Intertypic reassortment of mammalian orthoreovirus identified in wastewater in Japan

Characterization of a mammalian orthoreovirus isolated from the large flying fox, Pteropus vampyrus, in Indonesia

Fruit bats serve as an important reservoir for many zoonotic pathogens, including Nipah virus, Hendra virus, Marburg virus and Lyssavirus. To gain a deeper insight into the virological characteristics, pathogenicity and zoonotic potential of bat-borne viruses, recovery of infectious viruses from field samples is important. Here, we report the isolation and characterization of a mammalian orthoreovirus (MRV) from a large flying fox (Pteropus vampyrus) in Indonesia, which is the first detection of MRV in Southeast Asia. MRV was recovered from faecal samples of three different P. vampyrus in Central Java. Nucleotide sequence analysis revealed that the genome of the three MRV isolates shared more than 99% nucleotide sequence identity. We tentatively named one isolated strain as MRV12-52 for further analysis and characterization. Among 10 genome segments, MRV12-52 S1 and S4, which encode the cell-attachment protein and outer capsid protein, had 93.6 and 95.1% nucleotide sequence identities with known MRV strains, respectively. Meanwhile, the remaining genome segments of MRV12-52 were divergent with 72.9-80.7 % nucleotide sequence identities. Based on the nucleotide sequence of the S1 segment, MRV12-52 was grouped into serotype 2, and phylogenetic analysis demonstrated evidence of past reassortment events. In vitro characterization of MRV12-52 showed that the virus efficiently replicated in BHK-21, HEK293T and A549 cells. In addition, experimental infection of laboratory mice with MRV12-52 caused severe pneumonia with 75% mortality. This study highlights the presence of pathogenic MRV in Indonesia, which could serve as a potential animal and public health concern.

Identification of multiple inter- and intra-genotype reassortment mammalian orthoreoviruses from Japanese black cattle in a beef cattle farm

Mammalian orthoreoviruses (MRVs), belonging to the genus Orthoreovirus in the family Spinareoviridae, possess a double-stranded RNA segmented genome. Due to the segmented nature of their genome, MRVs are prone to gene reassortment, which allows for evolutionary diversification. Recently, a genotyping system for each MRV gene segment was proposed based on nucleotide differences. In the present study, MRVs were isolated from the fecal samples of Japanese Black cattle kept on a farm in Japan. Complete genome sequencing and analysis of 41 MRV isolates revealed that these MRVs shared almost identical sequences in the L1, L2, L3, S3, and S4 gene segments, while two different sequences were found in the S1, M1, M2, M3, and S2 gene segments. By plaque cloning, at least six genetic constellation patterns were identified, indicating the occurrence of multiple inter- (S1 and M2) and intra- (M1, M3, and S2) reassortment events. This paper represents the first report describing multiple reassortant MRVs on a single cattle farm. These MRV gene segments exhibited sequence similarity to those of MRVs isolated from cattle in the U.S. and China, rather than to MRVs previously isolated in Japan. Genotypes consisting solely of bovine MRVs were observed in the L1, M1, and M2 segments, suggesting that they might have evolved within the cattle population.

Genetic characterization and pathogenicity in a mouse model of newly isolated bat-originated mammalian orthoreovirus in South Korea

Mammalian orthoreoviruses (MRVs) infect a wide range of hosts, including humans, livestock, and wildlife. In the present study, we isolated a novel Mammalian orthoreovirus from the intestine of a microbat (Myotis aurascens) and investigated its biological and pathological characteristics. Phylogenetic analysis indicated that the new isolate was serotype 2, sharing the segments with those from different hosts. Our results showed that it can infect a wide range of cell lines from different mammalian species, including human, swine, and non-human primate cell lines. Additionally, media containing trypsin, yeast extract, and tryptose phosphate broth promoted virus propagation in primate cell lines and most human cell lines, but not in A549 and porcine cell lines. Mice infected with this strain via the intranasal route, but not via the oral route, exhibited weight loss and respiratory distress. The virus is distributed in a broad range of organs and causes lung damage. In vitro and in vivo experiments also suggested that the new virus could be a neurotropic infectious strain that can infect a neuroblastoma cell line and replicate in the brains of infected mice. Additionally, it caused a delayed immune response, as indicated by the high expression levels of cytokines and chemokines only at 14 days post-infection (dpi). These data provide an important understanding of the genetics and pathogenicity of mammalian orthoreoviruses in bats at risk of spillover infections.IMPORTANCEMammalian orthoreoviruses (MRVs) have a broad range of hosts and can cause serious respiratory and gastroenteritis diseases in humans and livestock. Some strains infect the central nervous system, causing severe encephalitis. In this study, we identified BatMRV2/SNU1/Korea/2021, a reassortment of MRV serotype 2, isolated from bats with broad tissue tropism, including the neurological system. In addition, it has been shown to cause respiratory syndrome in mouse models. The given data will provide more evidence of the risk of mammalian orthoreovirus transmission from wildlife to various animal species and the sources of spillover infections.

Isolation and genetic characterization of a mammalian orthoreovirus from Vespertilio sinensis in Japan

Throughout East Asia, Europe, and North America, mammalian orthoreovirus (MRV), for which bats have been proposed to be natural reservoirs, has been detected in a variety of domestic and wild mammals, as well as in humans. Here, we isolated a novel MRV strain (designated as Kj22-33) from a fecal sample from Vespertilio sinensis bats in Japan. Strain Kj22-33 has a 10-segmented genome with a total length of 23,580 base pairs. Phylogenetic analysis indicated that Kj22-33 is a serotype 2 strain, the segmented genome of which has undergone reassortment with that of other MRV strains.

Monitoring Enteroviruses and SARS-CoV-2 in Wastewater Using the Polio Environmental Surveillance System in Japan

In the global strategy for polio eradication, environmental surveillance (ES) has been established worldwide to monitor polioviruses. In addition, nonpolio enteroviruses are simultaneously isolated from wastewater under this ES program. Hence, ES can be used to monitor enteroviruses in sewage to supplement clinical surveillance. In response to the coronavirus disease 2019 (COVID-19) pandemic, we also monitored severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in sewage using the polio ES system in Japan. Enterovirus and SARS-CoV-2 were detected in sewage from January 2019 to December 2021 and from August 2020 to November 2021, respectively. Enterovirus species such as echoviruses and coxsackieviruses were frequently detected by ES in 2019, indicating the circulation of these viruses. After the onset of the COVID-19 pandemic, sewage enterovirus detection and related patient reports were notably reduced in 2020 to 2021, suggesting changes in the hygiene behaviors of the human population in response to the pandemic. Our comparative experiment with a total of 520 reverse transcription-quantitative PCR (RT-qPCR) assays for SARS-CoV-2 detection demonstrated that the solid-based method had a significantly higher detection rate than that of the liquid-based method (24.6% and 15.9%, respectively). Moreover, the resulting RNA concentrations were correlated with the number of new COVID-19 cases (Spearman's r = 0.61). These findings indicate that the existing polio ES system can be effectively used for enterovirus and SARS-CoV-2 sewage monitoring using different procedures such as virus isolation and molecular-based detection. IMPORTANCE Long-term efforts are required to implement surveillance programs for the ongoing COVID-19 pandemic, and they will be required even in the postpandemic era. We adopted the existing polio environmental surveillance (ES) system for SARS-CoV-2 sewage monitoring in Japan as a practical and cost-effective approach. Moreover, the ES system routinely detects enteroviruses from wastewater and, therefore, can be used for enterovirus monitoring. The liquid fraction of the sewage sample is used for poliovirus and enterovirus detection, and the solid fraction can be used for SARS-CoV-2 RNA detection. The present study demonstrates how the existing ES system can be used for monitoring enteroviruses and SARS-CoV-2 in sewage.

Isolation, molecular characterization, and disinfectants susceptibility of swine-carried mammalian orthoreoviruses in Japan in 2020-2022

Biosecurity enhancement contributes to the reduction of various microbial pathogens. Mammalian orthoreoviruses (MRVs) which are increasingly recognized as potentially serious problems on swine industry were used as indicators of biosecurity enhancement on two pig farms. Twelve MRVs were detected and isolated from fecal specimens of healthy pigs collected from one of the two farms in Japan. By sequencing based on the partial S1 gene, MRV isolates were classified as MRV1 and MRV2. Additionally, the virucidal activities of disinfectants toward the isolated MRV1 were evaluated using quaternary ammonium compound (QAC) diluted 500 times with water (QAC-500), 0.17% food additive glade calcium hydroxide (FdCa(OH)₂) solution, QAC diluted with 0.17% FdCa(OH)₂ solution (Mix-500), sodium hypochlorite at 100 or 1,000 parts per million (ppm) of total chlorine (NaClO-100 or NaClO-1000, respectively). To efficiently inactivate MRV1 (≥3 log₁₀ reductions), 0.17% FdCa(OH)₂, Mix-500 and NaClO-1000 required 5 min, whereas it took 30 min for QAC-500. The number of MRV detections has decreased over time, after using Mix-500 for disinfection on the positive farm. These results suggest that different serotypes of MRVs are circulating among pigs, and that the occurrence of MRVs in the farms decreased consequent to more effective disinfection.

Genetic diversity, reassortment, and recombination of mammalian orthoreoviruses from Japanese porcine fecal samples

Mammalian orthoreoviruses (MRVs) are non-enveloped double-stranded RNA viruses with a broad host range. MRVs are prevalent worldwide, and in Japan, they have been isolated from various hosts, including humans, dogs, cats, wild boars, and pigs, and they have also been found in sewage. However, Japanese porcine MRVs have not been genetically characterized. While investigating porcine enteric viruses including MRV, five MRVs were isolated from the feces of Japanese pigs using MA104 cell culture. Genetic analysis of the S1 gene revealed that the Japanese porcine MRV isolates could be classified as MRV-2 and MRV-3. Whole genome analysis showed that Japanese porcine MRVs exhibited genetic diversity, although they shared sequence similarity with porcine MRV sequences in the DDBJ/EMBL/GenBank database. Several potential intragenetic reassortment events were detected among MRV strains from pigs, sewage, and humans in Japan, suggesting zoonotic transmission. Furthermore, homologous recombination events were identified in the M1 and S1 genes of Japanese porcine MRV. These findings imply that different strains of Japanese porcine MRV share a porcine MRV genomic backbone and have evolved through intragenetic reassortment and homologous recombination events.