Anthrax

March 23rd, 2010

Bacterial pathogens in soil

• Many bacteria are natural residents of the soil

• Some are pathogens• Some are zoonoses• For the most important ones,

humans are incidental or dead-end hosts

• This is the case with anthrax

The genus Bacillus

• Naturally occurring soil bacteria; large diverse genus

• Ubiquitous in the environment• Some useful for pest control• Major human pathogens

– Bacillus cereus (food)– B. anthracis

Bacillus anthracis

• Gram +• Spore former• 1st bacterium to be proven as a

cause of disease

Life cycle

• soil-animal-soil• Spores in the soil• Vegetative bacteria in the host• Domestic and wild animals• Herbivores• Goats, sheep, horses, cattle• Infection causes hemorrhage; dying and

dead animals release organisms back into the soil

Occurrence

• Endemic in many areas of the world• Sub-Saharan Africa• Asia• Central and South America• Central and southern Europe

Anthrax

• Three distinct forms of the disease, depending on the route of exposure

• Cutaneous– Treatable, rarely fatal

• Gastrointestinal– Treatable, but dangerous; can be fatal

• Inhalational– Almost universally fatal before modern

intensive care

Pathogenesis

• An exotoxin mediated disease• Bacteria release the toxin into the

tissue• Toxin is carried on a plasmid (X01);

bacteria must have the plasmid to cause anthrax

• Toxin has three components– Edema factor– Lethal factor– Protective antigen

Pathogenesis

• These components must assemble into the exotoxin to cause disease

• Increase in CO2 levels triggers toxin production

• Toxin affects cyclic AMP within the cell

• Similarity to cholera• Edema

Cutaneous anthrax

• Skin infection• Spores get into skin and become

vegetative bacteria• Release toxin• Forms an eschar• Untreated fatality rate up to 20%• Rarely fatal with treatment

Gastrointestinal anthrax

• Ingested spores• Usually from consuming meat of an

animal that died of anthrax• become vegetative bacteria in the GI

tract• Release toxin• Large explosive outbreaks• Treatable, but can be fatal

Inhalational anthrax

Inhalational anthrax

• Inhalation of spores directly into the lungs

• Spores are ingested by macrophages• Undergo transition to vegetative

bacteria• Release toxin• Massive edema• Progress to septicemia• High fatality rate

Inhalational anthrax

• Treatable in the prodomal period• Ciprofloxacin, other

fluoroquinolones• Survival decreases sharply once

symptoms appear• Intensive supportive care• Survival of inhalational anthrax is a

recent medical phenomenon

Exposures

• Organism is ubiquitous in soil• Contact with infected animal

products• Hides• Wool• Bones • Meat

Control

• Avoidance of products from animals that have died of anthrax

• Education about the risks of eating livestock that have died suddenly of unknown cause

• Incineration or very deep burial of carcasses

Control

• Occupational exposure control• Hides and bones• Vets and animal handlers• Control at herd level• Vaccination