Abstract:
The Sterne live spore vaccine (34F2) is the most widely used veterinary vaccine against anthrax in animals. Antibody
responses to several antigens of Bacillus anthracis have been described with a large focus on those against protective
antigen (PA). The focus of this study was to evaluate the protective humoral immune response induced by the
live spore anthrax vaccine in goats. Boer goats vaccinated twice (week 0 and week 12) with the Sterne live spore
vaccine and naive goats were used to monitor the anti-PA and toxin neutralizing antibodies at week 4 and week 17
(after the second vaccine dose) post vaccination. A/J mice were passively immunized with different dilutions of sera
from immune and naive goats and then challenged with spores of B. anthracis strain 34F2 to determine the protective
capacity of the goat sera. The goat anti-PA ELISA titres indicated significant sero-conversion at week 17 after the
second doses of vaccine (p = 0.009). Mice receiving undiluted sera from goats given two doses of vaccine (twice
immunized) showed the highest protection (86%) with only 20% of mice receiving 1:1000 diluted sera surviving lethal
challenge. The in vitro toxin neutralization assay (TNA) titres correlated to protection of passively immunized A/J
mice against lethal infection with the vaccine strain Sterne 34F2 spores using immune goat sera up to a 1:10 dilution
(
rs ≥ 0.522, p = 0.046). This study suggests that the passive mouse protection model could be potentially used
to evaluate the protective immune response in livestock animals vaccinated with the current live vaccine and new
vaccines.
