Shared Common Ancestry of Rodent Alphacoronaviruses Sampled Globally

RNA virus diversity in rodents

Many zoonotic disease emergencies are associated with RNA viruses in rodents that substantially impact public health. With the widespread application of meta-genomics and meta-transcriptomics for virus discovery over the last decade, viral sequences deposited in public databases have expanded rapidly, and the number of novel viruses discovered in rodents has increased. As important reservoirs of zoonotic viruses, rodents have attracted increasing attention for the risk of potential spillover of rodent-borne viruses. However, knowledge of rodent viral diversity and the major factors contributing to the risk of zoonotic epidemic outbreaks remains limited. Therefore, this study analyzes the diversity and composition of rodent RNA viruses using virus records from the Database of Rodent-associated Viruses (DRodVir/ZOVER), which covers the published literatures and records in GenBank database, reviews the main rodent RNA virus-induced human infectious diseases, and discusses potential challenges in this field.

Detection and characterization of novel luchacoviruses, genus Alphacoronavirus, in saliva and feces of meso-carnivores in the northeastern United States

IMPORTANCE

Several coronaviruses (CoVs) have been detected in domesticated, farmed, and wild meso-carnivores, causing a wide range of diseases and infecting diverse species, highlighting their important but understudied role in the epidemiology of these viruses. Assessing the viral diversity hosted in wildlife species is essential to understand their significance in the cross-species transmission of CoVs. Our focus here was on CoV discovery in meso-carnivores in the Northeast United States as a potential "hotspot" area with high density of humans and urban wildlife. This study identifies novel alphacoronaviruses circulating in multiple free-ranging wild and domestic species in this area and explores their potential epidemiological importance based on regions of the Spike gene, which are relevant for virus-host interactions.

Detection and characterization of novel luchacoviruses, genus Alphacoronavirus, shed in saliva and feces of meso-carnivores in the northeastern United States

Small to mid-sized carnivores, or meso-carnivores, comprise a group of diverse mammals, many of which can adapt to anthropogenically disturbed environments. Wild meso-carnivores living in urban areas may get exposed to or spread pathogens to other species, including stray/feral domestic animals. Several coronaviruses (CoVs) have been detected in domesticated and farmed meso-carnivores, but knowledge of CoVs circulating in free-ranging wild meso-carnivores remains limited. In this study, we analyzed 321 samples collected between 2016 and 2022 from 9 species of free-ranging wild meso-carnivores and stray/feral domestic cats in the northeastern United States. Using a pan-CoV PCR, we screened tissues, feces, and saliva, nasal, and rectal swabs. We detected CoV RNA in fecal and saliva samples of animals in four species: fisher (Pekania pennanti), bobcat (Lynx rufus), red fox (Vulpes vulpes), and domestic cat (Felis catus). Next-generation sequencing revealed that all these viruses belonged to the Luchacovirus subgenus (Alphacoronavirus genus), previously reported only in rodents and lagomorphs (i.e., rabbits). Genetic comparison of the 3'-end of the genome (~12,000bp) revealed that although the viruses detected group with, and have a genetic organization similar to other luchacoviruses, they are genetically distinct from those from rodents and lagomorphs. Genetic characterization of the spike protein revealed that the meso-carnivore luchacoviruses do not have an S1/S2 cleavage motif but do have highly variable structural loops containing cleavage motifs similar to those identified in certain pathogenic CoVs. This study highlights the importance of characterizing the spike protein of CoVs in wild species for further targeted epidemiologic monitoring.

Investigations into SARS-CoV-2 and other coronaviruses on mink farms in France late in the first year of the COVID-19 pandemic

Soon after the beginning of the COVID-19 pandemic in early 2020, the Betacoronavirus SARS-CoV-2 infection of several mink farms breeding American minks (Neovison vison) for fur was detected in various European countries. The risk of a new reservoir being formed and of a reverse zoonosis from minks quickly became a major concern. The aim of this study was to investigate the four French mink farms to see whether SARS-CoV-2 was circulating there in late 2020. The investigations took place during the slaughtering period, thus facilitating different types of sampling (swabs and blood). On one of the four mink farms, 96.6% of serum samples were positive when tested with a SARS-CoV-2 ELISA coated with purified N protein recombinant antigen, and 54 out of 162 (33%) pharyngo-tracheal swabs were positive by RT-qPCR. The genetic variability among 12 SARS-CoV-2 genomes sequenced from this farm indicated the co-circulation of several lineages at the time of sampling. All the SARS-CoV-2 genomes detected were nested within the 20A clade (Nextclade), together with SARS-CoV-2 genomes from humans sampled during the same period. The percentage of SARS-CoV-2 seropositivity by ELISA varied between 0.3 and 1.1% on the other three farms. Interestingly, among these three farms, 11 pharyngo-tracheal swabs and 3 fecal pools from two farms were positive by end-point RT-PCR for an Alphacoronavirus very similar to a mink coronavirus sequence observed on Danish farms in 2015. In addition, a mink Caliciviridae was identified on one of the two farms positive for Alphacoronavirus. The clinical impact of these inapparent viral infections is not known. The co-infection of SARS-CoV-2 with other viruses on mink farms could help explain the diversity of clinical symptoms noted on different infected farms in Europe. In addition, the co-circulation of an Alphacoronavirus and SARS-CoV-2 on a mink farm would potentially increase the risk of viral recombination between alpha and betacoronaviruses as already suggested in wild and domestic animals, as well as in humans.

Intragenomic rearrangements involving 5'-untranslated region segments in SARS-CoV-2, other betacoronaviruses, and alphacoronaviruses

BACKGROUND

Variation of the betacoronavirus SARS-CoV-2 has been the bane of COVID-19 control. Documented variation includes point mutations, deletions, insertions, and recombination among closely or distantly related coronaviruses. Here, we describe yet another aspect of genome variation by beta- and alphacoronaviruses that was first documented in an infectious isolate of the betacoronavirus SARS-CoV-2, obtained from 3 patients in Hong Kong that had a 5'-untranslated region segment at the end of the ORF6 gene that in its new location translated into an ORF6 protein with a predicted modified carboxyl terminus. While comparing the amino acid sequences of translated ORF8 genes in the GenBank database, we found a subsegment of the same 5'-UTR-derived amino acid sequence modifying the distal end of ORF8 of an isolate from the United States and decided to carry out a systematic search.

METHODS

Using the nucleotide and in the case of SARS-CoV-2 also the translated amino acid sequence in three reading frames of the genomic termini of coronaviruses as query sequences, we searched for 5'-UTR sequences in regions other than the 5'-UTR in SARS-CoV-2 and reference strains of alpha-, beta-, gamma-, and delta-coronaviruses.

RESULTS

We here report numerous genomic insertions of 5'-untranslated region sequences into coding regions of SARS-CoV-2, other betacoronaviruses, and alphacoronaviruses, but not delta- or gammacoronaviruses. To our knowledge this is the first systematic description of such insertions. In many cases, these insertions would change viral protein sequences and further foster genomic flexibility and viral adaptability through insertion of transcription regulatory sequences in novel positions within the genome. Among human Embecorivus betacoronaviruses, for instance, from 65% to all of the surveyed sequences in publicly available databases contain inserted 5'-UTR sequences.

CONCLUSION

The intragenomic rearrangements involving 5'-untranslated region sequences described here, which in several cases affect highly conserved genes with a low propensity for recombination, may underlie the generation of variants homotypic with those of concern or interest and with potentially differing pathogenic profiles. Intragenomic rearrangements thus add to our appreciation of how variants of SARS-CoV-2 and other beta- and alphacoronaviruses may arise.

Investigations on SARS-CoV-2 and other coronaviruses in mink farms in France at the end of the first year of COVID-19 pandemic

Soon after the beginning of the COVID-19 pandemic in early 2020, the Betacoronavirus SARS-CoV-2 infection of several mink farms breeding American minks ( Neovison vison ) for fur was detected in several countries of Europe. The risk of a new reservoir formation and of a reverse zoonosis from minks was then a major concern. The aim of this study was to investigate the four French mink farms for the circulation of SARS-CoV-2 at the end of 2020. The investigations took place during the slaughtering period thus facilitating different types of sampling (swabs and blood). In one of the four mink farms, 96.6% of serum samples were positive in SARS-CoV-2 ELISA coated with purified N protein recombinant antigen and 54 out of 162 (33%) pharyngo-tracheal swabs were positive by RT-qPCR. The genetic variability among 12 SARS-CoV-2 genomes sequenced in this farm indicated the co-circulation of several lineages at the time of sampling. All SARS-CoV-2 genomes detected were nested within the 20A clade (Nextclade), together with SARS-CoV-2 genomes from humans sampled at the same period. The percentage of SARS-CoV-2 seropositivity by ELISA varied between 0.5 and 1.2% in the three other farms. Interestingly, among these three farms, 11 pharyngo-tracheal swabs and 3 fecal pools from two farms were positive by end-point RT-PCR for an Alphacoronavirus highly similar to a mink coronavirus sequence observed in Danish farms in 2015. In addition, a mink Caliciviridae was identified in one of the two positive farms for Alphacoronavirus . The clinical impact of these unapparent viral infections is not known. The co-infection of SARS-CoV-2 with other viruses in mink farms could contribute to explain the diversity of clinical symptoms noted in different infected farms in Europe. In addition, the co-circulation of an Alphacoronavirus and SARS-CoV-2 within a mink farm would increase potentially the risk of viral recombination between alpha and betacoronaviruses already suggested in wild and domestic animals, as well as in humans.

Author summary

France is not a country of major mink fur production. Following the SARS-CoV-2 contamination of mink farms in Denmark and the Netherlands, the question arose for the four French farms.The investigation conducted at the same time in the four farms revealed the contamination of one of them by a variant different from the one circulating at the same time in Denmark and the Netherlands mink farms. Investigation of three other farms free of SARS-CoV-2 contamination revealed the circulation of other viruses including a mink Alphacoronavirus and Caliciviridae , which could modify the symptomatology of SARS-CoV-2 infection in minks.

Discovery of a Novel Coronavirus in Swedish Bank Voles (Myodes glareolus)

The unprecedented pandemic COVID-19, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), with bats as original reservoirs, has once again highlighted the importance of exploring the interface of wildlife diseases and human health. In this study, we identified a novel Betacoronavirus from bank voles (Myodes glareolus) in Grimsö, Sweden, and this virus is designated as Grimso virus. Repeated detection over three years and an overall prevalence of 3.4% suggest that the virus commonly occurs in bank voles. Furthermore, phylogenetic analyses indicate that the Grimso virus belongs to a highly divergent Embecovirus lineage predominantly associated with bank voles. Given that bank voles are one of the most common rodent species in Sweden and Europe, our findings indicate that Grimso virus might be circulating widely in bank voles and further point out the importance of sentinel surveillance of coronaviruses in wild small mammalian animals, especially in wild rodents.

Homology-based classification of accessory proteins in coronavirus genomes uncovers extremely dynamic evolution of gene content

Coronaviruses (CoVs) have complex genomes that encode a fixed array of structural and nonstructural components, as well as a variety of accessory proteins that differ even among closely related viruses. Accessory proteins often play a role in the suppression of immune responses and may represent virulence factors. Despite their relevance for CoV phenotypic variability, information on accessory proteins is fragmentary. We applied a systematic approach based on homology detection to create a comprehensive catalogue of accessory proteins encoded by CoVs. Our analyses grouped accessory proteins into 379 orthogroups and 12 super‐groups. No orthogroup was shared by the four CoV genera and very few were present in all or most viruses in the same genus, reflecting the dynamic evolution of CoV genomes. We observed differences in the distribution of accessory proteins in CoV genera. Alphacoronaviruses harboured the largest diversity of accessory open reading frames (ORFs), deltacoronaviruses the smallest. However, the average number of accessory proteins per genome was highest in betacoronaviruses. Analysis of the evolutionary history of some orthogroups indicated that the different CoV genera adopted similar evolutionary strategies. Thus, alphacoronaviruses and betacoronaviruses acquired phosphodiesterases and spike‐like accessory proteins independently, whereas horizontal gene transfer from reoviruses endowed betacoronaviruses and deltacoronaviruses with fusion‐associated small transmembrane (FAST) proteins. Finally, analysis of accessory ORFs in annotated CoV genomes indicated ambiguity in their naming. This complicates cross‐communication among researchers and hinders automated searches of large data sets (e.g., PubMed, GenBank). We suggest that orthogroup membership is used together with a naming system to provide information on protein function.

Discovery and Evolutionary Analysis of a Novel Bat-Borne Paramyxovirus

Paramyxoviruses are a group of RNA viruses, such as mumps virus, measles virus, Nipah virus, Hendra virus, Newcastle disease virus, and parainfluenza virus, usually transmitted by airborne droplets that are predominantly responsible for acute respiratory diseases. In this paper, we identified a novel paramyxovirus belonging to genus Jeilongvirus infecting 4/112 (3.6%) bats from two trapping sites of Hainan Province of China. In these animals, the viral RNA was detected exclusively in kidney tissues. This is the first full-length Jeilongvirus genome (18,095 nucleotides) from bats of genus Hipposideros, which exhibits a canonical genome organization and encodes SH and TM proteins. Results, based on phylogenic analysis and genetic distances, indicate that the novel paramyxovirus formed an independent lineage belonging to genus Jeilongvirus, representing, thus, a novel species. In addition, the virus-host macro-evolutionary analysis revealed that host-switching was not only a common co-phylogenetic event, but also a potential mechanism by which rats are infected by bat-origin Jeilongvirus through cross-species virus transmission, indicating a bat origin of the genus Jeilongvirus. Overall, our study broadens the viral diversity, geographical distribution, host range, and evolution of genus Jeilongvirus.

The Neighborhood of the Spike Gene Is a Hotspot for Modular Intertypic Homologous and Nonhomologous Recombination in Coronavirus Genomes

Coronaviruses (CoVs) have very large RNA viral genomes with a distinct genomic architecture of core and accessory open reading frames (ORFs). It is of utmost importance to understand their patterns and limits of homologous and nonhomologous recombination, because such events may affect the emergence of novel CoV strains, alter their host range, infection rate, tissue tropism pathogenicity, and their ability to escape vaccination programs. Intratypic recombination among closely related CoVs of the same subgenus has often been reported; however, the patterns and limits of genomic exchange between more distantly related CoV lineages (intertypic recombination) need further investigation. Here, we report computational/evolutionary analyses that clearly demonstrate a substantial ability for CoVs of different subgenera to recombine. Furthermore, we show that CoVs can obtain-through nonhomologous recombination-accessory ORFs from core ORFs, exchange accessory ORFs with different CoV genera, with other viruses (i.e., toroviruses, influenza C/D, reoviruses, rotaviruses, astroviruses) and even with hosts. Intriguingly, most of these radical events result from double crossovers surrounding the Spike ORF, thus highlighting both the instability and mobile nature of this genomic region. Although many such events have often occurred during the evolution of various CoVs, the genomic architecture of the relatively young SARS-CoV/SARS-CoV-2 lineage so far appears to be stable.

Furin cleavage sites in the spike proteins of bat and rodent coronaviruses: Implications for virus evolution and zoonotic transfer from rodent species

Bats and rodents comprise two of the world's largest orders of mammals and the order Chiroptera (bats) has been implicated as a major reservoir of coronaviruses in nature and a source of zoonotic transfer to humans. However, the order Rodentia (rodents) also harbors coronaviruses, with two human coronaviruses (HCoV-OC43 and HCoV-HKU1) considered to have rodent origins. The coronavirus spike protein mediates viral entry and is a major determinant of viral tropism; importantly, the spike protein is activated by host cell proteases at two distinct sites, designated as S1/S2 and S2'. SARS-CoV-2, which is considered to be of bat origin, contains a cleavage site for the protease furin at S1/S2, absent from the rest of the currently known betacoronavirus lineage 2b coronaviruses (Sarbecoviruses). This cleavage site is thought to be critical to its replication and pathogenesis, with a notable link to virus transmission. Here, we examine the spike protein across coronaviruses identified in both bat and rodent species and address the role of furin as an activating protease. Utilizing two publicly available furin prediction algorithms (ProP and PiTou) and based on spike sequences reported in GenBank, we show that the S1/S2 furin cleavage site is typically not present in bat virus spike proteins but is common in rodent-associated sequences, and suggest this may have implications for zoonotic transfer. We provide a phylogenetic history of the Embecoviruses (betacoronavirus lineage 2a), including context for the use of furin as an activating protease for the viral spike protein. From a One Health perspective, continued rodent surveillance should be an important consideration in uncovering novel circulating coronaviruses.

The taxonomy, host range and pathogenicity of coronaviruses and other viruses in the Nidovirales order

The frequent emergence of coronavirus (CoV) epidemics has seriously threatened public health and stock farming. The major hosts for CoVs are birds and mammals. Although most CoVs inhabit their specific natural hosts, some may occasionally cross the host barrier to infect livestock and even people, causing a variety of diseases. Since the beginning of the new century, increasing attention has been given to research on CoVs due to the emergence of highly pathogenic and genetically diverse CoVs that have caused several epidemics, including the recent COVID-19 pandemic. CoVs belong to the Coronaviridae family of the Nidovirales order. Recently, advanced techniques for viral detection and viral genome analyses have enabled characterization of many new nidoviruses than ever and have greatly expanded the Nidovirales order with new classification and nomenclature. Here, we first provide an overview of the latest research progress in the classification of the Nidovirales order and then introduce the host range, genetic variation, genomic pattern and pathogenic features of epidemic CoVs and other epidemic viruses. This information will promote understanding of the phylogenetic relationship and infectious transmission of various pathogenic nidoviruses, including epidemic CoVs, which will benefit virological research and viral disease control.

Discovery and Evolution of a Divergent Coronavirus in the Plateau Pika From China That Extends the Host Range of Alphacoronaviruses

Although plateau pikas are the keystone species in the plateau ecosystem of the Qinghai Province of China, little is known about their role in the evolution and transmission of viral pathogens, especially coronaviruses. Here, we describe the characterization and evolution of a novel alphacoronavirus, termed plateau pika coronavirus (PPCoV) P83, which has a prevalence of 4.5% in plateau pika fecal samples. In addition to classical gene order, the complete viral genome contains a unique nonstructural protein (NS2), several variable transcription regulatory sequences and a highly divergent spike protein. Phylogenetic analysis indicates that the newly discovered PPCoV falls into the genus Alphacoronavirus and is most closely related to rodent alphacoronaviruses. The co-speciation analysis shows that the phylogenetic trees of the alphacoronaviruses and their hosts are not always matched, suggesting inter-species transmission is common in alphacoronaviruses. And, PPCoV origin was estimated by molecular clock based on membrane and RNA-dependent RNA polymerase encoding genes, respectively, which revealed an apparent discrepancy with that of co-speciation analysis. PPCoV was detected mainly in intestinal samples, indicating a potential enteric tropism for the virus. Overall, this study extends the host range of alphacoronaviruses to a new order (Lagomorpha), indicating that plateau pikas may be the natural reservoir of PPCoV and play an important and long-term role in alphacoronavirus evolution.

Update on the Phylodynamics of SADS-CoV

Coronaviruses are known to be harmful and heterogeneous viruses, able to infect a large number of hosts. Among them, SADS-CoV (Swine Acute Diarrhea Syndrome Coronavirus), also known as PEAV (Porcine Enteric Alphacoronavirus), or SeA-CoV (Swine Enteric Alphacoronavirus), is the most recent Alphacoronavirus discovered, and caused several outbreaks reported in Chinese swine herds between late 2016 and 2019. We performed an upgraded phylodinamic reconstruction of SADS-CoV based on all whole genomes available on 21 June 2021. Results showed a very close relationship between SADS-CoV and HKU2-like CoV, which may represent the evolutionary intermediate step towards the present SADS-CoV. The direct progenitor of SADS-CoV is so far unknown and, although it is well known that horseshoe bats are reservoirs for Rhinolophus bat coronavirus HKU2-like (HKU2-like CoVs), the transmission path from bats to pigs is still unclear. The discrepancies in the phylogenetic position of rodent CoV, when different molecular markers were considered, corroborate the recombination hypothesis, suggesting that wild rats, which are frequent in farms, may have played a key role. The failure of the attempt at molecular dating, due to the lack of a clock signal, also corroborates the occurrence of a recombination event hypothesis. Zoonotic infections originating in wildlife can easily become a significant threat for human health. In such a context, due to the high recombination and cross-species capabilities of Coronavirus, SADS-CoV represents a possible high-risk pathogen for humans which needs a constant molecular monitoring.

SARS-CoV-2 infection, neuropathogenesis and transmission among deer mice: Implications for spillback to New World rodents

Coronavirus disease-19 (COVID-19) emerged in late 2019 in China and rapidly became pandemic. As with other coronaviruses, a preponderance of evidence suggests the virus originated in horseshoe bats (Rhinolophus spp.) and may have infected an intermediate host prior to spillover into humans. A significant concern is that SARS-CoV-2 could become established in secondary reservoir hosts outside of Asia. To assess this potential, we challenged deer mice (Peromyscus maniculatus) with SARS-CoV-2 and found robust virus replication in the upper respiratory tract, lungs and intestines, with detectable viral RNA for up to 21 days in oral swabs and 6 days in lungs. Virus entry into the brain also occurred, likely via gustatory-olfactory-trigeminal pathway with eventual compromise to the blood-brain barrier. Despite this, no conspicuous signs of disease were observed, and no deer mice succumbed to infection. Expression of several innate immune response genes were elevated in the lungs, including IFNα, IFNβ, Cxcl10, Oas2, Tbk1 and Pycard. Elevated CD4 and CD8β expression in the lungs was concomitant with Tbx21, IFNγ and IL-21 expression, suggesting a type I inflammatory immune response. Contact transmission occurred from infected to naive deer mice through two passages, showing sustained natural transmission and localization into the olfactory bulb, recapitulating human neuropathology. In the second deer mouse passage, an insertion of 4 amino acids occurred to fixation in the N-terminal domain of the spike protein that is predicted to form a solvent-accessible loop. Subsequent examination of the source virus from BEI Resources determined the mutation was present at very low levels, demonstrating potent purifying selection for the insert during in vivo passage. Collectively, this work has determined that deer mice are a suitable animal model for the study of SARS-CoV-2 respiratory disease and neuropathogenesis, and that they have the potential to serve as secondary reservoir hosts in North America.

Discovery of Novel Coronaviruses in Rodents

The recent emergence of SARS, SARS-CoV2 and MERS and the discovery of novel coronaviruses in animals and birds suggest that the Coronavirus family is far more diverse than previously thought. In the last decade, several new coronaviruses have been discovered in rodents around the globe, suggesting that they are the natural reservoirs of the virus. In this chapter we describe the process of screening rodent tissue for novel coronaviruses with PCR, a method that is easily adaptable for screening a range of animals.

SARS-CoV-2 infection, neuropathogenesis and transmission among deer mice: Implications for reverse zoonosis to New World rodents

Coronavirus disease-19 (COVID-19) emerged in November, 2019 in China and rapidly became pandemic. As with other coronaviruses, a preponderance of evidence suggests the virus originated in horseshoe bats (Rhinolophus spp.) and likely underwent a recombination event in an intermediate host prior to entry into human populations. A significant concern is that SARS-CoV-2 could become established in secondary reservoir hosts outside of Asia. To assess this potential, we challenged deer mice (Peromyscus maniculatus) with SARS-CoV-2 and found robust virus replication in the upper respiratory tract, lungs and intestines, with detectable viral RNA for up to 21 days in oral swabs and 14 days in lungs. Virus entry into the brain also occurred, likely via gustatory-olfactory-trigeminal pathway with eventual compromise to the blood brain barrier. Despite this, no conspicuous signs of disease were observed and no deer mice succumbed to infection. Expression of several innate immune response genes were elevated in the lungs, notably IFNα, Cxcl10, Oas2, Tbk1 and Pycard. Elevated CD4 and CD8β expression in the lungs was concomitant with Tbx21, IFNγ and IL-21 expression, suggesting a type I inflammatory immune response. Contact transmission occurred from infected to naive deer mice through two passages, showing sustained natural transmission. In the second deer mouse passage, an insertion of 4 amino acids occurred to fixation in the N-terminal domain of the spike protein that is predicted to form a solvent-accessible loop. Subsequent examination of the source virus from BEI Resources indicated the mutation was present at very low levels, demonstrating potent purifying selection for the insert during in vivo passage. Collectively, this work has determined that deer mice are a suitable animal model for the study of SARS-CoV-2 pathogenesis, and that they have the potential to serve as secondary reservoir hosts that could lead to periodic outbreaks of COVID-19 in North America.

Swine enteric alphacoronavirus (swine acute diarrhea syndrome coronavirus): An update three years after its discovery

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A summary of the research progress in SeACoV (SADS-CoV) from 2017 to 2020.

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Bat-derived SeACoV was most recently recognized prior to SARS-CoV-2 associated with COVID-19.

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Focusing on the etiology, epidemiology, evolutionary perspective, potential for interspecies transmission, pathogenesis and diagnosis.

Discovered in 2017, swine enteric alphacoronavirus (SeACoV), also known as swine acute diarrhea syndrome coronavirus (SADS-CoV) or porcine enteric alphacoronavirus (PEAV), is the fifth porcine CoV identified in diarrheal piglets. The presumed name “SADS-CoV” may not be appropriate since current studies have not provided strong evidence for high pathogenicity of the virus. SeACoV was the most recently recognized CoV of potential bat origin prior to the novel human severe acute respiratory syndrome CoV 2 (SARS-CoV-2), associated with the pandemic CoV disease 2019 (COVID-19). Although SeACoV is recognized as a regional epizootic virus currently, it possesses the most extensive cell species tropism in vitro among known CoVs. This review summarizes the emergence of SeACoV and updates the research progress made from 2017 to early 2020, mainly focusing on the etiology, epidemiology, evolutionary perspective, potential for interspecies transmission, pathogenesis and diagnosis.

Discovery and Prevalence of Divergent RNA Viruses in European Field Voles and Rabbits

The advent of unbiased metagenomic virus discovery has revolutionized studies of virus biodiversity and evolution. Despite this, our knowledge of the virosphere, including in mammalian species, remains limited. We used unbiased metagenomic sequencing to identify RNA viruses in European field voles and rabbits. Accordingly, we identified a number of novel RNA viruses including astrovirus, rotavirus A, picorna-like virus and a morbilli-like paramyxovirus. In addition, we identified a sobemovirus and a novel luteovirus that likely originated from the rabbit diet. These newly discovered viruses were often divergent from those previously described. The novel astrovirus was most closely related to a virus sampled from the rodent-eating European roller bird (Coracias garrulous). PCR screening revealed that the novel morbilli-like paramyxovirus in the UK field vole had a prevalence of approximately 4%, and shared common ancestry with other rodent morbilli-like viruses sampled globally. Two novel rotavirus A sequences were detected in a UK field vole and a French rabbit, the latter with a prevalence of 5%. Finally, a highly divergent picorna-like virus found in the gut of the French rabbit virus was only ~35% similar to an arilivirus at the amino acid level, suggesting the presence of a novel viral genus within the Picornaviridae.

Infection Load and Prevalence of Novel Viruses Identified from the Bank Vole Do Not Associate with Exposure to Environmental Radioactivity

Bank voles (Myodes glareolus) are host to many zoonotic viruses. As bank voles inhabiting areas contaminated by radionuclides show signs of immunosuppression, resistance to apoptosis, and elevated DNA repair activity, we predicted an association between virome composition and exposure to radionuclides. To test this hypothesis, we studied the bank vole virome in samples of plasma derived from animals inhabiting areas of Ukraine (contaminated areas surrounding the former nuclear power plant at Chernobyl, and uncontaminated areas close to Kyiv) that differed in level of environmental radiation contamination. We discovered four strains of hepacivirus and four new virus sequences: two adeno-associated viruses, an arterivirus, and a mosavirus. However, viral prevalence and viral load, and the ability to cause a systemic infection, was not dependent on the level of environmental radiation.

Broad Cross-Species Infection of Cultured Cells by Bat HKU2-Related Swine Acute Diarrhea Syndrome Coronavirus and Identification of Its Replication in Murine Dendritic Cells In Vivo Highlight Its Potential for Diverse Interspecies Transmission

Infections with bat-origin coronaviruses (CoVs) (severe acute respiratory syndrome CoV [SARS-CoV] and Middle East respiratory syndrome CoV [MERS-CoV]) have caused severe illness in humans after “host jump” events. Recently, a novel bat-HKU2-like CoV named swine acute diarrhea syndrome CoV (SADS-CoV) has emerged in southern China, causing lethal diarrhea in newborn piglets. It is important to assess the species barriers of SADS-CoV infection since the animal hosts (other than pigs and bats) and zoonotic potential are still unknown. An in vitro susceptibility study revealed a broad species tropism of SADS-CoV, including various rodent and human cell lines. We established a mouse model of SADS-CoV infection, identifying its active replication in splenic dendritic cells, which suggests that SADS-CoV has the potential to infect rodents. These findings highlight the potential cross-species transmissibility of SADS-CoV, although further surveillance in other animal populations is needed to fully understand the ecology of this bat-HKU2-origin CoV.

Outbreaks of severe diarrhea in neonatal piglets in Guangdong, China, in 2017 resulted in the isolation and discovery of a novel swine enteric alphacoronavirus (SeACoV) derived from the species Rhinolophus bat coronavirus HKU2 (Y. Pan, X. Tian, P. Qin, B. Wang, et al., Vet Microbiol 211:15–21, 2017). SeACoV was later referred to as swine acute diarrhea syndrome CoV (SADS-CoV) by another group (P. Zhou, H. Fan, T. Lan, X.-L. Yang, et al., Nature 556:255–258, 2018). The present study was set up to investigate the potential species barriers of SADS-CoV in vitro and in vivo. We first demonstrated that SADS-CoV possesses a broad species tropism and is able to infect cell lines from diverse species, including bats, mice, rats, gerbils, hamsters, pigs, chickens, nonhuman primates, and humans. Trypsin contributes to but is not essential for SADS-CoV propagation in vitro. Furthermore, C57BL/6J mice were inoculated with the virus via oral or intraperitoneal routes. Although the mice exhibited only subclinical infection, they supported viral replication and prolonged infection in the spleen. SADS-CoV nonstructural proteins and double-stranded RNA were detected in splenocytes of the marginal zone on the edge of lymphatic follicles, indicating active replication of SADS-CoV in the mouse model. We identified that splenic dendritic cells (DCs) are the major targets of virus infection by immunofluorescence and flow cytometry approaches. Finally, we demonstrated that SADS-CoV does not utilize known CoV receptors for cellular entry. The ability of SADS-CoV to replicate in various cells lines from a broad range of species and the unexpected tropism for murine DCs provide important insights into the biology of this bat-origin CoV, highlighting its possible ability to cross interspecies barriers.

IMPORTANCE Infections with bat-origin coronaviruses (CoVs) (severe acute respiratory syndrome CoV [SARS-CoV] and Middle East respiratory syndrome CoV [MERS-CoV]) have caused severe illness in humans after “host jump” events. Recently, a novel bat-HKU2-like CoV named swine acute diarrhea syndrome CoV (SADS-CoV) has emerged in southern China, causing lethal diarrhea in newborn piglets. It is important to assess the species barriers of SADS-CoV infection since the animal hosts (other than pigs and bats) and zoonotic potential are still unknown. An in vitro susceptibility study revealed a broad species tropism of SADS-CoV, including various rodent and human cell lines. We established a mouse model of SADS-CoV infection, identifying its active replication in splenic dendritic cells, which suggests that SADS-CoV has the potential to infect rodents. These findings highlight the potential cross-species transmissibility of SADS-CoV, although further surveillance in other animal populations is needed to fully understand the ecology of this bat-HKU2-origin CoV.

Characterization of a novel bat-HKU2-like swine enteric alphacoronavirus (SeACoV) infection in cultured cells and development of a SeACoV infectious clone

Swine enteric alphacoronavirus (SeACoV), also known as swine acute diarrhea syndrome coronavirus (SADS-CoV), belongs to the species Rhinolophus bat coronavirus HKU2. Herein, we report on the primary characterization of SeACoV in vitro. Four antibodies against the SeACoV spike, membrane, nucleocapsid and nonstructural protein 3 capable of reacting with viral antigens in SeACoV-infected Vero cells were generated. We established a DNA-launched SeACoV infectious clone based on the cell adapted passage-10 virus and rescued the recombinant virus with a unique genetic marker in cultured cells. Six subgenomic mRNAs containing the leader-body junction sites, including a bicistronic mRNA encoding the accessory NS7a and NS7b genes, were experimentally identified in SeACoV-infected cells. Cellular ultrastructural changes induced by SeACoV infection were visualized by electron microscopy. The availability of the SeACoV infectious clone and a panel of antibodies against different viral proteins will facilitate further studies on understanding the molecular mechanisms of SeACoV replication and pathogenesis.