"Anthrax" means "charcoal," which describes appearance lesions it produces on the skin.
Is the causative agent of anthrax, the infection.
Resides in the soil, where its spores can persist for years; spores are also found on animals, especially on hides and wool.
Non-motile
In clinical specimens, spores are rarely seen; colonies are non-hemolytic.
Treatment: ciprofloxacin or doxycycline with antitoxins; amoxicillin is often used to treat cutaneous anthrax.
Prevention: In areas where
B. anthracis is endemic, vaccination of humans and animals can help control disease.
Infected animals should be incinerated, as spores can remain in the soil for many years.
Virulence factors:
Capsule
Unique polypeptide capsule comprising D-glutamic acid, which enables host immune evasion (recall most bacterial capsules comprise polysaccharides).
Exotoxins: Edema toxin and Lethal toxin.
Toxins comprise A and B subunits:
B subunit = Protective antigen (PA); this is the region of the toxin that binds with host cells.
A subunits = Factors that combine with Protective antigen to form active toxins:
Edema factor (EF) is an adenylate cyclase that increases intracellular cyclic adenosine monophosphate (cAMP), resulting in edema.
Lethal factor (LF) is a protease that inactivates mitogen-activated protein kinase (MAPK) pathways, resulting in cell death.
Be aware that these factors are nontoxic on their own; they must combine with protective antigen to enter host cells and cause damage.
Infections:
B. anthracis primarily infects non-human animals.
Interaction with contaminated animal products can lead to three types of human infections:
- Cutaneous, Inhalation, Gastrointestinal.
Cutaneous anthrax
Most common form.
Skin lesions with central necrotic eschar surrounded by edema. The pustule is initially painless, but infection can progress to produce systemic signs of edema, and bacteremia can be fatal.
Typically, cutaneous anthrax is due to exposure to contaminated soil or animal hides, hair, or wool; however, outbreaks have also been reported among injection drug users.
Inhalation anthrax
Initially presents with nonspecific symptoms, including fever, non-productive cough, and myalgias.
However, as the spores travel from the lungs to the nearby lymph nodes, edema and mediastinal lymph node enlargement occurs; in chest X-rays, mediastinal widening is an important diagnostic cue. Respiratory failure can ensue, and, in about half the cases, meningeal symptoms occur.
Historically, inhalation anthrax in humans was associated with spore inhalation while working with animal products. However, weaponized anthrax has been used in bioterrorism; person-to-person transmission does not occur, because bacterial replication occurs in the lymph nodes.
Gastrointestinal anthrax
Aka, ingestion anthrax, occurs upon consumption of contaminated meat.
Manifests in the upper and lower gastrointestinal tract:
In the oral cavity, pharynx, and esophagus, anthrax produces lymphadenopathy, edema, sore throat, and can lead to sepsis. In some patients, pseudeomembranes form; these are grayish coverings that comprise fibrin, leukocytes, and
other exudates.
In the lower gastrointestinal tract, particularly the ileum and cecum, infection causes ulcerative lesions and edema, with nausea, vomiting, and bloody diarrhea.
