Identification and characterization of a novel alpaca respiratory coronavirus most closely related to the human coronavirus 229E

The reverse zoonotic potential of SARS-CoV-2

There has been considerable emphasis recently on the zoonotic origins of emerging infectious diseases in humans, including the SARS-CoV-2 pandemic; however, reverse zoonoses (infections transmitted from humans to other animals) have received less attention despite their potential importance. The effects can be devastating for the infected species and can also result in transmission of the pathogen back to human populations or other animals either in the original form or as a variant. Humans have transmitted SARS-CoV-2 to other animals, and the virus is able to circulate and evolve in those species. As global travel resumes, the potential of SARS-CoV-2 as a reverse zoonosis threatens humans and endangered species. Nonhuman primates are of particular concern given their susceptibility to human respiratory infections. Enforcing safety measures for all people working in and visiting wildlife areas, especially those with nonhuman primates, and increasing access to safety measures for people living near protected areas that are home to nonhuman primates will help mitigate reverse zoonotic transmission.

Codon usage bias analysis of the spike protein of human coronavirus 229E and its host adaptability

Human coronavirus 229E (HCoV-229E) represents one of the known coronaviruses capable of infecting humans and causes mild respiratory symptoms. It is also considered to have a zoonotic source, originating from animals and being transmitted the humans. In this study, a comprehensive phylogenetic and codon usage analysis of the spike (S) gene of HCoV-229E was conducted. Utilizing phylogenetic analysis and principal component analysis, HCoV-229E was categorized into four distinct clusters, each demonstrating unique host affiliations. Furthermore, it was observed that the codon usage bias within the S gene of HCoV-229E is relatively low, primarily influenced by natural selection patterns, with contributions from mutation pressure and dinucleotide abundance. Comparative analysis involving Codon Adaptation Index (CAI) and Relative Codon Deoptimization Index (RCDI) revealed that the codon usage pattern of HCoV-229E mirrors more closely that of camels, as opposed to alpacas and humans. The elucidation of the codon usage pattern within HCoV-229E, which we have meticulously examined, offers valuable insights for a more comprehensive comprehension of viral features, history, and evolutionary trajectory.

Co-Circulation of Multiple Coronavirus Genera and Subgenera during an Epizootic of Lethal Respiratory Disease in Newborn Alpacas (Vicugna pacos) in Peru: First Report of Bat-like Coronaviruses in Alpacas

Coronaviruses (CoVs) infect a wide range of hosts, including humans, domestic animals, and wildlife, typically causing mild-to-severe respiratory or enteric disease. The main objective of this study was to identify CoV genera and subgenera detected in Peruvian alpacas. Lung lavage specimens were collected from 32 animals aged 1 to 6 weeks. CoVs were identified by using RT-PCR to amplify a pan-CoV conserved region of the RNA-dependent RNA polymerase-encoding gene. A nested PCR was performed to identify β-CoVs. Then, β-CoV-positive samples were subjected to RT-PCR using specific primers to identify the Embecovirus subgenus. Out of 32 analyzed samples, 30 (93.8%) tested positive for at least one CoV genus. β-, α-, or unclassified CoVs were identified in 24 (80%), 1 (3.3%), and 1 (3.3%) of the positive samples, respectively. A CoV genus could not be identified in two (6.7%) samples. A mixture of different CoV genera was detected in two (6.7%) samples: one was co-infected with β- and α-CoVs, and the other contained a β- and an unclassified CoV. A sequence analysis of the amplicons generated by the PCR identified 17 β-CoV strains belonging to the subgenus Embecovirus and two α-CoV strains belonging to Decacovirus. A phylogenetic analysis of two strains revealed a relationship with an unclassified Megaderma BatCoV strain. A subgenus could not be identified in nine β-CoV samples. Our data show a high prevalence and a high genetic diversity of CoV genera and subgenera that infect alpacas, in which the β-CoV subgenus Embecovirus predominated. Our data also suggest a new role for bats in the dissemination and transmission of uncommon CoVs to alpacas raised in rural Peru.

SARS-CoV-2 prevalence in domestic and wildlife animals: A genomic and docking based structural comprehensive review

The SARS-CoV-2 virus has been identified as the infectious agent that led to the COVID-19 pandemic, which the world has seen very recently. Researchers have linked the SARS-CoV-2 outbreak to bats for the zoonotic spread of the virus to humans. Coronaviruses have a crown-like shape and positive-sense RNA nucleic acid. It attaches its spike glycoprotein to the host angiotensin-converting enzyme 2 (ACE2) receptor. Coronavirus genome comprises 14 ORFs and 27 proteins, spike glycoprotein being one of the most critical proteins for viral pathogenesis. Many mammals and reptiles, including bats, pangolins, ferrets, snakes, and turtles, serve as the principal reservoirs for this virus. But many experimental investigations have shown that certain domestic animals, including pigs, chickens, dogs, cats, and others, may also be able to harbor this virus, whether they exhibit any symptoms. These animals act as reservoirs for SARS-CoV, facilitating its zoonotic cross-species transmission to other species, including humans. In this review, we performed a phylogenetic analysis with multiple sequence alignment and pairwise evolutionary distance analysis, which revealed the similarity of ACE2 receptors in humans, chimpanzees, domestic rabbits, house mice, and golden hamsters. Pairwise RMSD analysis of the spike protein from some commonly reported SARS-CoV revealed that bat and pangolin coronavirus shared the highest structural similarity with human coronavirus. In a further experiment, molecular docking confirmed a higher affinity of pig, bat, and pangolin coronavirus spike proteins' affinity to the human ACE2 receptor. Such comprehensive structural and genomic analysis can help us to forecast the next likely animal source of these coronaviruses that may infect humans. To combat these zoonotic illnesses, we need a one health strategy that considers the well-being of people and animals and the local ecosystem.

Spike-Independent Infection of Human Coronavirus 229E in Bat Cells

Bats are the reservoir for numerous human pathogens, including coronaviruses. Despite many coronaviruses having descended from bat ancestors, little is known about virus-host interactions and broader evolutionary history involving bats. Studies have largely focused on the zoonotic potential of coronaviruses with few infection experiments conducted in bat cells. To determine genetic changes derived from replication in bat cells and possibly identify potential novel evolutionary pathways for zoonotic virus emergence, we serially passaged six human 229E isolates in a newly established Rhinolophus lepidus (horseshoe bat) kidney cell line. Here, we observed extensive deletions within the spike and open reading frame 4 (ORF4) genes of five 229E viruses after passaging in bat cells. As a result, spike protein expression and infectivity of human cells was lost in 5 of 6 viruses, but the capability to infect bat cells was maintained. Only viruses that expressed the spike protein could be neutralized by 229E spike-specific antibodies in human cells, whereas there was no neutralizing effect on viruses that did not express the spike protein inoculated on bat cells. However, one isolate acquired an early stop codon, abrogating spike expression but maintaining infection in bat cells. After passaging this isolate in human cells, spike expression was restored due to acquisition of nucleotide insertions among virus subpopulations. Spike-independent infection of human coronavirus 229E may provide an alternative mechanism for viral maintenance in bats that does not rely on the compatibility of viral surface proteins and known cellular entry receptors. IMPORTANCE Many viruses, including coronaviruses, originated from bats. Yet, we know little about how these viruses switch between hosts and enter human populations. Coronaviruses have succeeded in establishing in humans at least five times, including endemic coronaviruses and the recent severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). In an approach to identify requirements for host switches, we established a bat cell line and adapted human coronavirus 229E viruses by serial passage. The resulting viruses lost their spike protein but maintained the ability to infect bat cells, but not human cells. Maintenance of 229E viruses in bat cells appears to be independent of a canonical spike receptor match, which in turn might facilitate cross-species transmission in bats.

Cross-species transmission of coronaviruses with a focus on severe acute respiratory syndrome coronavirus 2 infection in animals: a review for the veterinary practitioner

AbstractIn 2019 a novel coronavirus termed severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged from an unidentified source and spread rapidly among humans worldwide. While many human infections are mild, some result in severe clinical disease that in a small proportion of infected people is fatal. The pandemic spread of SARS-CoV-2 has been facilitated by efficient human-to-human transmission of the virus, with no data to indicate that animals contributed to this global health crisis. However, a range of domesticated and wild animals are also susceptible to SARS-CoV-2 infection under both experimental and natural conditions. Humans are presumed to be the source of most animal infections thus far, although natural transmission between mink and between free-ranging deer has occurred, and occasional natural transmission between cats cannot be fully excluded. Considering the ongoing circulation of the virus among people, together with its capacity to evolve through mutation and recombination, the risk of the emergence of animal-adapted variants is not negligible. If such variants remain infectious to humans, this could lead to the establishment of an animal reservoir for the virus, which would complicate control efforts. As such, minimising human-to-animal transmission of SARS-CoV-2 should be considered as part of infection control efforts. The aim of this review is to summarise what is currently known about the species specificity of animal coronaviruses, with an emphasis on SARS-CoV-2, in the broader context of factors that facilitate cross-species transmission of viruses.

Evaluating the Virology and Evolution of Seasonal Human Coronaviruses Associated with the Common Cold in the COVID-19 Era

Approximately 15-30% of all cases of the common cold are due to human coronavirus infections. More recently, the emergence of the more severe respiratory coronaviruses, SARS-CoV and MERS-CoV, have highlighted the increased pathogenic potential of emergent coronaviruses. Lastly, the current emergence of SARS-CoV-2 has demonstrated not only the potential for significant disease caused by emerging coronaviruses, but also the capacity of novel coronaviruses to promote pandemic spread. Largely driven by the global response to the COVID-19 pandemic, significant research in coronavirus biology has led to advances in our understanding of these viruses. In this review, we evaluate the virology, emergence, and evolution of the four endemic coronaviruses associated with the common cold, their relationship to pandemic SARS-CoV-2, and discuss the potential for future emergent human coronaviruses.

Coronaviruses: Troubling Crown of the Animal Kingdom

The existence of coronaviruses has been known for many years. These viruses cause significant disease that primarily seems to affect agricultural species. Human coronavirus disease due to the 2002 outbreak of Severe Acute Respiratory Syndrome and the 2012 outbreak of Middle East Respiratory Syndrome made headlines; however, these outbreaks were controlled, and public concern quickly faded. This complacency ended in late 2019 when alarms were raised about a mysterious virus responsible for numerous illnesses and deaths in China. As we now know, this novel disease called Coronavirus Disease 2019 (COVID-19) was caused by Severe acute respiratory syndrome-related-coronavirus-2 (SARS-CoV-2) and rapidly became a worldwide pandemic. Luckily, decades of research into animal coronaviruses hastened our understanding of the genetics, structure, transmission, and pathogenesis of these viruses. Coronaviruses infect a wide range of wild and domestic animals, with significant economic impact in several agricultural species. Their large genome, low dependency on host cellular proteins, and frequent recombination allow coronaviruses to successfully cross species barriers and adapt to different hosts including humans. The study of the animal diseases provides an understanding of the virus biology and pathogenesis and has assisted in the rapid development of the SARS-CoV-2 vaccines. Here, we briefly review the classification, origin, etiology, transmission mechanisms, pathogenesis, clinical signs, diagnosis, treatment, and prevention strategies, including available vaccines, for coronaviruses that affect domestic, farm, laboratory, and wild animal species. We also briefly describe the coronaviruses that affect humans. Expanding our knowledge of this complex group of viruses will better prepare us to design strategies to prevent and/or minimize the impact of future coronavirus outbreaks.

Extensive Recombination-driven Coronavirus Diversification Expands the Pool of Potential Pandemic Pathogens

The ongoing SARS-CoV-2 pandemic is the third zoonotic coronavirus identified in the last 20 years. Enzootic and epizootic coronaviruses of diverse lineages also pose a significant threat to livestock, as most recently observed for virulent strains of porcine epidemic diarrhea virus (PEDV) and swine acute diarrhea-associated coronavirus (SADS-CoV). Unique to RNA viruses, coronaviruses encode a proofreading exonuclease (ExoN) that lowers point mutation rates to increase the viability of large RNA virus genomes, which comes with the cost of limiting virus adaptation via point mutation. This limitation can be overcome by high rates of recombination that facilitate rapid increases in genetic diversification. To compare the dynamics of recombination between related sequences, we developed an open-source computational workflow (IDPlot) that bundles nucleotide identity, recombination, and phylogenetic analysis into a single pipeline. We analyzed recombination dynamics among three groups of coronaviruses with noteworthy impacts on human health and agriculture: SARSr-CoV, Betacoronavirus-1, and SADSr-CoV. We found that all three groups undergo recombination with highly diverged viruses from undersampled or unsampled lineages, including in typically highly conserved regions of the genome. In several cases, no parental origin of recombinant regions could be found in genetic databases, demonstrating our shallow characterization of coronavirus diversity and expanding the genetic pool that may contribute to future zoonotic events. Our results also illustrate the limitations of current sampling approaches for anticipating zoonotic threats to human and animal health.

Structural Requirements and Plasticity of Receptor-Binding Domain in Human Coronavirus Spike

The most recent human coronaviruses including severe acute respiratory syndrome coronavirus-2 causing severe respiratory tract infection and high pathogenicity bring significant global public health concerns. Infections are initiated by recognizing host cell receptors by coronavirus spike protein S1 subunit, and then S2 mediates membrane fusion. However, human coronavirus spikes undergo frequent mutation, which may result in diverse pathogenesis and infectivity. In this review, we summarize some of these recent structural and mutational characteristics of RBD of human coronavirus spike protein and their interaction with specific human cell receptors and analyze the structural requirements and plasticity of RBD. Stability of spike protein, affinity toward receptor, virus fitness, and infectivity are the factors controlling the viral tropisms. Thus, understanding the molecular details of RBDs and their mutations is critical in deciphering virus evolution. Structural information of spike and receptors of human coronaviruses not only reveals the molecular mechanism of host–microbe interaction and pathogenesis but also helps develop effective drug to control these infectious pathogens and cope with the future emerging coronavirus outbreaks.

Why do some coronaviruses become pandemic threats when others do not?

Despite multiple spillover events and short chains of transmission on at least 4 continents, Middle East Respiratory Syndrome Coronavirus (MERS-CoV) has never triggered a pandemic. By contrast, its relative, Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) has, despite apparently little, if any, previous circulation in humans. Resolving the unsolved mystery of the failure of MERS-CoV to trigger a pandemic could help inform how we understand the pandemic potential of pathogens, and probing it underscores a need for a more holistic understanding of the ways in which viral genetic changes scale up to population-level transmission.

Virome characterization of game animals in China reveals a spectrum of emerging pathogens

Game animals are wildlife species traded and consumed as food and are potential reservoirs for SARS-CoV and SARS-CoV-2. We performed a meta-transcriptomic analysis of 1,941 game animals, representing 18 species and five mammalian orders, sampled across China. From this, we identified 102 mammalian-infecting viruses, with 65 described for the first time. Twenty-one viruses were considered as potentially high risk to humans and domestic animals. Civets (Paguma larvata) carried the highest number of potentially high-risk viruses. We inferred the transmission of bat-associated coronavirus from bats to civets, as well as cross-species jumps of coronaviruses from bats to hedgehogs, from birds to porcupines, and from dogs to raccoon dogs. Of note, we identified avian Influenza A virus H9N2 in civets and Asian badgers, with the latter displaying respiratory symptoms, as well as cases of likely human-to-wildlife virus transmission. These data highlight the importance of game animals as potential drivers of disease emergence.

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.

Evolutionary Dynamics and Epidemiology of Endemic and Emerging Coronaviruses in Humans, Domestic Animals, and Wildlife

Diverse coronavirus (CoV) strains can infect both humans and animals and produce various diseases. CoVs have caused three epidemics and pandemics in the last two decades, and caused a severe impact on public health and the global economy. Therefore, it is of utmost importance to understand the emergence and evolution of endemic and emerging CoV diversity in humans and animals. For diverse bird species, the Infectious Bronchitis Virus is a significant one, whereas feline enteric and canine coronavirus, recombined to produce feline infectious peritonitis virus, infects wild cats. Bovine and canine CoVs have ancestral relationships, while porcine CoVs, especially SADS-CoV, can cross species barriers. Bats are considered as the natural host of diverse strains of alpha and beta coronaviruses. Though MERS-CoV is significant for both camels and humans, humans are nonetheless affected more severely. MERS-CoV cases have been reported mainly in the Arabic peninsula since 2012. To date, seven CoV strains have infected humans, all descended from animals. The severe acute respiratory syndrome coronaviruses (SARS-CoV and SARS-CoV-2) are presumed to be originated in Rhinolopoid bats that severely infect humans with spillover to multiple domestic and wild animals. Emerging alpha and delta variants of SARS-CoV-2 were detected in pets and wild animals. Still, the intermediate hosts and all susceptible animal species remain unknown. SARS-CoV-2 might not be the last CoV to cross the species barrier. Hence, we recommend developing a universal CoV vaccine for humans so that any future outbreak can be prevented effectively. Furthermore, a One Health approach coronavirus surveillance should be implemented at human-animal interfaces to detect novel coronaviruses before emerging to humans and to prevent future epidemics and pandemics.

Evolutionary trajectory of SARS-CoV-2 and emerging variants

The emergence of a novel coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and more recently, the independent evolution of multiple SARS-CoV-2 variants has generated renewed interest in virus evolution and cross-species transmission. While all known human coronaviruses (HCoVs) are speculated to have originated in animals, very little is known about their evolutionary history and factors that enable some CoVs to co-exist with humans as low pathogenic and endemic infections (HCoV-229E, HCoV-NL63, HCoV-OC43, HCoV-HKU1), while others, such as SARS-CoV, MERS-CoV and SARS-CoV-2 have evolved to cause severe disease. In this review, we highlight the origins of all known HCoVs and map positively selected for mutations within HCoV proteins to discuss the evolutionary trajectory of SARS-CoV-2. Furthermore, we discuss emerging mutations within SARS-CoV-2 and variants of concern (VOC), along with highlighting the demonstrated or speculated impact of these mutations on virus transmission, pathogenicity, and neutralization by natural or vaccine-mediated immunity.

Extensive recombination-driven coronavirus diversification expands the pool of potential pandemic pathogens

The ongoing SARS-CoV-2 pandemic is the third zoonotic coronavirus identified in the last twenty years. Enzootic and epizootic coronaviruses of diverse lineages also pose a significant threat to livestock, as most recently observed for virulent strains of porcine epidemic diarrhea virus (PEDV) and swine acute diarrhea-associated coronavirus (SADS-CoV). Unique to RNA viruses, coronaviruses encode a proofreading exonuclease (ExoN) that lowers point mutation rates to increase the viability of large RNA virus genomes, which comes with the cost of limiting virus adaptation via point mutation. This limitation can be overcome by high rates of recombination that facilitate rapid increases in genetic diversification. To compare dynamics of recombination between related sequences, we developed an open-source computational workflow (IDPlot) to measure nucleotide identity, locate recombination breakpoints, and infer phylogenetic relationships. We analyzed recombination dynamics among three groups of coronaviruses with noteworthy impacts on human health and agriculture: SARSr-CoV, Betacoronavirus-1, and SADSr-CoV. We found that all three groups undergo recombination with highly diverged viruses from sparsely sampled or undescribed lineages, which can disrupt the inference of phylogenetic relationships. In most cases, no parental origin of recombinant regions could be found in genetic databases, suggesting that much coronavirus diversity remains unknown. These patterns of recombination expand the genetic pool that may contribute to future zoonotic events. Our results also illustrate the limitations of current sampling approaches for anticipating zoonotic threats to human and animal health.

Coronavirus surveillance in wildlife from two Congo basin countries detects RNA of multiple species circulating in bats and rodents

Coronaviruses play an important role as pathogens of humans and animals, and the emergence of epidemics like SARS, MERS and COVID-19 is closely linked to zoonotic transmission events primarily from wild animals. Bats have been found to be an important source of coronaviruses with some of them having the potential to infect humans, with other animals serving as intermediate or alternate hosts or reservoirs. Host diversity may be an important contributor to viral diversity and thus the potential for zoonotic events. To date, limited research has been done in Africa on this topic, in particular in the Congo Basin despite frequent contact between humans and wildlife in this region. We sampled and, using consensus coronavirus PCR-primers, tested 3,561 wild animals for coronavirus RNA. The focus was on bats (38%), rodents (38%), and primates (23%) that posed an elevated risk for contact with people, and we found coronavirus RNA in 121 animals, of which all but two were bats. Depending on the taxonomic family, bats were significantly more likely to be coronavirus RNA-positive when sampled either in the wet (Pteropodidae and Rhinolophidae) or dry season (Hipposideridae, Miniopteridae, Molossidae, and Vespertilionidae). The detected RNA sequences correspond to 15 alpha- and 6 betacoronaviruses, with some of them being very similar (>95% nucleotide identities) to known coronaviruses and others being more unique and potentially representing novel viruses. In seven of the bats, we detected RNA most closely related to sequences of the human common cold coronaviruses 229E or NL63 (>80% nucleotide identities). The findings highlight the potential for coronavirus spillover, especially in regions with a high diversity of bats and close human contact, and reinforces the need for ongoing surveillance.

Molecular diversity of coronavirus host cell entry receptors

Coronaviruses are a group of viruses causing disease in a wide range of animals, and humans. Since 2002, the successive emergence of bat-borne severe acute respiratory syndrome coronavirus (SARS-CoV), Middle East respiratory syndrome coronavirus (MERS-CoV), swine acute diarrhea syndrome coronavirus (SADS-CoV) and SARS-CoV-2 has reinforced efforts in uncovering the molecular and evolutionary mechanisms governing coronavirus cell tropism and interspecies transmission. Decades of studies have led to the discovery of a broad set of carbohydrate and protein receptors for many animal and human coronaviruses. As the main determinant of coronavirus entry, the spike protein binds to these receptors and mediates membrane fusion. Prone to mutations and recombination, spike evolution has been studied extensively. The interactions between spike proteins and their receptors are often complex and despite many advances in the field, there remains many unresolved questions concerning coronavirus tropism modification and cross-species transmission, potentially leading to delays in outbreak responses. The emergence of SARS-CoV-2 underscores the need to address these outstanding issues in order to better anticipate new outbreaks. In this review, we discuss the latest advances in the field of coronavirus receptors emphasizing on the molecular and evolutionary processes that underlie coronavirus receptor usage and host range expansion.

Compositional diversity and evolutionary pattern of coronavirus accessory proteins

Accessory proteins play important roles in the interaction between coronaviruses and their hosts. Accordingly, a comprehensive study of the compositional diversity and evolutionary patterns of accessory proteins is critical to understanding the host adaptation and epidemic variation of coronaviruses. Here, we developed a standardized genome annotation tool for coronavirus (CoroAnnoter) by combining open reading frame prediction, transcription regulatory sequence recognition and homologous alignment. Using CoroAnnoter, we annotated 39 representative coronavirus strains to form a compositional profile for all of the accessary proteins. Large variations were observed in the number of accessory proteins of 1–10 for different coronaviruses, with SARS-CoV-2 and SARS-CoV having the most (9 and 10, respectively). The variation between SARS-CoV and SARS-CoV-2 accessory proteins could be traced back to related coronaviruses in other hosts. The genomic distribution of accessory proteins had significant intra-genus conservation and inter-genus diversity and could be grouped into 1, 4, 2 and 1 types for alpha-, beta-, gamma-, and delta-coronaviruses, respectively. Evolutionary analysis suggested that accessory proteins are more conservative locating before the N-terminal of proteins E and M (E-M), while they are more diverse after these proteins. Furthermore, comparison of virus-host interaction networks of SARS-CoV-2 and SARS-CoV accessory proteins showed that they share multiple antiviral signaling pathways, those involved in the apoptotic process, viral life cycle and response to oxidative stress. In summary, our study provides a tool for coronavirus genome annotation and builds a comprehensive profile for coronavirus accessory proteins covering their composition, classification, evolutionary pattern and host interaction.

Clinical and molecular aspects of veterinary coronaviruses

Coronaviruses are a large group of RNA viruses that infect a wide range of animal species. The replication strategy of coronaviruses involves recombination and mutation events that lead to the possibility of cross-species transmission. The high plasticity of the viral receptor due to a continuous modification of the host species habitat may be the cause of cross-species transmission that can turn into a threat to other species including the human population. The successive emergence of highly pathogenic coronaviruses such as the Severe Acute Respiratory Syndrome (SARS) in 2003, the Middle East Respiratory Syndrome Coronavirus in 2012, and the recent SARS-CoV-2 has incentivized a number of studies on the molecular basis of the coronavirus and its pathogenesis. The high degree of interrelatedness between humans and wild and domestic animals and the modification of animal habitats by human urbanization, has favored new viral spreads. Hence, knowledge on the main clinical signs of coronavirus infection in the different hosts and the distinctive molecular characteristics of each coronavirus is essential to prevent the emergence of new coronavirus diseases. The coronavirus infections routinely studied in veterinary medicine must be properly recognized and diagnosed not only to prevent animal disease but also to promote public health.

Coronavirus Infections of Animals: Future Risks to Humans

Coronaviruses have tremendous evolutionary potential, and three major outbreaks of new human coronavirus infections have occurred in the recent history of humankind. In this paper, the patterns of occurrence of new zoonotic coronavirus infections and the role of bioveterinary control in preventing their potential outbreaks in the future are determined. The possibility of SARS-CoV-2 infection in companion animals is considered. Diverse human activities may trigger various interactions between animal species and their viruses, sometimes causing the emergence of new viral pathogens. In addition, the possibility of using probiotics for the control of viral infections in animals is discussed.

Pathology of Coronavirus Infections: A Review of Lesions in Animals in the One-Health Perspective

Coronaviruses (CoVs) are worldwide distributed RNA-viruses affecting several species, including humans, and causing a broad spectrum of diseases. Historically, they have not been considered a severe threat to public health until two outbreaks of COVs-related atypical human pneumonia derived from animal hosts appeared in 2002 and in 2012. The concern related to CoVs infection dramatically rose after the COVID-19 global outbreak, for which a spill-over from wild animals is also most likely. In light of this CoV zoonotic risk, and their ability to adapt to new species and dramatically spread, it appears pivotal to understand the pathophysiology and mechanisms of tissue injury of known CoVs within the "One-Health" concept. This review specifically describes all CoVs diseases in animals, schematically representing the tissue damage and summarizing the major lesions in an attempt to compare and put them in relation, also with human infections. Some information on pathogenesis and genetic diversity is also included. Investigating the lesions and distribution of CoVs can be crucial to understand and monitor the evolution of these viruses as well as of other pathogens and to further deepen the pathogenesis and transmission of this disease to help public health preventive measures and therapies.

Novel SARS-CoV-2 outbreak and COVID19 disease; a systemic review on the global pandemic

Since the beginning of the 21st century, several viral outbreaks have threatened humankind and posed a new challenge to the modern healthcare system. The recent outbreak in Wuhan (December 2019), China, represents a beta coronavirus classified as novel Severe Acute Respiratory Syndrome Corona Virus-2 (SARS-CoV-2) which belongs to the Coronaviridae family. Novel SARS-CoV-2 represents a significant similarity with previous coronaviruses such as SARS-CoV in 2002, China and MERS-CoV in 2015, Middle East. However, preliminary research investigations have shown the novel SARS-CoV-2 evolved with several mutations and developed the capacity to cross the species, i.e., animal to human. The initial findings have shown that spike proteins are vital molecules target hACE2 receptor for its attachment and entry into cells. After successful entry virus primarily focuses on respiratory airway cell lines and triggers a massive immune response leading to mucus generation. In severe conditions, the virus is capable of forcing viral pneumonia leading to the collapse of the respiratory system, i.e., COVID19. So far, there is a lack of immunity against the virus in humans. At the same in the absence of therapeutic interventions, many countries experienced high mortality, such as the United States, European countries, i.e., Italy, Spain, France, and the United Kingdom. The vaccine development is underway and experiencing challenges, as many reports demonstrated genetic variations in viral genome and proteins as well. The present study provides a complete comprehensive overview of the novel SARS-CoV-2 outbreak, human transmission, and global spread.

Realization of novel corona virus kit using silicon based 2D photonic structure via finite difference time domain method

The present research proposes the novel corona virus kit using silicon based two (2D) photonic structure. The basic principle of the estimation of different corona viruses relies on the computation of reflectance, absorbance, and transmittance at the signal of 412 nm. Here reflectance is investigated through the analysis of photonic band gap where absorbance is calculated using analytical treatment. The present investigation is made for different corona virus such as N5H1, N5H2, H9N2, H4N6, FAdV, and IBV. The numerical analysis indicates that the sample could be affected by novel corona virus if the transmitted signal lies with red spectrum. Similarly, sample could be normal viruses if the transmitted signal would green spectrum.

A proposal for testing kit of corona viruses using 3D photonic structure

Design of corona virus testing kit is proposed in this paper using silicon based 3D photonic structure through zirconium quantum dot solution at the signal of 412 nm. The principle of measurement depends on the computation of reflectance, absorbance and transmittance of virus based quantum dot solution. In this paper, the reflectance is studied through the analysis of photonic band gap and absorbance is made through its numerical treatment. Further, the numerical investigation shows that the transmitted energy through photonic structure would determine the type of corona virus. For example; if the transmitted energy lies within the visible spectrum the sample would be normal corona virus. However, the sample could be IBV (SARS COV-2) if the transmitted energy would be Infrared.

Coronavirus Infections in Companion Animals: Virology, Epidemiology, Clinical and Pathologic Features

Coronaviruses are enveloped RNA viruses capable of causing respiratory, enteric, or systemic diseases in a variety of mammalian hosts that vary in clinical severity from subclinical to fatal. The host range and tissue tropism are largely determined by the coronaviral spike protein, which initiates cellular infection by promoting fusion of the viral and host cell membranes. Companion animal coronaviruses responsible for causing enteric infection include feline enteric coronavirus, ferret enteric coronavirus, canine enteric coronavirus, equine coronavirus, and alpaca enteric coronavirus, while canine respiratory coronavirus and alpaca respiratory coronavirus result in respiratory infection. Ferret systemic coronavirus and feline infectious peritonitis virus, a mutated feline enteric coronavirus, can lead to lethal immuno-inflammatory systemic disease. Recent human viral pandemics, including severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS), and most recently, COVID-19, all thought to originate from bat coronaviruses, demonstrate the zoonotic potential of coronaviruses and their potential to have devastating impacts. A better understanding of the coronaviruses of companion animals, their capacity for cross-species transmission, and the sharing of genetic information may facilitate improved prevention and control strategies for future emerging zoonotic coronaviruses. This article reviews the clinical, epidemiologic, virologic, and pathologic characteristics of nine important coronaviruses of companion animals.

Novel human coronavirus (SARS-CoV-2): A lesson from animal coronaviruses

The recent pandemic caused by the novel human coronavirus, referrred to as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), not only is having a great impact on the health care systems and economies in all continents but it is also causing radical changes of common habits and life styles. The novel coronavirus (CoV) recognises, with high probability, a zoonotic origin but the role of animals in the SARS-CoV-2 epidemiology is still largely unknown. However, CoVs have been known in animals since several decades, so that veterinary coronavirologists have a great expertise on how to face CoV infections in animals, which could represent a model for SARS-CoV-2 infection in humans. In the present paper, we provide an up-to-date review of the literature currently available on animal CoVs, focusing on the molecular mechanisms that are responsible for the emergence of novel CoV strains with different antigenic, biologic and/or pathogenetic features. A full comprehension of the mechanisms driving the evolution of animal CoVs will help better understand the emergence, spreading, and evolution of SARS-CoV-2.

Genetic diversity and ecology of coronaviruses hosted by cave-dwelling bats in Gabon

Little research on coronaviruses has been conducted on wild animals in Africa. Here, we screened a wide range of wild animals collected in six provinces and five caves of Gabon between 2009 and 2015. We collected a total of 1867 animal samples (cave-dwelling bats, rodents, non-human primates and other wild animals). We explored the diversity of CoVs and determined the factors driving the infection of CoVs in wild animals. Based on a nested reverse transcription-polymerase chain reaction, only bats, belonging to the Hipposideros gigas (4/156), Hipposideros cf. ruber (13/262) and Miniopterus inflatus (1/249) species, were found infected with CoVs. We identified alphacoronaviruses in H. gigas and H. cf. ruber and betacoronaviruses in H. gigas. All Alphacoronavirus sequences grouped with Human coronavirus 229E (HCoV-229E). Ecological analyses revealed that CoV infection was significantly found in July and October in H. gigas and in October and November in H. cf ruber. The prevalence in the Faucon cave was significantly higher. Our findings suggest that insectivorous bats harbor potentially zoonotic CoVs; highlight a probable seasonality of the infection in cave-dwelling bats from the North-East of Gabon and pointed to an association between the disturbance of the bats' habitat by human activities and CoV infection.

Zoonotic origins of human coronaviruses

Mutation and adaptation have driven the co-evolution of coronaviruses (CoVs) and their hosts, including human beings, for thousands of years. Before 2003, two human CoVs (HCoVs) were known to cause mild illness, such as common cold. The outbreaks of severe acute respiratory syndrome (SARS) and the Middle East respiratory syndrome (MERS) have flipped the coin to reveal how devastating and life-threatening an HCoV infection could be. The emergence of SARS-CoV-2 in central China at the end of 2019 has thrusted CoVs into the spotlight again and surprised us with its high transmissibility but reduced pathogenicity compared to its sister SARS-CoV. HCoV infection is a zoonosis and understanding the zoonotic origins of HCoVs would serve us well. Most HCoVs originated from bats where they are non-pathogenic. The intermediate reservoir hosts of some HCoVs are also known. Identifying the animal hosts has direct implications in the prevention of human diseases. Investigating CoV-host interactions in animals might also derive important insight on CoV pathogenesis in humans. In this review, we present an overview of the existing knowledge about the seven HCoVs, with a focus on the history of their discovery as well as their zoonotic origins and interspecies transmission. Importantly, we compare and contrast the different HCoVs from a perspective of virus evolution and genome recombination. The current CoV disease 2019 (COVID-19) epidemic is discussed in this context. In addition, the requirements for successful host switches and the implications of virus evolution on disease severity are also highlighted.

The human coronavirus HCoV-229E S-protein structure and receptor binding

The coronavirus S-protein mediates receptor binding and fusion of the viral and host cell membranes. In HCoV-229E, its receptor binding domain (RBD) shows extensive sequence variation but how S-protein function is maintained is not understood. Reported are the X-ray crystal structures of Class III-V RBDs in complex with human aminopeptidase N (hAPN), as well as the electron cryomicroscopy structure of the 229E S-protein. The structures show that common core interactions define the specificity for hAPN and that the peripheral RBD sequence variation is accommodated by loop plasticity. The results provide insight into immune evasion and the cross-species transmission of 229E and related coronaviruses. We also find that the 229E S-protein can expose a portion of its helical core to solvent. This is undoubtedly facilitated by hydrophilic subunit interfaces that we show are conserved among coronaviruses. These interfaces likely play a role in the S-protein conformational changes associated with membrane fusion.

Bovine-like coronaviruses in domestic and wild ruminants

Coronaviruses (CoVs) produce a wide spectrum of disease syndromes in different mammalian and avian host species. These viruses are well-recognized for their ability to change tissue tropism, to hurdle the interspecies barriers and to adapt ecological variations. It is predicted that the inherent genetic diversity of CoVs caused by accumulation of point mutations and high frequency of homologous recombination is the principal determinant of these competences. Several CoVs (e.g. Severe acute respiratory syndrome-CoV, Middle East respiratory syndrome-CoV) have been recorded to cross the interspecies barrier, inducing different disease conditions in variable animal hosts. Bovine CoV (BCoV) is a primary cause of gastroenteritis and respiratory disease in cattle calves, winter dysentery in lactating cows and shipping fever pneumonia in feedlot cattle. Although it has long been known as a restrictive cattle pathogen, CoVs that are closely related to BCoV have been recognized in dogs, humans and in other ruminant species. Biologic, antigenic and genetic analyses of the so-called ‘bovine-like CoVs’ proposed classification of these viruses as host-range variants rather than distinct virus species. In this review, the different bovine-like CoVs that have been identified in domesticated ruminants (water buffalo, sheep, goat, dromedary camel, llama and alpaca) and wild ruminants (deer, wild cattle, antelopes, giraffes and wild goats) are discussed in terms of epidemiology, transmission and virus characteristics. The presented data denote the importance of these viruses in the persistence of BCoV in nature, spread to new geographical zones, and continuous emergence of disease epidemics in cattle farms.

Metagenomic Next-Generation Sequencing Reveal Presence of a Novel Ungulate Bocaparvovirus in Alpacas

Viruses belonging to the genus Bocaparvovirus(BoV) are a genetically diverse group of DNA viruses known to cause respiratory, enteric, and neurological diseases in animals, including humans. An intestinal sample from an alpaca (Vicugnapacos) herd with reoccurring diarrhea and respiratory disease was submitted for next-generation sequencing, revealing the presence of a BoV strain. The alpaca BoV strain (AlBoV) had a 58.58% whole genome nucleotide percent identity to a camel BoV from Dubai, belonging to a tentative ungulate BoV 8 species (UBoV8). Recombination events were lacking with other UBoV strains. The AlBoV genome was comprised of the NS1, NP1, and VP1 proteins. The NS1 protein had the highest amino acid percent identity range (57.89-67.85%) to the members of UBoV8, which was below the 85% cut-off set by the International Committee on Taxonomy of Viruses. The low NS1 amino acid identity suggests that AlBoV is a tentative new species. The whole genome, NS1, NP1, and VP1 phylogenetic trees illustrated distinct branching of AlBoV, sharing a common ancestor with UBoV8. Walker loop and Phospholipase A2 (PLA2) motifs that are vital for virus infectivity were identified in NS1 and VP1 proteins, respectively. Our study reports a novel BoV strain in an alpaca intestinal sample and highlights the need for additional BoV research.

Potential Intermediate Hosts for Coronavirus Transmission: No Evidence of Clade 2c Coronaviruses in Domestic Livestock from Ghana

The emergence of Middle East Respiratory Syndrome Coronavirus (MERS-CoV), nearly a decade ago with worldwide distribution, was believed to be of zoonotic origin from bats with dromedary camels as intermediate hosts. There is a likelihood of other domestic livestock serving as intermediate hosts for this virus. The presence of coronaviruses, closely related to MERS-CoV in Ghanaian bats, presented the opportunity to test the hypothesis of transmissibility of this virus through domestic livestock species. The possible interactions between livestock and bats in 31 household farms were accessed by observation and interviews with farmers. Rectal swabs and serum from cattle, sheep, goats, donkeys, and swine from commercial and household farms were tested for MERS-CoV and a Nycteris sp. bat coronavirus, previously detected in Ghana. A pan-PCR assay to detect clade 2c viruses and recombinant immunofluorescence assay to detect anti-spike IgG antibodies against the target viruses were used. Likely contact between livestock and bats was determined for 13 farms (41.9%) that reported confining their livestock and also observing bats in their homes. Livestock were left unconfined on eight farms (25.8%) that also observed bats roosting in trees close to their homes. No viral RNA or antibodies against the two coronaviruses were detected in any of the livestock species tested. Cattle, sheep, goats, donkeys, and swine are not likely hosts of clade 2c coronaviruses.

Bats and Coronaviruses

Bats are speculated to be reservoirs of several emerging viruses including coronaviruses (CoVs) that cause serious disease in humans and agricultural animals. These include CoVs that cause severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS), porcine epidemic diarrhea (PED) and severe acute diarrhea syndrome (SADS). Bats that are naturally infected or experimentally infected do not demonstrate clinical signs of disease. These observations have allowed researchers to speculate that bats are the likely reservoirs or ancestral hosts for several CoVs. In this review, we follow the CoV outbreaks that are speculated to have originated in bats. We review studies that have allowed researchers to identify unique adaptation in bats that may allow them to harbor CoVs without severe disease. We speculate about future studies that are critical to identify how bats can harbor multiple strains of CoVs and factors that enable these viruses to “jump” from bats to other mammals. We hope that this review will enable readers to identify gaps in knowledge that currently exist and initiate a dialogue amongst bat researchers to share resources to overcome present limitations.

Hosts and Sources of Endemic Human Coronaviruses

The four endemic human coronaviruses HCoV-229E, -NL63, -OC43, and -HKU1 contribute a considerable share of upper and lower respiratory tract infections in adults and children. While their clinical representation resembles that of many other agents of the common cold, their evolutionary histories, and host associations could provide important insights into the natural history of past human pandemics. For two of these viruses, we have strong evidence suggesting an origin in major livestock species while primordial associations for all four viruses may have existed with bats and rodents. HCoV-NL63 and -229E may originate from bat reservoirs as assumed for many other coronaviruses, but HCoV-OC43 and -HKU1 seem more likely to have speciated from rodent-associated viruses. HCoV-OC43 is thought to have emerged from ancestors in domestic animals such as cattle or swine. The bovine coronavirus has been suggested to be a possible ancestor, from which HCoV-OC43 may have emerged in the context of a pandemic recorded historically at the end of the 19th century. New data suggest that HCoV-229E may actually be transferred from dromedary camels similar to Middle East respiratory syndrome (MERS) coronavirus. This scenario provides important ecological parallels to the present prepandemic pattern of host associations of the MERS coronavirus.

Epidemiology characteristics of human coronaviruses in patients with respiratory infection symptoms and phylogenetic analysis of HCoV-OC43 during 2010-2015 in Guangzhou

Human coronavirus (HCoV) is one of the most common causes of respiratory tract infection throughout the world. To investigate the epidemiological and genetic variation of HCoV in Guangzhou, south China, we collected totally 13048 throat and nasal swab specimens from adults and children with fever and acute upper respiratory infection symptoms in Gunazhou, south China between July 2010 and June 2015, and the epidemiological features of HCoV and its species were studied. Specimens were screened for HCoV by real-time RT-PCR, and 7 other common respiratory viruses were tested simultaneously by PCR or real-time PCR. HCoV was detected in 294 cases (2.25%) of the 13048 samples, with most of them inpatients (251 cases, 85.4% of HCoV positive cases) and young children not in nursery (53.06%, 156 out of 294 HCoV positive cases). Four HCoVs, as OC43, 229E, NL63 and HKU1 were detected prevalent during 2010–2015 in Guangzhou, and among the HCoV positive cases, 60.20% were OC43, 16.67% were 229E, 14.97% were NL63 and 7.82% were HKU1. The month distribution showed that totally HCoV was prevalent in winter, but differences existed in different species. The 5 year distribution of HCoV showed a peak-valley distribution trend, with the detection rate higher in 2011 and 2013 whereas lower in 2010, 2012 and 2014. The age distribution revealed that children (especially those <3 years old) and old people (>50 years) were both high risk groups to be infected by HCoV. Of the 294 HCoV positive patients, 34.69% (101 cases) were co-infected by other common respiratory viruses, and influenza virus was the most common co-infecting virus (30/101, 29.70%). Fifteen HCoV-OC43 positive samples of 2013–2014 were selected for S gene sequencing and phylogenetic analysis, and the results showed that the 15 strains could be divided into 2 clusters in the phylogenetic tree, 12 strains of which formed a separate cluster that was closer to genotype G found in Malaysia. It was revealed for the first time that genotype B and genotype G of HCoV-OC43 co-circulated and the newly defined genotype G was epidemic as a dominant genotype during 2013–2014 in Guanzhou, south China.

Camelidae

New world (NW) camelids, alpaca, llama, vicuña, and guanaco, and old world (OW) camelids, Bactrian and dromedary camels are related and have many of the same anatomical features and disease susceptibilities though they are also very different. Only the free-ranging population of wild Bactrian camel is endangered. Bactrian camels held in zoos are generally of domestic origin. Vicuña are listed as vulnerable. In addition to those camelids held in captivity, there are domesticated populations of camelids (except vicuña and guanaco) maintained throughout the world. Most are fairly hardy animals, but there are some specific disease concerns. Domesticated llamas and alpacas have become hobby pets and thus management and genetic issues are an increasing source of disease. These include obesity, vitamin and mineral deficiencies and intoxications, metabolic derangements, and congenital malformations (particularly in the young). Domesticated animals are also more prone to degenerative arthropathy and dental disease as they age than wild camelids. Ovarian hydrobursitis is an important source of infertility in dromedaries. Important infectious diseases include coccidiosis, bovine viral diarrhea virus, alpaca fever, and meningeal worm of NW camelids, trypanosomiasis and camelpox in OW camels, and foot and mouth disease in Bactrian camels and NW camelids. These and other disease processes are discussed in this chapter.

Myeloablation-associated deletion of ORF4 in a human coronavirus 229E infection

We describe metagenomic next-generation sequencing (mNGS) of a human coronavirus 229E from a patient with AML and persistent upper respiratory symptoms, who underwent hematopoietic cell transplantation (HCT). mNGS revealed a 548-nucleotide deletion, which comprised the near entirety of the ORF4 gene, and no minor allele variants were detected to suggest a mixed infection. As part of her pre-HCT conditioning regimen, the patient received myeloablative treatment with cyclophosphamide and 12 Gy total body irradiation. Iterative sequencing and RT-PCR confirmation of four respiratory samples over the 4-week peritransplant period revealed that the pre-conditioning strain contained an intact ORF4 gene, while the deletion strain appeared just after conditioning and persisted over a 2.5-week period. This sequence represents one of the largest genomic deletions detected in a human RNA virus and describes large-scale viral mutation associated with myeloablation for HCT.

Molecular detection of viruses in Kenyan bats and discovery of novel astroviruses, caliciviruses and rotaviruses

This is the first country-wide surveillance of bat-borne viruses in Kenya spanning from 2012–2015 covering sites perceived to have medium to high level bat-human interaction. The objective of this surveillance study was to apply a non-invasive approach using fresh feces to detect viruses circulating within the diverse species of Kenyan bats. We screened for both DNA and RNA viruses; specifically, astroviruses (AstVs), adenoviruses (ADVs), caliciviruses (CalVs), coronaviruses (CoVs), flaviviruses, filoviruses, paramyxoviruses (PMVs), polyomaviruses (PYVs) and rotaviruses. We used family-specific primers, amplicon sequencing and further characterization by phylogenetic analysis. Except for filoviruses, eight virus families were detected with varying distributions and positive rates across the five regions (former provinces) studied. AstVs (12.83%), CoVs (3.97%), PMV (2.4%), ADV (2.26%), PYV (1.65%), CalVs (0.29%), rotavirus (0.19%) and flavivirus (0.19%). Novel CalVs were detected in Rousettus aegyptiacus and Mops condylurus while novel Rotavirus-A-related viruses were detected in Taphozous bats and R. aegyptiacus. The two Rotavirus A (RVA) strains detected were highly related to human strains with VP6 genotypes I2 and I16. Genotype I16 has previously been assigned to human RVA-strain B10 from Kenya only, which raises public health concern, particularly considering increased human-bat interaction. Additionally, 229E-like bat CoVs were detected in samples originating from Hipposideros bats roosting in sites with high human activity. Our findings confirm the presence of diverse viruses in Kenyan bats while providing extended knowledge on bat virus distribution. The detection of viruses highly related to human strains and hence of public health concern, underscores the importance of continuous surveillance.

Middle East respiratory syndrome (MERS) coronavirus and dromedaries

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Middle East Respiratory Syndrome (MERS) is a zoonotic viral disease transmissible from dromedaries to human beings.

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MERS coronavirus (MERS-CoV) infection in dromedaries is usually asymptomatic but mild respiratory signs may occur.

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No MERS-CoV or antibodies against the virus have been detected in camelids other than dromedaries.

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Dromedaries acquire MERS-CoV at less than 1 year of age and 100% of adult dromedaries are seropositive for the virus.

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MERS-CoV in dromedaries is detected by virus isolation, quantitative reverse transcriptase-PCR or antigen detection.

Middle East Respiratory Syndrome (MERS) is a zoonotic viral disease that can be transmitted from dromedaries to human beings. More than 1500 cases of MERS have been reported in human beings to date. Although MERS has been associated with 30% case fatality in human beings, MERS coronavirus (MERS-CoV) infection in dromedaries is usually asymptomatic. In rare cases, dromedaries may develop mild respiratory signs. No MERS-CoV or antibodies against the virus have been detected in camelids other than dromedaries. MERS-CoV is mainly acquired in dromedaries when they are less than 1 year of age, and the proportion of seropositivity increases with age to a seroprevalence of 100% in adult dromedaries. Laboratory diagnosis of MERS-CoV infection in dromedaries can be achieved through virus isolation using Vero cells, RNA detection by real-time quantitative reverse transcriptase-PCR and antigen detection using respiratory specimens or serum. Rapid nucleocapsid antigen detection using a lateral flow platform allows efficient screening of dromedaries carrying MERS-CoV. In addition to MERS-CoV, which is a lineage C virus in the Betacoronavirus (betaCoV) genus, a lineage B betaCoV and a virus in the Alphacoronavirus (alphaCoV) genus have been detected in dromedaries. Dromedary CoV UAE-HKU23 is closely related to human CoV OC43, whereas the alphaCoV has not been detected in human beings to date.

Molecular Evolution of Human Coronavirus Genomes

Human coronaviruses (HCoVs), including SARS-CoV and MERS-CoV, are zoonotic pathogens that originated in wild animals. HCoVs have large genomes that encode a fixed array of structural and nonstructural components, as well as a variety of accessory proteins that differ in number and sequence even among closely related CoVs. Thus, in addition to recombination and mutation, HCoV genomes evolve through gene gains and losses. In this review we summarize recent findings on the molecular evolution of HCoV genomes, with special attention to recombination and adaptive events that generated new viral species and contributed to host shifts and to HCoV emergence. VIDEO ABSTRACT.

Coronavirus Spike Protein and Tropism Changes

Coronaviruses (CoVs) have a remarkable potential to change tropism. This is particularly illustrated over the last 15 years by the emergence of two zoonotic CoVs, the severe acute respiratory syndrome (SARS)- and Middle East respiratory syndrome (MERS)-CoV. Due to their inherent genetic variability, it is inevitable that new cross-species transmission events of these enveloped, positive-stranded RNA viruses will occur. Research into these medical and veterinary important pathogens—sparked by the SARS and MERS outbreaks—revealed important principles of inter- and intraspecies tropism changes. The primary determinant of CoV tropism is the viral spike (S) entry protein. Trimers of the S glycoproteins on the virion surface accommodate binding to a cell surface receptor and fusion of the viral and cellular membrane. Recently, high-resolution structures of two CoV S proteins have been elucidated by single-particle cryo-electron microscopy. Using this new structural insight, we review the changes in the S protein that relate to changes in virus tropism. Different concepts underlie these tropism changes at the cellular, tissue, and host species level, including the promiscuity or adaptability of S proteins to orthologous receptors, alterations in the proteolytic cleavage activation as well as changes in the S protein metastability. A thorough understanding of the key role of the S protein in CoV entry is critical to further our understanding of virus cross-species transmission and pathogenesis and for development of intervention strategies.

Link of a ubiquitous human coronavirus to dromedary camels

The four human coronaviruses (HCoVs) are globally endemic respiratory pathogens. The Middle East respiratory syndrome (MERS) coronavirus (CoV) is an emerging CoV with a known zoonotic source in dromedary camels. Little is known about the origins of endemic HCoVs. Studying these viruses' evolutionary history could provide important insight into CoV emergence. In tests of MERS-CoV-infected dromedaries, we found viruses related to an HCoV, known as HCoV-229E, in 5.6% of 1,033 animals. Human- and dromedary-derived viruses are each monophyletic, suggesting ecological isolation. One gene of dromedary viruses exists in two versions in camels, full length and deleted, whereas only the deleted version exists in humans. The deletion increased in size over a succession starting from camelid viruses via old human viruses to contemporary human viruses. Live isolates of dromedary 229E viruses were obtained and studied to assess human infection risks. The viruses used the human entry receptor aminopeptidase N and replicated in human hepatoma cells, suggesting a principal ability to cause human infections. However, inefficient replication in several mucosa-derived cell lines and airway epithelial cultures suggested lack of adaptation to the human host. Dromedary viruses were as sensitive to the human type I interferon response as HCoV-229E. Antibodies in human sera neutralized dromedary-derived viruses, suggesting population immunity against dromedary viruses. Although no current epidemic risk seems to emanate from these viruses, evolutionary inference suggests that the endemic human virus HCoV-229E may constitute a descendant of camelid-associated viruses. HCoV-229E evolution provides a scenario for MERS-CoV emergence.

Co-circulation of three camel coronavirus species and recombination of MERS-CoVs in Saudi Arabia

Outbreaks of Middle East respiratory syndrome (MERS) raise questions about the prevalence and evolution of the MERS coronavirus (CoV) in its animal reservoir. Our surveillance in Saudi Arabia in 2014 and 2015 showed that viruses of the MERS-CoV species and a human CoV 229E-related lineage co-circulated at high prevalence, with frequent co-infections in the upper respiratory tract of dromedary camels. viruses of the betacoronavirus 1 species, we found that dromedary camels share three CoV species with humans. Several MERS-CoV lineages were present in camels, including a recombinant lineage that has been dominant since December 2014 and that subsequently led to the human outbreaks in 2015. Camels therefore serve as an important reservoir for the maintenance and diversification of the MERS-CoVs and are the source of human infections with this virus.

Evidence for an Ancestral Association of Human Coronavirus 229E with Bats

We previously showed that close relatives of human coronavirus 229E (HCoV-229E) exist in African bats. The small sample and limited genomic characterizations have prevented further analyses so far. Here, we tested 2,087 fecal specimens from 11 bat species sampled in Ghana for HCoV-229E-related viruses by reverse transcription-PCR (RT-PCR). Only hipposiderid bats tested positive. To compare the genetic diversity of bat viruses and HCoV-229E, we tested historical isolates and diagnostic specimens sampled globally over 10 years. Bat viruses were 5- and 6-fold more diversified than HCoV-229E in the RNA-dependent RNA polymerase (RdRp) and spike genes. In phylogenetic analyses, HCoV-229E strains were monophyletic and not intermixed with animal viruses. Bat viruses formed three large clades in close and more distant sister relationships. A recently described 229E-related alpaca virus occupied an intermediate phylogenetic position between bat and human viruses. According to taxonomic criteria, human, alpaca, and bat viruses form a single CoV species showing evidence for multiple recombination events. HCoV-229E and the alpaca virus showed a major deletion in the spike S1 region compared to all bat viruses. Analyses of four full genomes from 229E-related bat CoVs revealed an eighth open reading frame (ORF8) located at the genomic 3' end. ORF8 also existed in the 229E-related alpaca virus. Reanalysis of HCoV-229E sequences showed a conserved transcription regulatory sequence preceding remnants of this ORF, suggesting its loss after acquisition of a 229E-related CoV by humans. These data suggested an evolutionary origin of 229E-related CoVs in hipposiderid bats, hypothetically with camelids as intermediate hosts preceding the establishment of HCoV-229E.

IMPORTANCE

The ancestral origins of major human coronaviruses (HCoVs) likely involve bat hosts. Here, we provide conclusive genetic evidence for an evolutionary origin of the common cold virus HCoV-229E in hipposiderid bats by analyzing a large sample of African bats and characterizing several bat viruses on a full-genome level. Our evolutionary analyses show that animal and human viruses are genetically closely related, can exchange genetic material, and form a single viral species. We show that the putative host switches leading to the formation of HCoV-229E were accompanied by major genomic changes, including deletions in the viral spike glycoprotein gene and loss of an open reading frame. We reanalyze a previously described genetically related alpaca virus and discuss the role of camelids as potential intermediate hosts between bat and human viruses. The evolutionary history of HCoV-229E likely shares important characteristics with that of the recently emerged highly pathogenic Middle East respiratory syndrome (MERS) coronavirus.

Necrotizing Enteritis and Hyperammonemic Encephalopathy Associated With Equine Coronavirus Infection in Equids

Equine coronavirus (ECoV) is a Betacoronavirus recently associated clinically and epidemiologically with emerging outbreaks of pyrogenic, enteric, and/or neurologic disease in horses in the United States, Japan, and Europe. We describe the pathologic, immunohistochemical, ultrastructural, and molecular findings in 2 horses and 1 donkey that succumbed to natural infection with ECoV. One horse and the donkey (case Nos. 1, 3) had severe diffuse necrotizing enteritis with marked villous attenuation, epithelial cell necrosis at the tips of the villi, neutrophilic and fibrinous extravasation into the small intestinal lumen (pseudomembrane formation), as well as crypt necrosis, microthrombosis, and hemorrhage. The other horse (case No. 2) had hyperammonemic encephalopathy with Alzheimer type II astrocytosis throughout the cerebral cortex. ECoV was detected by quantitative polymerase chain reaction in small intestinal tissue, contents, and/or feces, and coronavirus antigen was detected by immunohistochemistry in the small intestine in all cases. Coronavirus-like particles characterized by spherical, moderately electron lucent, enveloped virions with distinct peplomer-like structures projecting from the surface were detected by negatively stained transmission electron microscopy in small intestine in case No. 1, and transmission electron microscopy of fixed small intestinal tissue from the same case revealed similar 85- to 100-nm intracytoplasmic particles located in vacuoles and free in the cytoplasm of unidentified (presumably epithelial) cells. Sequence comparison showed 97.9% to 99.0% sequence identity with the ECoV-NC99 and Tokachi09 strains. All together, these results indicate that ECoV is associated with necrotizing enteritis and hyperammonemic encephalopathy in equids.

Thinking Outside the Triangle: Replication Fidelity of the Largest RNA Viruses

When judged by ubiquity, adaptation, and emergence of new diseases, RNA viruses are arguably the most successful biological organisms. This success has been attributed to a defect of sorts: high mutation rates (low fidelity) resulting in mutant swarms that allow rapid selection for fitness in new environments. Studies of viruses with small RNA genomes have identified fidelity determinants in viral RNA-dependent RNA polymerases and have shown that RNA viruses likely replicate within a limited fidelity range to maintain fitness. In this review we compare the fidelity of small RNA viruses with that of the largest RNA viruses, the coronaviruses. Coronaviruses encode the first known viral RNA proofreading exoribonuclease, a function that likely allowed expansion of the coronavirus genome and that dramatically increases replication fidelity and the range of tolerated variation. We propose models for regulation of coronavirus fidelity and discuss the implications of altered fidelity for RNA virus replication, pathogenesis, and evolution.

Rooting the phylogenetic tree of middle East respiratory syndrome coronavirus by characterization of a conspecific virus from an African bat

The emerging Middle East respiratory syndrome coronavirus (MERS-CoV) causes lethal respiratory infections mainly on the Arabian Peninsula. The evolutionary origins of MERS-CoV are unknown. We determined the full genome sequence of a CoV directly from fecal material obtained from a South African Neoromicia capensis bat (NeoCoV). NeoCoV shared essential details of genome architecture with MERS-CoV. Eighty-five percent of the NeoCoV genome was identical to MERS-CoV at the nucleotide level. Based on taxonomic criteria, NeoCoV and MERS-CoV belonged to one viral species. The presence of a genetically divergent S1 subunit within the NeoCoV spike gene indicated that intraspike recombination events may have been involved in the emergence of MERS-CoV. NeoCoV constitutes a sister taxon of MERS-CoV, placing the MERS-CoV root between a recently described virus from African camels and all other viruses. This suggests a higher level of viral diversity in camels than in humans. Together with serologic evidence for widespread MERS-CoV infection in camelids sampled up to 20 years ago in Africa and the Arabian Peninsula, the genetic data indicate that camels act as sources of virus for humans rather than vice versa. The majority of camels on the Arabian Peninsula is imported from the Greater Horn of Africa, where several Neoromicia species occur. The acquisition of MERS-CoV by camels from bats might have taken place in sub-Saharan Africa. Camelids may represent mixing vessels for MERS-CoV and other mammalian CoVs.

IMPORTANCE

It is unclear how, when, and where the highly pathogenic MERS-CoV emerged. We characterized the full genome of an African bat virus closely related to MERS-CoV and show that human, camel, and bat viruses belong to the same viral species. The bat virus roots the phylogenetic tree of MERS-CoV, providing evidence for an evolution of MERS-CoV in camels that preceded that in humans. The revised tree suggests that humans are infected by camels rather than vice versa. Although MERS-CoV cases occur mainly on the Arabian Peninsula, the data from this study together with serologic and molecular investigations of African camels indicate that the initial host switch from bats may have taken place in Africa. The emergence of MERS-CoV likely involved exchanges of genetic elements between different viral ancestors. These exchanges may have taken place either in bat ancestors or in camels acting as mixing vessels for viruses from different hosts.