Abstract:
The Sterne 34F2 live spore vaccine (SLSV) developed in 1937 is the most widely used
veterinary vaccine against anthrax. However, literature on the immunogenicity of this vaccine
in a target ruminant host is scarce. In this study, we evaluated the humoral response to the
B. anthracis protective antigen (rPA), a recombinant bacillus collagen-like protein of
anthracis (rBclA), formaldehyde inactivated spores (FIS) prepared from strain 34F2
and a vegetative antigen formulation prepared from a capsule and toxin deficient strain
(CDC 1014) in Boer goats. The toxin neutralizing ability of induced antibodies was
evaluated using an in vitro toxin neutralization assay. The protection afforded by the
vaccine was also assessed in vaccinates. Anti-rPA, anti-FIS and lethal toxin neutralizing titres
were superior after booster vaccinations, compared to single vaccinations. Qualitative
analysis of humoral responses to rPA, rBclA and FIS antigens revealed a
preponderance of anti-FIS IgG titres following either single or double vaccinations with
the SLSV. Antibodies against FIS and rPA both increased by 350 and 300-fold following
revaccinations respectively. There was no response to rBclA following vaccinations with
the SLSV. Toxin neutralizing titres increased by 80-fold after single vaccination and
700-fold following a double vaccination. Lethal challenge studies in naïve goats indicated a
minimum infective dose of 36 B. anthracis spores. Single and double vaccination with the
SLSV protected 4/5 and 3/3 of goats challenged with > 800 spores respectively. An early booster vaccination following the first immunization is suggested in order to achieve a robust
immunity. Results from this study indicate that this crucial second vaccination can be
administered as early as 3 months after the initial vaccination.
