Abstract
Sterne live spore vaccine (SLSV) is the current veterinary anthrax vaccine of choice. Unlike the non-living anthrax vaccine (NLAV) prototype, SLSV is incompatible with concurrent antibiotics use in an anthrax outbreak scenario. The NLAV candidates used in this study include a crude recombinant protective antigen (CrPA) and a purified recombinant protective antigen (PrPA) complemented by formalin-inactivated spores and Emulsigen-D®/Alhydrogel® adjuvants. Cattle were vaccinated twice (week 0 and 3) with NLAVs plus penicillin-G (Pen-G) treatment and compared to cattle vaccinated twice with SLSV alone and with Pen-G treatment. The immunogenicity was assessed using ELISA against rPA and FIS, toxin neutralisation assay (TNA) and opsonophagocytic assay. The protection was evaluated using an in vivo passive immunisation mouse model. The anti-rPA IgG titres for NLAVs plus Pen-G and SLSV without Pen-G treatment showed a significant increase, whereas the titres for SLSV plus Pen-G were insignificant compared to pre-vaccination values. A similar trend was measured for IgM, IgG1, and IgG2 and TNA titres (NT50) showed similar trends to anti-rPA titres across all vaccine groups. The anti-FIS IgG and IgM titres increased significantly for all vaccination groups at week 3 and 5 when compared to week 0. The spore opsonising capacity increased significantly in the NLAV vaccinated groups including Pen-G treatment and the SLSV without Pen-G but much less in the SLSV group with Pen-G treatment. Passive immunization of A/J mice challenged with a lethal dose of 34F2 spores indicated significant protective capacity of antibodies raised in the SLSV and the PrPA + FIS + adjuvants vaccinated and Pen-G treated groups but not for the NLAV with the CrPA + FIS + adjuvants and the SLSV vaccinated and Pen-G treated group. Our findings indicate that the PrPA + FIS + Emulsigen-D®/Alhydrogel® vaccine candidate may provide the same level of antibody responses and protective capacity as the SLSV. Advantageously, it can be used concurrently with Penicillin-G in an outbreak situation and as prophylactic treatment in feedlots and valuable breeding stocks.
Highlights
Anthrax is a bacterial disease caused by the spore-forming bacilli, Bacillus anthracis, which infect both animals and humans but is primarily a disease of herbivores [1]
Plus Pen-G stimulated a significant IgG response against recombinant PA (rPA), at week 3, whereas the anti-rPA IgG titres were insignificant among the animal groups that were vaccinated with Sterne live spore vaccine (SLSV) + Pen-G as well as SLSV alone at week 3 (Table S1)
Our study indicates the ability of a non-living vaccine candidate (NLAV)
Summary
Anthrax is a bacterial disease caused by the spore-forming bacilli, Bacillus anthracis, which infect both animals and humans but is primarily a disease of herbivores [1]. B. anthracis causes systemic bacteraemia and toxaemia in its host via virulence factors [2] which are regulated by two plasmids [3]. The pXO1 encodes the tripartite toxin components, namely protective antigen (PA), edema factor (EF), and lethal factor (LF). The second plasmid, pXO2, encodes the poly-γ-D-glutamic acid capsule that enables the bacterium to evade host phagocytosis [3]. The vegetative cells produce the toxins resulting in bacteraemia and subsequently toxaemia as well as oedema in anthrax infection that eventually results in the host death [7,8]
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