An overview of anthrax infection including the recently identified form of disease in injection drug users

Abstract

Purpose: Bacillus anthracis infection (anthrax) can be highly lethal. Two recent outbreaks related to contaminated mail in the USA and heroin in the UK and Europe and its potential as a bioterrorist weapon have greatly increased concerns over anthrax in the developed world.

Methods: This review summarizes the microbiology, pathogenesis, diagnosis, and management of anthrax.

Results and conclusions: Anthrax, a gram-positive bacterium, has typically been associated with three forms of infection: cutaneous, gastrointestinal, and inhalational. However, the anthrax outbreak among injection drug users has emphasized the importance of what is now considered a fourth disease form (i.e., injectional anthrax) that is characterized by severe soft tissue infection. While cutaneous anthrax is most common, its early stages are distinct and prompt appropriate treatment commonly produces a good outcome. However, early symptoms with the other three disease forms can be nonspecific and mistaken for less lethal conditions. As a result, patients with gastrointestinal, inhalational, or injectional anthrax may have advanced infection at presentation that can be highly lethal. Once anthrax is suspected, the diagnosis can usually be made with gram stain and culture from blood or tissue followed by confirmatory testing (e.g., PCR). While antibiotics are the mainstay of anthrax treatment, use of adjunctive therapies such as anthrax toxin antagonists are a consideration. Prompt surgical therapy appears to be important for successful management of injectional anthrax.

Fig. 1

Gram stain of B. anthracis at ×1,500 magnification. In its vegetative form, B. anthracis is a gram-positive, nonmotile, large rod-shaped bacterium that actively replicates and produces virulence factors that cause disease. In its dormant state, B. anthracis exists as an ellipsoid-shaped spore that is highly refractive to light and resistant to staining [22]

Fig. 2

Cutaneous anthrax. These lesions appeared on the arms of a man who 6 days earlier had handled ill cattle. The extensive edema and hemorrhagic vesicles and bullae are typical of cutaneous anthrax and appear prior to the formation of a black eschar [35]. (Reprinted with permission of the American Thoracic Society. Copyright © 2012 American Thoracic Society [17])

Fig. 3

Gastrointestinal anthrax. Coronal reconstruction images from a CT scan of the abdomen and pelvis after the administration of intravenous contrast material show a large amount of ascites and concentric wall thickening of a long segment of the distal small bowel (a, arrows). Numerous slightly enlarged lymph nodes are enhanced with intravenous contrast material and are seen at the root of the small bowel mesentery (a, arrowheads) and in the retroperitoneum (b, arrowheads) [12]. (Reprinted with permission of the American Thoracic Society. Copyright © 2012 American Thoracic Society [17])

Fig. 4

Inhalational anthrax. The contrast-enhanced chest CT scans (a, b) from a patient with inhalational anthrax show perihilar parenchymal lung disease (arrow, a), widening mediastinum, hilar adenopathy, pleural effusions, and peribronchial infiltrates as well as patchy peribronchial air-space disease, especially on the right (arrow, b). Photomicrographs of histopathologic specimens of hilar soft tissue (c–e) from the same patient at autopsy show perivascular and peribronchial hemorrhage (arrow, c; H & E, ×10), and necrosis (arrow, d; H & E, ×20) and abundant gram-positive bacilli (arrow, e; Brown–Brenn, ×100) [47]. (Reprinted with permission of the American Thoracic Society. Copyright © 2012 American Thoracic Society [17])

Fig. 5

Injectional anthrax. Preoperative photographs of a woman (a) with skin necrosis involving the medial aspect of her left thigh and labia majora and a man (b) with swelling of his scrotum and skin necrosis involving his buttock [54]. Surgical debridement of necrotic skin and fascia of a patient with injectional anthrax and compartment syndrome of the right arm (c) [55]. (Reprinted with permission of the American Thoracic Society. Copyright © 2012 American Thoracic Society [17])