This photomicrograph depicted a number of Gram-positive, endospore-forming Bacillus anthracis bacteria. B. anthracis is the pathologic microorganism responsible for the disease “anthrax”, an acute infectious disease, which most commonly occurs in wild and domestic vertebrates (cattle, sheep, goats, camels, antelopes, and other herbivores), but it can also occur in humans when they are exposed to infected animals, or tissue from infected animals.
Human anthrax has three major clinical forms depending on the route of infection: cutaneous, inhalation, and gastrointestinal. Cutaneous anthrax begins as a pruritic papule or vesicle that enlarges and erodes (1-2 days) leaving a necrotic ulcer with subsequent formation of a central black eschar; inhalation anthrax may begin as a prodrome of fever, chills, nonproductive cough, chest pain, headache, myalgias, and malaise, with more distinctive clinical hallmarks of hemorrhagic mediastinal lymphadenitis, hemorrhagic pleural effusions, bacteremia and toxemia resulting in severe dyspnea, hypoxia and septic shock; gastrointestinal anthrax may result in pharyngeal lesions with sore throat, dypshagia marked neck swelling and regional lymphadenopathy, or intestinal infection characterized by fever, severe abdominal pain, massive ascites, hematemesis, and bloody diarrhea. In any form of anthrax, hemorrhagic meningitis can result from hematogenous spread of the organism from the primary site.