Pathophysiology
1) cause is infection with Bacillus anthracis 2) largely a disease of herbivores 3) occurs in three forms – cutaneous, GI, and respiratory (woolsorter’s disease)
Signs and Symptoms
Cutaneous – 1) pustule develops 12-36 hours after infection 2) pustule turns to painless necrotic ulcer with black eschar at base 3) eschar is surrounded by characteristic expanding halo of brawny edema 4) may have painful regional lymphadenitis GI – 5) fever 6) vomiting 7) bloody diarrhea 8) abdominal pain Respiratory – 9) dyspnea 10) fever 11) stridor 12) hypoxia 13) pulmonary hemorrhage with hemoptysis 14) septic shock 15) death usually within 24 hours
Characteristic Test Findings
Radiology – 1) chest radiograph shows hilar edema Laboratory – 2) increased white blood cell count 3) positive antibody test
Histology/Gross Pathology
1) gram-positive aerobic or facultative anaerobic rods with square ends 2) capsulated and nonmotile 3) spores located at center of cell 4) cells line up like “boxcars” 5) lungs show marked congestion and gelatinous hilar edema
Biochemistry
poly-d-glutamic capsule allows B. anthracis to escape phagocytosis
Inheritance/Epidemiology
Cutaneous – 1) most common form (95% of cases outside of bioterrorism) 2) infection is through direct contamination of spores in skin wound or bite of infected fly 3) spontaneous healing in 80-90% of cases 4) 10-20% of cases become systemic with high mortality GI and respiratory – 5) naturally occurring infections extremely rare (<10 per year in USA) 6) mortaility is 90% if antibiotics are not started within 24 hours of symptom onset
Treatment
1) spores can be destroyed by boiling for 10 min 2) GI and respiratory forms – 95% mortality after onset of symptoms even with antibiotic treatment 3) a nonliving vaccine is available but is restricted to military and researchers working in the field 4) antibiotics – high-dose penicillin, ciprofloxacin, tetracyclines, erythromycin, and clindamycin
Tips for USMLE
1) if question mentions a 34 year old male who works in the tanning business, who develops sudden onset of shortness of breath, and who in 12 hours becomes hypotensive and is intubated in the ICU, think anthrax 2) if woolsorter’s disease is mentioned, think anthrax 3) respiratory anthrax via spore dispersal and inhalation is a major bioterrorism fear
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