ESSENTIALS OF DIAGNOSIS
Epidemiologic setting: exposure to animals, animal hides, or potential bioterrorism.
A painless cutaneous black eschar on exposed skin, with marked surrounding edema and vesicles.
Nonspecific flu-like symptoms that rapidly progress to extreme dyspnea and shock; mediastinal widening and pleural effusions on chest radiograph.
Naturally occurring anthrax is a disease of sheep, cattle, horses, goats, and swine. Bacillus anthracis is a gram-positive spore-forming aerobic rod. Spores—not vegetative bacteria—are the infectious form of the organism. These are transmitted to humans from contact with contaminated animals, animal products, or animal hides, or from soil by inoculation of broken skin or mucous membranes; by inhalation of aerosolized spores; or, rarely, by ingestion resulting in cutaneous, inhalational, or GI forms of anthrax, respectively. Inhalation of aerosolized spores that were deliberately placed in the mail as an act of bioterrorism occurred in the United States in 2001. Spores germinate into vegetative bacteria that multiply locally in cutaneous and GI anthrax but may also disseminate to cause systemic infection. Inhaled spores are ingested by pulmonary macrophages and carried via lymphatics to regional lymph nodes, where they germinate. The bacteria rapidly multiply within the lymphatics, causing a hemorrhagic lymphadenitis. Invasion of the bloodstream leads to overwhelming sepsis, killing the host.
This occurs within 2 weeks after exposure to spores; there is no latency period for cutaneous disease as there is with inhalational anthrax. The initial lesion is an erythematous papule, often on an exposed area of skin that vesiculates and then ulcerates and undergoes necrosis, ultimately progressing to a purple to black eschar (eFigure 33–8). The eschar typically is painless; pain indicates secondary bacterial infection. The surrounding area is edematous and vesicular but not purulent. Regional adenopathy, fever, malaise, headache, and nausea and vomiting may be present. The infection is self-limited in most cases, but hematogenous spread with sepsis or meningitis may occur.
Large cutaneous lesion on the left forearm caused by cutaneous anthrax. (Public Health Image Library, CDC.)
Illness occurs in two stages, beginning on average 10 days after exposure, but may have a latent onset 6 weeks after exposure. Nonspecific viral-like symptoms such as fever, malaise, headache, dyspnea, cough, and congestion of the nose, throat, and larynx are characteristic of the initial stage. Anterior chest pain is an early symptom of mediastinitis. Within hours to a few days, progression to the fulminant stage of infection occurs in which symptoms or signs of overwhelming sepsis predominate. Delirium, obtundation, or findings of meningeal irritation suggest an accompanying hemorrhagic meningitis.