Abstract
An oral vaccine against anthrax (Bacillus anthracis) is urgently needed to prevent annual anthrax outbreaks that are causing catastrophic losses in free-ranging livestock and wildlife worldwide. The Sterne vaccine, the current injectable livestock vaccine, is a suspension of live attenuated B. anthracis Sterne strain 34F2 spores (Sterne spores) in saponin. It is not effective when administered orally and individual subcutaneous injections are not a practical method of vaccination for wildlife. In this study, we report the development of a microencapsulated oral vaccine against anthrax. Evaluating Sterne spore stability at varying pH’s in vitro revealed that spore exposure to pH 2 results in spore death, confirming that protection from the gastric environment is of main concern when producing an oral vaccine. Therefore, Sterne spores were encapsulated in alginate and coated with a protein shell containing poly-L-lysine (PLL) and vitelline protein B (VpB), a non-immunogenic, proteolysis resistant protein isolated from Fasciola hepatica. Capsule exposure to pH 2 demonstrated enhanced acid gel character suggesting that alginate microcapsules provided the necessary protection for spores to survive the gastric environment. Post vaccination IgG levels in BALBc/J mouse serum samples indicated that encapsulated spores induced anti-anthrax specific responses in both the subcutaneous and the oral vaccination groups. Furthermore, the antibody responses from both vaccination routes were protective against anthrax lethal toxin in vitro, suggesting that further optimization of this vaccine formulation may result in a reliable oral vaccine that will conveniently and effectively prevent anthrax in wildlife populations.
Highlights
Anthrax infections have plagued humans and animals alike for millennia, possibly even causing the fifth and sixth plagues of Egypt[1]
The most feasible way to protect wildlife in these areas would be via oral vaccination after results from a previous study demonstrated that the Sterne vaccine is incapable of eliciting an immune response following oral vaccination, the urgent need for an effective oral anthrax vaccine for wildlife has never been more evident[12]
Many wildlife health professionals have demanded a new veterinary anthrax vaccine because individual hand-injections for each and every animal is not a practical method of vaccination for wildlife and a recent study demonstrated that oral vaccination with the Sterne vaccine is not effective[1,12]
Summary
Anthrax infections have plagued humans and animals alike for millennia, possibly even causing the fifth and sixth plagues of Egypt[1]. Without a reasonable method of wildlife vaccination, yearly anthrax outbreaks in national parks and other wildlife areas worldwide pose economic, ecological and conservational burdens to wildlife and wildlife health professionals[3,7,9,10]. Even with these yearly outbreaks, the anthrax spore distribution in these areas is undetermined so it isn’t possible to vaccinate wildlife based on an estimated risk of exposure[11]. The most feasible way to protect wildlife in these areas would be via oral vaccination after results from a previous study demonstrated that the Sterne vaccine is incapable of eliciting an immune response following oral vaccination, the urgent need for an effective oral anthrax vaccine for wildlife has never been more evident[12]
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