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

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

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

Mortality Inhalational 86-100% (despite

treatment) Era of crude intensive supportive care

Cutaneous <5% (treated) – 20% (untreated)

GI approaches 100%

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

Human cases – historical risk factors Agricultural

Exposure to livestock Occupational

Exposure to wool and hides Woolsorter’s disease = inhalational

anthrax Rarely laboratory-acquired

Transmission No human-to-human Naturally occurring cases

Skin exposure Ingestion Airborne

Bioterrorism Aerosol (likely) Small volume powder (possible) Foodborne (unlikely)

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

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

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

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

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

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

Virulence Factors All necessary for full virulence Two plasmids

Capsule (plasmid pXO2) Antiphagocytic

3 Exotoxin components (plasmid pXO1) Protective Antigen Edema Factor Lethal Factor

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

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

Forms of natural disease Inhalational Cutaneous Gastrointestinal

Determined by route of entry Disease occurs wherever spores

germinate

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

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

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

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

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

. 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.

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.

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.

Cutaneous Systemic disease

Can occur, especially if untreated Spores/bacteria carried to regional lymph

nodes Lymphangitis/lymphadenitis Same syndrome as inhalational Sepsis, multiorgan failure

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

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

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.

Clinical Features

Symptoms depend on form of disease Inhalational Cutaneous Gastrointestinal

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

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

Laboratory Findings

Gram positive bacilli in direct blood smear

Electrolyte imbalances common Radiographic Findings

Widened mediastinumMinimal or no infiltrates

Can appear during prodrome phase

Cutaneous

Most common areas of exposureHands/armsNeck/head

Incubation period3-5 days typical12 days maximum

Cutaneous – progression of painless lesions

Papule – pruritic

Vesicle/bulla

Ulcer – contains organisms, sig. edema

Eschar – black, rarely scars

Systemic disease may developLymphangitis and lymphadenopathy

If untreated, can progress to sepsis, death

Gastrointestinal

OropharyngealOral or esophageal ulcer Regional lymphadenopathy Edema, ascites Sepsis

AbdominalEarly symptoms - nausea, vomiting, malaise

Late - hematochezia, acute abdomen, ascites

Diagnosis.

Early diagnosis is difficult Non specific symptoms Initially mild No readily available rapid specific tests

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

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

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

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

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 ptsNo infiltrate

No prior surgeryBloody CSF with GPBsFever

Cutaneous Spider bite Ecthyma gangrenosum Pyoderma gangrenosum Ulceroglandular

tularemia Mycobacterial ulcer Cellulitis

Expect if anthraxfever

no response to 3º cephs

painless, black eschar

+/- lymphadenopathy

usually sig. local edema

Gastrointestinal Gastroenteritis Typhoid Peritonitis Perforated ulcer Bowel

obstruction

Expect if anthraxCritically illAcute abdomenBloody diarrheaFever

Treatment.

Hospitalization IV antibiotics

Empiric until sensitivities are known Intensive supportive care

Electrolyte and acid-base imbalances Mechanical ventilation Hemodynamic support

Antibiotic selection Naturally occurring strains

Rare penicillin resistance, but inducible β-lactamase

Penicillins, aminoglycosides, tetracyclines, erythromycin, chloramphenicol have been effective

Ciprofloxacin very effective in vitro, animal studies

Other fluoroquinolones probably effective Engineered strains

Known penicillin, tetracycline resistance Highly resistant strains = mortality of

untreated

Empiric Therapy Until susceptibility patterns known Adults

Ciprofloxacin 400 mg IV q12° OR

Doxycycline 100mg IV q12°AND (for inhalational)

One or two other antibiotics

Pregnant womenSame as other adultsWeigh small risks (fetal arthropathy) vs benefit

Immunosuppressedsame as other adults

Susceptibility testing should be done Narrow antibiotic if possible Must be cautious

Multiple strains with engineered resistance to different antibiotics may be coinfecting

Watch for clinical response after switching antibiotic

Antibiotic therapy Duration

60 days Risk of delayed spore germination Vaccine availability

Could reduce to 30-45 days therapy Stop antibiotics after 3rd vaccine dose

Switch to oral Clinical improvement Patient able to tolerate oral medications

Other therapies Passive immunization

Anthrax immunoglobulin from horse serum Risk of serum sickness

Antitoxin Mutated Protective Antigen

Blocks cell entry of toxin Still immunogenic, could be an alternative

vaccine Animal models promising

Postexposure Prophylaxis

Who should receive PEP? Anyone exposed to anthrax Not for contacts of cases, unless also

exposed Empiric antibiotic therapy Vaccination

Avoid unnecessary antibiotic usage Potential shortages of those who

need them Potential adverse effects

HypersensitivityNeurological side effects, especially elderly

Bone/cartilage disease in childrenOral contraceptive failure

Future antibiotic resistance Individual’s own floraCommunity resistance patterns

Post exposure prophylaxis. Antibiotic therapy

Treat ASAP Prompt therapy can improve survival Continue for 60 days

30-45 days if vaccine administered

Antibiotic therapy Same regimen as active treatment

Substituting oral equivalent for IV Ciprofloxacin 500 mg po bid empirically Alternatives

Doxycycline 100 mg po bid Amoxicillin 500 mg po tid

Prevention.

Vaccine Anthrax Vaccine Adsorpbed (AVA) Supply

Limited, controlled by CDC Production problems

Single producer – Bioport, Michigan Failed FDA standards None produced since 1998

Vaccine Inactivated, cell-free filtrate Adsorbed onto Al(OH)3

Protective Antigen Immunogenic componentNecessary but not sufficient

Vaccine Administration

Dose schedule 0, 2 & 4 wks; 6, 12 & 18 months initial series

Annual booster0.5 ml SQ

Vaccine Adverse Effects

>1.6 million doses given to military by 4/2000

No deaths <10% moderate/severe local reactions

Erythema, edema <1% systemic reactions

Fever, malaise

Infection control.

No person to person transmission

Standard Precautions Laboratory safety

Biosafety Level (BSL) 2 Precautions

Decontamination.

Skin, clothing Thorough washing with soap and water Avoid bleach on skin

Instruments for invasive procedures Sterilize, e.g. 5% hypochlorite solution

Sporicidal agents Sodium or calcium hypochlorite (bleach)