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Newcastle disease (ND), caused by Newcastle disease virus (NDV), is a contagious disease that affects a variety of domestic and wild avian species. Though ND is vaccine-preventable, it is a persistent threat to poultry industry across the globe. The disease represents a leading cause of morbidity and mortality in chickens. To better understand the epidemiology of NDV among commercial and backyard chickens of Odisha, where chicken farming is being prioritized to assist with poverty alleviation, a cross-sectional study was conducted in two distinct seasons during 2018. Choanal swabs ( n = 1361) from live birds (commercial layers, broilers, and backyard chicken) and tracheal tissues from dead birds ( n = 10) were collected and tested by real-time reverse transcription polymerase chain reaction (RT-PCR) for the presence of matrix (M) and fusion (F) genes of NDV. Risk factors at the flock and individual bird levels (health status, ND vaccination status, geographical zone, management system, and housing) were assessed using multivariable logistic regression analyses. Of the 1371 samples tested, 160 were positive for M gene amplification indicating an overall apparent prevalence of 11.7% (95% CI 10.1–13.5%). Circulation of virulent NDV strains was also evident with apparent prevalence of 8.1% (13/160; 95% CI: 4.8–13.4%). In addition, commercial birds had significantly higher odds (75%) of being infected with NDV as compared to backyard poultry ( p = 0.01). This study helps fill a knowledge gap in the prevalence and distribution of NDV in apparently healthy birds in eastern India, and provides a framework for future longitudinal research of NDV risk and mitigation in targeted geographies—a step forward for effective control of ND in Odisha.

Infectious bursal disease virus (IBDV) is an acute and highly infectious RNA virus known for its immunosuppressive capabilities, chiefly inflicting rapid damage to the bursa of Fabricius (BF) of chickens. Current clinical control of IBDV infection relies on vaccination. However, the emergence of novel variant IBDV (nVarIBDV) has posed a threat to the poultry industry across the globe, underscoring the great demand for innovative and effective vaccines. Our previous studies have highlighted the critical role of IBDV VP5 as an apoptosis-inducer in host cells. In this study, we engineered IBDV mutants via a reverse genetic system to introduce amino acid mutations in VP5. We found that the mutant IBDV-VP5/3m strain caused reduced host cell mortality, and that strategic mutations in VP5 reduced IBDV replication early after infection, thereby delaying cell death. Furthermore, inoculation of chickens with IBDV-VP5/3m effectively reduced damage to BF and induced neutralizing antibody production comparable to that of parental IBDV WT strain. Importantly, vaccination with IBDV-VP5/3m protected chickens against challenges with nVarIBDV, an emerging IBDV variant strain in China, reducing nVarIBDV loads in BF while alleviating bursal atrophy and splenomegaly, suggesting that IBDV-VP5/3m might serve as a novel vaccine candidate that could be further developed as an effective vaccine for clinical control of IBD. This study provides a new clue to the development of novel and effective vaccines.

Marek’s disease (MD), caused by Marek’s disease virus (MDV), is a commercially important neoplastic disease of poultry which is only controlled by mass vaccination. Importantly, vaccines that can provide sterile immunity and inhibit virus transmission are lacking; such that vaccines are only capable of preventing neuropathy, oncogenic disease and immunosuppression, but are unable to prevent MDV transmission or infection, leading to emergence of increasingly virulent pathotypes. Hence, to address these issues, developing more efficacious vaccines that induce sterile immunity have become one of the important research goals for avian immunologists today. MDV shares very close genomic functional and structural characteristics to most mammalian herpes viruses such as herpes simplex virus (HSV). MD also provides an excellent T cell lymphoma model for gaining insights into other herpesvirus-induced oncogenesis in mammals and birds. For these reasons, we need to develop an in-depth knowledge and understanding of the host-viral interaction and host immunity against MD. Similarly, the underlying genetic variation within different chicken lines has a major impact on the outcome of infection. In this review article, we aim to investigate the pathogenesis of MDV infection, host immunity to MD and discuss areas of research that need to be further explored.

A Newcastle disease virus (NDV)-vectored vaccine expressing clade 2.3.4.4b H5 Hemagglutinin was developed and assessed for efficacy against H5N1 highly pathogenic avian influenza (HPAI) in specific pathogen-free (SPF) chickens, broilers, and domestic ducks. In SPF chickens, the live recombinant NDV-vectored vaccine, rK148/22-H5, achieved complete survival against HPAI and NDV challenges and significantly reduced viral shedding. Notably, the live rK148/22-H5 vaccine conferred good clinical protection in broilers despite the presence of maternally derived antibodies. Good clinical protection was observed in domestic ducks, with decreased viral shedding. It demonstrated complete survival and reduced cloacal viral shedding when used as an inactivated vaccine from SPF chickens. The rK148/22-H5 vaccine is potentially a viable and supportive option for biosecurity measure, effectively protecting in chickens against the deadly clade 2.3.4.4b H5 HPAI and NDV infections. Furthermore, it aligns with the strategy of Differentiating Infected from Vaccinated Animals (DIVA).

Avian pathogenic Escherichia coli (APEC) strains cause severe respiratory and systemic diseases, threatening food security and avian welfare worldwide. Intensification of poultry production and the quick expansion of free-range production systems will increase the incidence of colibacillosis through greater exposure of birds to pathogens and stress. Therapy is mainly based on antibiotherapy and current vaccines have poor efficacy. Serotyping remains the most frequently used diagnostic method, only allowing the identification of a limited number of APEC strains. Several studies have demonstrated that the most common virulence factors studied in APEC are all rarely present in the same isolate, showing that APEC strains constitute a heterogeneous group. Different isolates may harbor different associations of virulence factors, each one able to induce colibacillosis. Despite its economical relevance, pathogenesis of colibacillosis is poorly understood. Our knowledge on the host response to APEC is based on very descriptive studies, mostly restricted to bacteriological and histopathological analysis of infected organs such as lungs. Furthermore, only a small number of APEC isolates have been used in experimental studies. In the present review, we discuss current knowledge on APEC diversity and virulence, including host response to infection and the associated inflammatory response with a focus on pulmonary colibacillosis. In the present review, we discuss current knowledge on APEC diversity and virulence, including host response to infection and the associated inflammatory response with a focus on pulmonary colibacillosis.

Campylobacter jejuni is the leading cause of bacterial food-borne infection; chicken meat is its main source. C. jejuni is considered commensal in chickens based on experimental models unrepresentative of commercial production. Here we show that the paradigm of Campylobacter commensalism in the chicken is flawed. Through experimental infection of four commercial breeds of broiler chickens, we show that breed has a significant effect on C. jejuni infection and the immune response of the animals, although these factors have limited impact on the number of bacteria in chicken ceca. All breeds mounted an innate immune response. In some breeds, this response declined when interleukin-10 was expressed, consistent with regulation of the intestinal inflammatory response, and these birds remained healthy. In another breed, there was a prolonged inflammatory response, evidence of damage to gut mucosa, and diarrhea. We show that bird type has a major impact on infection biology of C. jejuni . In some breeds, infection leads to disease, and the bacterium cannot be considered a harmless commensal. These findings have implications for the welfare of chickens in commercial production where C. jejuni infection is a persistent problem. IMPORTANCE Campylobacter jejuni is the most common cause of food-borne bacterial diarrheal disease in the developed world. Chicken is the most common source of infection. C. jejuni infection of chickens had previously not been considered to cause disease, and it was thought that C. jejuni was part of the normal microbiota of birds. In this work, we show that modern rapidly growing chicken breeds used in intensive production systems have a strong inflammatory response to C. jejuni infection that can lead to diarrhea, which, in turn, leads to damage to the feet and legs on the birds due to standing on wet litter. The response and level of disease varied between breeds and is related to regulation of the inflammatory immune response. These findings challenge the paradigm that C. jejuni is a harmless commensal of chickens and that C. jejuni infection may have substantial impact on animal health and welfare in intensive poultry production . Campylobacter jejuni is the most common cause of food-borne bacterial diarrheal disease in the developed world. Chicken is the most common source of infection. C. jejuni infection of chickens had previously not been considered to cause disease, and it was thought that C. jejuni was part of the normal microbiota of birds. In this work, we show that modern rapidly growing chicken breeds used in intensive production systems have a strong inflammatory response to C. jejuni infection that can lead to diarrhea, which, in turn, leads to damage to the feet and legs on the birds due to standing on wet litter. The response and level of disease varied between breeds and is related to regulation of the inflammatory immune response. These findings challenge the paradigm that C. jejuni is a harmless commensal of chickens and that C. jejuni infection may have substantial impact on animal health and welfare in intensive poultry production .

The inflammatory response is an essential component of innate immunity to defense against pathogens. Infectious bursal disease (IBD) is the most important immunosuppressive disease in chickens and is caused by the infectious bursal disease virus (IBDV). Acute inflammation is a typical pathogenic process for IBD, however, the underlying mechanism is not clear. Here, we report that IBDV induces obvious inflammatory response in vivo and in vitro . Furthermore, viral VP2 is identified as an important inflammatory stimulus. It is observed that IBDV VP2 can activate NF-κB signaling pathway and then increase IL-1β production. In detail, IBDV VP2 interacts with myeloid differentiation primary response gene 88 (MyD88), potentiates the oligomerization of MyD88 and assembly of MyD88 complex, which is one important element leading to NF-κB signaling pathway activation and IL-1β production increase. More meaningfully, residues 253/284 of viral VP2 are significantly involved in IBDV-induced inflammatory response through modulating the interaction strength between VP2 and MyD88 and the following MyD88-NF-κB-IL-1β signaling pathway. This study reveals one molecular mechanism that trigger inflammation during IBDV infection, which is of great significance for a deeper understanding of the pathogenic mechanisms of IBDV.

Newcastle disease is regarded as one of the most important avian diseases throughout the world and continues to be a threat and economic burden to the poultry industry. With no effective treatment, poultry producers rely primarily on stringent biosecurity and vaccination regimens to control the spread of this devastating disease. This concise review provides an historical perspective of Newcastle disease vaccination and how fundamental research has paved the way for the development of instrumental techniques which are still in use today. Although vaccination programmes have reduced the impact of clinical disease, they have historically been ineffective in controlling the spread of virulent viruses and therefore do not always offer an adequate solution to the world’s food security problems. However, the continued development of novel vaccine technology and improved biosecurity measures through education may offer a solution to help reduce the global threat of Newcastle disease on the poultry industry.

Avian metapneumovirus (aMPV) infects turkeys and chickens. It replicates primarily in the upper respiratory tract, causing respiratory disease. Animals may also exhibit lower feed and water consumption and weight loss. Despite the high morbidity and often high mortality associated with aMPV in the field, the pathogenicity of field isolates has been difficult to assess in the laboratory. Usually, only mild respiratory clinical signs with low presentation can be reproduced in experimental infections. Hence, the aim of this study was to develop a simple and reproducible aMPV infection model in chicken, to test vaccines' efficacy. It was hypothesized that the evaluation of ciliary activity of tracheal explants, a parameter used in the evaluation of avian infectious bronchitis vaccines, would be suitable for evaluating aMPV vaccines' efficacy after an experimental challenge. Chickens of commercial origin, with maternally-derived antibodies or SPF chickens were vaccinated at one day of age. Challenges were performed at different ages (17 days to 16 weeks of age). Ciliary activity of tracheal explants was evaluated together with more common parameters of efficacy: clinical signs, body weight gain and serum antibodies. In all cases, the vaccine provided protection against the challenge in terms of ciliary activity. Body weight gain and clinical signs were not suitable in all the experiments for showing efficacy, and a very mild serologic response was observed after vaccination, and only in SPF animals. The results of this study confirmed the working hypothesis: that the ciliary activity of tracheal explants is a suitable method for testing aMPV vaccines in commercial or SPF chickens in ages from 17 days to 16 weeks. •Tracheal ciliary activity was assessed for testing avian metapneumovirus vaccines.•Ciliary activity resulted more reliable than other parameters, such as clinical signs or weight gain.•The new method is suitable for commercial, or SPF animals ranging in age from 17 days to 16 weeks.

In recent years, fowl adenovirus (FAdV)-induced diseases became a global problem with considerable impact on chicken health and welfare. This has prompted numerous studies to focus on experimental immunization strategies using whole virus formulations (live or killed vaccines), some of them modified as recombinantly constructed vector vaccines. In addition, FAdV capsid proteins were frequently reported as immunizing antigens (subunit vaccines), with fiber proteins being amongst the most successful candidates. To date, there is no standardized protocol to assess vaccine efficacy in experimental FAdV protection studies, with the consequence that the experimental settings present several degrees of variations even when sharing similar premises. Differences in formulation preparations, route of inoculation, antigen dose, vaccination scheme, choice of challenge strain, or type and age of the birds are capable to greatly influence the magnitude of the immune response and the consequent protective efficacy, altogether addressing remaining challenges. Beyond the antigen composition of a vaccine, the epidemiology of FAdVs with the potential of vertical transmission of virus and/or antibodies from breeders to progenies has a substantial impact on protection strategies. The goal of this review is to outline a broad overview of the findings made thus far regarding immunization strategies against diseases associated to FAdV infections, considering the literature published since the appearance of hepatitis-hydropericardium syndrome (HHS) in the late Eighties, in order to emphasize the current knowledge on FAdV vaccines and highlight fields of future research and intervention.