Detection of viral antigen following exposure of one‐day‐old chickens to the Holland 52 strain of infectious bronchitis virus

Assessing a respiratory toxic infectious bronchitis virus (IBV) strain: isolation, identification, pathogenicity, and immunological failure insights

Infectious bronchitis virus (IBV) is caused by avian coronavirus and poses a global economic threat to the poultry industry. In 2023, a highly pathogenic IBV strain, IBV/CN/GD20230501, was isolated and identified from chickens vaccinated with IBV-M41 in Guangdong, China. This study comprehensively investigated the biological characteristics of the isolated IBV strain, including its genotype, whole genome sequence analysis of its S1 gene, pathogenicity, host immune response, and serum non-targeted metabolomics. Through the analysis of the S1 gene sequence, serum neutralization tests, and comparative genomics, it was proven that IBV/CN/GD20230501 belongs to the GI-I type of strain and is serotype II. One alanine residue in the S1 subunit of the isolated strain was mutated into serine, and some mutations were observed in the ORF1ab gene and the terminal region of the genome. Animal challenge experiments using the EID50 and TCID50 calculations showed that IBV/CN/GD20230501 possesses strong respiratory pathogenicity, with early and long-term shedding of viruses and rapid viral spread. Antibody detection indicated that chickens infected with IBV/CN/GD20230501 exhibited delayed expression of early innate immune genes, while those infected with M41 showed rapid gene induction and effective viral control. Metabolomics analysis demonstrated that this virus infection led to differential expression of 291 ions in chicken serum, mainly affecting the citric acid cycle (tricarboxylic acid cycle).IMPORTANCEThis study identified an infectious bronchitis virus (IBV) strain isolated from vaccinated chickens in an immunized population that had certain sequence differences compared to IBV-M41, resulting in significantly enhanced pathogenicity and host defense. This strain has the potential to replace M41 as a more suitable challenge model for drug research. The non-targeted metabolomics analysis highlighting the citric acid cycle provides a new avenue for studying this highly virulent strain.

Pathogenicity of GI-23 Avian Infectious Bronchitis Virus Strain Isolated in Brazil

IBV variants belonging to the GI-23 lineage have circulated since 1998 in the Middle East and have spread to several countries over time. In Brazil, the first report of GI-23 occurred in 2022. The study aimed to evaluate the in vivo pathogenicity of exotic variant GI-23 isolates. Biological samples were screening by real-time RT-PCR and classified in to GI-1 or G1-11 lineages. Interestingly, 47.77% were not classified in these lineages. Nine of the unclassified strains were sequenced and showed a high similarity to the GI-23 strain. All nine were isolated and three, were studied for pathogenicity. At necropsy, the main observations were the presence of mucus in the trachea and congestion in the tracheal mucosa. In addition, lesions on the tracheas showed marked ciliostasis, and the ciliary activity confirmed the high pathogenicity of isolates. This variant is highly pathogenic to the upper respiratory tract and can cause severe kidney lesions. This study confirm a circulation of GI-23 strain in the country and report, to first time, the isolation of an exotic variant of IBV in Brazil.

Pathogenesis and host responses in lungs and kidneys following Canadian 4/91 infectious bronchitis virus (IBV) infection in chickens

The infectious bronchitis virus (IBV) 4/91 was one of the common IBV variants isolated in Eastern Canada between 2013 and 2017 from chicken flocks showing severe respiratory and production problems. We designed an in vivo experiment, using specific pathogen free (SPF) chickens, to study the pathogenesis of, and host response to, Canadian (CAN) 4/91 IBV infection. At one week of age, the chickens were infected with 4/91 IBV/Ck/Can/17-038913 isolate. Swab samples were collected at predetermined time points. Five birds from the infected and the control groups were euthanized at 3, 7- and 10-days post-infection (dpi) to collect lung and kidney tissues. The results indicate IBV replication in these tissues at all three time points with prominent histological lesions, significant immune cell recruitment and up regulation of proinflammatory mediators. Overall, our findings add to the understanding of the pathogenesis of 4/91 infection and the subsequent host responses in the lungs and kidneys following experimental infection.

Comparative Evaluation of Immune Responses and Protection of Chitosan Nanoparticles and Oil-Emulsion Adjuvants in Avian Coronavirus Inactivated Vaccines in Chickens

Efficient vaccines are the main strategy to control the avian coronavirus (AvCoV), although several drawbacks related to traditional attenuated and inactivated vaccines have been reported. These counterpoints highlight the importance of developing new alternative vaccines against AvCoV, especially those able to induce long-lasting immune responses. This study evaluated and compared two inactivated vaccines formulated with AvCoV BR-I variants, one composed of chitosan nanoparticles (AvCoV-CS) and the second by Montanide oily adjuvant (AvCoV-O). Both developed vaccines were administered in a single dose or associated with the traditional Mass attenuated vaccine. The AvCoV-CS vaccine administered alone or associated with the Mass vaccine was able to induce strong humoral and cell-mediated immune (CMI) responses and complete protection against IBV virulent infection, wherein single administration was characterized by high IgA antibody levels in the mucosa, whereas when associated with the Mass vaccine, the serum IgG antibody was predominantly observed. On the other hand, single administration of the oily vaccine presented poor humoral and CMI responses and consequently incomplete protection against virulent challenge, but when associated with the Mass vaccine, immune responses were developed, and complete protection against infection was observed. Both of our experimental vaccines were able to induce full protection against virulent IBV challenge. A single dose of AvCoV-CS vaccine was sufficient to achieve complete protection, while AvCoV-O required a previous priming by a Mass strain to complete the protection.

Phylodynamic and Recombination Analyses of Avian Infectious Bronchitis GI-23 Reveal a Widespread Recombinant Cluster and New Among-Countries Linkages

Simple Summary

Infectious bronchitis virus (IBV) is one of the main infectious agents affecting the avian industry. The remarkable evolutionary rate of this virus represents an often unsurmountable challenge to its control, leading to the emergence of different lineages featured by different biological properties and limited cross-protection. In the present study, the origin, spreading and evolution of GI-23, one of the most important IBV emerging lineages, has been reconstructed using a phylodynamic approach. To this purpose, the broadest available collection of complete and partial S1 sequences was downloaded from GenBank and merged with specifically sequenced European strains. After a likely ancient origin, GI-23 circulated undetected in the Middle East for a considerable time, thereafter emerging as a threat in parallel with the intensification of the poultry industry and its introduction in other countries. An intensive viral circulation affecting mainly neighbouring countries or those with strong economic and political relationships was demonstrated, even though some nations appear to play a major role as a “bridge” among less related locations. Of note, a big recombinant cluster, likely originating in the Middle East but spreading thereafter, especially to Europe through Turkey, demonstrated a much-marked increase in viral population size, and potentially fitness, compared to previously circulating variants.

Abstract

Infectious bronchitis virus GI-23 lineage, although described approximately two decades ago in the Middle East, has recently drawn remarkable attention and is considered an “emerging” lineage due to its current spread to several other regions, including Europe. Despite the relevance, no comprehensive studies are available investigating its epidemiologic and evolutionary pattern. The present phylodynamic study was designed to fill this gap, benefitting from a collection of freely available GI-23 sequences and ad-hoc generated European ones. After a relatively ancient origin in the Middle East, likely in the first half of the previous century, GI-23 circulated largely undetected or underdiagnosed for a long time in this region, likely causing little damage, potentially because of low virulence coupled with limited development of avian industry in the considered years and regions and insufficient diagnostic activity. The following development of the poultry industry and spread to other countries led to a progressive but slow increase of viral population size between the late ‘90s and 2010. An increase in viral virulence could also be hypothesized. Of note, a big recombinant cluster, likely originating in the Middle East but spreading thereafter, especially to Europe through Turkey, demonstrated a much-marked increase in viral population size compared to previously circulating variants. The extensive available GI-23 sequence datasets allowed to demonstrate several potential epidemiological links among African, Asian, and European countries, not described for other IBV lineages. However, differently from previously investigated IBV lineages, its spread appears to primarily involve neighbouring countries and those with strong economic and political relationships. It could thus be speculated that frequent effective contacts among locations are necessary for efficient strain transmission. Some countries appear to play a major role as a “bridge” among less related locations, being Turkey the most relevant example. The role of vaccination in controlling the viral population was also tentatively evaluated. However, despite some evidence suggesting such an effect, the bias in sequence and data availability and the variability in the applied vaccination protocols prevent robust conclusions and warrant further investigations.

Replication and vaccine protection of multiple infectious bronchitis virus strains in pheasants (Phasianus colchicus)

This study demonstrates that infectious bronchitis virus (IBV) strain M41, which is pathogenic for chickens, is nonpathogenic for pheasants. However, M41 replicated in the respiratory tracts of most inoculated pheasants and the virus was shed from their respiratory tracts in the early stages of infection (4 and 8 dpc). Similarly, the attenuated IBV H120 vaccine strain also replicated and the virus was shed from their respiratory tracts of most inoculated pheasants, whereas the pheasant coronavirus (PhCoV) I0623/17 replicated in the respiratory tracts of all challenged pheasants, which then shed virus for a long period of time. Strain M41 also replicated in selected tissues of the inoculated pheasants, including the lung, kidney, proventriculus, and cecal tonsil, although the viral titers were very low. Therefore, it was important to establish whether the H120 vaccine, which has a limited replication capacity in pheasants, induces a protective immune response to both "homologous" M41 and "heterologous" I0623/17 challenge. Vaccination with H120 induced humoral responses, and the replication of M41 was reduced or restricted in the tissues of the H120-vaccinated pheasants compared with its replication in unvaccinated birds. This implies that partial protection was conferred on pheasants by vaccination with the H120 vaccine. Prolonged viral replication and a large number of birds shedding virus into the respiratory tract were also observed in the unvaccinated pheasants after inoculation with M41. However, only limited protection against challenge with PhCoV I0623/17 was conferred on pheasants vaccinated with H120, largely because the replication of H120 in pheasants was limited, thus, limiting the immune responses induced by it. The low amino acid identity of the S1 subunit of the S proteins of H120 and I0623/17 might also account, at least in part, for the poor cross-protective immunity induced by H120. These results suggest that further work is required to rationally design vaccines that confer effective protection against PhCoV infection in commercial pheasant stocks.

The emergence, evolution and spread of infectious bronchitis virus genotype GI-23

Avian infectious bronchitis is a contagious viral disease, caused by avian infectious bronchitis virus (IBV), that leads to severe losses in the poultry industry all over the world. Since the 1950s, IBV has circulated in the Middle East and North Africa, and no tangible evidence has shown any effects of measures taken to control its spread or evolution. Furthermore, new IBV variants are continually discovered. Although several genetic studies on IBV have been conducted, many IBV strains from this region have either been misclassified or remain unclassified. The genotype 23 (GI-23) variant emerged and has prevailed in the Middle East by continuously evolving through inter- and/or intra-genotypic recombination. The GI-23 genotype is currently enzootic throughout Europe and Asia. Although many studies of protection against the circulating strains have been conducted, they have not been standardized according to regulatory requirements. In this review, we provide an overview of the evolution and genetic diversity of IBV genotypes and a genetic classification of IBV strains, with a focus on the GI-23 genotype. The high prevalence of IBV GI-23 strains necessitates the adoption of vaccination schemes using GI-23-based vaccines.

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.

Hassan MS, C. Cork S, Abdul-Careem MF. Infectious Bronchitis Coronavirus Infection in Chickens: Multiple System Disease with Immune Suppression

In the early 1930s, infectious bronchitis (IB) was first characterized as a respiratory disease in young chickens; later, the disease was also described in older chickens. The etiology of IB was confirmed later as being due to a coronavirus: the infectious bronchitis virus (IBV). Being a coronavirus, IBV is subject to constant genome change due to mutation and recombination, with the consequence of changing clinical and pathological manifestations. The potential use of live attenuated vaccines for the control of IBV infection was demonstrated in the early 1950s, but vaccine breaks occurred due to the emergence of new IBV serotypes. Over the years, various IBV genotypes associated with reproductive, renal, gastrointestinal, muscular and immunosuppressive manifestations have emerged. IBV causes considerable economic impacts on global poultry production due to its pathogenesis involving multiple body systems and immune suppression; hence, there is a need to better understand the pathogenesis of infection and the immune response in order to help developing better management strategies. The evolution of new strains of IBV during the last nine decades against vaccine-induced immune response and changing clinical and pathological manifestations emphasize the necessity of the rational development of intervention strategies based on a thorough understanding of IBV interaction with the host.

Simple, Low-Cost and Long-Lasting Film for Virus Inactivation Using Avian Coronavirus Model as Challenge

The COVID-19 infection, caused by SARS-CoV-2, is inequitably distributed and more lethal among populations with lower socioeconomic status. Direct contact with contaminated surfaces has been among the virus sources, as it remains infective up to days. Several disinfectants have been shown to inactivate SARS-CoV-2, but they rapidly evaporate, are flammable or toxic and may be scarce or inexistent for vulnerable populations. Therefore, we are proposing simple, easy to prepare, low-cost and efficient antiviral films, made with a widely available dishwashing detergent, which can be spread on hands and inanimate surfaces and is expected to maintain virucidal activity for longer periods than the current sanitizers. Avian coronavirus (ACoV) was used as model of the challenge to test the antivirus efficacy of the proposed films. Polystyrene petri dishes were covered with a thin layer of detergent formula. After drying, the films were exposed to different virus doses for 10 min and virus infectivity was determined using embryonated chicken eggs, and RNA virus quantification in allantoic fluids by RT-qPCR. The films inactivated the ACoV (ranging from 103.7 to 106.7 EID50), which is chemically and morphologically similar to SARS-CoV-2, and may constitute an excellent alternative to minimize the spread of COVID-19.

The Characterization of chIFITMs in Avian Coronavirus Infection In Vivo, Ex Vivo and In Vitro

The coronaviruses are a large family of enveloped RNA viruses that commonly cause gastrointestinal or respiratory illnesses in the infected host. Avian coronavirus infectious bronchitis virus (IBV) is a highly contagious respiratory pathogen of chickens that can affect the kidneys and reproductive systems resulting in bird mortality and decreased reproductivity. The interferon-inducible transmembrane (IFITM) proteins are activated in response to viral infections and represent a class of cellular restriction factors that restrict the replication of many viral pathogens. Here, we characterize the relative mRNA expression of the chicken IFITM genes in response to IBV infection, in vivo, ex vivo and in vitro using the pathogenic M41-CK strain, the nephropathogenic QX strain and the nonpathogenic Beaudette strain. In vivo we demonstrate a significant upregulation of chIFITM1, 2, 3 and 5 in M41-CK- and QX-infected trachea two days post-infection. In vitro infection with Beaudette, M41-CK and QX results in a significant upregulation of chIFITM1, 2 and 3 at 24 h post-infection. We confirmed a differential innate response following infection with distinct IBV strains and believe that our data provide new insights into the possible role of chIFITMs in early 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.

Gonadal pathogenicity of an infectious bronchitis virus strain from the Massachusetts genotype

An outbreak of infectious bronchitis caused by the IBVPR03 strain of the Massachusetts genotype affected H-120 vaccinated laying hens in South Brazil. We investigated the cross protection of the vaccine by assessing the traqueal ciliostasis, virus recovery, and histopathological changes typically observed in the respiratory tract. Although the IBVPR03 strain is S1-genotyped as Massachusetts with a high genomic similarity to the H-120 vaccine strains, surprisingly, we found no tropism or pathogenicity to the trachea in birds infected with this strain. On the other hand, we observed ovarian and testicle lesions. Here, we show that, despite belonging in the Massachusetts genotype, the IBVPR03 pathotype differs from the expected respiratory pattern, causing instead marked histopathological changes in the gonads, so far not associated with this group.

Inactivated infectious bronchitis virus vaccine encapsulated in chitosan nanoparticles induces mucosal immune responses and effective protection against challenge

Avian infectious bronchitis virus (IBV) is one of the most important viral diseases of poultry. The mucosa of upper respiratory tract, specially the trachea, is the primary replication site for this virus. However, conventional inactivate IBV vaccines usually elicit reduced mucosal immune responses and local protection. Thus, an inactivated IBV vaccine containing BR-I genotype strain encapsulated in chitosan nanoparticles (IBV-CS) was produced by ionic gelation method to be administered by oculo-nasal route to chickens. IBV-CS vaccine administered alone resulted in markedly mucosal immune responses, characterized by high levels of anti-IBV IgA isotype antibodies and IFNγ gene expression at 1dpi. The association of live attenuated Massachusetts IBV and IBV-CS vaccine also induced strong mucosal immune responses, though a switch from IgA isotype to IgG was observed, and IFNγ gene expression peak was late (at 5 dpi). Efficacy of IBV-CS was evaluated by tracheal ciliostasis analysis, histopathology examination, and viral load determination in the trachea and kidney. The results indicated that IBV-CS vaccine administered alone or associated with a live attenuated heterologous vaccine induced both humoral and cell-mediated immune responses at the primary site of viral replication, and provided an effective protection against IBV infection at local (trachea) and systemic (kidney) sites.

Rapid detection and differentiation of avian infectious bronchitis virus: an application of Mass genotype by melting temperature analysis in RT-qPCR using SYBR Green I

A method based on Melting Temperature analysis of Hypervariable regions (HVR) of S1 gene within a RT-qPCR was developed to detect different genotypes of avian infectious bronchitis virus (IBV) and identify the Mass genotype. The method was able to rapidly identify the Mass genotype among IBV field isolates, vaccine attenuated strains and reference M41 strain in allantoic liquid and also directly in tissues. The RT-qPCR developed detected the virus in both tracheal and pulmonary samples from M41-infected or H120-infected birds, in a larger post-infection period compared to detection by standard method of virus isolation. RT-qPCR method tested provided a sensitivity and rapid approach for screening on IBV detection and Mass genotyping from IBV isolates.

Assessment of molecular and genetic evolution, antigenicity and virulence properties during the persistence of the infectious bronchitis virus in broiler breeders

The infectious bronchitis virus (IBV) causes a highly contagious disease [infectious bronchitis (IB)] that results in substantial economic losses to the poultry industry worldwide. We conducted a molecular and phylogenetic analysis of the S1 gene of Brazilian (BR) IBV isolates from a routinely vaccinated commercial flock of broiler breeders, obtained from clinical IB episodes that occurred in 24-, 46- and 62-week-old chickens. We also characterized the antigenicity, pathogenesis, tissue tropism and spreading of three IBV isolates by experimental infection of specific pathogen-free (SPF) chickens and contact sentinel birds. The results reveal that the three IBV isolates mainly exhibited mutations in the hypervariable regions (HVRs) of the S1 gene and protein, but were phylogenetically and serologically closely related, belonging to lineage 11 of the GI genotype, the former BR genotype I. All three isolates caused persistent infection in broiler breeders reared in the field, despite high systemic anti-IBV antibody titres, and exhibited tropism and pathogenicity for the trachea and kidney after experimental infection in SPF chickens and contact birds. In conclusion, BR genotype I isolates of IBV evolve continuously during the productive cycle of persistently infected broiler breeders, causing outbreaks that are not impaired by the current vaccination programme with Massachusetts vaccine strains. In addition, the genetic alterations in the S1 gene of these isolates were not able to change their tissue tropism and pathogenicity, but did seem to negatively influence the effectiveness of the host immune responses against these viruses, and favour viral persistence.

Early immune responses and development of pathogenesis of avian infectious bronchitis viruses with different virulence profiles

Avian infectious bronchitis virus (IBV) primarily replicates in epithelial cells of the upper respiratory tract of chickens, inducing both morphological and immune modulatory changes. However, the association between the local immune responses induced by IBV and the mechanisms of pathogenesis has not yet been completely elucidated. This study compared the expression profile of genes related to immune responses in tracheal samples after challenge with two Brazilian field isolates (A and B) of IBV from the same genotype, associating these responses with viral replication and with pathological changes in trachea and kidney. We detected a suppressive effect on the early activation of TLR7 pathway, followed by lower expression levels of inflammatory related genes induced by challenge with the IBV B isolate when compared to the challenge with to the IBV A isolate. Cell-mediated immune (CMI) related genes presented also lower levels of expression in tracheal samples from birds challenged with B isolate at 1dpi. Increased viral load and a higher percentage of birds with relevant lesions were observed in both tracheal and renal samples from chickens exposed to challenge with IBV B isolate. This differential pattern of early immune responses developed after challenge with IBV B isolate, related to the downregulation of TLR7, leading to insufficient pro-inflammatory response and lower CMI responses, seem to have an association with a most severe renal lesion and an enhanced capability of replication of this isolate in chicken.

Productive replication of nephropathogenic infectious bronchitis virus in peripheral blood monocytic cells, a strategy for viral dissemination and kidney infection in chickens

In the present study, the replication kinetics of nephropathogenic (B1648) and respiratory (Massachusetts-M41) IBV strains were compared in vitro in respiratory mucosa explants and blood monocytes (KUL01⁺ cells), and in vivo in chickens to understand why some IBV strains have a kidney tropism. B1648 was replicating somewhat better than M41 in the epithelium of the respiratory mucosa explants and used more KUL01⁺ cells to penetrate the deeper layers of the respiratory tract. B1648 was productively replicating in KUL01⁺ monocytic cells in contrast with M41. In B1648 inoculated animals, 10^2.7–6.8 viral RNA copies/100 mg were detected in tracheal secretions at 2, 4, 6, 8, 10 and 12 days post inoculation (dpi), 10^2.4–4.5 viral RNA copies/mL in plasma at 2, 4, 6, 8, 10 and 12 dpi and 10^1.8–4.4 viral RNA copies/10⁶ mononuclear cells in blood at 2, 4, 6 and 8 dpi. In M41 inoculated animals, 10^2.6–7.0 viral RNA copies/100 mg were detected in tracheal secretions at 2, 4, 6, 8 and 10 dpi, but viral RNA was not demonstrated in plasma and mononuclear cells (except in one chicken at 6 dpi). Infectious virus was detected only in plasma and mononuclear cells of the B1648 group. At euthanasia (12 dpi), viral RNA and antigen positive cells were detected in lungs, liver, spleen and kidneys of only the B1648 group and in tracheas of both the B1648 and M41 group. In conclusion, only B1648 can easily disseminate to internal organs via a cell-free and -associated viremia with KUL01⁺ cells as important carrier cells.

Assessment of pathogenicity and tissue distribution of infectious bronchitis virus strains (Italy 02 genotype) isolated from moroccan broiler chickens

Background

Avian infectious bronchitis (IB) is one of the most important viral diseases of poultry, affecting chickens of all ages and causing major economic losses in poultry flocks. Mass vaccination is conducted in Morocco using a vaccine against Massachusetts, which is the most dominant serotype; however no information about the pathogenesis and tissue distribution of the Moroccan Italy 02 genotype was reported.

40 one-day-old specific pathogen free chickens were divided randomly into four groups. Group1, 2 and 3 were inoculated intra oculo-nasally with 103.5 EID50 of Italy02 viruses, and group 4 was kept as control. Chickens in each group were monitored for 14 days post-infection (pi).

Results

Chickens in all infected groups showed severe respiratory signs, which most of them have been reproduced on 2dpi, with varying times of appearance and disappearance. The infected birds appeared lethargic, reluctant to move, with specific respiratory clinical signs and macroscopic lesions. However no nephritis lesions or mortality were recorded in all groups. The specific histological lesions finding in all infected birds, exhibited tracheal lesions with mucosal thickening, hyperplasia of the surface epithelium, mononuclear inflammatory cell infiltrate of lamina propria. Primary and secondary bronchi, epithelial hyperplasia and mononuclear inflammatory cell infiltrate of the lamina propria were also observed. Tracheal lesions developed in all infected birds, confirm the ability of the three tested strains to induce respiratory disease. The results at 14 dpi also revealed that all strains were able to induce serological response. Virus re-isolation from infected organs and amplification of the viral RNA by real-time PCR proved the presence of the virus in lung and trachea of infected chicks. Neither re-isolation nor significant viral RNA detection were detected in the kidney.

Conclusion

The results demonstrated that the three strains Italy02 genotype emerging in Moroccan poultry farms have a wide distribution for respiratory system, without kidney damage and without causing mortality.

The avian coronavirus spike protein

Avian coronaviruses of the genus Gammacoronavirus are represented by infectious bronchitis virus (IBV), the coronavirus of chicken. IBV causes a highly contagious disease affecting the respiratory tract and, depending on the strain, other tissues including the reproductive and urogenital tract. The control of IBV in the field is hampered by the many different strains circulating worldwide and the limited protection across strains due to serotype diversity. This diversity is believed to be due to the amino acid variation in the S1 domain of the major viral attachment protein spike. In the last years, much effort has been undertaken to address the role of the avian coronavirus spike protein in the various steps of the virus' live cycle. Various models have successfully been developed to elucidate the contribution of the spike in binding of the virus to cells, entry of cell culture cells and organ explants, and the in vivo tropism and pathogenesis. This review will give an overview of the literature on avian coronavirus spike proteins with particular focus on our recent studies on binding of recombinant soluble spike protein to chicken tissues. With this, we aim to summarize the current understanding on the avian coronavirus spike's contribution to host and tissue predilections, pathogenesis, as well as its role in therapeutic and protective interventions.

Inflammatory and cell-mediated immune responses in the respiratory tract of chickens to infection with avian infectious bronchitis virus

Tracheal mucosa is the primary site of replication of avian infectious bronchitis virus (IBV), which leads to both morphologic and immune modulatory changes in this organ. To increase the understanding of the mechanisms involved in these processes, we focused on the evaluation of local inflammatory and cell-mediated immune responses after challenge with the M41 strain of IBV, associating these responses with pathologic changes in the tracheal mucosa. At 24 h post-infection, inflammatory cytokines related genes were significantly upregulated, including peaks of TNFSF15 and TGFβ mRNA production, although no tracheal microscopic alterations were observed and only a slightly increase in viral load occurred. At 3 days post-infection (dpi), we observed that the highest upregulation of IL6, IL1β, and IFNγ coincided with highest scores of viral load and microscopic lesions, suggesting a role of both these cytokines and virus load on the development of tracheal lesions. Later, at 7 dpi, the most prominent increases of CD8αα mRNA and Granzyme homolog A mRNA were followed by a significant decrease of scores of tracheal lesions and viral load. In conclusion, an early upregulation of expression of proinflammatory cytokines such as IL6, IL1β, and IFNγ induced by the M41 strain of IBV may be partially implicated in the viral pathogenicity on trachea tissues of nonimmune challenged chickens, in addition to a late induction of a putative protective immune responses by this virus through upregulation of CD8αα and Granzyme homolog A genes in this organ.

Humoral and cell-mediated immune responses to different doses of attenuated vaccine against avian infectious bronchitis virus

The antibody and cellular immune responses against infectious bronchitis virus (IBV) were evaluated at mucosal sites of chickens after immunization with various doses of an attenuated vaccine at 1 day of age. The correlation of these immune responses with protection of tracheal tissues was evaluated after experimental infection of these birds. Significantly reduced tracheal pathologic effects, measured according to ciliostasis and histology lesions, and reduced viral load were observed only in the full-dose vaccinated group at 5 days post-infection (dpi), while incomplete protection was observed for the subdose vaccinated groups. Moreover, birds of vaccinated groups, especially with full dose, developed higher levels of lachrymal IBV-specific IgG and IgA and increased the expression of cell-mediated immunity (CMI) genes, such as gamma interferon (IFNγ), CD8+ T cell marker, and granzyme homolog A more rapidly. In addition, these humoral and cellular immune responses evaluated at mucosal sites correlated significantly with tracheal protection against homologous IBV challenge in a vaccine dose-dependent manner. The results indicate that IgG, IgA and CD8+ T cell responses developed at mucosal sites after IBV vaccination of day-old chicks, could be taken as good correlates of protection against this virus.

Experimental study on histopathological changes and tissue tropism of Iranian infectious bronchitis serotype 793/B-like virus in SPF chickens

Avian infectious bronchitis virus (IBV) is prevalent in all countries with intensive poultry flocks. This disease is characterised primarily by respiratory signs, but some IBV strains may also infect other organs such as the intestinal and urogenital tracts. The aim of this study was to characterise the histopathological lesions and tissue tropism of Iranian isolate IR/773/2001(793/B) of avian infectious bronchitis virus in different organs of experimentally infected SPF chickens. Forty-two one-day-old, specific pathogen-free (SPF) chicks were divided randomly into two groups (21 chicks to each group). At the age of 12 days, one group was inoculated intra-ocularly with 103 EID50 of the 793/B isolate, and the other was kept as the control group. Tissue samples were collected at 2, 4, 6, 8, 10 and 12 days post-inoculation (PI). The IBV virus was detected in the caecal tonsils and cloaca from the 2nd to the 12th day PI. The virus was also detected in the kidneys from days 4–10 PI and in the bursa of Fabricius from days 4–12 PI. The virus was detected in the trachea, lungs and thymus. The most obvious histopathological lesions were found in the trachea, kidney, lungs and bursa of Fabricius. Amongst the lymphoid tissues, histopathological changes were found most frequently in the bursa of Fabricius. The results of this study indicated that the 793/B serotype of IBV is unlikely to cause mortality, severe clinical signs or gross lesions in infected chickens, but its replication in some tissues including the bursa of Fabricius could render birds susceptible to other micro-organisms.

Cytopathology of chick renal epithelial cells experimentally infected with avian infectious bronchitis virus

The renal ducto-tubular epithelial cells of chicks infected with the MA-87 strain of avian infectious bronchitis virus (IBV) were examined ultrastructurally. Infected epithelial cells containing IBV particles were more numerous in the collecting ducts, collecting tubules, distal convoluted tubules and Henle's loops than in the proximal convoluted tubules. Virus particles invaded host cells through endocytotic vesicles. Cytopathologic changes in the infected epithelial cells were manifested by a variety of organlle alterations including swelling of mitochondria, dilation of Golgi vesicles and an increase in the amount of rough endoplasmic reticulum (RER). Virus particles were produced by budding into RER and, rarely, toward the perinuclear space. As virus replication progressed, virus particles were enclosed mainly in the dilated RER, cytoplasmic vesicles or virus-containing electron-dense bodies. Virus particles were also found in vesicles of Golgi complex, the dilated perinuclear space, in some autophagic vacuoles or free in the cytoplasm. Virus particles were released by exocytosis through cytoplasmic vesicles, or appeared to be discharged through disrupted cell membranes. It was concluded that epithelial cells of lower nephron and ducts are the primary target cells in IBV-infected kidneys.

Histopathology and immunohistochemistry of renal lesions due to avian infectious bronchitis virus in chicks uninoculated and previously inoculated with highly virulent infectious bursal disease virus

A nephropathogenic strain of infectious bronchitis virus (IBV) was inoculated intra-tracheally into 14-day-old specific-pathogen-free chicks or ones previously inoculated with highly virulent infectious bursal disease virus (IBDV) at 7 days of age. The renal lesions were examined histopathologically and immunohistochemi-cally at intervals up to 30 days post-inoculation. The mortality was 20% in the IBDV + IBV-inoculated group, but not in the IBV-inoculated one. Swollen and pale kidneys due to IBV infection were more severe and of longer duration in dually infected chicks. At the early stage of infection, the histopathological changes in the kidneys were similar in both groups, but the ducto-tubular damage was more severe in the dually infected chicks. At the late stage of infection, the renal lesions were characterized by chronic interstitial nephritis with formation of lymphoplasmacytic nodules in IBV-inoculated chicks and by chronic active nephritis which consisted of tubular degeneration, lymphoid cell reaction and interstitial fibrosis in IBDV + IBV-inoculated ones. More IBV antigen-positive cells persisted longer in the kidneys of dually infected chicks than in those of IBV-inoculated ones.

Detection of 793/B serotype of infectious bronchitis virus in tissue sample by indirect immunoperoxidase assay

The indirect immunoperoxidase (IIP) assay was compared with the reverse transcription-polymerase chain reaction (RT-PCR) for detection of 793/B serotype of infectious bronchitis virus in tissues samples collected from experimentally infected chickens. This technique was optimized in specific pathogen-free (SPF)-embryonated chicken eggs and broiler chickens inoculated with the Iranian IR/773/2001 strain of 793/B serotype The trachea, lung, kidney, and cecal tonsil tissue samples from experimentally infected chicken embryos and chickens were collected in order to prepare tissue sections in IIP assay and to detect in RT-PCR. The sensitivity and specificity values of IIP assay were, respectively, 83 and 84 %, and the positive and negative prediction values were 71 and 91 % when compared with RT-PCR.

New insights on infectious bronchitis virus pathogenesis: characterization of Italy 02 serotype in chicks and adult hens

Infectious bronchitis (IB) is a worldwide disease affecting chickens of all ages and causing important economic losses in poultry industry. Despite being one of the predominant IB virus (IBV) serotype in several European countries, slightly is known about pathogenesis and pathogenicity of Italy 02 serotype. In this study chicks and old hens were infected by oculo-nasal route with Italy 02 serotype. Clinical signs, gross and microscopic findings were evaluated, viral nucleic acid detection was assessed by in situ hybridization (ISH) in several tissues and viral RNA was detected by RT-PCR in trachea, kidney and nasal and cloacal swabs. Italy 02 serotype was demonstrated to cause severe respiratory and renal damage in one-day old chicks but not in adult hens in which only respiratory disease and drop in egg production was observed. The use of ISH technique demonstrated the presence of viral RNA in nasal turbinates prior to trachea, but more consistent and longer replication periods in enterocytes of lower gastrointestinal tract. The detection of viral nucleic acid in gut by RT-PCR was consistent and more persistent viral shedding was detected in faeces than in nasal exudates. We describe a complete update of IBV distribution in tissues by the use of molecular techniques and we also provide and in-depth pathological characterization of the new Italy 02 IBV serotype. Furthermore, new data about IBV pathogenesis essential in field control is afforded.

Comparative histopathology and immunohistochemistry of QX-like, Massachusetts and 793/B serotypes of infectious bronchitis virus infection in chickens

The aim of this study was to compare experimentally the pathogenicity and tissue distribution of the recently emerged QX-like strain of infectious bronchitis virus (IBV) with the widespread M41 and 793/B serotypes of the virus. Histopathological and immunohistochemical methods were employed to define the main sites of virus replication. One-day-old specific pathogen free chickens were inoculated with five different QX-like strains, or with the M41 and 793/B IBV strains and monitored for 42 days post-infection. Tracheal lesions developed in all infected birds, confirming the ability of all of the tested strains to induce respiratory disease. Replication of the isolates in the alimentary tract was detected, but the infection did not cause significant gut lesions. Four of the five QX-like IBV strains induced severe kidney lesions. Dilation of the oviduct with accumulation of serum-like fluid in the lumen of this structure, reported previously from field cases of QX-like IBV infection, was observed following experimental infection with all of the five QX-like strains. Microscopical and immunohistochemical examination of the affected oviducts did not help to elucidate the pathogenesis of this lesion.

CLONAGEM, EXPRESSÃO E CARACTERIZAÇÃO DA NUCLEOPROTEÍNA RECOMBINANTE DO VÍRUS DA BRONQUITE INFECCIOSA EM ESCHERICHIA COLI E EM PICHIA PASTORIS

RESUMO O gene da proteína de nucleocapsídeo (1.230 pb) da estirpe M41 do vírus da bronquite infecciosa (VBI) foi amplificado pelas reações de transcrição reversa e em cadeia da polimerase (RT-PCR) e clonado, em seguida, em dois sistemas; pET28a - Escherichia coli e pFLD -Pichia pastoris. Os produtos recombinantes construídos para expressão (pET28a-N ou pFLD-N) foram identificados por análises de PCR e de sequenciamento de nucleotídeos. Os clones transformantes da linhagem BL21 de E. coli e da linhagem GS115 de P. pastoris foram submetidos aos protocolos apropriados de indução. A expressão da proteína N de fusão com etiqueta de poli-histidina e com massa molecular de 54 kDa foi determinada pelas técnicas de SDS-PAGE e de Western blotting, confirmando-se que ambas proteínas N recombinantes apresentaram tamanhos e antigenicidade compatíveis com a proteína N nativa do próprio VBI. O sistema E. coli expressou uma quantidade relevante da proteína N recombinante, enquanto que o sistema P. pastoris produziu uma baixa recuperação dessa proteína recombinante. A proteína N recombinante gerada pelo sistema bacteriano foi purificada em resina de níquel-sepharose. O conjunto de resultados indica que o sistema de expressão constituído por pET28a – E. coli é mais efetivo para produzir a proteína N recombinante do VBI destinada ao uso como antígeno para detectar anticorpos anti-virais específicos em ensaios de imunodiagnóstico para essa infecção viral.

Histopathology and immunohistochemistry of renal lesions due to infectious bronchitis virus in chicks

Two-day-old specific-pathogen-free chicks were inoculated intranasally with the MA-87 strain of infectious bronchitis virus, and trachea and kidney lesions studied histologically and immunohistochemically. Lesions and viral antigen were first detected in the trachea; severe damage was then observed in the kidney. Viral antigen appeared prior to the development of renal lesions and was detected in the cytoplasm of epithelial cells by 4 days post-inoculation (p.i.). The epithelial cells of the collecting ducts, collecting tubules and distal convoluted tubules were first affected, followed by involvement of Henle's loops, whereas the proximal convoluted tubules were only minimally affected. Antigen-positive cells of ducts and tubules were degenerated and desquamated. The severe epithelial cell damage resulted in infiltration of heterophils and macrophages in the interstitium, ducts and tubules. The detection of viral antigen was consistent with the distribution of histological lesions at 6 to 8 days p.i. At a later stage, antigen-positive cells disappeared and repair of epithelial cells was seen, accompanied by interstitial lymphoplasmacytic infiltration and lymphoid nodular formation.

Challenge experiments to evaluate cross-protection induced at the trachea and kidney level by vaccine strains and Belgian nephropathogenic isolates of avian infectious bronchitis virus

Intravenous and aerosol challenge experiments were conducted to evaluate tracheal and renal cross-protection in chickens immunized either with infectious bronchitis virus vaccine strains or with nephropathogenic infectious bronchitis virus (NIBV)-isolates. Intravenous challenge was carried out with four Belgian NIBV-isolates and with the Italian NIBV-strain AZ23.74. Virus titrations of tracheas collected at different times after aerosol challenge with the Belgian reference NIBV-strain B1648 demonstrated that only chickens immunized with the serologically closely related Belgian NIBV-field isolates showed strong trachea protection. The three vaccine strains H120, H52 and D274 and the heterologous NIBV-strain AZ23.74 did not induce protection of the respiratory tract against B1648. However, immunization with the latter strains shortened the period of replication of the challenge virus in the trachea. All chickens immunized with NIBV were strongly protected against nephritis after challenge with a homologous or heterologous NIBV-isolate. Vaccination with H52 gave partial kidney protection against NIBV challenge. Vaccination with H120 or D274 did not reduce kidney infection after NIBV challenge, as demonstrated by the incidence of mortality and kidney-immunofluorescence. Protection of the kidney was similar whether the challenge was performed intravenously or by aerosol. The results of both challenge experiments show that the development of a vaccine strain based on the Belgian NIBV-serotype is indicated to control NIBV in Belgian broiler flocks.

Development and use of the H strain of avian infectious bronchitis virus from the Netherlands as a vaccine: a review

The H strain of infectious bronchitis (IB) was one of the earliest live attenuated IB vaccines to be developed and has continued to be use in most parts of the world for almost 50 years. It was developed for used at both the 52nd (H52) and 120th (H120) vaccine levels and, because of it ability to provide heterologous cross-protection against a number of IB viruses of different serotypes, has proved to be one of the most enduring live attenuated IB vaccines. In fact, the H120 vaccine is possibly the most widely used live attenuated IB vaccine globally to this day. The use of H52 has, however, declined with the introduction of safe and highly efficacious inactivated IB vaccines. This review documents the original studies to isolate and attenuate the H strain by serial embryo passage, and describes the early studies to demonstrate its efficacy in laboratory studies and under field conditions. The efficacy of the H vaccine in providing cross-protection against some of the many IB variants now reported worldwide is also discussed, and possible future vaccination strategies for IB considered.

Nephropathogenesis of chickens experimentally infected with various strains of infectious bronchitis virus

Four-day-old specific-pathogen-free chickens were inoculated by eyedrop with four different strains (Gray, JMK, CV56b, and Wolgemuth) of infectious bronchitis virus (IBV). Birds were monitored clinically and euthanatized at 1, 4, 7, and 14 days postinfection and tissues were collected for virus isolation, histopathologic examination, in situ hybridization (ISH), and immunohistochemistry (IHC). Clinical disease was severe in chickens infected with Wolgemuth, but no overt disease was observed with the other strains. Virus was isolated from the kidneys of chickens infected with the Gray-, CV56b-, and Wolgemuth-strains of IBV. Histologically, interstitial nephritis was evident in chickens infected with these same 3 strains. However, viral nucleic acid and antigen were detected only with Wolgemuth-infected kidneys by ISH and IHC. These results indicate that the pathological changes in kidneys from chickens infected with Gray and CV56b may not have resulted from the cytolytic action of the virus.

Immunohistochemical detection of avian pneumovirus in formalin-fixed tissues

An immunohistochemical staining technique (IHC) was developed to detect avian pneumovirus (APV) antigen in formalin-fixed, paraffin-embedded tissue sections using streptavidin-biotin immunoperoxidase staining. Samples of nasal turbinates and infraorbital sinuses were collected from 4-week-old poults experimentally inoculated with APV and from older turkeys infected during naturally occurring outbreaks of avian pneumovirus. Tissue was fixed in 10% buffered neutral formalin, embedded in paraffin, sectioned and stained. Inflammatory changes were observed microscopically in the mucosa and submucosa of the nasal turbinates and infraorbital sinuses of both experimentally inoculated poults and naturally infected birds. Viral antigen was detected by IHC in the ciliated epithelial cells of nasal turbinates and infraorbital sinuses.

Infectious bronchitis virus: Immunopathogenesis of infection in the chicken

The immunopathogenesis of infectious bronchitis virus (IBV) infection in the chicken is reviewed. While infectious bronchitis (IB) is considered primarily a disease of the respiratory system, different IBV strains may show variable tissue tropisms and also affect the oviduct and the kidneys, with serious consequences. Some strains replicate in the intestine but apparently without pathological changes. Pectoral myopathy has been associated with an important recent variant. Several factors can influence the course of infection with IBV, including the age, breed and nutrition of the chicken, the environment and intercurrent infection with other infectious agents. Immunogenic components of the virus include the S (spike) proteins and the N nucleoprotein. The humoral, local and cellular responses of the chicken to IBV are reviewed, together with genetic resistance of the chicken. In long-term persistence of IBV, the caecal tonsil or kidney have been proposed as the sites of persistence. Antigenic variation among IBV strains is related to relatively small differences in amino acid sequences in the S1 spike protein. However, antigenic studies alone do not adequately define immunological relationships between strains and cross-immunisation studies have been used to classify IBV isolates into 'protectotypes'. It has been speculated that changes in the S1 protein may be related to differences in tissue tropisms shown by different strains. Perhaps in the future, new strains of IBV may arise which affect organs or systems not normally associated with IB.