human reovirus isolated from children with acute necrotizing encephalopathy

For many encephalitis cases, the cause remains unidentified. After 2 children (from the same family) received a diagnosis of acute necrotizing encephalopathy at Centre Hospitalier Universitaire (Tours, France), we attempted to identify the etiologic agent. Because clinical samples from the 2 patients were negative for all pathogens tested, urine and throat swab specimens were added to epithelial cells, and virus isolates detected were characterized by molecular analysis and electron microscopy. We identified a novel reovirus strain (serotype 2), MRV2Tou05, which seems to be closely related to porcine and human strains. A specific antibody response directed against this new reovirus strain was observed in convalescent-phase serum specimens from the patients, whereas no response was observed in 38 serum specimens from 38 healthy adults. This novel reovirus is a new etiologic agent of encephalitis.

Comparative sequence analyses of a new mammalian reovirus genome and the mammalian reovirus S1 genes from six new serotype 2 human isolates

We previously described isolation of a potentially new mammalian reovirus, designated BYD1, which can cause clinical symptoms similar to that of severe acute respiratory syndrome (SARS) in guinea pigs and macaques, from throat swabs of one SARS patient of Beijing, in 2003. For this study, we determined the genome sequences of BYD1 and the S1 gene sequences of other five mammalian reovirus isolates (BLD, JP, and BYL were isolated from different SARS patients during the outbreak, 302I and 302II were isolated from fecal specimens of two children of Beijing in 1982) to allow molecular comparison with other previously reported mammalian reoviruses (MRVs). Comparative analyses of the BYD1 genome with those of three prototype mammalian reovirus strains demonstrated that BYD1 is a novel reassortant virus, with its S1 gene segment coming from a previously unidentified serotype 2 isolate and other nine segments coming from ancestors of homologous T1L and T3D segments, which supports the hypothesis that mammalian reovirus gene segments reassort in nature. Further analyses of the S1 segments of the six isolates showed that all the isolates are novel serotype 2 MRVs based on their S1 gene sequences, which are markedly different from those of all previously reported, and the S1 genes of the four new isolates share more than 99% identity with each other, proving that they diverged from a common ancestor most recently, and the S1 genes of the four new isolates share about 65% identity with those of the two strains isolated in 1982.