Process Of Infection: Colonisation

Infectious microorganisms exist in reservoirs.

Transmitted via direct contact, or indirectly by vectors (insects) 

Human-to-human transmission by aerosolized microorganisms in droplets (coughing/sneezing) or physical contact (sexual contact, blood transfusion, direct contact contaminated materials)

After deposit in receptive environment - microorganism stabilizes adherence to the tissue through specific surface receptors e.g. infectious agents causing respiratory tract infections bind to molecules on respiratory epithelium.

This helps protect removal of the pathogen by mechanical forces e.g. coughing mucus

• Infectious agent can invade surrounding tissues/other sites.

• Developed mechanisms to penetrate tissues & avoidhost’s nonspecific and specific defences (inflammation & immunity)

• replicate within infected cells (viral pathogens)
• replicate in macrophages & other cells (bacterial pathogens)

Successful spread relies on virulence factors:

 adhesion molecules, toxins & protection against host’sinflammatory and immune system 

If host has:
▪ Intact immune system – microorganism remains localized
▪ Immune or inflammatory system compromised – infection may rapidly spread