Pathogenesis of Infectious Diseases – Study Notes

Pathogenesis of Infectious Diseases

Introduction

The study of the pathogenesis of infectious diseases focuses on how diseases develop and progress in the human body. Understanding key terminology is essential for grasping the mechanisms of infection and disease.

• Pathogenicity: The ability of a microorganism to cause disease.

• Pathogenesis: The steps or mechanisms involved in the development of a disease.

Infection versus Infectious Disease

It is important to distinguish between infection and infectious disease, as not all infections result in disease.

• Infectious disease: A disease caused by a microorganism (pathogen).

• Pathogens: Microbes that cause infectious diseases.

• Infection: Colonization by a pathogen; may or may not result in disease.

• A person can be infected with a pathogen without developing an infectious disease.

Interactions between Pathogens, Host, and the Environment

The occurrence of infectious disease depends on a complex interplay between the pathogen, the host, and environmental factors.

• Pathogen factors: Virulence, mode of entry, and number of organisms.

• Host factors: Health status, nutritional status, hygiene, age, travel, and lifestyle.

• Environmental factors: Climate, season, geography, reservoirs, sanitation, housing, and water availability.

Why Infection Does Not Always Occur

Not every exposure to a pathogen results in infection or disease due to several protective mechanisms.

• The microbe may not land at a suitable site for multiplication.

• Pathogens often require attachment to specific receptors to multiply and cause damage.

• Antibacterial factors (e.g., bacteriocins) produced by indigenous microbiota may destroy the pathogen.

• Microbial antagonism: Indigenous microbiota inhibit growth of foreign microbes.

• The individual's nutrition and health status influence the outcome.

• The person may be immune to the pathogen.

• Phagocytes in the blood may destroy the pathogen.

Chain of Infection

The infectious disease process involves a sequence of events known as the chain of infection. Breaking any link in this chain can prevent disease transmission.

• Pathogen

• Source of the pathogen (reservoir)

• Portal of exit

• Mode of transmission

• Portal of entry

• Susceptible host

Example: The diagram in the original material illustrates the chain of infection, showing how a pathogen moves from a source through various portals and modes to a susceptible host.

*Additional info: The chain of infection is a foundational concept in infection control and epidemiology, emphasizing the importance of interrupting transmission routes to prevent outbreaks.*