Anthrax Infection

Excerpt

Anthrax is an acute zoonotic infection caused by the spore-forming, gram-positive Bacillus anthracis (see Image. Gram-Positive Rods). The disease primarily affects herbivorous mammals, such as cattle, sheep, and goats. Humans can acquire the infection through direct or indirect contact with infected animals, contaminated animal products, ingesting undercooked meat, inhaling aerosolized spores, or, more rarely, by injecting contaminated drugs. The United States (US) Centers for Disease Control and Prevention (CDC) notes that anthrax remains endemic in agricultural regions of the Americas, sub-Saharan Africa, Asia, and parts of Europe. However, sporadic outbreaks still occur in the US, particularly in areas with unvaccinated livestock.

Anthrax manifests in 4 principal clinical forms, defined by the route of spore entry: cutaneous, inhalational, gastrointestinal (ingestion), and injectional. Cutaneous anthrax is the most common, accounting for over 95% of human cases, and typically presents as a painless ulcer with a characteristic black eschar (see Image. Eschar). Inhalational anthrax, the most lethal form, is associated with rapid progression to severe respiratory distress and high mortality if untreated. Gastrointestinal anthrax results from ingestion of contaminated meat and can present as oropharyngeal or intestinal disease, while injected anthrax, recognized in recent outbreaks among heroin users, is characterized by severe soft tissue infection and sepsis.

The pathogenesis of anthrax is mediated by potent exotoxins and a poly-D-glutamic acid capsule, which together facilitate immune evasion, systemic dissemination, and rapid clinical deterioration. B anthracis is classified as a Tier 1 select agent due to its potential for use as a bioterrorism weapon, given the ease of spore production and environmental persistence. Advances in antimicrobial therapy and critical care have improved outcomes, but anthrax remains a disease with significant morbidity and mortality, particularly in systemic and meningitic forms.