Summary Plague caused by the Gram‐negative bacterium, Yersinia pestis, is still endemic in parts of the world today. Protection against pneumonic plague is essential to prevent the development and spread of epidemics. Despite this, there are currently no licensed plague vaccines in the western world. Here we describe the means of delivering biologically active plague vaccine antigens directly to mucosal sites of plague infection using highly stable microvesicles (outer membrane vesicles; OMVs) that are naturally produced by the abundant and harmless human commensal gut bacterium Bacteroides thetaiotaomicron (Bt). Bt was engineered to express major plague protective antigens in its OMVs, specifically Fraction 1 (F1) in the outer membrane and LcrV (V antigen) in the lumen, for targeted delivery to the gastrointestinal (GI) and respiratory tracts in a non‐human primate (NHP) host. Our key findings were that Bt OMVs stably expresses F1 and V plague antigens, particularly the V antigen, in the correct, immunogenic form. When delivered intranasally V‐OMVs elicited substantive and specific immune and antibody responses, both in the serum [immunoglobulin (Ig)G] and in the upper and lower respiratory tract (IgA); this included the generation of serum antibodies able to kill plague bacteria. Our results also showed that Bt OMV‐based vaccines had many desirable characteristics, including: biosafety and an absence of any adverse effects, pathology or gross alteration of resident microbial communities (microbiotas); high stability and thermo‐tolerance; needle‐free delivery; intrinsic adjuvanticity; the ability to stimulate both humoral and cell‐mediated immune responses; and targeting of primary sites of plague infection.

The efficacy of 15 nm gold nanoparticles (AuNP) coated with Yersinia pestis F1-antigen, as an immunogen in mice, has been assessed. The nanoparticles were decorated with F1-antigen using N-hydroxysuccinimide and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide coupling chemistry. Mice given AuNP-F1 in alhydrogel generated the greatest IgG antibody response to F1-antigen when compared with mice given AuNP-F1 in PBS or given unconjugated F1-antigen in PBS or alhydrogel. Compared with unconjugated F1-antigen, the IgG2a response was enhanced in mice dosed with AuNP-F1 in PBS (p < 0.05) but not in mice immunised with AuNP-F1 in alhydogel. All treatment groups developed a memory response to F1-antigen, the polarity of which was inflenced by formulation in alhydrogel. The sera raised against F1-antigen coupled to AuNPs was able to competitively bind to rF1-antigen, displacing protective macaque sera.

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Aims: The aim of this study is to identify common household disinfectants that combine significant activity against the type orthopoxvirus, vaccinia virus with minimal impact in terms of potential toxicity and/or damage to household or personal items. Methods and Results: Laboratory scale experiments assessed common disinfectants containing anionic and nonionic detergents, oxygen-based bleach, potassium peroxomonosulfate, chloroxylenol or halogenated phenols. Disinfectants were assessed for their ability to inactivate the virus on contact or after a short incubation period in the presence and absence of foetal bovine serum as a potential interferant. Significant differences were observed ranging from negligible effect of detergents to complete inactivation on contact with chloroxylenol. Conclusions: At least one chloroxylenol-based household disinfectant is available, which inactivates vaccinia virus on contact. Significance and Impact of the Study: In the event of a release or major outbreak of a pathogenic orthopoxvirus there is likely to be significant public demand for disinfectants with activity against these viruses. The identification of common household disinfectants with such activity obviates any requirement to stockpile or distribute laboratory/industrial disinfectants for this purpose.

Background: The need for an updated plague vaccine is highlighted by outbreaks in endemic regions together with the pandemic potential of this disease. There is no easily available, approved vaccine. Methods: Here we have used a murine model of pneumonic plague to examine the factors that maximise immunogenicity and contribute to survival following vaccination. We varied vaccine type, as either a genetic fusion of the F1 and V protein antigens or a mixture of these two recombinant antigens, as well as antigen dose-level and formulation in order to correlate immune response to survival. Results: Whilst there was interaction between each of the variables of vaccine type, dose level and formulation and these all contributed to survival, vaccine formulation in protein-coated microcrystals (PCMCs) was the key contributor in inducing antibody titres. From these data, we propose a cut-off in total serum antibody titre to the F1 and V proteins of 100 µg/mL and 200 µg/mL, respectively. At these thresholds, survival is predicted in this murine pneumonic model to be >90%. Within the total titre of antibody to the V antigen, the neutralising antibody component correlated with dose level and was enhanced when the V antigen in free form was formulated in PCMCs. Antibody titre to F1 was limited by fusion to V, but this was compensated for by PCMC formulation. Conclusions: These data will enable clinical assessment of this and other candidate plague vaccines that utilise the same vaccine antigens by identifying a target antibody titre from murine models, which will guide the evaluation of clinical titres as serological surrogate markers of efficacy.