Transmission of pathogens

A traditional model of the of infectious disease transmission occurs within the triad of, an external agent (pathogen), susceptible host, and an environment that brings the host and agent together.

Transmission mechanisms for the spread of infection include:

• direct physical contact of a susceptible host portal of entry with contaminated: blood and bodily fluids, soil, water, food etc.
• inhalation of infectious airborne microorganisms.
• exposure of a susceptible host to a pathogen from a carrier by aerosolization, injection, secretion, excretion or
• physical contact with, or bite by a vector.

Factors that can influence the acquisition of infection include:

• the environment and mechanism of exposure, e.g., Heating, Ventilation, and Air Conditioning (HVAC) dissemination of aerosolized Legionella pneumophila.
• the reproduction number (R0) of the pathogen
• the dose of pathogen and the portal of entry
• pathogenicity of the organism (ability to cause disease)
• behaviors that increase the opportunity for exposure such as sexual practices, hygiene, and other personal choices.
• susceptibility and response to an agent are influenced
  • previous exposure or vaccination status
  • age and sex.
  • genetic composition, nutritional and immunologic status, anatomic structure, comorbidities or medications, etc..
  • environmental factors include: geology and climate, biologic factors such as vector population, and socioeconomic factors such as crowding, sanitation, and the availability of health services.

Reference

Lesson 1: Introduction of Epidemiology. Section 8: Concepts of Disease Occurrence. Centers for Disease Control and Prevention (CDC). Retrieved November 1, 2022. from https://www.cdc.gov/csels/dsepd/ss1978/Lesson1/Section8.html

Lesson 1: Introduction of Epidemiology. Section 10: Chain of Infection. Centers for Disease Control and Prevention (CDC). Retrieved November 1, 2022, from https://www.cdc.gov/csels/dsepd/ss1978/Lesson1/Section10.html