Tularemia and Francisella tularensis Overview

General Information

• Francisella tularensis: A pathogenic bacterium responsible for tularemia.
• Gram-negative: Has a thin cell wall and does not retain crystal violet dye during Gram staining.
• Shape: Small, coccobacillus (rod-shaped).
• Oxygen requirements: Facultatively anaerobic, can grow in both aerobic and anaerobic conditions.

Epidemiology

• Transmission: Zoonotic; primarily affects wildlife, especially rabbits and rodents.
• Human infection: Occurs through:
  • Tick and deer fly bites.
  • Handling infected animal tissues.
  • Ingestion of contaminated water or food.
  • Inhalation of aerosols.

Disease Manifestation (Tularemia)

• Forms of tularemia:
  1. Ulceroglandular: Most common; skin ulcer with local lymphadenopathy.
  2. Glandular: Similar but without ulcer formation; swollen lymph nodes.
  3. Pneumonic: Inhalation form; severe respiratory symptoms.
  4. Oculoglandular: Infection through the eye leading to conjunctivitis.
  5. Oral: Rare; caused by ingestion of contaminated food or water.
  6. Typhoidal: Systemic; lacks a localized infection, presenting fever and systemic symptoms.

Pathophysiology

• Virulence factors:
  • Capsule: Protects against phagocytosis.
  • Lipopolysaccharide: Induces strong immune response.
  • Intracellular lifestyle: Survives and replicates within host cells (macrophages).

Diagnosis

• Clinical symptoms: Presentation varies by form; often includes fever, chills, headaches, and fatigue.
• Lab tests:
  • Serological tests (e.g., agglutination tests).
  • PCR for DNA detection in specimens.
  • Culture from clinical samples (less common due to biohazard risks).

Treatment

• Antibiotics:
  • Doxycycline is the first-line treatment.
  • Other options include ciprofloxacin and streptomycin.
• Supportive care: May be necessary for severe cases.

Prevention

• Avoiding animal contact: Especially with sick or dead wildlife.
• Protective measures: When handling animals or during outdoor activities.
• Vaccination: No widely available vaccine for humans; research is ongoing.

Public Health Considerations

• Bioterrorism potential: Considered a category A bioterrorism agent due to its infectivity and lethality in untreated cases.
• Outbreak management: Requires prompt identification and treatment to prevent spread.

Francisella tularensis

• Gram-negative, coccobacillus bacteria responsible for tularemia.
• Facultatively anaerobic: capable of surviving with or without oxygen.

Epidemiology

• Causes zoonotic disease, primarily affecting wildlife like rabbits and rodents.
• Human infection occurs through various routes:
  • Tick and deer fly bites
  • Contact with infected animal tissue
  • Ingestion of contaminated water or food
  • Inhalation of aerosols

Disease Manifestation

• Tularemia (rabbit fever) presents in six forms:
  • Ulceroglandular: Most common; skin ulcer with swollen lymph nodes.
  • Glandular: Swollen lymph nodes without ulcer formation.
  • Pneumonic: Severe respiratory symptoms, potentially fatal.
  • Oculoglandular: Infection through the eye, causing conjunctivitis.
  • Oral: Rare; caused by ingesting contaminated food or water.
  • Typhoidal: Systemic infection presenting with fever and systemic symptoms.

Pathophysiology

• Virulence factors:
  • Capsule: Protects against phagocytosis by immune cells.
  • Lipopolysaccharide: Triggers strong immune response.
  • Intracellular lifestyle: Survives and reproduces within host cells like macrophages.

Diagnosis

• Clinical symptoms vary depending on the form, often including fever, chills, headache, and fatigue.
• Laboratory tests:
  • Serological tests: Detect antibodies against the bacteria.
  • PCR: Detects bacterial DNA in clinical samples.
  • Culture: Rarely used due to biohazard risks.

Treatment

• Antibiotics are crucial:
  • Doxycycline: First-line treatment.
  • Ciprofloxacin and streptomycin: Alternative options.
• Supportive care: May be necessary for severe cases.

Prevention

• Avoid contact with animals: Especially sick or dead wildlife.
• Protective measures: Utilize when handling animals or participating in outdoor activities.
• Vaccination: No widely available human vaccine, but ongoing research.

Public Health Considerations

• Classified as a Category A bioterrorism agent: Highly infectious and lethal in untreated cases.
• Outbreak management requires prompt identification and treatment: To prevent disease spread.