ABSTRACT
Anthrax is a disease caused by Bacillus anthracis, which are small (0.4-1.0 µm in length), rod-shaped bacteria. These pathogens are Gram positive and not capable of movement. When grown in blood or tissue samples, they appear as short chains of a few cells and have a square end similar to a railroad box car (Figure 7.1). Anthrax is mainly a disease of mammalian herbivores, but it can infect all warm-blooded animals, including humans. The bacteria are obligate pathogens and cannot multiply outside of a living animal host. The bacteria start producing spores when exposed to the atmosphere: conditions occur after an infected animal has died and body uids leak from the carcass or when the carcass is opened by scavengers (hereafter, the carcasses of animals killed by anthrax will be called anthrax carcasses). It is these spores that allow B. anthracis to infect new hosts. Half the spore’s volume is taken up by the spore’s coat, which protects the spore from environmental extremes of temperature, pH, chemicals, and desiccation. Spores can survive in the environment until conditions are suitable for germination. These conditions, which would occur inside a mammal’s body, include high humidity, temperatures between 46°F and 113°F (8°C and 45°C), pH between 5 and 9, and the presence of amino acids (WHO 2008). The ability of anthrax spores to survive for long periods of time is astounding. Spores prepared by Dr. Louis Pasteur were still viable when retested 68 years later. Viable spores were also recovered from horse hair used more than a century earlier to bind plaster in London buildings (WHO 2008). Spore survival is enhanced in areas where the soil is dry, alkaline (pH greater than 8), and rich in calcium. The spores can germinate in less than 16 minutes when exposed to organic chemicals (e.g., l-alanine and ribosides).
