Heterologous maternal antibodies derived from infectious bronchitis vaccines prevent the development of lesions associated with false layer syndrome.

Infectious bronchitis virus (IBV) strains of the Delmarva (DMV)/1639 genotype have been causing false layer syndrome (FLS) in the Eastern Canadian layer operations since the end of 2015. FLS is characterized by the development of cystic oviducts in layer pullets infected at an early age. Currently, there are no homologous vaccines for the control of this IBV genotype. Our previous research showed that a heterologous vaccination regimen incorporating Massachusetts (Mass) and Connecticut (Conn) IBV types protects layers against DMV/1639 genotype IBV. The aim of this study was to investigate the role of maternal antibodies conferred by breeders received the same vaccination regimen in the protection against the development of DMV/1639-induced FLS in pullets. Maternal antibody-positive (MA+) and maternal antibody-negative (MA-) female progeny chicks were challenged at 1 day of age and kept under observation for 16 weeks. Oviductal cystic formations were observed in 3 of 14 birds (21.4 %) in the MA- pullets, while the lesions were notably absent in the MA+ pullets. Milder histopathological lesions were observed in the examined tissues of the MA+ pullets. However, the maternal derived immunity failed to demonstrate protection against the damage to the tracheal ciliary activity, viral shedding, and viral tissue distribution. Overall, this study underscores the limitations of maternal derived immunity in preventing certain aspects of viral pathogenesis, emphasizing the need for comprehensive strategies to address different aspects of IBV infection.

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.

Comparative pathogenicity of CA1737/04 and Mass infectious bronchitis virus genotypes in laying chickens.

Infectious bronchitis virus (IBV) is a respiratory virus causing atropism in multiple body systems of chickens. Recently, the California 1737/04 (CA1737/04) IBV strain was identified as one of the circulating IBV variants among poultry operations in North America. Here, the pathogenicity and tissue tropism of CA1737/04 IBV strain in specific-pathogen-free (SPF) hens were characterized in comparison to Massachusetts (Mass) IBV. In 30 weeks-old SPF hens, Mass or CA1737/04 IBV infections were carried out, while the third group was maintained as a control group. Following infection, we evaluated clinical signs, egg production, viral shedding, serology, necropsy examination, and histopathology during a period of 19 days. Also, certain tissue affinity parameters were investigated, which involved the localization of viral antigens and the detection of viral RNA copies in designated tissues. Our findings indicate that infection with CA1737/04 or Mass IBV strain could induce significant clinical signs, reduced egg production, and anti-IBV antibodies locally in oviduct wash and systemically in serum. Both IBV strains showed detectable levels of viral RNA copies and induced pathology in respiratory, renal, enteric, and reproductive tissues. However, the CA1737/04 IBV strain had higher pathogenicity, higher tissue tropism, and higher replication in the kidney, large intestine, and different segments of the oviduct compared to the Mass IBV strain. Both IBV strains shed viral genome from the cloacal route, however, the Mass IBV infected hens shed higher IBV genome loads via the oropharyngeal route compared to CA1737/04 IBV-infected hens. Overall, the current findings could contribute to a better understanding of CA1737/04 IBV pathogenicity in laying hens.

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.

Detection and Phylogenetic Analysis of Orf Virus and Muskox Rhadinovirus 1 from Muskoxen (Ovibos moschatus) in the Canadian Arctic.

Orf virus (genus Parapoxvirus) has been associated with gross skin lesions on muskoxen (Ovibos moschatus) from Victoria Island, Nunavut, Canada, where muskox populations are experiencing population declines. Orf virus causes painful proliferative and necrotizing dermatitis upon viral replication and shedding, which may lead to animal morbidity or mortality through secondary infections and starvation. Herpesvirus, known to cause gross lesions on skin and mucosa during active viral replication, has also been documented in muskoxen but to date has not been associated with clinical disease. Our objective was to characterize the variation of orf virus and herpesvirus in wild muskoxen of the Canadian Arctic. Tissue samples including gross skin lesions from the nose, lips, and/or legs were opportunistically collected from muskoxen on Victoria Island, Nunavut and Northwest Territories, and mainland Nunavut, Canada, from 2015 to 2017. Sampled muskoxen varied in age, sex, location, hunt type, and body condition. Tissues from 60 muskoxen were tested for genetic evidence of orf virus and herpesvirus infection using PCR targeting key viral genes. Tissues from 38 muskoxen, including 15 with gross lesions, were also examined for histological evidence of orf virus and herpesvirus infection. Eleven muskoxen (10 from Victoria Island and one from mainland Nunavut) with gross lesions had microscopic lesions consistent with orf virus infection. Muskox rhadinovirus 1, a gammaherpesvirus endemic to muskoxen, was detected in 33 (55%) muskoxen including 17 with gross lesions. In all tissues examined, there was no histological evidence of herpesvirus-specific disease. Sequencing and characterization of amplified PCR products using phylogenetic analysis indicated that a strain of orf virus, which appears to be unique, is likely to be endemic in muskoxen from Victoria Island and mainland Nunavut. Many of the muskoxen are also subclinically infected with a known muskox-endemic strain of herpesvirus.

Determination of the virulence status of Clostridium perfringens strains using a chicken intestinal ligated loop model is important for understanding the pathogenesis of necrotic.

Necrotic enteritis (NE) is a poultry intestinal disease caused by virulent strains of the bacterium Clostridium perfringens (C. perfringens). This anaerobic bacterium produces a wide range of enzymes and toxins in the gut which leads to NE development. It is generally accepted by the poultry veterinarians that netB-positive C. perfringens strains are virulent and netB-negative strains do not cause NE. However, NE pathogenesis remains unclear as contradictory results have been reported. The use of experimental in vivo models is a valuable tool to understand the pathogenesis of a disease. In this study, a chicken ligated loop model was used to determine the virulence status of 79 C. perfringens strains from various geographical locations, sources, and genotype profiles. According to our model and based on histologic lesion scoring, 9 C. perfringens strains were classified as commensal, 35 as virulent, and 34 as highly virulent. The virulence of only 1 C. perfringens strain could not be classified as its lesion score was variable (from <10 to >15). In general, NE lesions were more severe in intestinal loops inoculated with netB-positive C. perfringens strains than those inoculated with netB-negative strains. The prevalence of netB among strains classified as commensal, virulent, and highly virulent was 56% (5/9), 54%, (19/35), and 59% (20/34). These results suggest that NetB is not required to cause NE lesions and that other factors are also involved. The classification of the virulence status of C. perfringens strains should not be based solely on the presence or absence of this toxin. Therefore, the use of an in vivo model is essential to distinguish commensal from virulent strains of C. perfringens.

Protection of laying chickens against the Canadian DMV/1639 infectious bronchitis virus infection through priming with heterologous live vaccine and boosting with heterologous or homologous inactivated vaccine.

The emergence of the Canadian Delmarva (DMV)/1639 infectious bronchitis virus (IBV) type strains was associated with egg production disorders in Eastern Canadian layer operations. While developing vaccines for novel IBV variants is not typically a reasonable approach, the consideration of an autogenous vaccine becomes more appealing, particularly when the new variant presents significant economic challenges. The current study aimed to compare the efficacies of two vaccination programs that included heterologous live priming by Massachusetts (Mass) and Connecticut (Conn) type vaccines followed by either a commercial inactivated Mass type vaccine or a locally prepared autogenous inactivated DMV/1639 type vaccine against DMV/1639 IBV challenge. The protection parameters evaluated were egg production, viral shedding, dissemination of the virus in tissues, gross and microscopic lesions, and immunological responses. The challenge with the DMV/1639 caused severe consequences in the non-vaccinated laying hens including significant drop in egg production, production of low-quality eggs, serious damage to the reproductive organs, and yolk peritonitis. The two vaccination programs protected the layers from the poor egg-laying performance and the pathology. The vaccination program incorporating the autogenous inactivated DMV/1639 type vaccine was more effective in reducing vial loads in renal and reproductive tissues. This was associated with a higher virus neutralization titer compared to the group that received the commercial inactivated Mass type vaccine. Additionally, the autogenous vaccine boost led to a significant reduction in the viral shedding compared to the non-vaccinated laying hens. However, both vaccination programs induced significant level of protection considering all parameters examined. Overall, the findings from this study underscore the significance of IBV vaccination for protecting laying hens.

Comparison of Infectious Bronchitis Virus (IBV) Pathogenesis and Host Responses in Young Male and Female Chickens.

Infectious bronchitis virus (IBV) is an avian coronavirus that causes a disease in chickens known as infectious bronchitis (IB). The pathogenesis of IBV and the host immune responses against it depend on multiple factors such as the IBV variant, breed and age of the chicken, and the environment provided by the management. Since there is limited knowledge about the influence of the sex of chickens in the pathogenesis of IBV, in this study we aim to compare IBV pathogenesis and host immune responses in young male and female chickens. One-week-old specific pathogen-free (SPF) White Leghorn male and female chickens were infected with Canadian Delmarva (DMV)/1639 IBV variant at a dose of 1 × 106 embryo infectious dose (EID)50 by the oculo-nasal route while maintaining uninfected controls, and these chickens were euthanized and sampled 4- and 11-days post-infection (dpi). No significant difference was observed between the infected male and female chickens in IBV shedding, IBV genome load in the trachea, lung, kidney, bursa of Fabricius (BF), thymus, spleen, and cecal tonsils (CT), and IBV-induced lesion in all the examined tissues at both 4 and 11 dpi. In addition, there was no significant difference in the percentage of IBV immune-positive area observed between the infected male and female chickens in all tissues except for the kidney, which expressed an increased level of IBV antigen in infected males compared with females at both 4 and 11 dpi. The percentage of B lymphocytes was not significantly different between infected male and female chickens in all the examined tissues. The percentage of CD8+ T cells was not significantly different between infected male and female chickens in all the examined tissues except in the trachea at 11 dpi, where female chickens had higher recruitment when compared with male chickens. Overall, although most of the findings of this study suggest that the sex of chickens does not play a significant role in the pathogenesis of IBV and the host immune response in young chickens, marginal differences in viral replication and host responses could be observed to indicate that IBV-induced infection in male chickens is more severe.

Comparative pathogenicity of infectious bronchitis virus Massachusetts and Delmarva (DMV/1639) genotypes in laying hens.

Infectious bronchitis (IB) is a highly contagious and acute viral disease of chicken caused by the infectious bronchitis virus (IBV) of the family Coronaviridae. Even with extensive vaccination against IB by the poultry industry, the occurrence of new IBV genotypes is a continuous challenge encountered by the global poultry industry. This experiment was designed to compare the pathogenicity of two IBV strains belonging to Massachusetts (Mass) and Delmarva DMV/1639 genotypes. Specific pathogen-free laying hens were challenged during the peak of production (30 weeks), keeping a mock-infected control group. During 21 days of observation following infection, a significant drop in egg production with miss-shaped and soft shells was observed in the DMV/1639 IBV-infected hens only. The DMV/1639 IBV infected group showed prolonged and higher cloacal viral shedding compared with the Mass IBV-infected group. At the end of the study (21 days post-infection), the viral genome loads in the respiratory, urogenital, and immune tissues were significantly higher in the DMV/1639 IBV-infected group compared with the Mass IBV-infected group. Macroscopic lesions such as distorted ova leading to egg peritonitis were observed only in the DMV/1639 IBV-infected group. Moreover, microscopic lesion scores were significantly higher in the lung, kidney, cecal tonsils, and oviduct of the DMV/1639 IBV-infected group compared with the Mass IBV-infected group. Finally, the apoptosis index in the kidney, ovary, magnum, isthmus, and shell gland was significantly higher in the DMV/1639 IBV-infected group compared with the control and Mass-infected groups. This study examined the pathogenicity of two IBV genotypes that are impacting the layer industry in North America.