The Pathology of Infectious Bronchitis

A vaccine programme comprising GA08 (GI-27) and Mass (GI-1) strains prevents DMV1639 (GI-17) infectious bronchitis virus transmission among broiler chickens

Effective control of infectious bronchitis is a challenge in commercial poultry operations due to the high transmissibility of the virus. Although multiple IBV lineages are circulating in the United States, the DMV1639-type IBV strain (GI-17) is currently the major circulating variant, creating production losses in the poultry industry. This study aimed to test whether the combination of a GA08 (GI-27) and a Mass-type (GI-1) IB vaccines could significantly reduce the transmission of a DMV1639-type (GI-17) field IBV strain in 4-week-old commercial broilers. Half of the birds were directly challenged, whereas the other half of the groupmates were put in contact 24 hours later. Two replicates of the same study setup, including 10 directly challenged and 10 contact birds per group, were run. Transmission of the challenge virus was significantly reduced in vaccinates (R = 0.0), whereas all unvaccinated birds became infected (R = 9.6). Reduced transmission of the DMV1639 IB challenge virus by the combined vaccination programme in broiler chickens was also accompanied by clinical protection. These data are important because prevention of IBV transmission by vaccination will result in overall reduced viral replication and consequently in reduced likelihood of genetic changes that can lead to new variants. This is the first published evidence of the successful transmission control of a DMV1639 IBV strain in chickens.

Mechanism, structural and functional insights into nidovirus-induced double-membrane vesicles

During infection, positive-stranded RNA causes a rearrangement of the host cell membrane, resulting in specialized membrane structure formation aiding viral genome replication. Double-membrane vesicles (DMVs), typical structures produced by virus-induced membrane rearrangements, are platforms for viral replication. Nidoviruses, one of the most complex positive-strand RNA viruses, have the ability to infect not only mammals and a few birds but also invertebrates. Nidoviruses possess a distinctive replication mechanism, wherein their nonstructural proteins (nsps) play a crucial role in DMV biogenesis. With the participation of host factors related to autophagy and lipid synthesis pathways, several viral nsps hijack the membrane rearrangement process of host endoplasmic reticulum (ER), Golgi apparatus, and other organelles to induce DMV formation. An understanding of the mechanisms of DMV formation and its structure and function in the infectious cycle of nidovirus may be essential for the development of new and effective antiviral strategies in the future.

Prevalence, Genotype Diversity, and Distinct Pathogenicity of 205 Gammacoronavirus Infectious Bronchitis Virus Isolates in China during 2019-2023

Gammacoronavirus infectious bronchitis virus (IBV) causes a highly contagious disease in chickens and seriously endangers the poultry industry. The emergence and co-circulation of diverse IBV serotypes and genotypes with distinct pathogenicity worldwide pose a serious challenge to the development of effective intervention measures. In this study, we report the epidemic trends of IBV in China from 2019 to 2023 and a comparative analysis on the antigenic characteristics and pathogenicity of isolates among major prevalent lineages. Phylogenetic and recombination analyses based on the nucleotide sequences of the spike (S) 1 gene clustered a total of 205 isolates into twelve distinct lineages, with GI-19 as a predominant lineage (61.77 ± 4.56%) exhibiting an overall increasing trend over the past five years, and demonstrated that a majority of the variants were derived from gene recombination events. Further characterization of the growth and pathogenic properties of six representative isolates from different lineages classified four out of the six isolates as nephropathogenic types with mortality rates in one-day-old SPF chickens varying from 20-60%, one as a respiratory type with weak virulence, and one as a naturally occurring avirulent strain. Taken together, our findings illuminate the epidemic trends, prevalence, recombination, and pathogenicity of current IBV strains in China, providing key information for further strengthening the surveillance and pathogenicity studies of IBV.

Deciphering infected cell types, hub gene networks and cell-cell communication in infectious bronchitis virus via single-cell RNA sequencing

Infectious bronchitis virus (IBV) is a coronavirus that infects chickens, which exhibits a broad tropism for epithelial cells, infecting the tracheal mucosal epithelium, intestinal mucosal epithelium, and renal tubular epithelial cells. Utilizing single-cell RNA sequencing (scRNA-seq), we systematically examined cells in renal, bursal, and tracheal tissues following IBV infection and identified tissue-specific molecular markers expressed in distinct cell types. We evaluated the expression of viral RNA in diverse cellular populations and subsequently ascertained that distal tubules and collecting ducts within the kidney, bursal mucosal epithelial cells, and follicle-associated epithelial cells exhibit susceptibility to IBV infection through immunofluorescence. Furthermore, our findings revealed an upregulation in the transcription of proinflammatory cytokines IL18 and IL1B in renal macrophages as well as increased expression of apoptosis-related gene STAT in distal tubules and collecting duct cells upon IBV infection leading to renal damage. Cell-to-cell communication unveiled potential interactions between diverse cell types, as well as upregulated signaling pathways and key sender-receiver cell populations after IBV infection. Integrating single-cell data from all tissues, we applied weighted gene co-expression network analysis (WGCNA) to identify gene modules that are specifically expressed in different cell populations. Based on the WGCNA results, we identified seven immune-related gene modules and determined the differential expression pattern of module genes, as well as the hub genes within these modules. Our comprehensive data provides valuable insights into the pathogenesis of IBV as well as avian antiviral immunology.

Host Immune Response Modulation in Avian Coronavirus Infection: Tracheal Transcriptome Profiling In Vitro and In Vivo

Infectious bronchitis virus (IBV) is a highly contagious Gammacoronavirus causing moderate to severe respiratory infection in chickens. Understanding the initial antiviral response in the respiratory mucosa is crucial for controlling viral spread. We aimed to characterize the impact of IBV Delmarva (DMV)/1639 and IBV Massachusetts (Mass) 41 at the primary site of infection, namely, in chicken tracheal epithelial cells (cTECs) in vitro and the trachea in vivo. We hypothesized that some elements of the induced antiviral responses are distinct in both infection models. We inoculated cTECs and infected young specific pathogen-free (SPF) chickens with IBV DMV/1639 or IBV Mass41, along with mock-inoculated controls, and studied the transcriptome using RNA-sequencing (RNA-seq) at 3 and 18 h post-infection (hpi) for cTECs and at 4 and 11 days post-infection (dpi) in the trachea. We showed that IBV DMV/1639 and IBV Mass41 replicate in cTECs in vitro and the trachea in vivo, inducing host mRNA expression profiles that are strain- and time-dependent. We demonstrated the different gene expression patterns between in vitro and in vivo tracheal IBV infection. Ultimately, characterizing host-pathogen interactions with various IBV strains reveals potential mechanisms for inducing and modulating the immune response during IBV infection in the chicken trachea.

Evaluation of the efficacy of commercial live vaccines against the local Thai QX field strain for the protection of specific pathogen-free chicks

Background and Aim

The high prevalence of QX-like variant among Thai isolates poses a significant threat to poultry production. In this study, we evaluated the protective efficacy of commercially available heterologous infectious bronchitis virus (IBV) vaccines against the local Thai QX-like strain in specific-pathogen-free (SPF) chicks from Thailand.

Materials and Methods

The experiment involved 100 SPF chicks divided into 4 arms. Arms I and II received the TAbic IB VAR (233A) and Ibird (1/96) vaccines, respectively, on day 1. After 10 days, both arms received the H120 vaccine. Arms III and IV were non-vaccinated positive and negative controls. Challenge infection was local Thai QX-like virus on birds of Arms I, II, and III, and negative control of Arm IV. Clinical signs of infectious bronchitis (IB) and IBV detection using reverse transcription polymerase chain reaction were assessed at 2, 4, and 6 days post-challenge (dpc). At 6 dpc, the birds were humanely euthanized for post-mortem examination with the ciliostasis test and histopathological analysis of the tracheas, lungs, and kidneys.

Results

Virus shedding started at 4 dpc (33.3% positive) and reached 100% positivity at 6 dpc with obvious clinical respiratory symptoms in non-vaccinated-challenged birds. No detection of IBV in vaccinated-challenged arms. Ciliary activity scores were significantly lower in non-vaccinated-challenged birds at 23.64 (standard deviation [SD] ± 1.74) and 96.50 (SD ± 1.91) and 95.64 (SD ± 1.77), respectively (p = 0.05) than in vaccinated-challenged birds. The most remarkable histopathological changes were observed in non-vaccinated-challenged birds, with moderately severe changes in the trachea, lungs, and kidneys. On the other hand, birds in vaccinated-challenged arms showed no significant changes.

Conclusion

This study demonstrated the efficacy of TAbic IB VAR (233A) or Ibird (1/96) vaccine combined with a Massachusetts serotype vaccine (H120) against the local Thai QX-like strain in SPF chicks, contributing valuable insights to the selection of suitable commercially available vaccines to combat the prevalent local QX-like strains in Thailand.

Differential analysis of IBV-infected primary chicken embryonic fibroblasts and immortalized DF-1

Infectious bronchitis virus (IBV), the causative agent of infectious bronchitis, is responsible for major economic losses in the poultry industry worldwide. While IBVs can usually be passaged in primary chicken embryonic fibroblasts (CEFs), most of the wild ones cannot adapt to passaged cell lines. In this study, the wild strain CK/CH/MY/2020 was used to infect primary CEF and immortalize DF-1 CEF cells. Results indicated that IBV was able to cause lesions and pass onto CEF, but not DF-1. Indeed, the virus could enter DF-1 cells and synthesize the associated structural gene but could not assemble into complete viral particles for release. Furthermore, transcriptome sequencing analysis showed significant differences in gene expression between CEF and DF-1 cells after viral infection, although the corresponding antiviral responses could be activated in both cell types. The biggest difference was in terms of the amino acid biosynthesis pathway and the cytokine receptor interaction pathway, which were significantly and specifically activated in CEF. This could actually explain why intact viruses can be assembled but not in DF-1. In addition, SLBP and P2RX7 affect the replication of IBV's structural genes to some extent. Overall, IBV can enter CEF and DF-1 cells, but the complex intracellular cytokine interactions affect the assembly and release of viral particles. The insight will be useful for the study of IBV through in vitro transmission and pathogenesis.

IMPORTANCE

Infectious bronchitis virus (IBV) is responsible for high morbidity and mortality as well as substantial economic losses worldwide. Transcriptome sequencing of IBV-infected chicken embryonic fibroblast and DF-1 cells revealed that the virus elicits antiviral immunity in cells after viral infection, but IBV cannot activate DF-1 cells to produce sufficient amounts of viral structures to assemble into complete virions, which may be caused by the interactions between cytokines. The study of IBV cellular adaptations is important for vaccine development and investigation of the pathogenesis of IBV.

Mitigation of False Layer Syndrome Through Maternal Antibodies Against Infectious Bronchitis Virus

The relationship between passive immunity and the development of false layer syndrome (FLS) and its associated lesions was investigated in this study by comparing the long-term reproductive effects of an infectious bronchitis virus (IBV) DMV/1639 wild-type strain and the GA08 vaccine in birds with and without maternal antibodies. There was a clear protective effect provided by maternal antibodies against both the early vaccination and challenge. It was also observed that vaccination at an early age, in the absence of maternal antibodies, can induce reproductive issues, such as reduced egg production and FLS-associated lesions (e.g., cystic oviduct and egg yolk coelomitis). This might indicate that maternal antibodies and the timing of IBV infection are more important in the generation of FLS than the IBV strain type.

Differential Impact of Massachusetts, Canadian 4/91, and California (Cal) 1737 Genotypes of Infectious Bronchitis Virus Infection on Lymphoid Organs of Chickens

Infectious bronchitis virus (IBV) induces severe economic losses in chicken farms due to the emergence of new variants leading to vaccine breaks. The studied IBV strains belong to Massachusetts (Mass), Canadian 4/91, and California (Cal) 1737 genotypes that are prevalent globally. This study was designed to compare the impact of these three IBV genotypes on primary and secondary lymphoid organs. For this purpose, one-week-old specific pathogen-free chickens were inoculated with Mass, Canadian 4/91, or Cal 1737 IBV variants, keeping a mock-infected control. We examined the IBV replication in primary and secondary lymphoid organs. The molecular, histopathological, and immunohistochemical examinations revealed significant differences in lesion scores and viral distribution in these immune organs. In addition, we observed B-cell depletion in the bursa of Fabricius and the spleen with a significant elevation of T cells in these organs. Further studies are required to determine the functional consequences of IBV replication in lymphoid organs.

Effects of Dietary Supplementation of Essential Oils, Lysozyme, and Vitamins' Blend on Layer Hen Performance, Viral Vaccinal Response, and Egg Quality Characteristics

Maintaining respiratory tract health is crucial for layers, impacting gut health, laying performance, and egg quality. Viral diseases and standard vaccinations can compromise tracheal epithelium function, leading to oxidative stress. This study assessed the impact of a blend of feed additives, predominantly lysozyme (L), essential oils (EO), and vitamins (VIT) (referred to as L + EO + VIT), on young layers during an oral vaccination schedule. The supplementation significantly enhanced antibody titers for Newcastle Disease Virus (NDV) and Infectious Bronchitis Virus (IBV) after vaccination, trachea functionality and intestinal health in the jejunum, increased egg production, and exhibited a trend toward higher egg weight. Although feed intake showed no significant difference, egg quality remained consistent across experimental groups. Moreover, L + EO + VIT supplementation elevated total phenolic content in eggs, improving oxidative stability in both fresh and stored eggs, particularly under iron-induced oxidation. Notably, it substantially reduced yolk lipid peroxidation and albumen protein carbonyls. In conclusion, water supplementation with L + EO + VIT may enhance humoral immune response to IBV and NDV, positively impacting hen productivity. These findings indicate improved tracheal function and enhanced oxidative stability, emphasizing the potential of this blend in promoting overall health and performance in layers.

Recombinant chimpanzee adenovirus expressing spike protein protects chickens against infectious bronchitis virus

Infectious bronchitis (IB) is an acute and highly contagious disease caused by avian infectious bronchitis virus (IBV), resulting in significant economic losses in the global poultry industry. In this study, we utilized a replication-incompetent adenovirus vector derived from chimpanzees for the first time to express the S gene of IBV. The adenovirus was successfully rescued and demonstrated convenient production, good growth performance, and stability on HEK293 A cells. Morphologically, the recombinant adenovirus (named PAD-S) appeared normal under transmission electron microscopy, and efficient expression of the exogenous gene was confirmed through immunofluorescence analysis and immunoblotting. Administration of PAD-S via ocular and nasal routes induced a strong immune response in the chicken population, as evidenced by specific antibody and cytokine measurements. PAD-S was unable to replicate within chickens and showed low pre-existing immunity, demonstrating high safety and environmental friendliness. The robust immune response triggered by PAD-S immunization effectively suppressed viral replication in various tissues, alleviating clinical symptoms and tissue damage, thus providing complete protection against viral challenges in the chicken population. In conclusion, this study successfully developed an IBV candidate vaccine strain that possesses biosafety, high protective efficacy, and ease of production.

Preparation of polyclonal antibodies to the chicken Beclin1 protein and its application in the detection of nephropathogenic infectious bronchitis virus

Beclin1, also known as ATG6, has been shown to be closely related to coronavirus, however, the link between Beclin1 and nephropathogenic infectious bronchitis virus (NIBV) has been poorly investigated and there are no available antibodies specifically targeting the chicken Beclin1 protein. The study aimed to prepare and assay a polyclonal antibody to Beclin1, enabling a deeper understanding of the mechanism of action of Beclin1 in NIBV. In this study, we amplified the chicken Beclin1 target gene and constructed a recombinant plasmid using prokaryotic expression techniques, then obtained the recombinant target protein by induced expression. Finally, the serum is obtained by immunizing rabbits with the purified and concentrated protein. The results show that the antiserum potency of the ELISA assay was >1:204800. By western blotting and immunofluorescence, the antibodies we prepared specifically recognized the chicken Beclin1 protein, which is mainly found in the nucleus of trachea, lung, kidney, spleen and fabricant cells. NIBV infection significantly decreased the expression of Beclin1 in the trachea, but increased in others. We have successfully prepared specific rabbit anti-chicken Beclin1 polyclonal antibodies, and detected changes in tissues of diseased chickens infected with NIBV, laying the foundation for further studies on the role of Beclin1 in avian diseases.

QX-type infectious bronchitis virus infection in roosters can seriously injure the reproductive system and cause sex hormone secretion disorder

Since its discovery, QX-type avian infectious bronchitis virus (IBV) has rapidly spread worldwide and become the most prevalent dominant genotype in Asia and Europe. Currently, although the pathogenicity of QX-type IBV in the reproductive system of hens is widely and deeply understood, its pathogenicity in the reproductive system of roosters remains largely unknown. In this study, 30-week-old specific pathogen-free (SPF) roosters were used to investigate the pathogenicity of QX-type IBV in the reproductive system after infection. The results showed that QX-type IBV infection caused abnormal testicular morphology, moderate atrophy and obvious dilatation of seminiferous tubules, and produced intense inflammation and obvious pathological injuries in the ductus deferens of infected chickens. Immunohistochemistry results showed that QX-type IBV can replicate in spermatogenic cells at various stages and in the mucous layer of the ductus deferens. Further studies showed that QX-type IBV infection affects plasma levels of testosterone, luteinizing hormone, and follicle-stimulating hormone as well as causes changes in transcription levels of their receptors in the testis. Furthermore, the transcription levels of StAR, P450scc, 3βHSD and 17βHSD4 also changed during testosterone synthesis after QX-type IBV infection, indicating that the virus can directly affect steroidogenesis. Finally, we found that QX-type IBV infection leads to extensive germ cell apoptosis in the testis. Collectively, our results suggest that QX-type IBV replicates in the testis and ductus deferens, causing severe tissue damage and disruption of reproductive hormone secretion. These adverse events eventually lead to mass germ cell apoptosis in the testis, affecting the reproductive function of roosters.

Comparison of Immune-Related Gene Expression in Two Chicken Breeds Following Infectious Bronchitis Virus Vaccination

This study aims to identify the immune-related genes and the corresponding biological pathways following infectious bronchitis virus vaccination in Taiwan Country and White Leghorn chicken breeds. Transcriptomic analyses of the spleen of these two breeds were conducted by next-generation sequencing. Compared to White Leghorn chicken, Taiwan Country chicken showed a significantly higher level of anti-infectious bronchitis virus (IBV) antibodies at 14 and 21 days pos vaccination. At 7 days post vaccination, in the Taiwan Country chicken, higher expression of mitogen-activated protein kinase 10, Major histocompatibility complex class 1, and V-set pre-B cell surrogate light chain 3 were found. In contrast, the White Leghorn chicken had a high expression of interleukin 4 induced 1, interleukin 6, and interleukin 22 receptor subunit alpha 2. These findings have highlighted the variations in immune induction between chickens with distinct genetic background and provided biological pathways and specific genes involved in immune responses against live attenuated IBV vaccine.

Key Aspects of Coronavirus Avian Infectious Bronchitis Virus

Infectious bronchitis virus (IBV) is an enveloped and positive-sense single-stranded RNA virus. IBV was the first coronavirus to be discovered and predominantly causes respiratory disease in commercial poultry worldwide. This review summarizes several important aspects of IBV, including epidemiology, genetic diversity, antigenic diversity, and multiple system disease caused by IBV as well as vaccination and antiviral strategies. Understanding these areas will provide insight into the mechanism of pathogenicity and immunoprotection of IBV and may improve prevention and control strategies for the disease.

Unique Variants of Avian Coronaviruses from Indigenous Chickens in Kenya

The avian gamma-coronavirus infectious bronchitis virus (AvCoV, IBV; Coronaviridae family) causes upper respiratory disease associated with severe economic losses in the poultry industry worldwide. Here, we report for the first time in Kenya and the Eastern African region two novel AvCoVs, designated IBV/ck/KE/1920/A374/2017 (A374/17) and AvCoV/ck/KE/1922/A376/2017 (A376/17), inadvertently discovered using random nontargeted next-generation sequencing (NGS) of cloacal swabs collected from indigenous chickens. Despite having genome organization (5'UTR-[Rep1a/1ab-S-3a-3b-E-M-4b-4c-5a-5b-N-6b]-3'UTR), canonical conservation of essential genes and size (~27.6 kb) typical of IBVs, the Kenyan isolates do not phylogenetically cluster with any genotypes of the 37 IBV lineages and 26 unique variants (UVs). Excluding the spike gene, genome sequences of A374/17 and A376/17 are only 93.1% similar to each other and 86.7-91.4% identical to genomes of other AvCoVs. All five non-spike genes of the two isolates phylogenetically cluster together and distinctly from other IBVs and turkey coronaviruses (TCoVs), including the indigenous African GI-26 viruses, suggesting a common origin of the genome backbone of the Kenyan isolates. However, isolate A376/17 contains a TCoV-like spike (S) protein coding sequence and is most similar to Asian TCoVs (84.5-85.1%) compared to other TCoVs (75.6-78.5%), whereas isolate A374/17 contains an S1 gene sequence most similar to the globally distributed lineage GI-16 (78.4-79.5%) and the Middle Eastern lineage GI-23 (79.8-80.2%) viruses. Unanswered questions include the actual origin of the Kenyan AvCoVs, the potential pathobiological significance of their genetic variations, whether they have indeed established themselves as independent variants and subsequently spread within Kenya and to the neighboring east/central African countries that have porous live poultry trade borders, and whether the live-attenuated Mass-type (lineage GI-1)-based vaccines currently used in Kenya and most of the African countries provide protection against these genetically divergent field variants.

Pathogenicity evaluation of GVI-1 lineage infectious bronchitis virus and its long-term effects on reproductive system development in SPF hens

Infectious bronchitis virus (IBV) has gained increasing attention in the poultry industry due to its ability to cause tissue injuries not only in the respiratory system and kidney but also in the reproductive system of layers. Recently, the GVI-1 lineage IBVs have spread widely in China, whereas their pathogenicity in egg-laying chickens has rarely been studied, especially its long-term influence in egg production upon the early infection in chicks. In this study, 10-day-old SPF chicks were infected with the GVI-1 lineage JX181 strain and monitored over a 170-day period after infection. The pathogenicity evaluation of the JX181 strain included clinical observations, immunohistochemical assay, viral load, viral shedding, gross autopsy, and laying rate. The results showed that JX181 has a high pathogenicity, causing severe system lesions, and the decrease in egg production. In summary, this study describes the long-term damages caused by the early infection with the IBV GVI-1 lineage on the reproductive system of hens, providing a comprehensive understanding of the pathogenicity of the IBV GVI-1 lineage and emphasizing the importance of its early prevention.

Establishment and Cross-Protection Efficacy of a Recombinant Avian Gammacoronavirus Infectious Bronchitis Virus Harboring a Chimeric S1 Subunit

Infectious bronchitis virus (IBV) is a gammacoronavirus that causes a highly contagious disease in chickens and seriously endangers the poultry industry. A diversity of serotypes and genotypes of IBV have been identified worldwide, and the currently available vaccines do not cross-protect. In the present study, an efficient reverse genetics technology based on Beaudette-p65 has been used to construct a recombinant IBV, rIBV-Beaudette-KC(S1), by replacing the nucleotides 21,704–22,411 with the corresponding sequence from an isolate of QX-like genotype KC strain. Continuous passage of this recombinant virus in chicken embryos resulted in the accumulation of two point mutations (G21556C and C22077T) in the S1 region. Further studies showed that the T248S (G21556C) substitution may be essential for the adaptation of the recombinant virus to cell culture. Immunization of chicks with the recombinant IBV elicited strong antibody responses and showed high cross-protection against challenges with virulent M41 and a QX-like genotype IBV. This study reveals the potential of developing rIBV-Beau-KC(S1) as a cell-based vaccine with a broad protective immunity against two different genotypes of IBV.

Infection with IBV DMV/1639 at a Young Age Leads to Increased Incidence of Cystic Oviduct Formation Associated with False Layer Syndrome

Infectious bronchitis virus (IBV) is an avian coronavirus that causes respiratory disease but can affect the reproductive tract of laying-type chickens. If infection occurs in pullets, false layer syndrome, which is characterized by the development of large, fluid-filled cystic oviducts, can occur. Recently, IBV strain DMV/1639 has been detected in parts of Canada and the U.S., where false layer syndrome has occurred, though it is not clear if IBV is the sole cause or if age at infection is an influencing variable. Our study investigates the role and timing of IBV infection on the development of false layer syndrome, using the IBV types DMV/1639 and Massachusetts (Mass). Six groups of 120 SPF chickens were challenged at either three, seven, or fourteen days of age, using either DMV/1639 or Mass IBV. Cystic oviducts were seen in all the challenged groups, and the pullets challenged at 14 days of age had fewer cystic oviducts than pullets challenged at 3 or 7 days of age. The highest percentage of severe histology lesion scores were seen in the 3-day challenge groups. The data collected in this experiment confirm that IBV DMV/1639 causes cystic oviducts and indicate that age at infection plays a role in the pathogenesis of false layer syndrome.