Sections View Full Chapter Figures Tables Videos Annotate Full Chapter Figures Tables Videos Supplementary Content + Download Section PDF Listen ++ For further information, see CMDT Part 33-06: Anthrax + Key Features Download Section PDF Listen +++ +++ Essentials of Diagnosis ++ Epidemiologic setting Exposure to animals or animal hides Potential 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, killing the host + Clinical Findings Download Section PDF Listen +++ +++ 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 (neutropenic, Pseudomonas) Tularemia Plague Brown recluse spider bite Aspergillosis or mucormycosis Antiphospholipid antibody syndrome Warfarin necrosis Rat-bite fever Rickettsialpox Orf (parapoxvirus infection) Cutaneous mycobacterial infection Cutaneous leishmaniasis +++ Inhalational anthrax ++ Influenza Bacterial mediastinitis Fibrous mediastinitis from Histoplasmosis Coccidioidomycosis Atypical or viral pneumonia Silicosis Sarcoidosis Other causes of mediastinal widening Ruptured aortic aneurysm Lymphoma Superior vena cava syndrome Tuberculosis +++ Gastrointestinal anthrax ++ Bowel obstruction Perforated viscus Peritonitis Gastroenteritis Peptic ulcer disease + Diagnosis Download Section PDF Listen +++ +++ Laboratory Tests ++ Pleural fluid in inhalational anthrax is hemorrhagic with few white blood cells Cerebrospinal fluid from meningitis cases is hemorrhagic Gram stain of fluid from a cutaneous lesion, pleural fluid, cerebrospinal fluid, unspun blood, or blood culture may show the characteristic boxcar-shaped encapsulated rods in chains The diagnosis is established by isolation of the organism from culture of the skin lesion (or fluid expressed from it), blood, or pleural fluid or cerebrospinal fluid (in cases of meningitis) In the absence of prior antimicrobial therapy, cultures are invariably positive +++ Imaging Studies ++ Chest radiograph is most sensitive test for inhalational disease, eg, being abnormal initially in every case of bioterrorism-associated inhalational anthrax Mediastinal widening from hemorrhagic lymphadenitis in 70% of the bioterrorism-related cases Pleural effusions were present initially or occurred over the course of illness in all cases, and approximately 75% had pulmonary infiltrates or signs of consolidation + Treatment Download Section PDF Listen +++ +++ Medications ++ B anthracis May express β-lactamases that confer resistance to cephalosporins and penicillins For this reason, penicillin and amoxicillin are not recommended for use as single agents in the treatment of disseminated disease Ciprofloxacin is the drug of choice Other fluoroquinolones are probably as effective Doxycycline is an alternative first-line agent Ciprofloxacin is used in combination with other agents (eTable 33–1) for inhalational anthrax, disseminated disease, cutaneous infections of the head, face or neck, or when associated with extensive local edema or signs of systemic infection Raxibacumab and obiltoxaximab Human monoclonal antibodies directed against the protective antigen component of lethal toxin FDA approved for the treatment of inhalation anthrax when used in combination with recommended antibacterial treatments ++Table Graphic Jump LocationeTable 33–1.Antimicrobial agents for treatment of anthrax or for prophylaxis against anthrax.View Table||Download (.pdf)eTable 33–1. Antimicrobial agents for treatment of anthrax or for prophylaxis against anthrax. First-line agents and recommended doses Ciprofloxacin, 500 mg twice daily orally or 400 mg every 12 hours intravenously Doxycycline, 100 mg every 12 hours orally or intravenously Second-line agents and recommended doses Amoxicillin, 500 mg three times daily orally Penicillin G, 2–4 million units every 4 hours intravenously Alternative agents with in vitro activity and suggested doses Rifampin, 10 mg/kg/day orally or intravenously Clindamycin, 450–600 mg every 8 hours orally or intravenously Clarithromycin, 500 mg orally twice daily Erythromycin, 500 mg every 6 hours intravenously Vancomycin, 1 g every 12 hours intravenously Imipenem, 500 mg every 6 hours intravenously + Outcome Download Section PDF Listen +++ +++ Prevention ++ Ciprofloxacin is considered the drug of choice (eTable 33–1) for prophylaxis following exposure to anthrax spores Vaccine Available for persons at high risk for exposure to anthrax spores It is a cell-free antigen prepared from an attenuated strain of B anthracis Multiple injections over 18 months and an annual booster dose are required to achieve and maintain protection Existing supplies have been reserved for military personnel Also available for preexposure and postexposure prophylaxis; administered at 0, 2, and 4 weeks postexposure combined with antimicrobial therapy +++ Prognosis ++ The prognosis for cutaneous infection is excellent; death is unlikely if the infection has remained localized and lesions heal without complications in most cases The reported mortality rate for gastrointestinal and inhalational infections is up to 85% +++ When to Refer ++ Any suspected case of anthrax should be immediately reported to the Centers for Disease Control and Prevention so that an investigation can be conducted + References Download Section PDF Listen +++ + +Adalja AA et al. Clinical management of potential bioterrorism-related conditions. N Engl J Med. 2015 Mar 5;372(10):954–62. [PubMed: 25738671] + +Bower WA et al; Centers for Disease Control and Prevention (CDC). Clinical framework and medical countermeasure use during an anthrax mass-casualty incident. MMWR Recomm Rep. 2015 Dec 4;64(4):1–22. [PubMed: 26632963] + +Hou AW et al. Obiltoxaximab: adding to the treatment arsenal for Bacillus anthracis infection. Ann Pharmacother. 2017 Oct;51(10):908–13. [PubMed: 28573869]