Oral immunization with a novel attenuated Salmonella Gallinarum encoding infectious bronchitis virus spike protein induces protective immune responses against fowl typhoid and infectious bronchitis in chickens

Development of cashew-alginate microbeads and powdered dose forms: prospects for oral vaccine delivery in chickens

Conventional oral vaccine delivery in poultry is challenging due to vaccine degradation in the gastrointestinal (GI) environment and the need for cold-chain storage. Microencapsulation offers a solution by protecting vaccines from GI degradation and improving stability. Natural polymers like alginate and cashew gum have mucoadhesive properties, making them promising candidates for oral vaccine delivery. This study developed cashew-alginate microbeads and a powdered dose form for oral vaccine delivery in chickens. The microbeads were created using ionotropic gelation, while the powdered form was obtained via freeze-drying. These formulations were characterized for size, shape, and stability using scanning electron microscopy (SEM), light microscopy, X-ray diffraction (XRD), and Energy Dispersive X-ray (EDX). Peak adhesion time (PAT) was determined using chicken intestinal and esophageal tissues, and antigenicity was assessed with in-vitro hemagglutination (HA) and hemagglutination inhibition (HI) assays. The microbeads exhibited a spherical shape with a porous structure, suggesting enhanced antigen accommodation. Hemagglutination Inhibition tests indicated that the experimental vaccine remained effective without cold-chain storage for three months. These findings suggest that cashew-alginate microbeads are promising for oral vaccine delivery in poultry.

The aroA and luxS Double-Gene Mutant Strain Has Potential to Be a Live Attenuated Vaccine against Salmonella Typhimurium

Salmonella Typhimurium (S. Typhimurium) is a zoonotic pathogen posing a threat to animal husbandry and public health. Due to the emergence of antibiotic-resistant strains, alternative prevention and control strategies are needed. Live attenuated vaccines are an ideal option that provide protection against an S. Typhimurium pandemic. To develop a safe and effective vaccine, double-gene mutations are recommended to attenuate virulence. In this study, we chose aroA and luxS genes, whose deletion significantly attenuates S. Typhimurium's virulence and enhances immunogenicity, to construct the double-gene mutant vaccine strain SAT52ΔaroAΔluxS. The results show that the mutant strain's growth rate, adherence and invasion of susceptible cells are comparable to a wild-type strain, but the intracellular survival, virulence and host persistence are significantly attenuated. Immunization assay showed that 106 colony-forming units (CFUs) of SAT52ΔaroAΔluxS conferred 100% protection against wild-type challenges; the bacteria persistence in liver and spleen were significantly reduced, and no obvious pathological lesions were observed. Therefore, the double-gene mutant strain SAT52ΔaroAΔluxS exhibits potential as a live attenuated vaccine candidate against S. Typhimurium infection.

Salmonella typhimurium Vaccine Candidate Delivering Infectious Bronchitis Virus S1 Protein to Induce Protection

Infectious bronchitis (IB) is a highly infectious viral disease of chickens which causes significant economic losses in the poultry industry worldwide. An effective vaccine against IB is urgently needed to provide both biosafety and high-efficiency immune protection. In this study, the S1 protein of the infectious bronchitis virus was delivered by a recombinant attenuated Salmonella typhimurium vector to form the vaccine candidate χ11246(pYA4545-S1). S. typhimurium χ11246 carried a sifA- mutation with regulated delayed systems, striking a balance between host safety and immunogenicity. Here, we demonstrated that S1 protein is highly expressed in HD11 cells. Immunization with χ11246(pYA4545-S1) induced the production of antibody and cytokine, leading to an effective immune response against IB. Oral immunization with χ11246(pYA4545-S1) provided 72%, 56%, and 56% protection in the lacrimal gland, trachea, and cloaca against infectious bronchitis virus infection, respectively. Furthermore, it significantly reduced histopathological lesions in chickens. Together, this study provides a new idea for the prevention of IB.

Single oral immunization of an attenuated Salmonella Gallinarium formulation consisting of equal quantities of strains secreting H9N2 hemagglutinin-HA1, HA2, and M2eCD154 induces significant protection against H9N2 and partial protection against Salmonella Gallinarium challenge in chickens

The present investigation describes a formulation of a live attenuated Salmonella Gallinarium (SG) vaccine candidate against H9N2 influenza and SG infections in chickens. The formulation consists of an equal ratio of three strains, JOL2158, JOL2113, and JOL2074, which deliver hemagglutinin; HA1, HA2, and matrix protein 2 (M2e):: CD154 fusion (M2eCD154) antigens designed for broad protection against the field-matched H9N2 serotypes. The vaccine was completely safe at the average inoculation doses of 10⁸ and 10⁹ CFU/bird/0.2 mL in phosphate-buffered saline (PBS) used in the study. Bird immunization as a single oral inoculation could significantly engage humoral IgG, mucosal IgA, and cell-mediated immune responses against each immunized antigen, compared to the PBS control group (P < 0.05). The immunological correlates were comparable with the level of protection derived against the H9N2 and SG challenge, which resulted in significant protection against the H9N2 but only partial protection against the SG challenge as we compared against the PBS control group. The level of protection against H9N2 was investigated by determining the viral copy number and histopathological assessment of lung tissues. The results indicated a significant reduction in viral activity and recovery of lung inflammation towards the 14th-day post-challenge in a dose-dependent manner. Upon SG challenge, birds in the PBS control group experienced 100 % mortality, while 40 % and 70 % protection was observed in the SG-immunized groups for each respective dose of inoculation. The present SG-mediated immunization strategy proposes a rapid and reliable vaccine development process that can be effectively used against influenza strains such as H9N2 and holds the potential to minimize fowl typhoid caused by SG strains, mitigating two economically important diseases in the poultry industry.

Antimicrobial peptides as an alternative to relieve antimicrobial growth promoters in poultry

1. This review describes different classes of antimicrobial peptides (AMP) found in the gastrointestinal (GI) tract of avian species, and their antimicrobial and immunomodulatory activities. The potential benefits of synthetic AMP in poultry production are examined, in the context of the use of AMP as alternatives to antimicrobial growth promoters (AGP).2. Since the mid-1950s, antibiotic growth promoters (AGP) have been used in feed at low prophylactic doses to modulate the homoeostasis of intestinal microbiota, decreasing the risk of intestinal dysbacteriosis and the growth of pathogens within the avian gut. Over the last three decades, AGP have faced major regulatory restrictions due to concerns of generating antimicrobial resistance (AMR). It is now well documented that the rate of infectious disease outbreaks is higher in flocks that are not fed prophylactic antibiotics, resulting in a compensatory increase in antimicrobial use for therapeutic purposes.3. Endogenous natural AMP production is associated with the presence of microbiota and their interaction with the intestinal epithelial and lamina propria lymphoid cells. Their antimicrobial activity shapes the beneficial microbiota population and controls intestinal pathogens such Clostridium and Salmonella spp., and stimulates the development and maturation of the local immune system.4. Similar to AGP, AMP can establish a well-balanced gut beneficial microbiota for adequate immune-competence, animal health and high growth performance parameters such as feed intake, daily weight, feed conversion and accumulated mortality.5. Antimicrobial proteins and peptides constitute an essential part of the innate immune system of all organisms and protect the host from invading pathogenic bacteria, viruses, fungi, and parasites by interacting with the negatively charged pathogen membranes.

Oral immunization with an attenuated Salmonella Gallinarum encoding the H9N2 haemagglutinin and M2 ectodomain induces protective immune responses against H9N2 infection in chickens

H9N2, a low pathogenic avian influenza virus, causes significant economic losses in the poultry industry worldwide. Herein, we describe the construction of an attenuated Salmonella Gallinarum (SG) strain for expression and delivery of H9N2 haemagglutinin (HA) 1 (SG-HA1), HA2 (SG-HA2) and/or the conserved matrix protein 2 ectodomain (SG-M2e). We demonstrated that recombinant SG strains expressing HA1, HA2 and M2e antigens were immunogenic and safe in a chicken model. Chickens (n = 8) were vaccinated once orally with SG alone, SG-HA1, SG-HA2, SG-M2e, or mixture of SG-HA1, SG-HA2 and SG-M2e, or vaccinated once intramuscularly with an oil-adjuvant inactivated H9N2 vaccine. Our results demonstrated that vaccination with SG mutants encoding influenza antigens, administered individually or as a mixture, elicited significantly (P < 0.05) greater antigen-specific humoral and cell-mediated immune responses in chickens compared with those vaccinated with SG alone. A conventional H9N2 vaccine induced significantly (P < 0.05) greater HA1 and HA2 antibody responses than SG-based H9N2 vaccine strains, but significantly (P < 0.05) less robust M2e-specific responses. Upon challenge with the virulent H9N2 virus on day 28 post-vaccination, chickens vaccinated with either the SG-based H9N2 or conventional H9N2 vaccines exhibited comparable lung inflammation and viral loads, although both were significantly lower (P < 0.05) than in the group vaccinated with SG alone. In conclusion, our results showed that SG-based vaccination stimulated efficient immune responses against virulent H9N2. Further studies are needed to fully develop this approach as a preventive strategy for low pathogenic avian influenza viruses affecting poultry. RESEARCH HIGHLIGHTS S. gallinarum expressing HA1, HA2 and M2e antigens are immunogenic and safe. Salmonella has dual function of acting as a delivery system and as a natural adjuvant. Vaccine constructs elicit specific humoral and cell-mediated immune responses.

Current knowledge about interactions between avian dendritic cells and poultry pathogens

In poultry production conditions today, birds are surrounded by viral, bacterial, and parasitic agents. DCs are the main antigen-presenting cells located in tissues of the body, and their role involves recognizing antigen structures, engulfing and processing them, and subsequently presenting antigen peptides on their surface by major histocompatibility complex, where T cells and B cells are stimulated and can begin appropriate cellular and antibody immune response. This unique function indicates that these cells can be used in producing vaccines, but first it is necessary to culture DCs in vitro to identify the principles of their interactions with pathogens. The following review summarizes our current knowledge about avian dendritic cells and their interactions with pathogens. It provides a basis for future studies of these unique cells and their use in vaccine development.

Salmonella Gallinarum delivering M2eCD40L in protein and DNA formats acts as a bivalent vaccine against fowl typhoid and H9N2 infection in chickens

Fowl typhoid (FT), a septicemic disease caused by Salmonella Gallinarum (SG), and H9N2 influenza infection are two economically important diseases that affect poultry industry worldwide. Herein, we exploited a live attenuated SG mutant (JOL967) to deliver highly conserved extracellular domains of H9N2 M2 (M2e) to induce protective immunity against both H9N2 infection and FT. To increase the immunogenicity of M2e, we physically linked it with CD40L and cloned the fusion gene into either prokaryotic constitutive expression vector pJHL65 or mammalian expression vector pcDNA3.1+. Then pJHL65-M2eCD40L or pcDNA-M2eCD40L recombinant plasmid was electroporated into JOL967 strain and the resultant clones were designated as JOL2074 and JOL2076, respectively. We demonstrated that the chickens vaccinated once orally with a co-mix of JOL2074 and JOL2076 strains elicited significantly (p < 0.05) higher M2e-specific humoral and cell-mediated immunity compared to JOL2074 alone vaccinated group. However, SG-specific immune responses were comparable in both the vaccination groups. On challenge with the virulent H9N2 virus (105 TCID50) at 28th day post-vaccination, chickens that received a co-mix of JOL2074 plus JOL2076 strains exhibited significantly (p < 0.05) lower lung inflammation and viral load in both lungs and cloacal samples than JOL2074 alone vaccinated group. Against challenge with the lethal wild-type SG, both the vaccination groups exhibited only 12.5% mortality compared to 75% mortality observed in the control group. In conclusion, we show that SG delivering M2eCD40L can act as a bivalent vaccine against FT and H9N2 infection and further studies are warranted to develop this SG-M2eCD40L vaccine as a broadly protective vaccine against avian influenza virus subtypes.