Evaluation of an on-farm preconditioning program and novel spore-based mucosal vaccine as tools to mitigate bovine respiratory disease
Creators: Uddin, Muhammed Salah
Publisher: name: University of Alberta Library
Year: 2024

<p>Bovine respiratory disease (BRD) is the most costly disease in the North American feedlot industry. Antimicrobials are mainly used to prevent BRD in feedlots. However, concerns over antimicrobial use and rising resistance in key BRD pathogens necessitate alternative strategies to reduce antimicrobial dependency and prevent BRD in feedlot cattle. The pathogenesis of BRD is associated with several stressors which impair calf immunity, such as abrupt weaning, transportation, auction barn sales, commingling, and feed adaptation. Preconditioning programs are designed to distribute stressful events over a period of time, so as to optimize animal health prior to feedlot placement. Despite this, there is limited information on how preconditioning affects immunity and respiratory microbiota. Study 1 (Chapter 2) investigated the impact of on-farm preconditioning (multiple vaccination, low-stress weaning, introduction to bunk feeding) on cattle stress, immunity, morbidity, and respiratory bacterial responses after feedlot placement. When transported to a feedlot, preconditioned calves exhibited reduced stress. However, BRD morbidity was not different between preconditioned and non-preconditioned calf groups up to 32 days after feedlot placement. This was attributed to low efficacy of the vaccine used to target Histophilus somni, which was the most abundant pathogenic genus in BRD cases from both cattle groups. Thus, this first study highlighted the need for improved mucosal vaccines to enhance protection against BRD pathogenesis. Therefore, a major component of this thesis aimed to develop a novel mucosal vaccine using spore adsorption technology. Mannheimia haemolytica was the targeted pathogen due to its significant role in BRD and well-characterized antigenic epitopes. Bacillus subtilis spores  were used as adjuvant because they have been shown to adsorb antigens for presentation to immune cells, eliciting an antibody response.  Study 2 (Chapter 3) developed a M. haemolytica chimeric protein (MhCP) containing a tandem repeat of M. haemolytica membrane protein PlpE, and the neutralizing epitope of leukotoxin (NLKT). The purified MhCP was then adsorbed to B. subtilis spores, and the resultant spore-based vaccine (Spore-MhCP) was evaluated in mice. In addition to inducing a systemic immune response, intranasal immunization of Spore-MhCP elicited a strong secretory IgA-specific response against both PlpE and NLKT in bronchoalveolar lavage, saliva, and feces. Study 3 (Chapter 4) developed two additional spore-based M. haemolytica vaccines, Spore-MhCP1 and Spore-MhCP2, using leukotoxin as the core component, along with either PlpE or GS60 membrane protein. Intranasal immunization of mice with these spore-bound vaccines induced stronger mucosal and systemic antibody responses compared to free antigens, indicating that binding antigens to Bacillus spores led to an enhanced immune response, emphasizing the potential of spores as an effective adjuvant for respiratory vaccines. In study 4 (Chapter 5), Spore-MhCP was further characterized using sheep as a ruminant model. The vaccine was administered intranasally and intragastrically, while unbound MhCP was evaluated intranasally and intramuscularly. A control group was administered saline intranasally. Study 4 demonstrated that intranasal Spore-MhCP elicited the strongest secretory IgA response against PlpE and NLKT in nasal swabs, bronchoalveolar lavage, and feces compared to control sheep. Intranasal Spore-MhCP also showed a tendency towards enhanced immune responses compared to unbound MhCP. In addition, intragastric administration of Spore-MhCP elicited antigen-specific secretory IgA and serum IgG. Thus, it was shown that immunity in sheep was conferred by both intranasal and intragastric vaccine administration. Sequencing analysis of the 16S rRNA gene from nasopharyngeal samples revealed that 27 genera were altered in their abundances for the intranasal Spore-MhCP group compared to the control. Notably, Mannheimia abundance decreased consistently from days 14 onwards in the intranasal Spore-MhCP group, likely due to vaccine-induced antibodies. Since the proliferation of respiratory pathogens in the upper respiratory tract is a precursor to lung infection, this spore-based technology may provide protection against both pathogen proliferation and subsequent lung infection. In summary, the technology developed in this thesis has the potential to expand protection against respiratory diseases through mucosal vaccination, and warrants further evaluation in challenge and field studies with cattle.</p>