Generation of Human Embryonic Stem Cell-Derived Lung Organoids for Modeling Infection and Replication Differences between Human Adenovirus Types 3 and 55 and Evaluating Potential Antiviral Drugs.

Human adenoviruses type 3 (HAdV-3) and type 55 (HAdV-55) are frequently encountered, highly contagious respiratory pathogens with high morbidity rate. In contrast to HAdV-3, one of the most predominant types in children, HAdV-55 is a reemergent pathogen associated with more severe community-acquired pneumonia (CAP) in adults, especially in military camps. However, the infectivity and pathogenicity differences between these viruses remain unknown as in vivo models are not available. Here, we report a novel system utilizing human embryonic stem cells-derived 3-dimensional airway organoids (hAWOs) and alveolar organoids (hALOs) to investigate these two viruses. Firstly, HAdV-55 replicated more robustly than HAdV-3. Secondly, cell tropism analysis in hAWOs and hALOs by immunofluorescence staining revealed that HAdV-55 infected more airway and alveolar stem cells (basal and AT2 cells) than HAdV-3, which may lead to impairment of self-renewal functions post-injury and the loss of cell differentiation in lungs. Additionally, the viral life cycles of HAdV-3 and -55 in organoids were also observed using Transmission Electron Microscopy. This study presents a useful pair of lung organoids for modeling infection and replication differences between respiratory pathogens, illustrating that HAdV-55 has relatively higher replication efficiency and more specific cell tropism in human lung organoids than HAdV-3, which may result in relatively higher pathogenicity and virulence of HAdV-55 in human lungs. The model system is also suitable for evaluating potential antiviral drugs, as demonstrated with cidofovir. IMPORTANCE Human adenovirus (HAdV) infections are a major threat worldwide. HAdV-3 is one of the most predominant respiratory pathogen types found in children. Many clinical studies have reported that HAdV-3 causes less severe disease. In contrast, HAdV-55, a reemergent acute respiratory disease pathogen, is associated with severe community-acquired pneumonia in adults. Currently, no ideal in vivo models are available for studying HAdVs. Therefore, the mechanism of infectivity and pathogenicity differences between human adenoviruses remain unknown. In this study, a useful pair of 3-dimensional (3D) airway organoids (hAWOs) and alveolar organoids (hALOs) were developed to serve as a model. The life cycles of HAdV-3 and HAdV-55 in these human lung organoids were documented for the first time. These 3D organoids harbor different cell types, which are similar to the ones found in humans. This allows for the study of the natural target cells for infection. The finding of differences in replication efficiency and cell tropism between HAdV-55 and -3 may provide insights into the mechanism of clinical pathogenicity differences between these two important HAdV types. Additionally, this study provides a viable and effective in vitro tool for evaluating potential anti-adenoviral treatments.

Isolation of novel simian adenoviruses from macaques for development of a vector for human gene therapy and vaccines.

IMPORTANCE: Adenoviruses are widely used in gene therapy and vaccine delivery. Due to the high prevalence of human adenoviruses (HAdVs), the pre-existing immunity against HAdVs in humans is common, which limits the wide and repetitive use of HAdV vectors. In contrast, the pre-existing immunity against simian adenoviruses (SAdVs) is low in humans. Therefore, we performed epidemiological investigations of SAdVs in simians and found that the SAdV prevalence was as high as 33.9%. The whole-genome sequencing and sequence analysis showed SAdV diversity and possible cross species transmission. One isolate with low level of pre-existing neutralizing antibodies in humans was used to construct replication-deficient SAdV vectors with E4orf6 substitution and E1/E3 deletion. Interestingly, we found that the E3 region plays a critical role in its replication in human cells, but the absence of this region could be compensated for by the E4orf6 from HAdV-5 and the E1 expression intrinsic to HEK293 cells.

Genome and proteomic analysis of risk factors for fatal outcome in children with severe community-acquired pneumonia caused by human adenovirus 7.

INTRODUCTION: Human adenovirus 7 (HAdV-7) is an important viral pathogen of severe pneumonia in children and a serious threat to health. METHODS: A cohort of 45 pediatric patients diagnosed with HAdV-7-associated severe pneumonia and admitted to the Pediatric Intensive Care Unit at the Children's Hospital of Chongqing Medical University from May 2018 to January 2020 were included. Risk factors of death were analyzed by the Cox proportional risk mode with Clinical data, serum, and nasopharyngeal aspirate adenovirus load, Genome analysis, Olink proteomics, and cytokine profile between dead and surviving patients were also analyzed. RESULTS: A total of 45 children with a median age of 12.0 months (interquartile range [IQR]: 6.5, 22.0) were included (female 14), including 14 (31.1%) who died. High serum viral load was an independent risk factor for mortality (hazard ratio [HR] = 2.16, 95% confidence interval [CI], 1.04-4.49, p = 0.039). BTB and CNC homology 1 (BACH1), interleukin-5 (IL-5), and IL-9 levels were significantly correlated with serum viral load (p = 0.0400, 0.0499, and 0.0290; r = 0.4663, 0.3339, and -0.3700, respectively), with significant differences between the dead and survival groups (p = 0.021, 0.001, and 0.021). CONCLUSIONS: Severe cytokine storm-associated high serum viral load after HAdV-7 infection may be the main mechanism responsible for poor prognosis in children.

V367F Mutation in SARS-CoV-2 Spike RBD Emerging during the Early Transmission Phase Enhances Viral Infectivity through Increased Human ACE2 Receptor Binding Affinity.

The current pandemic of COVID-19 is caused by a novel coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The SARS-CoV-2 spike protein receptor-binding domain (RBD) is the critical determinant of viral tropism and infectivity. To investigate whether naturally occurring RBD mutations during the early transmission phase have altered the receptor binding affinity and infectivity, we first analyzed in silico the binding dynamics between SARS-CoV-2 RBD mutants and the human angiotensin-converting enzyme 2 (ACE2) receptor. Among 32,123 genomes of SARS-CoV-2 isolates (December 2019 through March 2020), 302 nonsynonymous RBD mutants were identified and clustered into 96 mutant types. The six dominant mutations were analyzed applying molecular dynamics simulations (MDS). The mutant type V367F continuously circulating worldwide displayed higher binding affinity to human ACE2 due to the enhanced structural stabilization of the RBD beta-sheet scaffold. The MDS also indicated that it would be difficult for bat SARS-like CoV to infect humans. However, the pangolin CoV is potentially infectious to humans. The increased infectivity of V367 mutants was further validated by performing receptor-ligand binding enzyme-linked immunosorbent assay (ELISA), surface plasmon resonance, and pseudotyped virus assays. Phylogenetic analysis of the genomes of V367F mutants showed that during the early transmission phase, most V367F mutants clustered more closely with the SARS-CoV-2 prototype strain than the dual-mutation variants (V367F+D614G), which may derivate from recombination. The analysis of critical RBD mutations provides further insights into the evolutionary trajectory of early SARS-CoV-2 variants of zoonotic origin under negative selection pressure and supports the continuing surveillance of spike mutations to aid in the development of new COVID-19 drugs and vaccines. IMPORTANCE A novel coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has caused the pandemic of COVID-19. The origin of SARS-CoV-2 was associated with zoonotic infections. The spike protein receptor-binding domain (RBD) is identified as the critical determinant of viral tropism and infectivity. Thus, whether mutations in the RBD of the circulating SARS-CoV-2 isolates have altered the receptor binding affinity and made them more infectious has been the research hot spot. Given that SARS-CoV-2 is a novel coronavirus, the significance of our research is in identifying and validating the RBD mutant types emerging during the early transmission phase and increasing human angiotensin-converting enzyme 2 (ACE2) receptor binding affinity and infectivity. Our study provides insights into the evolutionary trajectory of early SARS-CoV-2 variants of zoonotic origin. The continuing surveillance of RBD mutations with increased human ACE2 affinity in human or other animals is critical to the development of new COVID-19 drugs and vaccines against these variants during the sustained COVID-19 pandemic.

Adenoviral Infections in Singapore: Should New Antiviral Therapies and Vaccines Be Adopted?

BACKGROUND: A number of serious human adenovirus (HAdV) outbreaks have been recently reported: HAdV-B7 (Israel, Singapore, and USA), HAdV-B7d (USA and China), HAdV-D8, -D54, and -C2 (Japan), HAdV-B14p1 (USA, Europe, and China), and HAdV-B55 (China, Singapore, and France). METHODS: To understand the epidemiology of HAdV infections in Singapore, we studied 533 HAdV-positive clinical samples collected from 396 pediatric and 137 adult patients in Singapore from 2012 to 2018. Genome sequencing and phylogenetic analyses were performed to identify HAdV genotypes, clonal clusters, and recombinant or novel HAdVs. RESULTS: The most prevalent genotypes identified were HAdV-B3 (35.6%), HAdV-B7 (15.4%), and HAdV-E4 (15.2%). We detected 4 new HAdV-C strains and detected incursions with HAdV-B7 (odds ratio [OR], 14.6; 95% confidence interval [CI], 4.1-52.0) and HAdV-E4 (OR, 13.6; 95% CI, 3.9-46.7) among pediatric patients over time. In addition, immunocompromised patients (adjusted OR [aOR], 11.4; 95% CI, 3.8-34.8) and patients infected with HAdV-C2 (aOR, 8.5; 95% CI, 1.5-48.0), HAdV-B7 (aOR, 3.7; 95% CI, 1.2-10.9), or HAdV-E4 (aOR, 3.2; 95% CI, 1.1-8.9) were at increased risk for severe disease. CONCLUSIONS: Singapore would benefit from more frequent studies of clinical HAdV genotypes to identify patients at risk for severe disease and help guide the use of new antiviral therapies, such as brincidofovir, and potential administration of HAdV 4 and 7 vaccine.

A Zoonotic Adenoviral Human Pathogen Emerged through Genomic Recombination among Human and Nonhuman Simian Hosts.

Genomics analysis of a historically intriguing and predicted emergent human adenovirus (HAdV) pathogen, which caused pneumonia and death, provides insight into a novel molecular evolution pathway involving "ping-pong" zoonosis and anthroponosis. The genome of this promiscuous pathogen is embedded with evidence of unprecedented multiple, multidirectional, stable, and reciprocal cross-species infections of hosts from three species (human, chimpanzee, and bonobo). This recombinant genome, typed as HAdV-B76, is identical to two recently reported simian AdV (SAdV) genomes isolated from chimpanzees and bonobos. Additionally, the presence of a critical adenoviral replication element found in HAdV genomes, in addition to genes that are highly similar to counterparts in other HAdVs, reinforces its potential as a human pathogen. Reservoirs in nonhuman hosts may explain periods of apparent absence and then reemergence of human adenoviral pathogens, as well as present pathways for the genesis of those thought to be newly emergent. The nature of the HAdV-D76 genome has implications for the use of SAdVs as gene delivery vectors in human gene therapy and vaccines, selected to avoid preexisting and potentially fatal host immune responses to HAdV.IMPORTANCE An emergent adenoviral human pathogen, HAdV-B76, associated with a fatality in 1965, shows a remarkable degree of genome identity with two recently isolated simian adenoviruses that contain cross-species genome recombination events from three hosts: human, chimpanzee, and bonobo. Zoonosis (nonhuman-to-human transmission) and anthroponosis (human to nonhuman transmission) may play significant roles in the emergence of human adenoviral pathogens.

Genomics-based re-examination of the taxonomy and phylogeny of human and simian Mastadenoviruses: an evolving whole genomes approach, revealing putative zoonosis, anthroponosis, and amphizoonosis.

With the advent of high-resolution and cost-effective genomics and bioinformatics tools and methods contributing to a large database of both human (HAdV) and simian (SAdV) adenoviruses, a genomics-based re-evaluation of their taxonomy is warranted. Interest in these particular adenoviruses is growing in part due to the applications of both in gene transfer protocols, including gene therapy and vaccines, as well in oncolytic protocols. In particular, the re-evaluation of SAdVs as appropriate vectors in humans is important as zoonosis precludes the assumption that human immune system may be naïve to these vectors. Additionally, as important pathogens, adenoviruses are a model organism system for understanding viral pathogen emergence through zoonosis and anthroponosis, particularly among the primate species, along with recombination, host adaptation, and selection, as evidenced by one long-standing human respiratory pathogen HAdV-4 and a recent re-evaluation of another, HAdV-76. The latter reflects the insights on amphizoonosis, defined as infections in both directions among host species including "other than human", that are possible with the growing database of nonhuman adenovirus genomes. HAdV-76 is a recombinant that has been isolated from human, chimpanzee, and bonobo hosts. On-going and potential impacts of adenoviruses on public health and translational medicine drive this evaluation of 174 whole genome sequences from HAdVs and SAdVs archived in GenBank. The conclusion is that rather than separate HAdV and SAdV phylogenetic lineages, a single, intertwined tree is observed with all HAdVs and SAdVs forming mixed clades. Therefore, a single designation of "primate adenovirus" (PrAdV) superseding either HAdV and SAdV is proposed, or alternatively, keeping HAdV for human adenovirus but expanding the SAdV nomenclature officially to include host species identification as in ChAdV for chimpanzee adenovirus, GoAdV for gorilla adenovirus, BoAdV for bonobo adenovirus, and ad libitum.

Selection Pressure in the Human Adenovirus Fiber Knob Drives Cell Specificity in Epidemic Keratoconjunctivitis.

Human adenoviruses (HAdVs) contain seven species (HAdV-A to -G), each associated with specific disease conditions. Among these, HAdV-D includes those viruses associated with epidemic keratoconjunctivitis (EKC), a severe ocular surface infection. The reasons for corneal tropism for some but not all HAdV-Ds are not known. The fiber protein is a major capsid protein; its C-terminal "knob" mediates binding with host cell receptors to facilitate subsequent viral entry. In a comprehensive phylogenetic analysis of HAdV-D capsid genes, fiber knob gene sequences of HAdV-D types associated with EKC formed a unique clade. By proteotyping analysis, EKC virus-associated fiber knobs were uniquely shared. Comparative structural modeling showed no distinct variations in fiber knobs of EKC types but did show variation among HAdV-Ds in a region overlapping with the known CD46 binding site in HAdV-B. We also found signature amino acid positions that distinguish EKC from non-EKC types, and by in vitro studies we showed that corneal epithelial cell tropism can be predicted by the presence of a lysine or alanine at residue 240. This same amino acid residue in EKC viruses shows evidence for positive selection, suggesting that evolutionary pressure enhances fitness in corneal infection, and may be a molecular determinant in EKC pathogenesis. IMPORTANCE: Viruses adapt various survival strategies to gain entry into target host cells. Human adenovirus (HAdV) types are associated with distinct disease conditions, yet evidence for connections between genotype and cellular tropism is generally lacking. Here, we provide a structural and evolutionary basis for the association between specific genotypes within HAdV species D and epidemic keratoconjunctivitis, a severe ocular surface infection. We find that HAdV-D fiber genes of major EKC pathogens, specifically the fiber knob gene region, share a distinct phylogenetic clade. Deeper analysis of the fiber gene revealed that evolutionary pressure at crucial amino acid sites has a significant impact on its structural conformation, which is likely important in host cell binding and entry. Specific amino acids in hot spot residues provide a link to ocular cell tropism and possibly to corneal pathogenesis.

Homologous recombination in E3 genes of human adenovirus species D.

Genes within the E3 transcription unit of human adenoviruses modulate host immune responses to infection. A comprehensive genomics and bioinformatics analysis of the E3 transcription unit for 38 viruses within human adenovirus species D (HAdV-D) revealed distinct and surprising patterns of homologous recombination. Homologous recombination was identified in open reading frames for E3 CR1α, CR1ß, and CR1γ, similar to that previously observed with genes encoding the three major structural capsid proteins, the penton base, hexon, and fiber.

Clinical characteristics and phylogenetic analysis of human enteric adenovirus type 41 (HAdV-F41) from children with gastroenteritis during SARS-CoV-2 pandemic.

Human adenovirus type 41 (HAdV-F41) usually causes pediatrics gastroenteritis. However, it was reported to be associated with the outbreaks of severe acute hepatitis of unknown aetiology (SAHUA) in pediatrics during COVID-19 pandemic. In this study, we investigated the prevalence of enteric HAdV-F41 in 37,920 paediatric gastroenteritis cases from 2017 to 2022 in Guangzhou, China. All children presented were tested negative for SARS-CoV-2 during the "zero-COVID" period. The main clinical symptom of the children was diarrhea (96.5%). No fatalities nor liver abnormal symptoms was found. In 2021, one year since the pandemic of COVID-19, the prevalence of HAdV-F41 abruptly increased from 3.71% to 8.64% (P < 0.001). All of HAdV-F41 circulating worldwide were classified into eight different subtypes (G1-G8) based on the phylogenetic clustering permutation of the four capsid genes of HAdV-F41. G3 was the predominant subtype (56.2%; 77/137). CRV5 isolates from SAHUA cases belong to this subtype, in which N312D and H335D mutations in the short fiber knob were identified in both Guangzhou and CRV5 isolates, presumably changing the virus tropism by directly interacting with the heparin sulfate (HS) receptor. Additionally, a novel recombinant G6 subtype, which is unique and only circulating in China was first identified in this study. This is the first study highlighting the prevalence of HAdV-F41 in paediatric cases of gastroenteritis during COVID-19 pandemic in China. The clinical and viral evolution finding of HAdV-F41 provide insight into the clinical characteristics of children with HAdV-F41 infections as well as the uncertain role of HAdV-F41 in the cause of SAHUA.

Genome sequence of human adenovirus type 55, a re-emergent acute respiratory disease pathogen in China.

Human adenovirus type 55 (HAdV-B55) is an acute respiratory disease (ARD) pathogen first completely characterized in China (2006). This is a unique Trojan horse microbe with the virus neutralization attribute of a renal pathogen and the cell tropism and clinical attributes of a respiratory pathogen, bypassing herd immunity. It appeared to be an uncommon pathogen, with earlier putative, sporadic occurrences in Spain (1969) and Turkey (2004); these isolates were incompletely characterized using only two epitopes. Reported here is the genome of a second recent isolate (China, 2011), indicating that it may occur more frequently. The availability of this HAdV-B55 genome provides a foundation for studying adenovirus molecular evolution, the dynamics of epidemics, and patterns of pathogen emergence and re-emergence. These data facilitate studies to predict genome recombination between adenoviruses, as well as sequence divergence rates and hotspots, all of which are important for vaccine development and because HAdVs are used for epitope and/or gene delivery vectors.

Genome sequence of the first human adenovirus type 14 isolated in China.

Emergent pathogens may be examined rapidly at high resolution on a molecular level using genomics, allowing an understanding of their evolution. China is a unique environment for studying pathogens, having a large, dense, and generally closed population. Human adenovirus type 14 (HAdV-14) was originally identified as an acute respiratory disease (ARD) pathogen in The Netherlands (1955), with a second isolation in England (1957). Since then, few reports of this virus appeared until an ARD pathogen with a similar genome caused multiple outbreaks in the United States (2006 to 2009). This report presents the first genome of HAdV-B14 isolated in China (2010). As China experienced two recent outbreaks of an emergent ARD pathogen, HAdV-B55, containing much of the HAdV-B14 genome, the availability of this HAdV-B14 sequence will facilitate studies of the epidemiology of these pathogens, as well as provide a foundation for studying adenovirus evolution and the genesis of emergent pathogens. These observations may be invaluable in predicting possible recombination between wild-type viruses and adenoviral gene delivery vectors, including adenovirus vaccines.

Overreliance on the hexon gene, leading to misclassification of human adenoviruses.

The genome of human adenovirus (HAdV) D30 was sequenced in depth. Sequence assembly and analysis revealed two distinct viral sequences with identical hexon genes, which were the same as the one previously reported for HAdV-D30. However, one of the two viruses was found to be a recombinant of HAdV-D29. Exclusive reliance on serum neutralization can lead to mischaracterization of adenoviruses and miss coinfections. Whole-genome sequencing remains the gold standard for proper classification of HAdVs.

Five genome sequences of subspecies B1 human adenoviruses associated with acute respiratory disease.

Five genomes of human subspecies B1 adenoviruses isolated from cases of acute respiratory disease have been sequenced and archived for reference. These include representatives of two prevalent genomic variants of HAdV-7, i.e., HAdV-7h and HAdV-7d2. The other three are HAdV-3/16, HAdV-16 strain E26, and HAdV-3+7 strain Takeuchi. All are recombinant genomes. Genomics and bioinformatics provide detailed views into the genetic makeup of these pathogens and insight into their molecular evolution. Retrospective characterization of particularly problematic older pathogens such as HAdV-7h (1987) and intriguing isolates such as HAdV-3+7 strain Takeuchi (1958) may provide clues to their phenotypes and serology and may suggest protocols for prevention and treatment.

Complete genome sequence of human adenovirus prototype 17.

As one of the first five human adenoviruses (HAdVs) to be sequenced, type 17 was important as a reference tool for comparative genomics of recently isolated HAdV pathogens in species D. HAdV-D17 was the first species D adenovirus to be sequenced and was deposited in GenBank in 1999. These genome data were not of high quality, and a redetermination of the same stock virus provides corrected data; among the differences are a length of 35,139 bp versus 35,100 bp in the original, and 160 mismatches to the original genome were found. Annotation of the coding sequences reveals 39 as opposed to 8, a finding which is important for phylogenomic studies.

CoreGenes5.0: An Updated User-Friendly Webserver for the Determination of Core Genes from Sets of Viral and Bacterial Genomes.

The determination of core genes in viral and bacterial genomes is crucial for a better understanding of their relatedness and for their classification. CoreGenes5.0 is an updated user-friendly web-based software tool for the identification of core genes in and data mining of viral and bacterial genomes. This tool has been useful in the resolution of several issues arising in the taxonomic analysis of bacteriophages and has incorporated many suggestions from researchers in that community. The webserver displays result in a format that is easy to understand and allows for automated batch processing, without the need for any user-installed bioinformatics software. CoreGenes5.0 uses group protein clustering of genomes with one of three algorithm options to output a table of core genes from the input genomes. Previously annotated "unknown genes" may be identified with homologues in the output. The updated version of CoreGenes is able to handle more genomes, is faster, and is more robust, providing easier analysis of custom or proprietary datasets. CoreGenes5.0 is accessible at coregenes.org, migrating from a previous site.

Molecular Typing and Rapid Identification of Human Adenoviruses Associated With Respiratory Diseases Using Universal PCR and Sequencing Primers for the Three Major Capsid Genes: Penton Base, Hexon, and Fiber.

Human adenoviruses (HAdVs) within species B, C, and E are responsible for highly contagious and potentially severe respiratory disease infections. The traditional method to type these pathogens was based on virus neutralization and hemagglutination assays, which are both time-consuming and difficult, particularly due to the nonavailability of reagents. Subsequent molecular typing based on the partial characterization of the hexon gene and/or the restriction enzyme analysis (REA) of the genomes is inadequate, particularly in identifying recombinants. Here, a rapid, simple, and cost-effective method for molecular typing HAdV respiratory pathogens is presented. This incorporates three pairs of universal PCR primers that target the variable regions of the three major capsid genes, i.e., hexon, penton base, and fiber genes, that span the genome. The protocol enables typing and characterization of genotypes within species B, C, and E, as well as of some genotypes within species D and F. To validate this method, we surveyed 100 children with HAdV-associated acute respiratory infections identified by direct immunofluorescence (Hong Kong; July through October, 2014). Throat swab specimens were collected and analyzed by PCR amplification and sequencing; these sequences were characterized by BLAST. HAdVs were detected in 98 out of 100 (98%) samples, distributing as follows: 74 HAdV-B3 (74%); 10 HAdV-E4 (10%); 7 HAdV-C2 (7%); 2 HAdV-C6 (2%); 1 HAdV-B7 (1%); 1 HAdV-C1 (1%); 2 co-infection (2%); and 1 novel recombinant (1%). This study is the first detailed molecular epidemiological survey of HAdVs in Hong Kong. The developed method allows for the rapid identification of HAdV respiratory pathogens, including recombinants, and bypasses the need for whole genome sequencing for real-time surveillance of circulating adenovirus strains in outbreaks and populations by clinical virologists, public health officials, and epidemiologists.

Tracking SARS-CoV-2 Omicron diverse spike gene mutations identifies multiple inter-variant recombination events.

The current pandemic of COVID-19 is fueled by more infectious emergent Omicron variants. Ongoing concerns of emergent variants include possible recombinants, as genome recombination is an important evolutionary mechanism for the emergence and re-emergence of human viral pathogens. In this study, we identified diverse recombination events between two Omicron major subvariants (BA.1 and BA.2) and other variants of concern (VOCs) and variants of interest (VOIs), suggesting that co-infection and subsequent genome recombination play important roles in the ongoing evolution of SARS-CoV-2. Through scanning high-quality completed Omicron spike gene sequences, 18 core mutations of BA.1 (frequency >99%) and 27 core mutations of BA.2 (nine more than BA.1) were identified, of which 15 are specific to Omicron. BA.1 subvariants share nine common amino acid mutations (three more than BA.2) in the spike protein with most VOCs, suggesting a possible recombination origin of Omicron from these VOCs. There are three more Alpha-related mutations in BA.1 than BA.2, and BA.1 is phylogenetically closer to Alpha than other variants. Revertant mutations are found in some dominant mutations (frequency >95%) in the BA.1. Most notably, multiple characteristic amino acid mutations in the Delta spike protein have been also identified in the "Deltacron"-like Omicron Variants isolated since November 11, 2021 in South Africa, which implies the recombination events occurring between the Omicron and Delta variants. Monitoring the evolving SARS-CoV-2 genomes especially for recombination is critically important for recognition of abrupt changes to viral attributes including its epitopes which may call for vaccine modifications.

Computational analysis of two species C human adenoviruses provides evidence of a novel virus.

Human adenovirus C (HAdV-C) species are a common cause of respiratory infections and can occasionally produce severe clinical manifestations. A deeper understanding of the variation and evolution in species HAdV-C is especially important since these viruses, including HAdV-C6, are used as gene delivery vectors for human gene therapy and in other biotechnological applications. Here, the full-genome analysis of the prototype HAdV-C6 and a recently identified virus provisionally termed HAdV-C57 are reported. Although the genomes of all species HAdV-C members are very similar to each other, the E3 region, hexon and fiber (ten proteins total) present a wide range of identity values at the amino acid level. Studies of these viruses in comparison to the other three HAdV-C prototypes (1, 2, and 5) comprise a comprehensive analysis of the diversity and conservation within HAdV-C species. HAdV-C6 contains a recombination event within the constant region of the hexon gene. HAdV-C57 is a recombinant virus with a fiber gene nearly identical to HAdV-C6 and a unique hexon distinguished by its loop 2 motif.