Anthrax: life cycle, mechanisms of pathogenesis and prospects in the development of veterinary vaccines (review)

Anthrax is an acute especially dangerous disease of agricultural and wild animals, as well as humans. Anthrax is induced by the gram-positive spore-forming bacterium Bacillus anthracis . This infection is global, but the incidence rate of livestock and people varies depending on the environmental situation and the implementation of control strategies (C.J. Carlson et al., 2019). Historical and modern experience suggests that uncontrolled outbreaks of anthrax can have disastrous consequences. This review describes the life cycle of the pathogen, environmental features of the anthrax spread and mechanisms of pathogenesis. Given these factors we discuss the optimal strategies that have been developed over the years taking into account the cost and outcome for combating the dangerous infection. The timely disposal of dead animals and the vaccination of healthy livestock, used together, can effectively stop the spread of the disease. Thus, the development of highly effective, safe and low-cost vaccines is extremely relevant and, moreover, in fact the only promising method for improving the epizootic situation with this hazardous disease. Vaccination of farm animals for several decades has significantly reduced the risk of anthrax, but it is not mandatory in many countries and is often used only after onset of the disease, and not to prevent it. Despite a significant decrease in the incidence rate, the current situation with anthrax in the Russian Federation is characterized as unstable (A.G. Ryazanova et al., 2018; E.G. Simonova et al., 2018). Animal epizootics and human cases are still being recorded in the country due to the presence of natural soil reservoirs of the pathogen and incomplete coverage of vaccination for farm animals. Currently, only live attenuated vaccines are used to vaccinate animals. The review summarizes their effectiveness and safety, as well as the limitations associated with the use of attenuated vaccines. Although existing vaccines have been shown to be effective, they have several serious flaws. Certainly, the relevance of the development of more effective veterinary vaccines against anthrax, based on modern approaches, is fully justified. In particular, there is a need to design a veterinary vaccine that does not contain the pathogen in any form and is compatible with the use of antibiotics, which are necessary, both during the outbreak of anthrax and for regular use in the treatment of various animal diseases. The application of new approaches, the devising modern recombinant vaccines and the rejection of the use of pathogens in an attenuated form is an important and promising task. This review provides an analysis of studies on the development of new candidate vaccines against anthrax. The main attention is paid to the development of subunit vaccines using B. anthracis recombinant antigens obtained in various expression systems, including vaccines for oral administration and compatible with antibiotics.