Identification and characterization of a new orthoreovirus from patients with acute respiratory infections

The influence of the cytoskeleton on the development and behavior of viral factories in mammalian orthoreovirus

Cytosolic viral factories (VFs) of mammalian orthoreovirus (MRV) are sites for viral genome replication and assembly of virus progeny. Despite advancements in reverse genetics, the formation and dynamics of VFs still need to be clarified. MRV exploits host cytoskeletal components like microtubules (MTs) throughout its life cycle, including cell entry, replication, and release. MRV VFs, membrane-less cytosolic inclusions, rely on the viral proteins μ2 and μNS for formation. Protein μ2 interacts and stabilizes MTs through acetylation, supporting VF formation and viral replication, while scaffold protein μNS influences cellular components to aid VF maturation. The disruption of the MT network reduces viral replication, underscoring its importance. Additionally, μ2 associates with MT-organizing centers, modulating the MT dynamics to favor viral replication. In summary, MRV subverts the cytoskeleton to facilitate VF dynamics and promote viral replication and assembly to promote VF dynamics, replication, and assembly, highlighting the critical role of the cytoskeleton in viral replication.

Unveiling the hidden threats: a review of pathogen diversity and public health risks from bats, rodents, and non-human primates in Zambia (1990-2022)

Background

Infectious disease agents of animal origin, which can cause mild to severe illnesses in humans, are increasingly spilling over into human populations. Southern Africa, particularly Zambia as a regional transport hub, has experienced notable outbreaks of zoonotic pathogens in recent years. This context underscores the importance of research, as numerous studies over the past 33 years have reported various infectious agents with differing zoonotic potential from bats, rodents, and non-human primates (NHPs) in Zambia. However, the data remained unaggregated, hampering comprehensive and organized understanding of these threats.

Methods

A review spanning January 1990 to December 2022 synthesised data from selected studies conducted in bats, rodents, and NHPs across 14 of Zambia's 116 districts.

Results

Among the reported pathogens, viruses predominated (62%, 31/50), followed by parasites (20%, 10/50)), and bacteria (18%, 9/50). Notable pathogens included Ebola virus, Marburg virus, Hantavirus, Zika virus, Human parainfluenza virus-3, Anaplasma phagocytophilum, Borrelia faini, Coxiella burnetii, Trypanosoma brucei rhodesiense, Calodium hepaticum, and Trichinella spiralis. Most identified infectious agents came from short term cross-sectional investigations, thus, the temporal dynamics related to abundance and likelihood of outbreaks remain unknown.

Conclusion

The findings starkly illuminate significant zoonotic public health threats amidst glaring under-surveillance of zoonoses in humans in Zambia. This critical gap calls urgently for enhanced active, passive and syndromic surveillance activities to identify new diseases and provide evidence-based measures to safeguard public health from emerging infectious risks in Zambia and the Southern African sub-region, considering the country's position as a regional transport hub.

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.

Detection of Dengue Virus 1 and Mammalian Orthoreovirus 3, with Novel Reassortments, in a South African Family Returning from Thailand, 2017

In July 2017, a family of three members, a 46-year-old male, a 45-year-old female and their 8-year-old daughter, returned to South Africa from Thailand. They presented symptoms consistent with mosquito-borne diseases, including fever, headache, severe body aches and nausea. Mosquito bites in all family members suggested recent exposure to arthropod-borne viruses. Dengue virus 1 (Genus Orthoflavivirus) was isolated (isolate no. SA397) from the serum of the 45-year-old female via intracerebral injection in neonatal mice and subsequent passage in VeroE6 cells. Phylogenetic analysis of this strain indicated close genetic identity with cosmopolitan genotype 1 DENV1 strains from Southeast Asia, assigned to major lineage K, minor lineage 1 (DENV1I_K.1), such as GZ8H (99.92%) collected in November 2018 from China, and DV1I-TM19-74 isolate (99.72%) identified in Bangkok, Thailand, in 2019. Serum samples from the 46-year-old male yielded a virus isolate that could not be confirmed as DENV1, prompting unbiased metagenomic sequencing for virus identification and characterization. Illumina sequencing identified multiple segments of a mammalian orthoreovirus (MRV), designated as Human/SA395/SA/2017. Genomic and phylogenetic analyses classified Human/SA395/SA/2017 as MRV-3 and assigned a tentative genotype, MRV-3d, based on the S1 segment. Genomic analyses suggested that Human/SA395/SA/2017 may have originated from reassortments of segments among swine, bat, and human MRVs. The closest identity of the viral attachment protein σ1 (S1) was related to a human isolate identified from Tahiti, French Polynesia, in 1960. This indicates ongoing circulation and co-circulation of Southeast Asian and Polynesian strains, but detailed knowledge is hampered by the limited availability of genomic surveillance. This case represents the rare concurrent detection of two distinct viruses with different transmission routes in the same family with similar clinical presentations. It highlights the complexity of diagnosing diseases with similar sequelae in travelers returning from tropical areas.

Isolation and identification of a novel porcine-related recombinant mammalian orthoreovirus type 3 strain from cattle in Guangxi Province, China

The Mammalian orthoreovirus (MRV) infects various mammals, including humans, and is linked to gastrointestinal, respiratory, and neurological diseases. A recent outbreak in Liuzhou, Guangxi, China, led to the isolation of a new MRV strain, GXLZ2301, from fecal samples. This strain replicates in multiple cell lines and forms lattice-like structures. Infected cells exhibit single-cell death and syncytia formation. The virus's titers peaked at 107.2 TCID50/0.1 mL in PK-15 and BHK cells, with the lowest at 103.88 TCID50/0.1 mL in A549 cells. Electron microscopy showed no envelope with a diameter of about 70 nm. Genetic analysis revealed GXLZ2301 as a recombinant strain with gene segments from humans, cows, and pigs, similar to type 3 MRV strains from Italy (2015-2016). Pathogenicity tests indicated that while the bovine MRV strain did not cause clinical symptoms in mice, it caused significant damage to the gut, lungs, liver, kidneys, and brain. The emergence of this MRV strain may pose a threat to the health of animals and humans, and it is recommended that its epidemiology and recombination be closely monitored.

Investigation of Salmonella, hepatitis E virus (HEV) and viral indicators of fecal contamination in four Italian pig slaughterhouses, 2021-2022

In the pork production chain, the control at slaughterhouse aims to ensure safe food thanks to proper hygienic conditions during all steps of the slaughtering. Salmonella is one of the main foodborne pathogens in the EU causing a great number of human cases, and pigs also contribute to its spreading. Pig is the main reservoir of the zoonotic hepatitis E virus (HEV) that can be present in liver, bile, feces and even rarely in blood and muscle. The aim of this study was to assess the presence of both Salmonella and HEV in several points of the slaughtering chain, including pig trucks. Other viruses hosted in the gut flora of pigs and shed in feces were also assayed (porcine adenovirus PAdV, rotavirus, norovirus, and mammalian orthoreovirus MRV). Torque teno sus virus (TTSuV) present in both feces, liver and blood was also considered. Four Italian pig abattoirs were sampled in 12 critical points, 5 of which were the outer surface of carcasses before processing. HEV and rotavirus (RVA) were not detected. Norovirus was detected once. Salmonella was detected in two of the 4 abattoirs: in the two lairage pens, in the site of evisceration and on one carcass, indicating the presence of Salmonella if carcass is improper handled. The sampling sites positive for Salmonella were also positive for PAdV. MRV was detected in 10 swabs, from only two abattoirs, mainly in outer surface of carcasses. TTSuV was also detected in all abattoirs. Our study has revealed a diverse group of viruses, each serving as indicator of either fecal (NoV, RVA, PAdV, MRV) or blood contamination (TTSuV). TTSuV could be relevant as blood contamination indicators, crucial for viruses with a viremic stage, such as HEV. The simultaneous presence of PAdV with Salmonella is relevant, suggesting PAdV as a promising indicator for fecal contamination for both bacterial and viruses. In conclusion, even in the absence of HEV, the widespread presence of Salmonella at various points in the chain, underscores the need for vigilant monitoring and mitigation strategies which could be achieved by testing not only bacteria indicators as expected by current regulation, but also some viruses (PAdV, TTSuV, MRV) which could represent other sources of fecal contamination.

First Specific Detection of Mammalian Orthoreovirus from Goats Using TaqMan Real-Time RT-PCR Technology

Mammalian orthoreovirus (MRV) infections are ubiquitous in multiple mammalian species including humans, and mainly causes gastroenteritis and respiratory disease. In this study, we developed a rapid and sensitive TaqMan qRT-PCR method for MRV detection based on the primers and probe designed within the conserved L1 gene. The qRT-PCR assay was evaluated for its sensitivity, specificity, efficiency and reproducibility. It was found that the detection sensitivity was equivalent to 10 DNA copies/μL, and the standard curves had a linear correlation of R2 = 0.998 with an amplification efficiency of 99.6%. The inter- and intra-assay coefficients of variation (CV%) were in the range of 0.29% to 2.16% and 1.60% to 3.60%, respectively. The primer sets specifically amplified their respective MRV segments and had the highest detection sensitivities of 100.25 TCID50/mL with amplification efficiencies of 99.5% (R2 = 0.999). qRT-PCR was used for MRV detection from samples of sheep, goats, and calves from four regions in China, and the overall MRV prevalence was 8.2% (35/429), whereas 17/429 (4.0%) were detected by RT-PCR and 14/429 (3.3%) by virus isolation. The qRT-PCR assay showed significantly higher sensitivity than RT-PCR and virus isolation. Results from an epidemiological survey indicated that the positive rate of MRV in rectal swabs from sheep and goats tested in Shaanxi, Jiangsu, and Xinjiang were 9/80 (11.3%), 12/93 (12.9%) and 14/128 (10.9%), respectively. In goats and sheep, MRV prevalence was obviously associated with season and age, with a high positive rate of more than 8% during September to April and approximately 13% in small ruminant animals under two months of age. This is the first instance of MRV infection in sheep and goats in China, thus broadening our knowledge of MRV hosts. Consequently, primer optimization for qRT-PCR should not only prioritize amplification efficiency and specificity, but also sensitivity. This assay will contribute to more accurate and rapid MRV monitoring by epidemiological investigation, viral load, and vaccination efficacy.

Human cytokeratin 1 plays a role in the interaction of Pteropine orthoreovirus with Hek293 cells but not HeLa cells

Pteropine orthoreovirus (PRV) causes respiratory tract infections in humans. Despite its emergence as a zoonotic and respiratory virus, little is known about its cell tropism, which hampers progress in fully understanding its pathogenesis in humans. Hek293 cells are most susceptible to PRV infection, while HeLa cells are the least. Human cytokeratin 1 (CK1) was identified as the protein that interacts with PRV. The immunofluorescence assay and qPCR results revealed prior treatment with anti-CK1 may provide Hek293 cells protection against PRV. The KRT1-knockout Hek293 cells were less susceptible to PRV infection. Further study into the pathogenesis of PRV in humans is needed.

Nelson Bay Reovirus Isolated from Bats and Blood-Sucking Arthropods Collected in Yunnan Province, China

Nelson Bay reovirus (NBV) is an emerging zoonotic virus that can cause acute respiratory disease in humans. These viruses are mainly discovered in Oceania, Africa, and Asia, and bats have been identified as their main animal reservoir. However, despite recent expansion of diversity for NBVs, the transmission dynamics and evolutionary history of NBVs are still unclear. This study successfully isolated two NBV strains (MLBC1302 and MLBC1313) from blood-sucking bat fly specimens (Eucampsipoda sundaica) and one (WDBP1716) from the spleen specimen of a fruit bat (Rousettus leschenaultii), which were collected at the China-Myanmar border area of Yunnan Province. Syncytia cytopathic effects (CPE) were observed in BHK-21 and Vero E6 cells infected with the three strains at 48 h postinfection. Electron micrographs of ultrathin sections showed numerous spherical virions with a diameter of approximately 70 nm in the cytoplasm of infected cells. The complete genome nucleotide sequence of the viruses was determined by metatranscriptomic sequencing of infected cells. Phylogenetic analysis demonstrated that the novel strains were closely related to Cangyuan orthoreovirus, Melaka orthoreovirus, and human-infecting Pteropine orthoreovirus HK23629/07. Simplot analysis revealed the strains originated from complex genomic reassortment among different NBVs, suggesting the viruses experienced a high reassortment rate. In addition, strains successfully isolated from bat flies also implied that blood-sucking arthropods might serve as potential transmission vectors. IMPORTANCE Bats are the reservoir of many viral pathogens with strong pathogenicity, including NBVs. Nevertheless, it is unclear whether arthropod vectors are involved in transmitting NBVs. In this study, we successfully isolated two NBV strains from bat flies collected from the body surface of bats, which implies that they may be vectors for virus transmission between bats. While the potential threat to humans remains to be determined, evolutionary analyses involving different segments revealed that the novel strains had complex reassortment histories, with S1, S2, and M1 segments highly similar to human pathogens. Further experiments are required to determine whether more NBVs are vectored by bat flies, their potential threat to humans, and transmission dynamics.

Evaluation of porcine intestinal organoids as an in vitro model for mammalian orthoreovirus 3 infection

BACKGROUND

Mammalian orthoreovirus type 3 (MRV3), which is responsible for gastroenteritis in many mammalian species including pigs, has been isolated from piglets with severe diarrhea. However, the use of pig-derived cells as an infection model for swine-MRV3 has rarely been studied.

OBJECTIVES

This study aims to establish porcine intestinal organoids (PIOs) and examine their susceptibility as an in vitro model for intestinal MRV3 infection.

METHODS

PIOs were isolated and established from the jejunum of a miniature pig. Established PIOs were characterized using polymerase chain reaction (PCR) and immunofluorescence assays (IFAs) to confirm the expression of small intestine-specific genes and proteins, such as Lgr5, LYZI, Mucin-2, ChgA, and Villin. The monolayered PIOs and three-dimensional (3D) PIOs, obtained through their distribution to expose the apical surface, were infected with MRV3 for 2 h, washed with Dulbecco's phosphate-buffered saline, and observed. Viral infection was confirmed using PCR and IFA. We performed quantitative real-time reverse transcription-PCR to assess changes in viral copy numbers and gene expressions linked to intestinal epithelial genes and antiviral activity.

RESULTS

The established PIOs have molecular characteristics of intestinal organoids. Infected PIOs showed delayed proliferation with disruption of structures. In addition, infection with MRV3 altered the gene expression linked to intestinal epithelial cells and antiviral activity, and these effects were observed in both 2D and 3D models. Furthermore, viral copy numbers in the supernatant of both models increased in a time-dependent manner.

CONCLUSIONS

We suggest that PIOs can be an in vitro model to study the infection mechanism of MRV3 in detail, facilitating pharmaceutical development.

Paired immunoglobulin-like receptor B is an entry receptor for mammalian orthoreovirus

Mammalian orthoreovirus (reovirus) infects most mammals and is associated with celiac disease in humans. In mice, reovirus infects the intestine and disseminates systemically to cause serotype-specific patterns of disease in the brain. To identify receptors conferring reovirus serotype-dependent neuropathogenesis, we conducted a genome-wide CRISPRa screen and identified paired immunoglobulin-like receptor B (PirB) as a receptor candidate. Ectopic expression of PirB allowed reovirus binding and infection. PirB extracelluar D3D4 region is required for reovirus attachment and infectivity. Reovirus binds to PirB with nM affinity as determined by single molecule force spectroscopy. Efficient reovirus endocytosis requires PirB signaling motifs. In inoculated mice, PirB is required for maximal replication in the brain and full neuropathogenicity of neurotropic serotype 3 (T3) reovirus. In primary cortical neurons, PirB expression contributes to T3 reovirus infectivity. Thus, PirB is an entry receptor for reovirus and contributes to T3 reovirus replication and pathogenesis in the murine brain.

Oncolytic Reoviruses: Can These Emerging Zoonotic Reoviruses Be Tamed and Utilized?

Orthoreovirus is a nonenveloped double-stranded RNA virus under the Reoviridae family. This group of viruses, especially mammalian orthoreovirus (MRV), are reported with great therapeutic values due to their oncolytic effects. In this review, the life cycle and oncolytic effect of MRV and a few emerging reoviruses were summarized. This article also highlights the challenges and strategies of utilizing MRV and the emerging reoviruses, avian orthoreovirus (ARV) and pteropine orthoreovirus (PRV), as oncolytic viruses (OVs). Besides, the emergence of potential ARV and PRV as OVs were discussed in comparison to MRV. Finally, the risk of reovirus as zoonosis or reverse zoonosis (zooanthroponosis) were debated, and concerns were raised in this article, which warrant continue surveillance of reovirus (MRV, ARV, and PRV) in animals, humans, and the environment.

Surveillance, isolation and genomic characterization of Pteropine orthoreovirus of probable bat origin among patients with acute respiratory infection in Malaysia

Pteropine orthoreovirus (PRV), an emerging bat-borne virus, has been linked to cases of acute respiratory infections (ARI) in humans. The prevalence, epidemiology and genomic diversity of PRV among ARI of unknown origin were studied. Among 632 urban outpatients tested negative for all known respiratory viruses, 2.2% were PRV-positive. Patients mainly presented with moderate to severe forms of cough, sore throat and muscle ache, but rarely with fever. Phylogenetic analysis revealed that over 90% of patients infected with the Melaka virus (MelV)-like PRV, while one patient infected with the Pulau virus previously found only in fruit bats. Human oral keratinocytes and nasopharyngeal epithelial cells were susceptible to clinical isolates of PRV, including the newly isolated MelV-like 12MYKLU1034. Whole genome sequence of 12MYKLU1034 using Nanopore technique revealed a novel reassortant strain. Evolutionary analysis of the global PRV strains suggests the continuous evolution of PRV through genetic reassortment among PRV strains circulating in human, bats and non-human primate hosts, creating a spectrum of reassortant lineages with complex evolutionary characteristics. In summary, the role of PRV as a common etiologic agent of ARI is evident. Continuous monitoring of PRV prevalence, pathogenicity and diversity among human and animal hosts is important to trace the emergence of novel reassortants.

Recombinant characteristics, pathogenicity, and transmissibility of a variant goose orthoreovirus derived from inter-lineage recombination

Since March 2021, an infectious characterized by white necrotic foci throughout the goose body has appeared in the major goose-producing regions in China. This disease has caused economic hardship for goose farms in many regions of China with approximately 50 % mortality. A novel goose-origin orthoreovirus was isolated from the spleen of diseased geese and designated as N-GRV/HN/Goose/2021/China (N-GRV-HN21) strain. Next-generation sequencing and phylogenetic analysis revealed that the isolate was a reassortant virus containing viral gene segments from three ARV serotypes that infect duck, muscovy duck, and goose. Geese infection test showed that both N-GRV-HN21-infected and contacted geese displayed whole-body white necrotic foci. N-GRV RNA was detected in different organs of both infected and contacted geese, indicating that the N-GRV isolate is pathogenic and transmissible in geese. Seroconversion was also observed in experimentally infected and contacted geese. A prevalence study of 323 goose serum samples collected from different goose breeding areas showed that 86 % of the geese were positive for N-GRV. In conclusion, all results warrant the necessity to monitor orthoreovirus epidemiology and reassortment as the orthoreovirus could be an important pathogen for the waterfowl industry and a novel orthoreovirus might emerge to threaten animal and public health.

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.

Molecular, ecological, and behavioral drivers of the bat-virus relationship

Bats perform important ecological roles in our ecosystem. However, recent studies have demonstrated that bats are reservoirs of emerging viruses that have spilled over into humans and agricultural animals to cause severe diseases. These viruses include Hendra and Nipah paramyxoviruses, Ebola and Marburg filoviruses, and coronaviruses that are closely related to severe acute respiratory syndrome coronavirus (SARS-CoV), Middle East respiratory syndrome coronavirus (MERS-CoV), and the recently emerged SARS-CoV-2. Intriguingly, bats that are naturally or experimentally infected with these viruses do not show clinical signs of disease. Here we have reviewed ecological, behavioral, and molecular factors that may influence the ability of bats to harbor viruses. We have summarized known zoonotic potential of bat-borne viruses and stress on the need for further studies to better understand the evolutionary relationship between bats and their viruses, along with discovering the intrinsic and external factors that facilitate the successful spillover of viruses from bats.

Isolation and characterization of an orthoreovirus from Indonesian fruit bats

Nelson Bay orthoreovirus (NBV) is an emerging bat-borne virus and causes respiratory tract infections in humans sporadically. Over the last two decades, several strains genetically related to NBV were isolated from humans and various bat species, predominantly in Southeast Asia (SEA), suggesting a high prevalence of the NBV species in this region. In this study, an orthoreovirus (ORV) belonging to the NBV species was isolated from Indonesian fruit bats' feces, tentatively named Paguyaman orthoreovirus (PgORV). Serological studies revealed that 81.2% (108/133) of Indonesian fruit bats sera had neutralizing antibodies against PgORV. Whole-genome sequencing and phylogenetic analysis of PgORV suggested the occurrence of past reassortments with other NBV strains isolated in SEA, indicating the dispersal and circulation of NBV species among bats in this region. Intranasal PgORV inoculation of laboratory mice caused severe pneumonia. Our study characterized PgORV's unique genetic background and highlighted the potential risk of PgORV-related diseases in Indonesia.

Revising the paradigm: Are bats really pathogen reservoirs or do they possess an efficient immune system?

While bats are often referred to as reservoirs of viral pathogens, a meta-analysis of the literature reveals many cases in which there is not enough evidence to claim so. In many cases, bats are able to confront viruses, recover, and remain immune by developing a potent titer of antibodies, often without becoming a reservoir. In other cases, bats might have carried an ancestral virus that at some time point might have mutated into a human pathogen. Moreover, bats exhibit a balanced immune response against viruses that have evolved over millions of years. Using genomic tools, it is now possible to obtain a deeper understanding of that unique immune system and its variability across the order Chiroptera. We conclude, that with the exception of a few viruses, bats pose little zoonotic danger to humans and that they operate a highly efficient anti-inflammatory response that we should strive to understand.

The nonstructural p17 protein of a fusogenic bat-borne reovirus regulates viral replication in virus species- and host-specific manners

Nelson Bay orthoreovirus (NBV), a member of the family Reoviridae, genus Orthoreovirus, is a bat-borne virus that causes respiratory diseases in humans. NBV encodes two unique nonstructural proteins, fusion-associated small transmembrane (FAST) protein and p17 protein, in the S1 gene segment. FAST induces cell–cell fusion between infected cells and neighboring cells and the fusogenic activity is required for efficient viral replication. However, the function of p17 in the virus cycle is not fully understood. Here, various p17 mutant viruses including p17-deficient viruses were generated by a reverse genetics system for NBV. The results demonstrated that p17 is not essential for viral replication and does not play an important role in viral pathogenesis. On the other hand, NBV p17 regulated viral replication in a bat cell line but not in other human and animal cell lines. Nuclear localization of p17 is associated with the regulation of NBV replication in bat cells. We also found that p17 dramatically enhances the cell–cell fusion activity of NBV FAST protein for efficient replication in bat cells. Furthermore, we found that a protein homologue of NBV p17 from another bat-borne orthoreovirus, but not those of avian orthoreovirus or baboon orthoreovirus, also supported efficient viral replication in bat cells using a p17-deficient virus-based complementation approach. These results provide critical insights into the functioning of the unique replication machinery of bat-borne viruses in their natural hosts.

Bat-borne viruses including the severe acute respiratory syndrome coronavirus and Nipah virus generally cause highly pathogenic diseases in humans but not in their bat reservoirs. Nelson Bay orthoreovirus (NBV), a bat-borne virus associated with acute respiratory tract infections in humans, possesses two unique nonstructural proteins, FAST and p17. FAST enhances viral replication through its cell–cell fusion activity, while the function of p17 in the viral life cycle is poorly understood. In this study, we show that p17 is non-essential for viral replication in several human and animal cell lines and does not play a critical role in pathogenesis in vivo. However, p17 localizes to the nucleus and regulates viral replication specifically in cells derived from bats by enhancing the cell–cell fusion activity of FAST in a host-specific manner. Furthermore, the expression of NBV p17 or an NBV p17 homologue from another bat-borne orthoreovirus enhanced the replication of an NBV mutant deficient in p17 in bat cells, suggesting that the function of p17 is virus species-specific. These findings will contribute to our understanding of how the replication of viruses is regulated in their natural reservoirs.

Climate Anomalies and Spillover of Bat-Borne Viral Diseases in the Asia-Pacific Region and the Arabian Peninsula

Climate variability and anomalies are known drivers of the emergence and outbreaks of infectious diseases. In this study, we investigated the potential association between climate factors and anomalies, including El Niño Southern Oscillation (ENSO) and land surface temperature anomalies, as well as the emergence and spillover events of bat-borne viral diseases in humans and livestock in the Asia-Pacific region and the Arabian Peninsula. Our findings from time series analyses, logistic regression models, and structural equation modelling revealed that the spillover patterns of the Nipah virus in Bangladesh and the Hendra virus in Australia were differently impacted by climate variability and with different time lags. We also used event coincidence analysis to show that the emergence events of most bat-borne viral diseases in the Asia-Pacific region and the Arabian Peninsula were statistically associated with ENSO climate anomalies. Spillover patterns of the Nipah virus in Bangladesh and the Hendra virus in Australia were also significantly associated with these events, although the pattern and co-influence of other climate factors differed. Our results suggest that climate factors and anomalies may create opportunities for virus spillover from bats to livestock and humans. Ongoing climate change and the future intensification of El Niño events will therefore potentially increase the emergence and spillover of bat-borne viral diseases in the Asia-Pacific region and the Arabian Peninsula.

Threat, challenges, and preparedness for future pandemics: A descriptive review of phylogenetic analysis based predictions

For centuries the world has been confronted with many infectious diseases, with a potential to turn into a pandemic posing a constant threat to human lives. Some of these pandemics occurred due to the emergence of new disease or re-emergence of previously known diseases with a few mutations. In such scenarios their optimal prevention and control options were not adequately developed. Most of these diseases are highly contagious and for their timely control, knowledge about the pathogens and disease progression is the basic necessity. In this review, we have presented a documented chronology of the earlier pandemics, evolutionary analysis of the infectious disease with pandemic potential, the role of RNA, difficulties in controlling pandemics, and the likely pathogens that could trigger future pandemics. In this study, the evolutionary history of the pathogens was identified by carrying out phylogenetic analysis. The percentage similarity between different infectious diseases is critically analysed for the identification of their correlation using online sequence matcher tools. The Baltimore classification system was used for finding the genomic nature of the viruses. It was observed that most of the infectious pathogens rise from their animal hosts with some mutations in their genome composition. The phylogenetic tree shows that the single-stranded RNA diseases have a common origin and many of them are having high similarity percentage. The outcomes of this study will help in the identification of potential pathogens that can cause future pandemics. This information will be helpful in the development of early detection techniques, devising preventive mechanism to limit their spread, prophylactic measures, Infection control and therapeutic options, thereby, strengthening our approach towards global preparedness against future pandemics.

Distinct interferon response in bat and other mammalian cell lines infected with Pteropine orthoreovirus

Bats serve as natural hosts of Pteropine orthoreovirus (PRV), an emerging group of bat-borne, zoonotic viruses. Bats appear to possess unique innate immune system responses that can inhibit viral replication, thus reducing clinical symptoms. We examined the innate immune response against PRV and assessed viral replication in cell lines derived from four bat species (Miniopterus fuliginosus, Pteropus dasymallus, Rhinolophus ferrumequinum, and Rousettus leschenaultii), one rodent (Mesocricetous auratus), and human (Homo sapiens). The expression levels of pattern recognition receptors (PRRs) (TLR3, RIG-I, and MDA5) and interferons (IFNB1 and IFNL1) were higher and PRV replication was lower in cell lines derived from M. fuliginosus, R. ferrumequinum, and R. leschenaultii. Reduction of IFNB1 expression by the knockdown of PRRs in the cell line derived from R. ferrumequinum was associated with increased PRV replication. The knockdown of RIG-I led to the most significant reduction in viral replication for all cell lines. These results suggest that RIG-I production is important for antiviral response against PRV in R. ferrumequinum.

Seroprevalence of Pteropine orthoreovirus in humans remain similar after nearly two decades (2001-2002 vs. 2017) in Tioman Island, Malaysia

Pteropine orthoreovirus (PRV) is an emerging zoonotic respiratory virus that can be transmitted from bats to humans. In Malaysia, aside from PRV2P (Pulau virus) being isolated from Pteropus hypomelanus sampled in Tioman Island, PRV3M (Melaka virus), PRV4K (Kampar virus), and PRV7S (Sikamat virus) were all isolated from samples of patients who reported having a disease spectrum from acute respiratory distress to influenza-like illness and sometimes even with enteric symptoms such as diarrhea and abdominal pain. Screening of sera collected from human volunteers on Tioman Island in 2001-2002 demonstrated that 12.8% (14/109) were positive for PRV2P and PRV3M. Taking all these together, we aim to investigate the serological prevalence of PRV (including PRV4K and PRV7S) among Tioman Island inhabitants again with the assumption that the seroprevalence rate will remain nearly similar to the above reported if human exposure to bats is still happening in the island. Using sera collected from human volunteers on the same island in 2017, we demonstrated seroprevalence of 17.8% (28/157) against PRV2P and PRV3M, respectively. Seropositivity of 11.4% among Tioman Island inhabitants against PRV4K and PRV7S, respectively, was described in this study. In addition, the seroprevalence of 89.5% (17/19), 73.6% (14/19), 63.0% (12/19), and 73.6% (14/19) against PRV2P, PRV3M, PRV4K, and PRV7S, respectively, were observed among pteropid bats in the island. We revealed that the seroprevalence of PRV among island inhabitants remains nearly similar after nearly two decades, suggesting that potential spill-over events in bat-human interface areas in the Tioman Island. We are unclear whether such spillover was directly from bats to humans, as suspected for the PRV3M human cases, or from an intermediate host(s) yet to be identified. There is a high possibility of the viruses circulating among the bats as demonstrated by high seroprevalence against PRV in the bats.

FAST Proteins: Development and Use of Reverse Genetics Systems for Reoviridae Viruses

Reverse genetics systems for viruses, the technology used to generate gene-engineered recombinant viruses from artificial genes, enable the study of the roles of the individual nucleotides and amino acids of viral genes and proteins in infectivity, replication, and pathogenicity. The successful development of a reverse genetics system for poliovirus in 1981 accelerated the establishment of protocols for other RNA viruses important for human health. Despite multiple efforts, rotavirus (RV), which causes severe gastroenteritis in infants, was refractory to reverse genetics analysis, and the first complete reverse genetics system for RV was established in 2017. This novel technique involves use of the fusogenic protein FAST (fusion-associated small transmembrane) derived from the bat-borne Nelson Bay orthoreovirus, which induces massive syncytium formation. Co-transfection of a FAST-expressing plasmid with complementary DNAs encoding RV genes enables rescue of recombinant RV. This review focuses on methodological insights into the reverse genetics system for RV and discusses applications and potential improvements to this system.

Attenuated infection by a Pteropine orthoreovirus isolated from an Egyptian fruit bat in Zambia

Background

Pteropine orthoreovirus (PRV) is an emerging bat-borne zoonotic virus that causes severe respiratory illness in humans. Although PRVs have been identified in fruit bats and humans in Australia and Asia, little is known about the prevalence of PRV infection in Africa. Therefore, this study performed an PRV surveillance in fruit bats in Zambia.

Methods

Egyptian fruit bats (Rousettus aegyptiacus, n = 47) and straw-colored fruit bats (Eidolon helvum, n = 33) captured in Zambia in 2017–2018 were screened for PRV infection using RT-PCR and serum neutralization tests. The complete genome sequence of an isolated PRV strain was determined by next generation sequencing and subjected to BLAST and phylogenetic analyses. Replication capacity and pathogenicity of the strain were investigated using Vero E6 cell cultures and BALB/c mice, respectively.

Results

An PRV strain, tentatively named Nachunsulwe-57, was isolated from one Egyptian fruit bat. Serological assays demonstrated that 98% of sera (69/70) collected from Egyptian fruit bats (n = 37) and straw-colored fruit bats (n = 33) had neutralizing antibodies against PRV. Genetic analyses revealed that all 10 genome segments of Nachunsulwe-57 were closely related to a bat-derived Kasama strain found in Uganda. Nachunsulwe-57 showed less efficiency in viral growth and lower pathogenicity in mice than another PRV strain, Miyazaki-Bali/2007, isolated from a patient.

Conclusions

A high proportion of Egyptian fruit bats and straw-colored fruit bats were found to be seropositive to PRV in Zambia. Importantly, a new PRV strain (Nachunsulwe-57) was isolated from an Egyptian fruit bat in Zambia, which had relatively weak pathogenicity in mice. Taken together, our findings provide new epidemiological insights about PRV infection in bats and indicate the first isolation of an PRV strain that may have low pathogenicity to humans.

Pteropine orthoreovirus (PRV) is a causative agent of acute respiratory illness in humans in tropical and sub-tropical regions in Southeast Asia. PRVs have been originally isolated from fruit bats, and it is assumed that PRVs spread to humans by both bat-to-human and human-to-human transmission. Recently, an PRV was also detected from a fruit bat in the Afrotropical region and might potentially cause an emerging infection of the bat-borne zoonotic virus in Africa. However, little is known about the prevalence of PRV infection in Africa. In this study, we demonstrated the high prevalence of PRV infection in bat populations in Zambia and isolated a new strain of PRV from Egyptian fruit bats. In addition, we found that the bat-derived PRV strain had lower pathogenicity in mice than a human-derived PRV strain isolated from a patient in Southeast Asia. Our findings provide new epidemiological information about PRV in fruit bats in the Afrotropical region and indicate the first isolation of an PRV strain that may cause attenuated infection in humans.

Update on Potentially Zoonotic Viruses of European Bats

Bats have been increasingly gaining attention as potential reservoir hosts of some of the most virulent viruses known. Numerous review articles summarize bats as potential reservoir hosts of human-pathogenic zoonotic viruses. For European bats, just one review article is available that we published in 2014. The present review provides an update on the earlier article and summarizes the most important viruses found in European bats and their possible implications for Public Health. We identify the research gaps and recommend monitoring of these viruses.

Isolation and characterization of novel reassortant mammalian orthoreovirus from pigs in the United States

Mammalian orthoreovirus (MRV) infects multiple mammalian species including humans. A United States Midwest swine farm with approximately one thousand 3-month-old pigs experienced an event, in which more than 300 pigs showed neurological signs, like "down and peddling", with approximately 40% mortality. A novel MRV was isolated from the diseased pigs. Sequence and phylogenetic analysis revealed that the isolate was a reassortant virus containing viral gene segments from three MRV serotypes that infect human, bovine and swine. The M2 and S1 segment of the isolate showed 94% and 92% nucleotide similarity to the M2 of the MRV2 D5/Jones and the S1 of the MRV1 C/bovine/Indiana/MRV00304/2014, respectively; the remaining eight segments displayed 93%-95% nucleotide similarity to those of the MRV3 FS-03/Porcine/USA/2014. Pig studies showed that both MRV-infected and native contact pigs displayed fever, diarrhoea and nasal discharge. MRV RNA was detected in different intestinal locations of both infected and contact pigs, indicating that the MRV isolate is pathogenic and transmissible in pigs. Seroconversion was also observed in experimentally infected pigs. A prevalence study on more than 180 swine serum samples collected from two states without disease revealed 40%-52% positive to MRV. All results warrant the necessity to monitor MRV epidemiology and reassortment as the MRV could be an important pathogen for the swine industry and a novel MRV might emerge to threaten animal and public health.

Enteric Viral Infections among Domesticated South American Camelids: First Detection of Mammalian Orthoreovirus in Camelids

Simple Summary

South American camelids (SACs) constitute the greatest livestock wealth of the Andean populations. Approximately half a million people from the high Andean areas are dedicated to the breeding of SACs as their main activity. In general, infectious diseases, particularly diarrheal infections, cause high morbidity and mortality in offspring and adult animals. In the study, we demonstrated that multiple virus pathogens circulate among neonatal SACs, and coinfections from other viruses might be common among SAC crias. We also demonstrated, for the first-time anywhere, the circulation of mammalian orthoreovirus in SACs or camelids. Diarrheal infections can potentially impact livestock productivity, which translates into serious economic losses for the Peruvian SAC industry, especially within rural communities, directly impacting their livelihood. Better knowledge of the infections that afflict these animals will enable the implementation of measures for the prevention and control of pathogens, the results of which will ultimately be reflected in improving the quality of life of these communities.

Abstract

Enteric infections are a major cause of neonatal death in South American camelids (SACs). The aim of this study was to determine the prevalence of enteric viral pathogens among alpacas and llamas in Canchis, Cuzco, located in the southern Peruvian highland. Fecal samples were obtained from 80 neonatal alpacas and llamas and tested for coronavirus (CoV), mammalian orthoreovirus (MRV), and rotavirus A (RVA) by RT-PCR. Of the 80 fecal samples analyzed, 76 (95%) were positive for at least one of the viruses tested. Overall, the frequencies of positive samples were 94.1% and 100% among alpacas and llamas, respectively. Of the positive samples, 33 (43.4%) were monoinfected, while 43 (56.6%) had coinfections with two (83.7%) or three (16.3%) viruses. CoV was the most commonly detected virus (87.5%) followed by MRV (50%). RVA was detected only in coinfections. To our knowledge, this is the first description of MRV circulation in SACs or camelids anywhere. These data show that multiple viruses circulate widely among young alpaca and llama crias within the studied areas. These infections can potentially reduce livestock productivity, which translates into serious economic losses for rural communities, directly impacting their livelihoods.

Rotavirus reverse genetics systems: Development and application

Rotaviruses (RVs) cause acute gastroenteritis in infants and young children. Since 2006, live-attenuated vaccines have reduced the number of RV-associated deaths; however, RV is still responsible for an estimated 228,047 annual deaths worldwide. RV, a member of the family Reoviridae, has an 11-segmented double-stranded RNA genome contained within a non-enveloped, triple layered virus particle. In 2017, a long-awaited helper virus-free reverse genetics system for RV was established. Since then, numerous studies have reported the generation of recombinant RVs; these studies verify the robustness of reverse genetics systems. This review provides technical insight into current reverse genetics systems for RVs, as well as discussing basic and applied studies that have used these systems.

The Evolutionary Significance of Generalist Viruses with Special Emphasis on Plant Viruses and their Hosts

The host range of a virus is defined as the number of species a virus potentially infects. The specialist virus infects one or few related species while the generalist virus infects several different species, possibly in different families. Origin of generalist viruses from their specialist nature and the expansion of the host range of the generalist virus occur with the host shift event in which the virus encounters and adapts to a new host. Host shift events have resulted in the majority of the newly emerging viral diseases. This review discusses the advantages and disadvantages of generalist over specialist viruses and the unique features of plant viruses and their hosts that result in a higher incidence of generalist viruses in plants.

Virus-Mediated Cell-Cell Fusion

Cell-cell fusion between eukaryotic cells is a general process involved in many physiological and pathological conditions, including infections by bacteria, parasites, and viruses. As obligate intracellular pathogens, viruses use intracellular machineries and pathways for efficient replication in their host target cells. Interestingly, certain viruses, and, more especially, enveloped viruses belonging to different viral families and including human pathogens, can mediate cell-cell fusion between infected cells and neighboring non-infected cells. Depending of the cellular environment and tissue organization, this virus-mediated cell-cell fusion leads to the merge of membrane and cytoplasm contents and formation of multinucleated cells, also called syncytia, that can express high amount of viral antigens in tissues and organs of infected hosts. This ability of some viruses to trigger cell-cell fusion between infected cells as virus-donor cells and surrounding non-infected target cells is mainly related to virus-encoded fusion proteins, known as viral fusogens displaying high fusogenic properties, and expressed at the cell surface of the virus-donor cells. Virus-induced cell-cell fusion is then mediated by interactions of these viral fusion proteins with surface molecules or receptors involved in virus entry and expressed on neighboring non-infected cells. Thus, the goal of this review is to give an overview of the different animal virus families, with a more special focus on human pathogens, that can trigger cell-cell fusion.

SARS-CoV-2 and COVID-19: A genetic, epidemiological, and evolutionary perspective

In less than five months, COVID-19 has spread from a small focus in Wuhan, China, to more than 5 million people in almost every country in the world, dominating the concern of most governments and public health systems. The social and political distresses caused by this epidemic will certainly impact our world for a long time to come. Here, we synthesize lessons from a range of scientific perspectives rooted in epidemiology, virology, genetics, ecology and evolutionary biology so as to provide perspective on how this pandemic started, how it is developing, and how best we can stop it.

Pteropine Orthoreovirus in an Angolan Soft-Furred Fruit Bat (Lissonycteris angolensis) in Uganda Dramatically Expands the Global Distribution of an Emerging Bat-Borne Respiratory Virus

Pteropine orthoreovirus (PRV; Reoviridae: Spinareovirinae) is an emerging bat-borne zoonotic virus that causes influenza-like illness (ILI). PRV has thus far been found only in Australia and Asia, where diverse old-world fruit bats (Pteropodidae) serve as hosts. In this study, we report the discovery of PRV in Africa, in an Angolan soft-furred fruit bat (Lissonycteris angolensis ruwenzorii) from Bundibugyo District, Uganda. Metagenomic characterization of a rectal swab yielded 10 dsRNA genome segments, revealing this virus to cluster within the known diversity of PRV variants detected in bats and humans in Southeast Asia. Phylogeographic analyses revealed a correlation between geographic distance and genetic divergence of PRVs globally, which suggests a geographic continuum of PRV diversity spanning Southeast Asia to sub-Saharan Africa. The discovery of PRV in an African bat dramatically expands the geographic range of this zoonotic virus and warrants further surveillance for PRVs outside of Southeast Asia.

Bacillus pumilus ribonuclease rescues mice infected by double-stranded RNA-containing reovirus serotype 1

Reoviruses (respiratory enteric orphan viruses) are nonenveloped viruses with segmented dsRNA genome. Viruses in the family Reoviridae are quite stable in the environment. Recently, they have been identified with various pathologies and physiologic dysfunctions in a wide range of organs and tissues, including the hepatobiliary system, the myocardium, lungs, and endocrine tissues. Although most cases of reovirus infection are mild or subclinical diseases, the prevention measures are currently needed, especially for young children suffering from dehydrating gastroenteritis. To inhibit viral replication, different RNases targeting viral RNA are proposed. Here, we first have shown that RNase from Bacillus pumilus (binase) acts as an antiviral agent at the level of the whole animal organism infected by Mammalian orthoreovirus 1 strain Lang (TL1). The results obtained on the mice model infected with 10 LD₅₀ and 20 LD₅₀ doses of reovirus indicate the restoration of mice physiological parameters under binase treatment at the dose of 50 μg/mouse. Thus, our research supports the relevance of binase as a promising antiviral agent that affects viral RNA.

Bat mammalian orthoreoviruses cause severe pneumonia in mice

Mammalian orthoreovirus (MRV) infections are ubiquitous in mammals. Increasing evidence suggests that some MRVs can cause severe respiratory disease and encephalitis in humans and other animals. Previously, we isolated six bat MRV strains. However, the pathogenicity of these bat viruses remains unclear. In this study, we investigated the host range and pathogenicity of 3 bat MRV strains (WIV2, 3 and 7) which represent three serotypes. Our results showed that all of them can infect cell lines from different mammalian species and displayed different replication efficiency. The BALB/c mice infected by bat MRVs showed clinical symptoms with systematic infection especially in lung and intestines. Obvious tissue damage were found in all infected lungs. One of the strains, WIV7, showed higher replication efficiency in vitro and vivo and more severe pathogenesis in mice. Our results provide new evidence showing potential pathogenicity of bat MRVs in animals and probable risk in humans.

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Bat MRVs show wide cell tropism in vivo and in vitro and have a high replication efficiency in lung and intestines.

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Mice infected by bat MRVs showed clinical illness, but without death.

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The higher replication in brain, lung damage and weak innate immune response may be responsible for severe diseases for WIV7.

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The results indicate the potential pathogenicity of bat MRV to human and animals.

Prevalence and genomic characteristics of a novel reassortment mammalian orthoreovirus type 2 in diarrhea piglets in Sichuan, China

Mammalian orthoreovirus (MRV), which can infect almost all mammals, is a zoonotic virus. In this study, six strains of type 2 MRV (MRV2) were isolated from 7 diarrhea piglets from a farm that had an outbreak of diarrhea in piglets in 2018, which tested negative for porcine epidemic diarrhea virus (PEDV), porcine transmissible gastroenteritis virus (TGEV), porcine deltacoronavirus (PDCoV), and porcine group A rotavirus (RAV). The MRV2 isolate infected neonatal piglets, in which it induced severe diarrhea, while the virus was detected in multiple organs of piglets. Moreover, the complete genome of an MRV2 isolate was obtained, which was a novel reassortant MRV strain of human MRV, porcine MRV, chamois MRV, bat MRV, and mink MRV based on the nucleotide identity and phylogenetic tree. The S1 gene of isolate had eight unique amino acid mutations compared with available MRV2 S1 in the GenBank. To investigate the prevalence of this MRV2, 78 samples of diarrhea feces were collected from 10 pig farms in seven regions of Sichuan province. The obtained results showed that the positive rate of samples was 14% (11/78), and positive rate of farms was 60% (6/10), while the amplified fragments shared the identical amino acid mutations with the isolated strain, thus suggesting that this MRV2 strain was already prevalent in Sichuan province. The present study was first to isolate a pig-derived type 2 MRV strain in China, obtaining the complete genome of this strain, which furthers our understanding of the MRV2 epidemic and evolution.

First identification of mammalian orthoreovirus type 3 by gut virome analysis in diarrheic child in Brazil

Diarrhea remains one of the most common causes of deaths in children. Although many studies have investigated the prevalence of enteric pathogens around the globe some diarrheal episodes remain unexplained. It is possible that some yet-unidentified viral agents could be related to these cases of gastroenteritis. By using viral metagenomics techniques, we screened 251 fecal samples of children between 0.5 to 2.5-year-old with acute diarrhea not associated with common pathogens. These children live in rural areas and have different levels of contact with animals such as pigs, cows and bats. Here we report a complete genome of one mammalian orthoreovirus (MRV) type 3, denoted TO-151/BR, detected in a female child in the state of Tocantins (north of Brazil). Brazilian TO-151/BR strain was classified as MRV-3 based on S1 phylogeny and was closely related to porcine Asian strains. Phylogenetic analyses showed that other segments were more similar to MRV-3s of different geographic locations and hosts, including human and bats, highlighting genome reassortment and lack of host-specific barriers. This is the first report of MRV-3 in South America and a hypothesis of a silent long-term circulation of this virus in Brazil has been raised.

Serological evidence and experimental infection of cynomolgus macaques with pteropine orthoreovirus reveal monkeys as potential hosts for transmission to humans

Pteropine orthoreoviruses (PRV) are emerging bat-borne viruses with proven zoonotic transmission. We recently demonstrated human exposure to PRV in Singapore, which together with previous reports from Malaysia and Vietnam suggest that human infection of PRV may occur periodically in the region. This raises the question whether bats are the only sources of human infection. In this study, we screened 517 cynomolgus macaques caught in Singapore for evidence of exposure to PRV3M (also known as Melaka virus), which was first isolated from human patients in Melaka, Malaysia. We found that 67 serum samples were PRV3M positive by ELISA and 34 were also positive by virus neutralization assay. To investigate whether monkeys could act as hosts for PRV transmission, we experimentally infected cynomolgus macaques with PRV3M and housed these animals with uninfected monkeys. Although no clinical signs of infection were observed in infected animals, viral RNA was detected in nasal and rectal swabs and all infected macaques seroconverted. Additionally, one of the uninfected animals seroconverted, implying active shedding and transmission of PRV3M. We provide evidence that PRV exposure in the macaque population in Singapore occurs at a relatively high prevalence and this study suggests that cynomolgus macaques may be an intermediate or reservoir host for PRVs.

The effects of autophagy on the replication of Nelson Bay orthoreovirus

BACKGROUND

Nelson Bay orthoreovirus (NBV) was first isolated over 40 years ago from a fruit bat in Australia. Normally, NBV does not cause human diseases, but recently several NBV strains have been associated with human respiratory tract infections, thus attracting clinical attention. Autophagy, an evolutionarily conserved process in eukaryotic cells, degrades intracellular substrates, participates in multiple physiological processes, and maintains cellular homeostasis. In addition, autophagy is intimately involved in viral infection.

METHODS

A new strain of NBV, isolated from a patient with a respiratory tract infection who returned to Japan from Bali, Indonesia, in 2007, was used in this study. NBV was rescued using a reverse genetics system involving cotransfection of BHK cells with 11 plasmids (pT7-L1 MB, pT7-L2 MB, pT7-L3 MB, pT7-M1 MB, pT7-M2 MB, pT7-M3 MB, pT7-S1 MB, pT7-S2 MB, pT7-S3 MB, pT7-S4 MB, and pcDNA3.1-T7), yielding NBV-MB. Recovered viruses were confirmed by immunofluorescence. The effect of NBV-MB on autophagy was evaluated by measuring the LC3-I/II proteins by immunoblot analysis after infection of BHK cells. Furthermore, after treatment with rapamycin (RAPA), 3-methyladenine (3-MA), chloroquine (CQ), or plasmid (GFP-LC3) transfection, the changes in expression of the LC3 gene and the amount of LC3-I/II protein were examined. In addition, variations in viral titer were assayed after treatment of BHK cells with drugs or after transfection with plasmids pCAGM3 and pCAGS3, which encode virus nonstructural proteins μNS and σNS, respectively.

RESULTS

NBV-MB infection induced autophagy in host cells; however, the level of induction was dependent on viral replication. Induction of autophagy increased viral replication. By contrast, inhibiting autophagy suppressed NBV replication, albeit not significantly. The NBV-MB nonstructural protein μNS was involved in the induction of autophagy with viral infection.

CONCLUSIONS

NBV-MB infection triggered autophagy. Also, the NBV nonstructural protein μNS may contribute to augmentation of autophagy upon viral infection.

Fusogenic Reoviruses and Their Fusion-Associated Small Transmembrane (FAST) Proteins

With no limiting membrane surrounding virions, nonenveloped viruses have no need for membrane fusion to gain access to intracellular replication compartments. Consequently, nonenveloped viruses do not encode membrane fusion proteins. The only exception to this dogma is the fusogenic reoviruses that encode fusion-associated small transmembrane (FAST) proteins that induce syncytium formation. FAST proteins are the smallest viral membrane fusion proteins and, unlike their enveloped virus counterparts, are nonstructural proteins that evolved specifically to induce cell-to-cell, not virus-cell, membrane fusion. This distinct evolutionary imperative is reflected in structural and functional features that distinguish this singular family of viral fusogens from all other protein fusogens. These rudimentary fusogens comprise specific combinations of different membrane effector motifs assembled into small, modular membrane fusogens. FAST proteins offer a minimalist model to better understand the ubiquitous process of protein-mediated membrane fusion and to reveal novel mechanisms of nonenveloped virus dissemination that contribute to virulence.

Earth observation for public health: Biodiversity change and emerging disease surveillance

One Health is an emerging concept in the health sciences that approaches human, animal and environmental health from a single framework. This policy approach is grounded in the knowledge that approximately 70 percent of emerging diseases in humans originate from other species, and that this species crossover is precipitated by stresses to environmental systems such as habitat change and biodiversity loss. Remote sensing tools apply well to this approach due to the multitude of variables that can be measured across borders in real-time. This paper explores the challenges and opportunities of using satellite remote sensing to monitor biodiversity loss in real time, with a goal of predictive surveillance for emerging disease events. Key findings include that (1) certain emerging disease events are preceded by biodiversity changes that can be observed from space; (2) refining quantitative assessments of biodiversity loss is a critical next step; and (3) biodiversity loss as observed from space merits inclusion in emerging disease surveillance programs as a complement to in situ and epidemiological surveillance data.

Exploiting the Legacy of the Arbovirus Hunters

In recent years, it has become evident that a generational gap has developed in the community of arbovirus research. This apparent gap is due to the dis-investment of training for the next generation of arbovirologists, which threatens to derail the rich history of virus discovery, field epidemiology, and understanding of the richness of diversity that surrounds us. On the other hand, new technologies have resulted in an explosion of virus discovery that is constantly redefining the virosphere and the evolutionary relationships between viruses. This paradox presents new challenges that may have immediate and disastrous consequences for public health when yet to be discovered arboviruses emerge. In this review we endeavor to bridge this gap by providing a historical context for the work being conducted today and provide continuity between the generations. To this end, we will provide a narrative of the thrill of scientific discovery and excitement and the challenges lying ahead.

Viruses in bats and potential spillover to animals and humans

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Bats are a very important source of emerging viruses.

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Bat coronavirus, filovirus, paramyxovirus and reovirus are known zoonotic viruses.

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Many of the emergent bat viruses are highly lethal in livestock and humans.

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Past incidents and viral genetic features predict bat coronaviruses as the highest risk.

In the last two decades, several high impact zoonotic disease outbreaks have been linked to bat-borne viruses. These include SARS coronavirus, Hendra virus and Nipah virus. In addition, it has been suspected that ebolaviruses and MERS coronavirus are also linked to bats. It is being increasingly accepted that bats are potential reservoirs of a large number of known and unknown viruses, many of which could spillover into animal and human populations. However, our knowledge into basic bat biology and immunology is very limited and we have little understanding of major factors contributing to the risk of bat virus spillover events. Here we provide a brief review of the latest findings in bat viruses and their potential risk of cross-species transmission.

Serological evidence of human infection by bat orthoreovirus in Singapore

To determine whether Pteropine orthoreovirus (PRV) exposure has occurred in Singapore, we tested 856 individuals from an existing serum panel collected from 2005-2013. After an initial screen with luciferase immunoprecipitation system and secondary confirmation with virus neutralization test, we identified at least seven individuals with specific antibodies against PRV in both assays. Our findings confirm that PRV spillover into human populations is relatively common in this region of the world.

Sialic Acids in Nonenveloped Virus Infections

Sialic acid-based glycoconjugates cover the surfaces of many different cell types, defining key properties of the cell surface such as overall charge or likely interaction partners. Because of this prominence, sialic acids play prominent roles in mediating attachment and entry to viruses belonging to many different families. In this review, we first describe how interactions between viruses and sialic acid-based glycan structures can be identified and characterized using a range of techniques. We then highlight interactions between sialic acids and virus capsid proteins in four different viruses, and discuss what these interactions have taught us about sialic acid engagement and opportunities to interfere with binding.

Mass spectrometry-based identification and whole-genome characterisation of the first pteropine orthoreovirus isolated from monkey faeces in Thailand

Background

The pteropine orthoreovirus (PRV) was isolated from monkey (Macaca fascicularis) faecal samples collected from human-inhabited areas in Lopburi Province, Thailand. These samples were initially obtained to survey for the presence of hepatitis E virus (HEV).

Results

Two virus isolates were retrieved by virus culture of 55 monkey faecal samples. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was successfully used to identify the viruses as the segmented dsRNA orthoreovirus. Phylogenetic analysis of the Lopburi orthoreovirus whole-genomes revealed relationships with the well-characterised PRVs Pulau (segment L1), Cangyuan (segments L2, M3 and S3), Melaka (segments L3 and M2), Kampar (segments M1 and S2) and Sikamat (segments S1 and S4) of Southeast Asia and China with nucleotide sequence identities of 93.5–98.9%. RT-PCR showed that PRV was detected in 10.9% (6/55) and HEV was detected in 25.5% (14/55) of the monkey faecal samples.

Conclusions

PRV was isolated from monkey faeces for the first time in Thailand via viral culture and LC-MS/MS. The genetic diversity of the virus genome segments suggested a re-assortment within the PRV species group. The overall findings emphasise that monkey faeces can be sources of zoonotic viruses, including PRV and HEV, and suggest the need for active virus surveillance in areas of human and monkey co-habitation to prevent and control emerging zoonotic diseases in the future.

Electronic supplementary material

The online version of this article (10.1186/s12866-018-1302-9) contains supplementary material, which is available to authorized users.

Isolation of Pteropine orthoreovirus from Pteropus vampyrus in Garut, Indonesia

Flying foxes belonging to the genus Pteropus are known to be reservoirs of zoonotic viruses. In this study, we describe the isolation of Pteropine orthoreovirus (PRV) from rectal swab samples of Pteropus vampyrus in Indonesia. PRV is an emerging zoonotic respiratory virus that can be transmitted from bats to humans. Rectal swabs (n = 91) were screened by PCR for PRV and 10 (11%) were positive. Phylogenetic analysis based on nucleotide sequences indicated that the S2, S3, S4, M3, L2, and L3 segments of one isolate (Garut-69) were closely related to previously isolated strains in Indonesia. The remaining gene segments showed both similarity and genetic divergence with other PRV strains, suggesting that re-assortment events had occurred. This is the first report of PRV infection to P. vampyrus in West Java, Indonesia.

Lethal murine infection model for human respiratory disease-associated Pteropine orthoreovirus

Pteropine orthoreovirus (PRV) is an emerging bat-borne human pathogen causing severe respiratory illness. To date, however, the evaluation of PRV virulence has largely depended on the limited numbers of clinical cases owing to the lack of animal models. To develop an in vivo model of PRV infection, an inbred C3H mouse strain was infected intranasally with pathogenic PRV strain Miyazaki-Bali/2007. C3H mice suffered severe lung infection with significant body weight reduction and died within 7 days after intranasal infection. Infectious viruses were isolated mainly from the lungs and trachea. Histopathological examination revealed interstitial pneumonia with monocytes infiltration. Following repeated intranasal infection, mice developed antibodies to particular structural and non-structural proteins of PRV. The results of these immunological assays will help to develop laboratory protocols for sero-epidemiological studies. Our small rodent model of lethal respiratory infection will further allow investigation of the molecular mechanisms underlying the high pathogenicity of PRV.

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A lethal PRV strain Miyazaki-Bali/2007 murine infection model was established.

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Susceptibility of different mouse strains to PRV infection was investigated.

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Antibody responses to PRV proteins in C3H mice post intranasal infection were studied.