Development of a Sterne-Based Complement Fixation Test to Monitor the Humoral Response Induced by Anthrax Vaccines

Animal, human, and environmental perspectives on anthrax in Bangladesh

Background

In Bangladesh, the zoonotic transmission of anthrax from animals to humans poses substantial challenges for prevention and control programs, especially in resource-constrained settings. A comprehensive literature review was conducted focusing on anthrax infections in animals, humans, and the environment to enable better design of prevention and control strategies.

Materials and methods

We followed PRISMA guidelines to collect data on anthrax infection in animals and humans from reports between 1980 and January 2023. We used a standardized data extraction template to collect data on study location, year, hosts, deaths and risk factors responsible for anthrax occurrences at the animal, human and environmental sectors. Subsequently, we conducted a thorough analysis of the data gathered to identify the factors responsible for anthrax occurrences and to propose updated strategies for anthrax prevention and control.

Results

Of the 27 articles analyzed, 20 focused on animal or human anthrax, while seven addressed environmental contaminations. A total of 6354 cases of anthrax infection in animals were recorded, with 998 fatalities and an overall case fatality of 15.7 %. In humans, inadequate knowledge about anthrax and its transmission was a significant factor. Risk factors for human cutaneous anthrax included activities such as slaughtering diseased animals and contact with contaminated raw meat or blood. Risky practices such as disposal of animal carcasses in floodwaters or water bodies were observed in some areas, contributing to the persistence of the anthrax pathogen in the environment.

Conclusions

Our study highlights the necessity of a multisectoral One Health approach to effectively control and prevent anthrax outbreaks in both animals and humans. This approach should include comprehensive vaccination programs, social and behavioral change activities, environmental management, and the establishment of surveillance systems. Implementing these recommendations will be crucial in addressing the complex challenges posed by anthrax in low-resource settings.

In Vitro Protection and Titer Duration of Anthrax-Specific Antibodies Following Subcutaneous Vaccination of White-tailed Deer (Odocoileus virginianus) with Bacillus anthracis Sterne 34F2 Strain Spores

Outbreaks of anthrax, caused by the soilborne bacterium Bacillus anthracis, are a continuous threat to free-ranging livestock and wildlife in enzootic regions of the United States, sometimes causing mass mortalities. Injectable anthrax vaccines are commercially available for use in livestock, and although hand injection is not a cost- or time-effective long-term management plan for prevention in wildlife, it may provide a tool for managers to target selectively animals of high conservation or economic value. Vaccine-induced anthrax-specific antibody responses have been reported previously in white-tailed deer (Odocoileus virginianus), but the protective nature was not determined. In this study, five white-tailed deer were subcutaneously vaccinated with one dose (1 mL) of the Anthrax Spore Vaccine. Eight blood collections by jugular venipuncture were conducted over 146 d to measure the anthrax-specific antibody response in each deer's serum over time. Antibodies were first detected by ELISA and later with toxin neutralization assays to estimate in vitro protection. Average peak absorbance by ELISA occurred at 14 d postvaccination, whereas average peak in vitro protection occurred at 28 d postvaccination. Observed in vitro protection on average for white-tailed deer after this single-dose vaccination protocol lasted 42-56 d postvaccination, although three individuals still maintained lethal toxin-neutralizing serum antibody titers out to 112 d postvaccination. Vaccination responses were variable but effective to some degree in all white-tailed deer.

Production of a Bacillus anthracis Secretome with Suitable Characteristics as Antigen in a Complement Fixation Test

In this study, we cultured the Bacillus anthracis vaccine strain Sterne 34F2 in a medium containing EDTA, and we assessed the best conditions to inhibit the activity of zinc-dependent metalloproteases to obtain a secretome containing a high concentration of non-degraded PA (PA₈₃), as evaluated by the SDS-PAGE analysis. Then, we used this secretome as the antigen in a Complement Fixation Test (CFT) to monitor the production of antibodies against PA₈₃ in the sera of rabbits vaccinated with Sterne 34F2 and then infected with a B. anthracis virulent strain to evaluate the potency of the vaccine. The PAS-based CFT results were compared with those obtained by using a commercial ELISA kit. The two serological tests gave similar results in terms of specificity and sensitivity, as the kinetics of the antibodies production was very similar. The Sterne 34F2 vaccine induced an antibody response to PA₈₃, whose titer was not inferior to 1:8 in PAS-based CFT and 42 kU/mL in PA₈₃-based ELISA, respectively, in all vaccinated rabbits. Our opinion is that the PAS-based CFT can be successfully employed in humans and in animals for epidemiological retrospective studies or post-vaccination monitoring. We also suggest the use of our method to test the efficacy of veterinary anthrax vaccines.

Maximization of Livestock Anthrax Vaccination Coverage in Bangladesh: An Alternative Approach

Low vaccination coverage of livestock is one of the major challenges to control anthrax in Bangladesh. This study was conducted to assess an alternate approach to maximize vaccination coverage. The method included traditional vaccination campaigns, livestock census, interviews, focus group discussions of cattle farmers, vaccination and livestock personnel, and validation workshops. It was observed that a mass vaccination program covered only 44% of the cattle population. It was found that 54.1% of the respondents did not bring their cattle to mass vaccination programs due to the difficulties of handling cattle and that there was no male member in the household. Only 12.5% of respondents acknowledged that they were not aware of the vaccine, and 3% of the respondents claimed that they ignored vaccination due to cost. All of the respondents from livestock personnel agreed that manpower was not enough to cover the total area. Further, 20% of vaccinators mentioned that they did not get enough vaccines. For an effective vaccination program, 58.33% of respondents recommended door-to-door service, and 54.16% of respondents suggested to arrange regular vaccination campaigns in six-month intervals. Thus, regular campaigns with door-to-door vaccination services are suggested to control anthrax outbreaks in Bangladesh.

Recent advances in lab-on-a-chip technologies for viral diagnosis

The global risk of viral disease outbreaks emphasizes the need for rapid, accurate, and sensitive detection techniques to speed up diagnostics allowing early intervention. An emerging field of microfluidics also known as the lab-on-a-chip (LOC) or micro total analysis system includes a wide range of diagnostic devices. This review briefly covers both conventional and microfluidics-based techniques for rapid viral detection. We first describe conventional detection methods such as cell culturing, immunofluorescence or enzyme-linked immunosorbent assay (ELISA), or reverse transcription polymerase chain reaction (RT-PCR). These methods often have limited speed, sensitivity, or specificity and are performed with typically bulky equipment. Here, we discuss some of the LOC technologies that can overcome these demerits, highlighting the latest advances in LOC devices for viral disease diagnosis. We also discuss the fabrication of LOC systems to produce devices for performing either individual steps or virus detection in samples with the sample to answer method. The complete system consists of sample preparation, and ELISA and RT-PCR for viral-antibody and nucleic acid detection, respectively. Finally, we formulate our opinions on these areas for the future development of LOC systems for viral diagnostics.

Unexpected human cases of cutaneous anthrax in Latium region, Italy, August 2017: integrated human-animal investigation of epidemiological, clinical, microbiological and ecological factors

On 31 August, a veterinarian and a farmworker were hospitalised for skin lesions. Both had been exposed to a dead cow on 19 August on a farm near Rome, where eight further cattle died of confirmed anthrax later the same month. At admission, the first case showed a black depressed eschar and another smaller lesion on one hand. The second case presented deep infection of the skin, with involvement of both arms. Anthrax diagnosis was confirmed by detection of B. anthracis DNA in eschar fragments from both patients. T-cell specific immunity was studied by flow cytometry and Elispot assay after stimulation with B. anthracis secretome in blood samples collected from Case 1. Immunoglobulin production was detected by complement fixation assay. In Case 1, specific CD4+ T-cell activation was detected, without antibody production. Specific antibodies were detected only in the second patient with severe cutaneous illness. Both patients recovered. The two human anthrax cases were epidemiologically linked, but anthrax was not suspected at admission in either case. The veterinarian had initially unrecognised professional exposure and the exposed farmworker did initially not report exposure to affected animals. A One Health strategy integrating human and animal investigations was essential to confirm the diagnosis.

Draft Genome Sequence of Bacillus anthracis Strain Sterne 09RA8929

A Bacillus anthracis vaccine strain (Sterne), used as an attenuated laboratory comparative strain, was sequenced and analyzed. A comparison to assemblies of B. anthracis strain Sterne (NZ_CP009541 and NZ_CP009540) was performed. The lack of the pX02 plasmid and pX01 in approximately five copies was confirmed.