Lecture Notes: ID-50 and LD-50

Introduction

• Presenter: Dr. O
• Topics: Infectious Dose-50 (ID-50) and Lethal Dose-50 (LD-50)

Infectious Dose-50 (ID-50)

• Definition: The number of organisms required to cause infection in 50% of a population.
• Measure of Virulence: Indicates how easily a microbe can cause an infection.
• Variability: Depends on individual's health status (e.g., immune system strength, stomach acid levels).
• Comparison Across Organisms: Useful for comparing virulence between different organisms.

Examples

• Salmonella enterica serovar Typhi
  • Infectious Dose: ~1,000 organisms.
  • Mortality Rate: ~10% for typhoid fever.
• Salmonella enterica serovar Typhimurium
  • Causes "basic Salmonellosis".
  • Mortality rate: ~1%, especially with treatment.
• E. coli 0157:H7
  • Infectious Dose: 10-100 organisms, potentially as low as 4-5 organisms.
  • Highly dangerous strain.
• Enterotoxigenic E. coli
  • Infectious Dose: 10 million to 10 billion organisms.
• Cholera
  • Infectious Dose: ~1 million organisms.

Portal of Entry

• Bacillus anthracis (Anthrax)
  • Cutaneous entry: 10-50 endospores.
  • Inhalation: 10,000-20,000 endospores.
  • Ingestion: 250,000 to 1 million endospores.

Lethal Dose-50 (LD-50)

• Definition: The amount of a toxin required to kill 50% of a population.
• Measure of Potency: Indicates how toxic a substance is.
• Application: Often used in reference to toxins rather than organisms.

Examples

• Botulinum Toxin
  • Lethal Dose: 0.03 ng/kg.
• Shiga Toxin (E. coli 0157:H7)
  • Lethal Dose: 250 ng/kg.
• Staphylococcal Enterotoxin
  • Lethal Dose: 1,350 ng/kg.

Conclusion

• ID-50 and LD-50 are essential metrics in understanding the potential impact of infectious agents and toxins.
• Highlight the variability and factors affecting these doses, such as host health and portal of entry.

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