MICRB 412 - Transmission

Transmission Objectives

• Discuss various routes of transmission, especially concerning vector-borne diseases.

Reading for Today

• “The Unified Theory of Perspiration” – Desowitz

• “Resurgent Vector-Borne Diseases” - Gubler

Reading for Thursday

• “Common Strategies for Antigenic Variation” Deitsch et al.

Transmission Overview

• Microbes must leave the infected body and be transmitted to new hosts to thrive.

• Factors affecting transmission:

  1. Number of microorganisms shed: More pathogens increase the likelihood of infection.

  2. Microorganism stability in the environment: Some microbes can survive extreme conditions through spores or cysts.

  3. Dose required for infection: Different pathogens require varying quantities to establish disease (e.g., 10 Shigella vs. 10,000,000 Salmonella bacteria for infection).

Other Factors Affecting Transmission

• Genetic susceptibility.

• Respiratory issues leading to sneezing/coughing.

• Intestinal disturbances, such as diarrhea.

Types of Human Transmission

• Transmission is possible through:

  • Bodily fluids (blood, mucous, urine, semen, milk, saliva).

  • Skin-to-skin contact.

  • Vertical transmission (from parents to offspring).

  • Invertebrate vectors (e.g., insects, ticks).

  • Vertebrate sources (e.g., zoonoses from mammals, birds).

Mask Usage and Transmission Reduction

• Proper mask use can significantly reduce transmission risk:

  • 90% risk reduction without a mask

  • 30% risk with an