Infectious bronchitis virus: an overview of the "chicken coronavirus"

Infectious bronchitis virus (IBV) is a highly contagious avian Gammacoronavirus that affects mainly chickens (Gallus gallus) but can circulate in other avian species. IBV constitutes a significant threat to the poultry industry, causing reduced egg yield, growth and mortality levels that can vary in impact. The virus can be transmitted horizontally by inhalation or direct/indirect contact with infected birds or contaminated fomites, vehicles, farm personnel and litter (Figure 1). The error-prone viral polymerase and recombination mechanisms mean diverse viral population results, with multiple genotypes, serotypes, pathotypes and protectotypes. This significantly complicates control and mitigation strategies based on vigilance in biosecurity and the deployment of vaccination.

An Amplicon-Based Application for the Whole-Genome Sequencing of GI-19 Lineage Infectious Bronchitis Virus Directly from Clinical Samples

Infectious bronchitis virus (IBV) causes a highly contagious respiratory disease in chickens, leading to significant economic losses in the poultry industry worldwide. IBV exhibits a high mutation rate, resulting in the continuous emergence of new variants and strains. A complete genome analysis of IBV is crucial for understanding its characteristics. However, it is challenging to obtain whole-genome sequences from IBV-infected clinical samples due to the low abundance of IBV relative to the host genome. Here, we present a novel approach employing next-generation sequencing (NGS) to directly sequence the complete genome of IBV. Through in silico analysis, six primer pairs were designed to match various genotypes, including the GI-19 lineage of IBV. The primer sets successfully amplified six overlapping fragments by long-range PCR and the size of the amplicons ranged from 3.7 to 6.4 kb, resulting in full coverage of the IBV genome. Furthermore, utilizing Illumina sequencing, we obtained the complete genome sequences of two strains belonging to the GI-19 lineage (QX genotype) from clinical samples, with 100% coverage rates, over 1000 × mean depth coverage, and a high percentage of mapped reads to the reference genomes (96.63% and 97.66%). The reported method significantly improves the whole-genome sequencing of IBVs from clinical samples; thus, it can improve understanding of the epidemiology and evolution of IBVs.

Chemical characteristics and biological activity screening of Pistacia lentiscus mastic gum and leaves from Türkiye

BACKGROUND

Mastic gum is a resin that is produced by Pistacia lentiscus. It has many traditional uses, dating from ancient times, such as the treatment of gastrointestinal disorders and as a food additive. In this study, the leaves and mastic gum of trees of different ages from Karaburun and the Cesme peninsula in Türkiye were examined chemically and biologically. Flavonoids, and phenolic and fatty acid components were evaluated by a liquid chromatography system coupled with high resolution mass spectrometry (LC-HRMS) and gas chromatography with flame ionization detection (GC-FID). Cytotoxicity was screened against several cancer and healthy cell lines using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay. Inducible nitric oxide synthase (iNOS) inhibition was determined on lipopolysaccharide (LPS)-induced murine macrophage cell line (RAW 264.7) cells. Antiviral activity was measured against avian coronavirus using an in ovo virucidal antiviral activity assay.

RESULTS

The main phenolic constituents of the gum were found to be salicylic, rosmarinic, and caffeic acids whereas the most abundant compounds detected were flavonoids in the leaf extracts. The most abundant fatty acids in hexane extracts were palmitic and oleic acids. All gum extracts except 3-year-old gum had significant cytotoxic activity on HeLa (IC50 1.74 ± 0.03-4.76 ± 0.95) and PC-3 (0.64 ± 0.25-6.22 ± 1.40) cells. Moreover, reducing virus activity by fivefold or sixfold logarithmically between the range of 5-10 μg g-1 of 30-year-old gum extracts underscored the biological activity.

CONCLUSION

In ovo antiviral activity studies on the P. lentiscus were conducted for the first time. The mastic gum and leaves obtained from P. lentiscus may have strong potential in terms of their chemical content and antiviral and cytotoxic activity. As a consequence of these properties, it is a sustainable, renewable natural resource that can be used as an additive and flavoring in the food and pharmaceutical industries. © 2023 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Genetic Analysis of Infectious Bronchitis Virus S1 Gene Reveals Novel Amino Acid Changes in the GI-16 Lineage in Peru

Infectious bronchitis is a highly contagious viral disease that represents an economic threat for poultry despite the wide use of vaccination. To characterize the virus circulating in Peru, we analyzed 200 samples, including nasopharyngeal swabs and multiple tissues collected from animals suspected of being infected with infectious bronchitis virus (IBV) between January and August in 2015. All animals had at least one positive sample for IBV by RT-PCR. Out of these positive samples, eighteen (18) were selected for viral isolation and a partial S1 sequencing. Phylogenetic analysis showed that sixteen isolates clustered with members of GI-16 lineage, also known as Q1, with nucleotide homology ranging from 93% to 98%. The two remaining isolates grouped with members of the GI-1 lineage. Our study reveals circulation of GI-16 lineage during this period in poultry systems in Peru, along with GI-1 lineage (vaccine-derived). Moreover, those IBV GI-16 isolates showed unique nucleotide and amino acid changes compared to their closest relatives. Altogether, these findings reveal the circulation of GI-16 lineage while describing changes at key regions of the S protein that might be of relevance for vaccine evasion. These results highlight the importance of genetic surveillance for improving vaccination strategies against infectious bronchitis.

Genomics and pathogenesis of the avian coronavirus infectious bronchitis virus

Infectious bronchitis virus (IBV) is a member of the family Coronaviridae, together with viruses such as SARS-CoV, MERS-CoV and SARS-CoV-2 (the causative agent of the COVID-19 global pandemic). In this family of viruses, interspecies transmission has been reported, so understanding their pathobiology could lead to a better understanding of the emergence of new serotypes. IBV possesses a single-stranded, non-segmented RNA genome about 27.6 kb in length that encodes several non-structural and structural proteins. Most functions of these proteins have been confirmed in IBV, but some other proposed functions have been based on research conducted on other members of the family Coronaviridae. IBV has variable tissue tropism depending on the strain, and can affect the respiratory, reproductive, or urinary tracts; however, IBV can also replicate in other organs. Additionally, the pathogenicity of IBV is also variable, with some strains causing only mild clinical signs, while infection with others results in high mortality rates in chickens. This paper extensively and comprehensibly reviews general aspects of coronaviruses and, more specifically, IBV, with emphasis on protein functions and pathogenesis. The pathogenicity of the Australian strains of IBV is also reviewed, describing the variability between the different groups of strains, from the classical to the novel and recombinant strains. Reverse genetic systems, cloning and cell culture growth techniques applicable to IBV are also reviewed.

The Genetic Stability, Replication Kinetics and Cytopathogenicity of Recombinant Avian Coronaviruses with a T16A or an A26F Mutation within the E Protein Is Cell-Type Dependent

The envelope (E) protein of the avian coronavirus infectious bronchitis virus (IBV) is a small-membrane protein present in two forms during infection: a monomer and a pentameric ion channel. Each form has an independent role during replication; the monomer disrupts the secretory pathway, and the pentamer facilitates virion production. The presence of a T16A or A26F mutation within E exclusively generates the pentameric or monomeric form, respectively. We generated two recombinant IBVs (rIBVs) based on the apathogenic molecular clone Beau-R, containing either a T16A or A26F mutation, denoted as BeauR-T16A and BeauR-A26F. The replication and genetic stability of the rIBVs were assessed in several different cell types, including primary and continuous cells, ex vivo tracheal organ cultures (TOCs) and in ovo. Different replication profiles were observed between cell cultures of different origins. BeauR-A26F replicated to a lower level than Beau-R in Vero cells and in ovo but not in DF1, primary chicken kidney (CK) cells or TOCs. Genetic stability and cytopathic effects were found to differ depending on the cell system. The effect of the T16A and A26F mutations appear to be cell-type dependent, which, therefore, highlights the importance of cell type in the investigation of the IBV E protein.

Engineering and Characterization of Avian Coronavirus Mutants Expressing Fluorescent Reporter Proteins from the Replicase Gene

Infectious bronchitis virus (IBV) is an avian coronavirus that causes infectious bronchitis, an acute and highly contagious respiratory disease of chickens. IBV evolution under the pressure of comprehensive and widespread vaccination requires surveillance for vaccine resistance, as well as periodic vaccine updates. Reverse genetics systems are very valuable tools in virology, as they facilitate rapid genetic manipulation of viral genomes, thereby advancing basic and applied research. We report here the construction of an infectious clone of IBV strain Beaudette as a bacterial artificial chromosome (BAC). The engineered full-length IBV clone allowed the rescue of an infectious virus that was phenotypically indistinguishable from the parental virus. We used the infectious IBV clone and examined whether an enhanced green fluorescent protein (EGFP) can be produced by the replicase gene ORF1 and autocatalytically released from the replicase polyprotein through cleavage by the main coronavirus protease. We show that IBV tolerates insertion of the EGFP ORF at the 3' end of the replicase gene, between the sequences encoding nsp13 and nsp16 (helicase, RNA exonuclease, RNA endonuclease, and RNA methyltransferase). We further show that EGFP is efficiently cleaved from the replicase polyprotein and can be localized in double-membrane vesicles along with viral RNA polymerase and double-stranded RNA, an intermediate of IBV genome replication. One of the engineered reporter EGFP viruses were genetically stable during passage in cultured cells. We demonstrate that the reporter EGFP viruses can be used to study virus replication in host cells and for antiviral drug discovery and development of diagnostic assays. IMPORTANCE Reverse genetics systems based on bacterial artificial chromosomes (BACs) are the most valuable systems in coronavirus research. Here, we describe the establishment of a reverse genetics system for the avian coronavirus strain Beaudette, the most intensively studied strain. We cloned a copy of the avian coronavirus genome into a BAC vector and recovered infectious virus in permissive cells. We used the new system to construct reporter viruses that produce enhanced green fluorescent protein (EGFP). The EGFP coding sequence was inserted into 11 known cleavage sites of the major coronavirus protease in the replicase gene ORF1. Avian coronavirus tolerated the insertion of the EGFP coding sequence at three sites. The engineered reporter viruses replicated with parental efficiency in cultured cells and were sufficiently genetically stable. The new system facilitates functional genomics of the avian coronavirus genome but can also be used for the development of novel vaccines and anticoronaviral drugs.

Genomic Analysis of Avian Infectious Bronchitis Viruses Recently Isolated in South Korea Reveals Multiple Introductions of GI-19 Lineage (QX Genotype)

Infectious bronchitis virus (IBV) was first identified in the 1930s and it imposes a major economic burden on the poultry industry. In particular, GI-19 lineage has spread globally and has evolved constantly since it was first detected in China. In this study, we analyzed S1 gene sequences from 60 IBVs isolated in South Korea. Two IBV lineages, GI-15 and GI-19, were identified in South Korea. Phylogenetic analysis suggested that there were six distinct subgroups (KM91-like, K40/09-like, and QX-like I to IV) of the South Korean GI-19 IBVs. Among them, QX-type III and IV subgroups, which are phylogenetically different from those reported in South Korea in the past, accounted for more than half of the total. Moreover, the phylogeographic analysis of the QX-like subgroups indicated at least four distinct introductions of GI-19 IBVs into South Korea during 2001–2020. The efficacy of commercialized vaccines against the recently introduced QX-like subgroups should be verified, and continuous international surveillance efforts and quarantine procedures should be enhanced to prevent the incursion of viruses.

Wild birds as reservoirs for diverse and abundant gamma- and deltacoronaviruses

Wild birds interconnect all parts of the globe through annual cycles of migration with little respect for country or continental borders. Although wild birds are reservoir hosts for a high diversity of gamma- and deltacoronaviruses, we have little understanding of the ecology or evolution of any of these viruses. In this review, we use genome sequence and ecological data to disentangle the evolution of coronaviruses in wild birds. Specifically, we explore host range at the levels of viral genus and species, and reveal the multi-host nature of many viral species, albeit with biases to certain types of avian host. We conclude that it is currently challenging to infer viral ecology due to major sampling and technical limitations, and suggest that improved assay performance across the breadth of gamma- and deltacoronaviruses, assay standardization, as well as better sequencing approaches, will improve both the repeatability and interpretation of results. Finally, we discuss cross-species virus transmission across both the wild bird - poultry interface as well as from birds to mammals. Clarifying the ecology and diversity in the wild bird reservoir has important ramifications for our ability to respond to the likely future emergence of coronaviruses in socioeconomically important animal species or human populations.

Alteration of immunological parameters in infectious bronchitis vaccinated-specific pathogen-free broilers after the use of different infectious bursal disease vaccines

The vaccines currently available to control infectious bursal disease (IBD) include live-attenuated and inactivated vaccines, immune-complex vaccines, and vaccines consisting of viral constructs of herpesvirus of turkeys genetically engineered to express VP2 surface protein. To evaluate the impact of vaccines on the chicken immune system, 2 animal trials were performed in specific pathogen-free broiler chickens. In trial 1, birds were either vaccinated when they are one-day old with a dual recombinant herpes virus of turkey construct vaccine, expressing VP2 protein of (IBDV) and F protein of Newcastle disease virus, or an immune-complex IBDV vaccine or birds were not vaccinated. At 14, 28, and 35 D, the bursa of Fabricius was collected for bursa:body weight (B:BW) ratio calculation. In trial 2, birds were vaccinated when they were 1-day old according to the same protocol as trial 1, but at day 14, all groups also received a live infectious bronchitis (IB) vaccine. At 0, 7, 14, 21, and 28 days after IB vaccination, birds were tested by ELISA for IB serology and, soon after the last blood sampling, they were euthanized for collection of Harderian glands, trachea, and spleen and testing by flow cytometry for characterization of mononuclear cells. The immune-complex vaccine groups showed significantly lower B:BW ratio, lower IBV antibody titers, and higher mean percentage of CD8+ T cells in the spleen, trachea, and Harderian glands than those in the other experimental groups. The results of the in vivo trials coupled with a depth analysis of the repertoire of parameters involved in the immune response to IBD and IB vaccinations show one vaccine may influence the immune response of other vaccines included in the vaccination program.

Comparative Analysis of Gene Expression in Virulent and Attenuated Strains of Infectious Bronchitis Virus at Subcodon Resolution

Like all coronaviruses, avian infectious bronchitis virus (IBV) possesses a long, single-stranded, positive-sense RNA genome (∼27 kb) and has a complex replication strategy that includes the production of a nested set of subgenomic mRNAs (sgmRNAs). Here, we used whole-transcriptome sequencing (RNASeq) and ribosome profiling (RiboSeq) to delineate gene expression in the IBV M41-CK and Beau-R strains at subcodon resolution. RNASeq facilitated a comparative analysis of viral RNA synthesis and revealed two novel transcription junction sites in the attenuated Beau-R strain, one of which would generate a sgmRNA encoding a ribosomally occupied open reading frame (dORF) located downstream of the nucleocapsid coding region. RiboSeq permitted quantification of the translational efficiency of virus gene expression and identified, for the first time, sites of ribosomal pausing on the genome. Quantification of reads flanking the programmed ribosomal frameshifting (PRF) signal at the genomic RNA ORF1a/ORF1b junction revealed that PRF in IBV is highly efficient (33 to 40%). Triplet phasing of RiboSeq data allowed precise determination of reading frames and revealed the translation of two ORFs (ORF4b and ORF4c on sgmRNA IR), which are widely conserved across IBV isolates. Analysis of differential gene expression in infected primary chick kidney cells indicated that the host cell response to IBV occurs primarily at the level of transcription, with global upregulation of immune-related mRNA transcripts following infection and comparatively modest changes in the translation efficiencies of host genes. Cellular genes and gene networks differentially expressed during virus infection were also identified, giving insights into the host cell response to IBV infection.IMPORTANCE IBV is a major avian pathogen and presents a substantial economic burden to the poultry industry. Improved vaccination strategies are urgently needed to curb the global spread of this virus, and the development of suitable vaccine candidates will be aided by an improved understanding of IBV molecular biology. Our high-resolution data have enabled a precise study of transcription and translation in cells infected with both pathogenic and attenuated forms of IBV and expand our understanding of gammacoronaviral gene expression. We demonstrate that gene expression shows considerable intraspecies variation, with single nucleotide polymorphisms being associated with altered production of sgmRNA transcripts, and our RiboSeq data sets enabled us to uncover novel ribosomally occupied ORFs in both strains. The numerous cellular genes and gene networks found to be differentially expressed during virus infection provide insights into the host cell response to IBV infection.

Memory immune responses and protection of chickens against a nephropathogenic infectious bronchitis virus strain by combining live heterologous and inactivated homologous vaccines

In this study, we evaluated antibody and cell-mediated immune (CMI) responses in the mucosal and systemic compartments and protection against challenge with a nephropathogenic Brazilian (BR-I) strain of infectious bronchitis virus (IBV) in chickens submitted to a vaccination regime comprising a priming dose of heterologous live attenuated Massachusetts vaccine followed by a booster dose of an experimental homologous inactivated vaccine two weeks later. This immunization protocol elicited significant increases in serum and lachrymal levels of anti-IBV IgG antibodies and upregulated the expression of CMI response genes, such as those encoding CD8β chain and Granzyme homolog A in tracheal and kidney tissues at 3, 7, and 11 days post-infection in the vaccinated chickens. Additionally, vaccinated and challenged chickens showed reduced viral loads and microscopic lesion counts in tracheal and kidney tissues, and their antibody and CMI responses were negatively correlated with viral loads in the trachea and kidney. In conclusion, the combination of live attenuated vaccine containing the Massachusetts strain with a booster dose of an inactivated vaccine, containing a BR-I IBV strain, confers effective protection against infection with nephropathogenic homologous IBV strain because of the induction of consistent memory immune responses mediated by IgG antibodies and TCD8 cells in the mucosal and systemic compartments of chickens submitted to this vaccination regime.

Genetic Diversity and Phylodynamics of Avian Coronaviruses in Egyptian Wild Birds

Avian coronaviruses (ACoVs) are continuously evolving and causing serious economic consequences in the poultry industry and around the globe. Owing to their extensive genetic diversity and high mutation rates, controlling ACoVs has become a challenge. In this context, the potential contribution of wild birds in the disease dynamics, especially in domesticated birds, remains largely unknown. In the present study, five hundred fifty-seven (n = 557) cloacal/fecal swabs were collected from four different wild bird species from eight Egyptian governorates during 2016 and a total of fourteen positive isolates were used for phylodynamics and evolutionary analysis. Genetic relatedness based on spike (S1) gene demonstrated the clustering of majority of these isolates where nine isolates grouped within Egy/variant 2 (IS/885 genotype) and five isolates clustered within Egy/variant 1 (IS/1494/06 genotype). Interestingly, these isolates showed noticeable genetic diversity and were clustered distal to the previously characterized Egy/variant 1 and Egy/variant 2 in Egyptian commercial poultry. The S1 gene based comparison of nucleotide identity percentages revealed that all fourteen isolates reported in this study were genetically related to the variant GI-23 lineage with 92–100% identity. Taken together, our results demonstrate that ACoVs are circulating in Egyptian wild birds and highlight their possible contributions in the disease dynamics. The study also proposes that regular monitoring of the ACoVs in wild birds is required to effectively assess the role of wild birds in disease spread, and the emergence of ACoVs strains in the country.

Phylogeny and S1 Gene Variation of Infectious Bronchitis Virus Detected in Broilers and Layers in Turkey

The avian coronavirus infectious bronchitis virus (AvCoV-IBV) is recognized as an important global pathogen because new variants are a continuous threat to the poultry industry worldwide. This study investigates the genetic origin and diversity of AvCoV-IBV by analysis of the S1 sequence derived from 49 broiler flocks and 14 layer flocks in different regions of Turkey. AvCoV-IBV RNA was detected in 41 (83.6%) broiler flocks and nine (64.2%) of the layer flocks by TaqMan real-time RT-PCR. In addition, AvCoV-IBV RNA was detected in the tracheas 27/30 (90%), lungs 31/49 (62.2%), caecal tonsils 7/22 (31.8%), and kidneys 4/49 (8.1%) of broiler flocks examined. Pathologic lesions, hemorrhages, and mononuclear infiltrations were predominantly observed in tracheas and to a lesser extent in the lungs and a few in kidneys. A phylogenetic tree based on partial S1 sequences of the detected AvCoV-IBVs (including isolates) revealed that 1) viruses detected in five broiler flocks were similar to the IBV vaccines Ma5, H120, M41; 2) viruses detected in 24 broiler flocks were similar to those previously reported from Turkey and to Israel variant-2 strains; 3) viruses detected in seven layer flocks were different from those found in any of the broiler flocks but similar to viruses previously reported from Iran, India, and China (similar to Israel variant-1 and 4/91 serotypes); and 4) that the AVCoV-IBV, Israeli variant-2 strain, found to be circulating in Turkey appears to be undergoing molecular evolution. In conclusion, genetically different AvCoV-IBV strains, including vaccine-like strains, based on their partial S1 sequence, are circulating in broiler and layer chicken flocks in Turkey and the Israeli variant-2 strain is undergoing evolution.

Relationship between different enteric viral infections and the occurrence of diarrhea in broiler flocks in Jordan

The aim of this study is to determine if enteric viruses are the cause of diarrhea in broiler flocks in Jordan. Intestinal content samples were collected from 101 broiler flocks from several regions of Jordan to detect the presence of astrovirus, coronavirus, reovirus, and rotavirus, by using reverse transcriptase polymerase chain reaction (RT-PCR). Forty-six of these flocks were clinically healthy with no enteric disease, and the other 55 flocks were clinically suffering from diarrhea. The samples were collected between 5 and 16 d of age. The results show that 79% of total 101 flocks tested were infected with one or more of the above enteric viruses. Coronavirus was the most common virus, detected in 56.4% of these flocks, with astrovirus in 29.7% of the flocks, and rotavirus (9.9%) and reovirus (5.6%) being the least common. None of these flocks were found to be infected with all four viruses, but one of the flocks was found to be infected with astrovirus, coronavirus, and rotavirus simultaneously. Individual infection was noted with astrovirus, coronavirus and rotavirus but not with reovirus, whereas all flocks infected with reovirus were also infected with coronavirus. There was no statistical evidence to link these viruses as the main cause of diarrhea in the flocks tested. This is the first study in Jordan to detect all of these viruses and to correlate their presence with diarrhea in chicken flocks.

Novel avian coronavirus and fulminating disease in guinea fowl, France

For decades, French guinea fowl have been affected by fulminating enteritis of unclear origin. By using metagenomics, we identified a novel avian gammacoronavirus associated with this disease that is distantly related to turkey coronaviruses. Fatal respiratory diseases in humans have recently been caused by coronaviruses of animal origin.

Recombination in avian gamma-coronavirus infectious bronchitis virus

Recombination in the family Coronaviridae has been well documented and is thought to be a contributing factor in the emergence and evolution of different coronaviral genotypes as well as different species of coronavirus. However, there are limited data available on the frequency and extent of recombination in coronaviruses in nature and particularly for the avian gamma-coronaviruses where only recently the emergence of a turkey coronavirus has been attributed solely to recombination. In this study, the full-length genomes of eight avian gamma-coronavirus infectious bronchitis virus (IBV) isolates were sequenced and along with other full-length IBV genomes available from GenBank were analyzed for recombination. Evidence of recombination was found in every sequence analyzed and was distributed throughout the entire genome. Areas that have the highest occurrence of recombination are located in regions of the genome that code for nonstructural proteins 2, 3 and 16, and the structural spike glycoprotein. The extent of the recombination observed, suggests that this may be one of the principal mechanisms for generating genetic and antigenic diversity within IBV. These data indicate that reticulate evolutionary change due to recombination in IBV, likely plays a major role in the origin and adaptation of the virus leading to new genetic types and strains of the virus.

Selection of and recombination between minor variants lead to the adaptation of an avian coronavirus to primate cells

An interesting question posed by the current evidence that severe acute respiratory syndrome coronavirus may be originated from an animal coronavirus is how such an animal coronavirus breaks the host species barrier and becomes zoonotic. In this report, we study the chronological order of genotypic changes in the spike protein of avian coronavirus infectious bronchitis virus (IBV) during its adaptation to a primate cell line. Adaptation of the Beaudette strain of IBV from chicken embryo to Vero cells showed the accumulation of 49 amino acid mutations. Among them, 26 (53.06%) substitutions were located in the S protein. Sequencing analysis and comparison of the S gene demonstrated that the majority of the mutations were accumulated and fixed at passage 7 on Vero cells and minor variants were isolated in several passages. Evidence present suggests that the dominant Vero cell-adapted IBV strain may be derived from the chicken embryo passages by selection of and potential recombination between the minor variants. This may explain why adaptation is a rapid process and the dominant strain, once adapted to a new host cell, becomes relatively stable.

Replication and morphogenesis of avian coronavirus in Vero cells and their inhibition by monensin

Avian infectious bronchitis virus (IBV) was adapted to Vero cells by serial passage. No significant inhibition of IBV replication was observed when infected Vero cells were treated with alpha-amanitin or actinomycin D. In thin sections of infected cells, assembly of IBV was observed at the rough endoplasmic reticulum (RER), and mature IBV particles were located in dilated cisternae of the RER as well as in smooth cytoplasmic vesicles. In addition to typical IBV particles, enveloped particles containing numerous ribosomes were identified at later times postinfection. Monensin, a sodium ionophore which blocks glycoprotein transport to plasma membranes at the level of the Golgi complex, was found to inhibit the formation of infectious IBV. In thin sections of infected Vero cells treated with the ionophore, IBV particles were located in dilated cytoplasmic vesicles, but fewer particles were found when compared to controls. A similar pattern of virus-specific proteins was detected in control or monensin-treated IBV-infected cells, which included two glycoproteins (170 000 and 24 000 daltons) and a polypeptide of 52 000 daltons. These results suggest that the ionophore inhibits assembly of a virus which matures at intracellular membranes.