Anthrax

Key Features

Essentials of Diagnosis

• Epidemiologic setting

  • Exposure to animals or animal hides

  • Exposure from an act of bioterrorism

• Cutaneous anthrax

  • Black eschar on exposed skin

  • Marked surrounding edema and vesicles

  • Typically painless

• Inhalational anthrax

  • Nonspecific flu-like symptoms

  • Rapidly progresses to extreme dyspnea and shock

  • Chest radiograph shows mediastinal widening and pleural effusions

General Considerations

• Naturally occurring anthrax is a disease of sheep, cattle, horses, goats, and swine

• Bacillus anthracis

  • A gram-positive spore-forming aerobic rod

  • Spores—not vegetative bacteria—are the infectious form of the organism

• Transmitted to humans from contaminated animals, animal products, or soil by inoculation of broken skin or mucous membranes, by inhalation of aerosolized spores or, rarely, by ingestion, resulting in cutaneous, inhalational, or gastrointestinal forms of anthrax, respectively

• Spores entering the lungs are ingested by 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, resulting in death

Clinical Findings

Symptoms and Signs

Cutaneous anthrax

• Onset occurs within 2 weeks of exposure

• Initial lesion is erythematous papule, often on exposed area of skin, that vesiculates, ulcerates, and undergoes necrosis, ultimately progressing to a purple-to-black eschar

• Surrounding area is edematous and vesicular but not purulent

• Infection is usually self-limited

Inhalational anthrax

• Nonspecific viral-like symptoms

• Anterior chest pain is an early symptom of mediastinitis

• Within hours to days, patient progresses to fulminant stage of infection, in which symptoms and signs of overwhelming sepsis predominate

• Dissemination may occur, resulting in meningitis

Gastrointestinal anthrax

• Symptoms begin 2–5 days after ingestion of food products contaminated with anthrax spores

• Fever, diffuse abdominal pain, rebound abdominal tenderness, vomiting, constipation, and diarrhea occur

• Because the primary lesion is ulcerative, emesis is blood tinged or has coffee-ground appearance; stool may be blood tinged or melenic

• Bowel perforation can occur

Differential Diagnosis

Cutaneous anthrax

• Ecthyma gangrenosum

• Rat-bite fever

• Ulceroglandular tularemia

• Plague

• Glanders

• Rickettsialpox

• Orf (parapoxvirus infection)

• Cutaneous mycobacterial infection

Inhalational anthrax

• Bacterial mediastinitis

• Fibrous mediastinitis from

  • Histoplasmosis

  • Coccidioidomycosis

  • Atypical or viral pneumonia

  • Silicosis

  • Sarcoidosis

• Other causes of mediastinal widening

  • Superior vena cava syndrome

  • Aortic aneurysm or dissection

Gastrointestinal anthrax

• Bowel obstruction

• Perforated viscus

• Peritonitis

• Gastroenteritis

• Peptic ulcer disease

Diagnosis

Laboratory Tests

• Laboratory findings are nonspecific

• Gram stain of pleural fluid, cerebrospinal fluid, unspun blood, blood culture, or fluid from a cutaneous lesion may show the characteristic boxcar-shaped encapsulated ...