Anthrax is an infection caused by the bacterium Bacillus anthracis. It can occur in four forms: skin, inhalation, intestinal, and injection. Symptoms begin between one day and two months after contracting the infection. The skin form presents with a small blister with surrounding swelling that often turns into a painless ulcer with a black center. The inhalation form presents with fever, chest pain, and shortness of breath.