History

3. History • Caused by Bacillus anthracis • Human zoonotic disease • Spores found in soil worldwide • Primarily disease of herbivorous animals • Sheep, goats, cattle • Many large documented epizootics • Occasional human disease • Epidemics have occurred but uncommon • Rare in developed world

4. Epidemiology • Three forms of natural disease • Inhalational • Rare (<5%) • Most likely encountered in bioterrorism event • Cutaneous • Most common (95%) • Direct contact of spores on skin • Gastrointestinal • Rare (<5%), never reported in U.S. • Ingestion

5. All ages and genders affected • Occurs worldwide • Endemic areas - Africa, Asia • True incidence not known • World 20,000-100,000 in 1958 • U.S. 235 total reported cases 1955-1994 • 18 cases inhalational since 1900, last one 1976 • Until 2001, last previous case cutaneous 1992

6. Mortality • Inhalational 86-100% (despite treatment) • Era of crude intensive supportive care • Cutaneous <5% (treated) – 20% (untreated) • GI approaches 100%

7. Incubation Period • Time from exposure to symptoms • Very variable for inhalational • 2-43 days reported • Theoretically may be up to 100 days • Delayed germination of spores

8. Human cases – historical risk factors • Agricultural • Exposure to livestock • Occupational • Exposure to wool and hides • Woolsorter’s disease = inhalational anthrax • Rarely laboratory-acquired

10. Transmission • No human-to-human • Naturally occurring cases • Skin exposure • Ingestion • Airborne • Bioterrorism • Aerosol (likely) • Small volume powder (possible) • Foodborne (unlikely)

11. Transmission • Cutaneous • Handling hides/skins of infected animals • Bites from arthropods (very rare) • Handling powdered form in letters, etc. • Intentional aerosol release • May see some cutaneous if large-scale

12. Microbiology • Bacillus anthracis • Aerobic, Gram positive rod • Long (1-10μm), thin (0.5-2.5μm) • Forms inert spores when exposed to O2 • Infectious form, hardy • Approx 1μm in size • Vegetative bacillus state in vivo • Result of spore germination • Non-infectious, fragile

13. Classification • Same family: B. cereus, B. thuringiensis • Differentiation from other Bacillus species • Non-motile • Non β-hemolytic on blood agar • Does not ferment salicin • Note: Gram positive rods are usually labeled as “contaminants” by micro labs

14. Environmental Survival • Spores are hardy • Resistant to drying, boiling <10 minutes • Survive for years in soil • Still viable for decades in perma-frost • Favorable soil factors for spore viability • High moisture • Organic content • Alkaline pH • High calcium concentration

15. Transmission • Inhalational • Handling hides/skins of infected animals • Microbiology laboratory • Intentional aerosol release • Small volume powdered form • In letters, packages, etc • Questionable risk, probably small

16. Transmission • Gastrointestinal • Ingestion of meat from infected animal • Ingestion of intentionally contaminated food • Not likely in large scale • Spores not as viable in large volumes of water • Ingestion from powder-contaminated hands • Inhalational of spores on particles >5 m • Land in oropharynx

17. Virulence Factors • All necessary for full virulence • Two plasmids • Capsule (plasmid pXO2) • Antiphagocytic • 3 Exotoxin components (plasmid pXO1) • Protective Antigen • Edema Factor • Lethal Factor

18. Protective Antigen • Binds Edema Factor to form Edema Toxin • Facilitates entry of Edema Toxin into cells • Edema Factor • Massive edema by increasing intracellular cAMP • Also inhibits neutrophil function • Lethal Factor • Stimulates macrophage release of TNF-α, IL-1β • Initiates cascade of events leading to sepsis

19. Pathogenesis • Disease requires entry of spores into body • Exposure does not always cause disease • Inoculation dose • Route of entry • Host immune status • May depend on pathogen strain characteristics

20. Forms of natural disease • Inhalational • Cutaneous • Gastrointestinal • Determined by route of entry • Disease occurs wherever spores germinate

21. Pathogenesis. • Inhalational • Spores on particles 1-5 m • Inhaled and deposited into alveoli • Estimated LD50 = 2500 – 55,000 spores • Dose required for lethal infection in 50% exposed • Contained in imperceptibly small volume

22. Inhalational • Phagocytosed by alveolar macrophages • Migration to mediastinal/hilar lymph nodes • Germination into vegetative bacilli • Triggered by nutrient-rich environment • May be delayed up to 60 days • Factors not completely understood • Dose, host factors likely play a role • Antibiotic exposure may contribute • Delayed germination after antibiotic suppression

24. Vegetative bacillus is the virulent phase • Active toxin production • Hemorrhagic necrotizing mediastinitis • Hallmark of inhalational anthrax • Manifests as widened mediastinum on CXR • Does NOT cause pneumonia • Followed by high-grade bacteremia • Seeding of multiple organs, including meninges

25. Toxin production • Has usually begun by time of early symptoms • Stimulates cascade of inflammatory mediators • Sepsis • Multiorgan failure • DIC • Eventual cause of death • Symptoms mark critical mass of bacterial burden • Usually irreversible by this time • Clearance of bacteria unhelpful as toxin-mediated

26. Pathogenesis of cutaneous form. • Cutaneous • Spores in contact with skin • Entry through visible cuts or microtrauma • Germination in skin • Disease begins following germination • Toxin production • Local edema, erythema, necrosis, lymphocytic infiltrate • No abscess or suppurative lesions • Eventual eschar formation

28. . In cutaneous anthrax, a malignant pustule develops at the infection site. This pustule is a central area of coagulation necrosis (ulcer) surrounded by a rim of vesicles filled with bloody or clear fluid. A black eschar forms at the ulcer site. Extensive edema surrounds the lesion.

29. The organisms multiply locally and may spread to the bloodstream or other organs (eg, spleen) via the efferent lymphatics. B anthracis remains in the capillaries of invaded organs, and the local and fatal effects of the infection are due, in large part, to the toxins elaborated by B anthracis.

30. Dissemination from the liver, spleen, and kidneys back into the bloodstream may result in bacteremia. Secondary hemorrhagic intestinal foci of anthrax result from B anthracis bacteremia.

31. Cutaneous • Systemic disease • Can occur, especially if untreated • Spores/bacteria carried to regional lymph nodes • Lymphangitis/lymphadenitis • Same syndrome as inhalational • Sepsis, multiorgan failure

32. Pathogenisis GI form • Gastrointestinal • Spores contact mucosa • Oropharynx • Ingestion • Aerosolized particles >5 m • Intestinal mucosa – terminal ileum, cecum • Ingestion • Larger number of spores required for disease • Incubation period 2-5 days

33. Gastrointestinal • Spores migrate to lymphatics • Submucosal, mucosal lymphatic tissue • Mesenteric nodes • Germination to vegetative bacilli • Toxin production • Massive mucosal edema • Mucosal ulcers, necrosis • Death from perforation or systemic disease

34. Oropharyngeal anthrax • Oropharyngeal anthrax is a variant of intestinal anthrax and occurs in the oropharynx after ingestion of meat products contaminated by anthrax. Oropharyngeal anthrax is characterized by throat pain and difficulty in swallowing. The lesion at the site of entry into the oropharynx resembles the cutaneous ulcer.

35. Clinical Features • Symptoms depend on form of disease • Inhalational • Cutaneous • Gastrointestinal

36. Inhalational • Asymptomatic incubation period • Duration 2-43 days, ~10 days in Sverdlovsk • Prodromal phase • Correlates with germination, toxin production • Nonspecific flu-like symptoms • Fever, malaise, myalgias • Dyspnea, nonproductive cough, mild chest discomfort • Duration several hours to ~3 days • Can have transient resolution before next phase

37. Fulminant Phase • Correlates with high-grade bacteremia/toxemia • Critically Ill • Fever, diaphoresis • Respiratory distress/failure, cyanosis • Septic shock, multiorgan failure, DIC • 50% develop hemorrhagic meningitis • Headache, meningismus, delirium, coma • May be most prominent finding • Usually progresses to death in <36 hrs • Mean time from symptom onset to death ~3 days

38. Laboratory Findings • Gram positive bacilli in direct blood smear • Electrolyte imbalances common • Radiographic Findings • Widened mediastinum • Minimal or no infiltrates • Can appear during prodrome phase

39. Cutaneous • Most common areas of exposure • Hands/arms • Neck/head • Incubation period • 3-5 days typical • 12 days maximum

40. Cutaneous – progression of painless lesions Papule – pruritic Vesicle/bulla Ulcer – contains organisms, sig. edema Eschar – black, rarely scars

41. Systemic disease may develop • Lymphangitis and lymphadenopathy • If untreated, can progress to sepsis, death

42. Gastrointestinal • Oropharyngeal • Oral or esophageal ulcer • Regional lymphadenopathy • Edema, ascites • Sepsis • Abdominal • Early symptoms - nausea, vomiting, malaise • Late - hematochezia, acute abdomen, ascites

43. Diagnosis. • Early diagnosis is difficult • Non specific symptoms • Initially mild • No readily available rapid specific tests

44. Presumptive diagnosis • History of possible exposure • Typical signs & symptoms • Rapidly progressing nonspecific illness • Widened mediastinum on CXR • Large Gram+ bacilli from specimens • Can be seen on Gram stain if hi-grade bacteremia • Appropriate colonial morphology • Necrotizing mediastinitis, meningitis at autopsy

45. Definitive diagnosis • Direct culture on standard blood agar • Gold standard, widely available • Alert lab to work up Gram + bacilli if found • 6-24 hours to grow • Sensitivity depends on severity, prior antibiotic • Blood, fluid from skin lesions, pleural fluid, CSF, ascites • Sputum unlikely to be helpful (not a pneumonia) • Very high specificity if non-motile, non-hemolytic • Requires biochemical tests for >99% confirmation • Available at Reference laboratories

46. Other diagnostic tests • Anthraxin skin test • Chemical extract of nonpathogenic B. anthracis • Subdermal injection • 82% sensitivity for cases within 3 days symptoms • 99% sensitivity 4 weeks after symptom onset

47. Testing for exposure • Nasal swabs • Can detect spores prior to illness • Currently used only as epidemiologic tool • Decision based on exposure risk • May be useful for antibiotic sensitivity in exposed • Culture on standard media • Swabs of nares and facial skin • Serologies • May be useful from epidemiologic standpoint • Investigational – only available at CDC

48. Differential diagnostics Inhalational Expect if anthrax • Influenza • Pneumonia • Community-acquired • Atypical • Pneumonic tularemia • Pneumonic plague • Mediastinitis • Bacterial meningitis • Thoracic aortic aneurysm Flu rapid diagnostic – More severe in young pts No infiltrate No prior surgery Bloody CSF with GPBs Fever

49. Cutaneous • Spider bite • Ecthyma gangrenosum • Pyoderma gangrenosum • Ulceroglandular tularemia • Mycobacterial ulcer • Cellulitis Expect if anthrax fever no response to 3º cephs painless, black eschar +/- lymphadenopathy usually sig. local edema

50. Gastrointestinal • Gastroenteritis • Typhoid • Peritonitis • Perforated ulcer • Bowel obstruction Expect if anthrax Critically ill Acute abdomen Bloody diarrhea Fever