Anthrax: An overview of the disease, toxicity and relevance of the protective antigen (PA) toxin

Anthrax is a complex and deadly multispecies disease with serious zoonotic implications. It is caused by the Gram- positive spore-forming soil bacterium Bacillus anthracis. Anthrax is one of the oldest known and extensively studied diseases, yet it continues to haunt the public and livestock health sector till date. With its resilient spore and ability to persist across various agro-climatic zones, the organism is like a dormant explosive among the population awaiting the right moment to strike. The anthrax toxin is composed of three different proteins, namely protective antigen (PA), and two alternative A-subunits, the lethal factor (LF) and the oedema factor (EF). PA stands as the most extensively characterised element among the anthrax toxins. It holds the distinction of being the first component identified, cloned, and sequenced, and remains the most easily produced in appreciable quantities. The application of the toxin-based assays has been mostly limited to human vaccine evaluation and diagnosis. Due to the antigenicity and role in pathogenicity, PA serves as a crucial component of the anthrax vaccine and diagnostics. The right diagnosis at the right time followed by the right therapy is the key to control the dreaded disease in both man and animals. The review provides a glimpse of the disease and the basis of its toxicity along with the relevance of the PA toxin in diagnostics, therapeutics and vaccines for addressing the gaps and aligning with the future course of research for the control and prevention of anthrax.