Micropara Anthrax (Midterm)

Anthrax

• Introduction:

  • Anthrax is a zoonotic disease caused by the bacterium Bacillus anthracis.

  • Bacilllus anthracis bacterial spores are soil-borne.

  • Because of their long lifespan, spores are present globally and remain at the burial sites of animals killed by anthrax for many decades.

  • people can get anthrax iif they are exposed to the spores.

• Characteristics of Bacillus anthracis:

  • Gram-positive (Gram +)

  • Rod-shaped

  • Spore-forming

  • Obligate aerobic: requires oxygen for growth

  • Facultative intracellular: can survive inside and outside host cells

  • Encapsulated: capsule is demonstrable during growth in infected animals

  • Non-motile: cannot move by itself

  • Spores remain viable in soil for decades

  • Spores are oval and centrally located

  • Examples of survival: WWII in Scotland - spores survived for over 40 years before eradication in 1987

• Reservoirs:

  • Humans (not normal flora)

  • Animals (primarily horses, cattle, sheep, swine)

  • Soil (mainly spores present)

• Contagiousness:

  • Anthrax is not contagious; it does not spread human-to-human

History of Anthrax

• Descriptions of anthrax date back to ancient texts; referenced in the Bible and described by Greeks and Romans (Anthrakites).

• In the Middle Ages, workers in wool ("wool sorters' disease") contracted it from sheep wool.

• 20th century saw significant declines in cases due to animal vaccination.

• Discovery credited to Pollender, Rayer, and Davaine; Robert Koch established its causative role.

Taxonomy

• Domain: Bacteria

• Phylum: Firmicutes

• Class: Bacilli

• Order: Bacillales

• Family: Bacillaceae

• Genus: Bacillus

• Species: anthracis

Pathogenesis

B atnhracis pathogenesis begins by the spores entering a skin abrasion, lungs or intestines. then, the spores are ingested by macrophages and brought to lymph nodes. lastly, the bacteria germinate in the lymph nodes or mediastinum, in the case of inhalation anthrax.

Transmission

• Contact with infected animal products is the primary transmission route

• Herbivorous grazing animals contract anthrax from soil spores.

• Human exposure can occur via inhalation of spores, open abrasions on skin, or consumption of undercooked infected meat.

Infectious Dose, Incubation and Forms of Anthrax

• Infectious Dose:

  • Criteria varies; estimates of 1-3 spores to 100 spores can cause infection; inhalation anthrax infection dose is notably higher (8-50,000 spores).

• Incubation Periods:

  • Inhalation: 2-5 days

  • Cutaneous: 2-3 days (some cases as rapid as 12 hours)

  • Gastrointestinal: unknown

• Inhalation Anthrax: spores reach alveolar spaces, transported to lymph nodes, germinating, leading to septicemia (blood poisoning by germs such as bacteria, viruses, and fungi).

• Cutaneous & Gastrointestinal Anthrax: spores enter through skin breaks/mucosa, engulfed by macrophages leading to symptoms upon replication.

Epidemiology

• Most inhalation cases occur in factory settings (e.g., exposure to contaminated wool).

• Rarely seen in the U.S. due to livestock vaccination.

• Gastrointestinal anthrax is rare; noted outbreaks minimal, e.g., 400-person outbreak from caribou meat.

• Largest outbreak: 10,000 cases of cutaneous anthrax in Zimbabwe (1979-1985).

Virulence Factors

• Bacillus anthracis exhibits virulence through toxins and capsules.

• Capsule: formed from D-Glutamyl Polypeptide; encoded by plasmid pXO2, protects from phagocytosis.

• Toxins: encoded by plasmid pX01, includes:

  • Edema factor (EF)

  • Lethal factor (LF)

  • Protective antigen (PA)

Toxins and Symptoms

• Protective Antigen: facilitates entry of toxins into host cells.

• Lethal Factor: immunosuppressive, damages endothelial cells, disrupts signaling pathways.

• Edema Factor: increases cAMP production, similar immunosuppressive effects as LF, can lead to pulmonary edema.

• Symptoms: vary by infection type, may develop from 1-2 months.

Types of Anthrax

Cutaneous Anthrax

• Rarely fatal with treatment; localized to skin prevents compound entry into vital organs.

• Cutaneous Anthrax is rarely fatal if treated because the infection area is limited to the skin, preventing the lethal factor, edema factor, and protective antigen from entering and destroying a vital organ.

• Without treatment, about 20% of cutaneous skin infection cases progress to Toxemia and Death.

• Symptoms: itching, raised bumps developing into painless sore with black center; swelling. Swelling in the sore and nearby lymph glands.

• Treatment: antibiotics (Doxycycline, Ciprofloxacin).

Gastrointestinal Anthrax

• Lesions have been found in the intestines and in the mouth and throat. After bacterium invades the bowel system, it spreads through the bloodstream throughout the body, while also continuing to make toxins.

• Symptoms arise from lesions in intestines/mouth, leading to systemic spread:

  • Fever and Chills, Swelling of Neck or Neck Glands, Sore Throat, Painful Swallowing, Hoarseness Nausea and Vomiting, especially Bloody Vomiting, Diarrhea or Bloody Diarrhea, Headache, Flushing (Red Face) and Red Eyes, Stomach Pain, Fainting, Swelling of Abdomen (Stomach).

• Treatment: antibiotics/supportive care; mortality rate 25-60%.

Diagnosis

1. Culture Characteristics:

   • Use Blood Agar and Nutrient Agar; cultivate aerobically at 37° C.

   • Blood Agar: irregular colonies, non-hemolytic

   • Nutrient Agar: “Medusa Head” or “Comet Tail” appearance.

Microscopy and Laboratory Samples

• Samples for Cutaneous Anthrax: swabs from lesions.

• Inhalation Anthrax: sputum and blood samples.

• Gastrointestinal Anthrax: gastric aspirate, feces, blood samples.

Inhalation Anthrax

• Uncommon; acquired by inhaling spores.

• Symptoms: flu-like—sore throat, mild fever, fatigue, progress to high fever, trouble breathing, shock, potential meningitis.

• Treatment:

  • Confirmed cases treated with antibiotics (Ciprofloxacin, Doxycycline), two-drug therapy recommended for inhalation anthrax especially (Vancomycin + any antibiotic).

• Preventive Measures:

  • Vaccinations (for high-risk groups), proper decontamination, prophylactic treatments.