Abstract
The Sterne live spore vaccine (SLSV, Bacillus anthracis strain 34F2) is the veterinary vaccine of choice against anthrax though contra-indicated for use with antimicrobials. However, the use of non-living anthrax vaccine (NLAV) candidates can overcome the SLSV limitation. In this study, cattle were vaccinated with either of the NLAV (purified recombinant PA (PrPA) or crude rPA (CrPA) and formaldehyde-inactivated spores (FIS of B. anthracis strain 34F2) and emulsigen-D®/alhydrogel® adjuvants) or SLSV. The immunogenicity of the NLAV and SLSV was assessed and the protective efficacies evaluated using a passive immunization mouse model. Polyclonal IgG (including the IgG1 subset) and IgM responses increased significantly across all vaccination groups after the first vaccination. Individual IgG subsets titres peaked significantly with all vaccines used after the second vaccination at week 5 and remained significant at week 12 when compared to week 0. The toxin neutralization (TNA) titres of the NLAV vaccinated cattle groups showed similar trends to those observed with the ELISA titres, except that the former were lower, but still significant, when compared to week 0. The opsonophagocytic assay indicated good antibody opsonizing responses with 75% (PrPA+FIS), 66% (CrPA+FIS) and 80% (SLSV) phagocytosis following spores opsonization. In the passive protection test, A/J mice transfused with purified IgG from cattle vaccinated with PrPA+FIS+Emulsigen-D®/Alhydrogel® and SLSV had 73% and 75% protection from challenge with B. anthracis strain 34F2 spores, respectively, whereas IgG from cattle vaccinated with CrPA+FIS+Emulsigen-D®/Alhydrogel® offered insignificant protection of 20%. There was no difference in protective immune response in cattle vaccinated twice with either the PrPA+FIS or SLSV. Moreover, PrPA+FIS did not show any residual side effects in vaccinated cattle. These results suggest that the immunogenicity and protective efficacy induced by the NLAV (PrPA+FIS) in the cattle and passive mouse protection test, respectively, are comparable to that induced by the standard SLSV.
Highlights
Anthrax is caused by the Gram-positive bacterium Bacillus anthracis known to primarily infect ruminants as well as other warm-blooded mammals [1]
The immunogenicity of the non-living vaccines was compared with Sterne live spore vaccine (SLSV)
PrPA: Purified recombinant protective antigen, CrPA: Crude recombinant protective antigen Formalin-Inactivated Spores (FIS): Formalin inactivated spores, SLSV: Sterne live spore vaccine, negative control (NegCtl): Negative control vaccinated with Emulsigen-D® /Alhydrogel® adjuvants
Summary
Anthrax is caused by the Gram-positive bacterium Bacillus anthracis known to primarily infect ruminants as well as other warm-blooded mammals [1]. The aforementioned process gives the vegetative forms of the bacteria leverage to produce the tripartite toxin proteins comprising the lethal factor (LF), oedema factor (EF) and protective antigen (PA), which are encoded by the plasmid pXO1. These proteins are nontoxic until united in the binary fusion with PA as the common binding moiety, and LF and EF as the catalytic moieties. PA facilitates the translocation of LF and EF into the cells where these toxins exert deleterious effects [6,7,8]
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