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ANTHRAX

AT-A-GLANCE

  • A large Gram-positive rod, Bacillus anthracis, changes into dormant spores under environmentally harsh conditions. Spores are infectious particles that revert to active bacillary form in host tissues.

  • Natural pathogen of livestock, especially sheep, goats, and cattle. Most human diseases are occupationally related to exposure to live animals or animal products.

  • Cutaneous anthrax is the most common form and is associated with the lowest morbidity. Inhalational and GI anthrax are more virulent and frequently lethal.

  • Cutaneous lesions arise from percutaneous spore inoculation, usually unnoticed. They present as painless edematous papules or plaques that develop jet-black central eschars.

  • The organism is a Centers for Disease Control and Prevention Category A bioweapon in aerosolizable micropowder form. There is no potential for human-to-human transmission of inhalational anthrax.

ETIOLOGY AND EPIDEMIOLOGY

Anthrax (Fig. 156-1) is a zoonotic infectious disease caused by Bacillus anthracis, a large aerobic, spore-forming Gram-positive rod.1 Anthrax occurs naturally in ruminant mammals, such as sheep, cattle, and goats. Human disease is seen most often in agrarian, livestock-dependent regions. Consequently, human anthrax usually follows agricultural or industrial exposure, either through direct handling of infected animals or contaminated soil or through the processing of hides, wool, hair, or meat.2 Anthrax has potential as a class A bioweapon (Table 156-1) because it is easily aerosolized and often lethal.

Figure 156-1

Anthrax. The classic cutaneous lesion of a primary infection in anthrax is a painless papule that evolves into a hemorrhagic bulla with surrounding brawny nonpitting edema. Note the typical localization on the hand. The name anthrax comes from the Greek word ανθραξ (anthrax), meaning coal, which refers to the coal-black hue of the lesions of cutaneous anthrax.

Table 156-1Overview of Bacterial Infections

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