Anthrax is caused by Bacillus anthracis, a sporulating, gram-negative bacillus. B. anthracis can be part of the normal soil, and poses a risk to grazing animals. Natural infection occurs when humans become accidentally infected through contact with infected animals or their products.
The primary lesion of cutaneous anthrax begins as a painless, pruritic papule that appears 1 to 7 days after inoculation. The papule enlarges, and within 1 to 2 days, small vesicles or a larger, 1- to 2-cm vesicle forms on the papule that is filled with clear or serosanguineous fluid. As the vesicle enlarges, satellite vesicles may form. Fluid within the vesicles may contain numerous, large gram-positive bacilli and a paucity of neutrophils. Within 1 to 2 days, the vesicle ruptures, undergoes necrosis, and enlarges, forming painless ulcer covered by a characteristic black eschar. Surrounding the ulcer and eschar is a characteristic, non-pitting, gelatinous edema that appears out of proportion to the size of the ulcer. Symptoms include low-grade fever and malaise. Regional lymphadenopathy is present early on.
Clinical characteristics highly suggestive of cutaneous anthrax include (1) a painless ulcer covered with black eschar (2) surrounding edema out of proportion to the size of the ulcer; and (3) a paucity of neutrophils in vesicular fluid.
Used with Permission from the Center for Public Health
and Disasters of California
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