Anthrax

KEY FEATURES

Essentials of Diagnosis

• Epidemiologic setting

  • Exposure to animals or animal hides

  • Exposure to 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 germinate into vegetative bacteria that multiply locally in cutaneous and gastrointestinal anthrax but may also disseminate to cause systemic infection

• 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 can lead to overwhelming sepsis and 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

• Eschar is typically painless

• Surrounding area is edematous and vesicular but not purulent

• Regional adenopathy, fever, malaise, headache, and nausea and vomiting may occur

• Infection is usually self-limited

Inhalational anthrax

• Occurs in two stages, beginning on average 10 days after exposure, but may have a latent onset 6 weeks after exposure

• Initial stage: Nonspecific viral-like symptoms such as fever, malaise, headache, dyspnea, cough, and congestion of the nose, throat, and larynx

• Anterior chest pain is an early symptom of mediastinitis

• Fulminant stage: Within hours to days, patient progresses to fulminant infection; symptoms or signs of overwhelming sepsis predominate

• Delirium, obtundation, or findings of meningeal irritation suggest an accompanying hemorrhagic 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 ...