• Bacillus anthracis is a large Gram-positive, endospore-producing bacillus. In clinical specimans it typically appears singly or in pairs; in culture it appears as a streptobacillus.
• While endospores appear in culture, they are not seen in clinical specimans.
• A facultative anaerobe (def).

Habitat

• B. anthracis primarily infects herbivores.

Source

• Contact with infected animals, animal materials, infected soil, or B. anthracis endospores used as a bioweapon.

Epidemiology

• B. anthracis primarily infects herbivores (def); humans are usually accidental hosts.
• Rare in developed countries but more prevalent in underdeveloped countries where animals are vaccinated against anthrax.
• There are three forms of anthrax: cutaneous, inhalation, and gastrointestinal. Around 95% of human anthax infections in nature are the cutaneous form as a result of B. anthracis endospores entering exposed skin.

Clinical Disease

• Cutaneous anthrax first appears as a painless papule (def) at the site of infection and rapidly progresses to an ulcer (def) surrounded by vesicles (def) and finally a necrotic eschar (def). The mortality rate from untreated cutaneous anthrax is approximately 20%.
• Inhalation anthrax may initially have an asymptomatic latent period of two months or more. Typically, alveolar macrophages (def) engulf the inhaled endospores of B. anthracis and transport them to the mediastinal lymph nodes (def) where they can germinate. Initial symptoms are nonspecific and include coughing, headache, fever, chills, vomiting, and chest and abdominal pain. This rapidly worsens and presents as worsening fever, edema, and massive enlargement if the mediastinum (def). About half of infected individuals have symptoms of meningitis (def). Almost all cases progress to shock (def) and death within about three days of the initial symptoms. This is the most deadly form of anthrax.
• Gastrointestinal anthrax as a result of ingestion of B. anthracis can appear two ways: ulceration of the mouth and esophagus (def) followed by localized lymphadenopathy (def), edema (def), and sepsis (def) if the bacterium invades the upper intestinal tract; and nausea, vomiting, and malaise (def) rapidly progressing to sepsis if the bacterium invades the large intestines. Commonly fatal.

From Anthrax, by Burke A Cunha, MD, Professor of Medicine, State University of New York at Stony Brook School of Medicine; Chief, Infectious Disease Division, Vice-Chair, Department of Internal Medicine, Winthrop-University Hospital.