Anthrax March 23 rd, 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 1 st 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 CO 2 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

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