Anthrax is an acute disease caused by the bacterium Bacillus anthracis. Most forms of the disease are lethal, and it affects mostly animals. It is contagious and can be transmitted through contact or consumption of infected meat.nthrax is an acute disease caused by the bacterium Bacillus anthracis. Most forms of the disease are lethal, and it affects mostly animals. It is contagious and can be transmitted through contact or consumption of infected meat.