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This chapter focuses on a group of unrelated bacterial diseases that are rarely encountered in a conventional urban or suburban setting but are acquired after a distinctive environmental exposure, such as saltwater immersion, animal bites, handling of an infected animal carcass, or travel to specific areas around the world. Several of these diseases present primarily as cutaneous disorders with rare systemic involvement (e.g., erysipeloid); others present primarily as systemic disorders with rare cutaneous involvement (e.g., brucellosis). Several of the pathogens can be aerosolized and disseminated for respiratory transmission, naturally or with human intervention. The ease of dissemination and the potential virulence of several organisms make them suitable for intentional spread as biologic weapons. The intentional spread of these diseases is discussed in greater detail in Chapter 213.

In this chapter, these infections are grouped by their most common, natural means of transmission to humans: atraumatic exposure to animals, animal bites, and contact with contaminated water (Fig. 183-1).

Figure 183-1

Algorithm for identifying cutaneous infections usually contracted in specific environmental settings.

aBrackish water may harbor the same organisms.

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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 gastrointestinal 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 human-to-human transmission.

Etiology and Epidemiology

Anthrax 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 183-1; see also Chapter 213).

Table 183-1 Overview of Bacterial Infections

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