Pathogenesis
Pathogenesis refers to the biological mechanisms that lead to the development and progression of a disease or disorder.
Adherence Factors
The initial step in pathogenesis is the attachment of the infectious agent to host cells. Adherence factors, such as fimbriae, pili, non-fimbrial adhesins and biofilms, enable pathogens to anchor themselves to host tissues, resisting physical removal. This attachment is crucial for establishing infection and initiating further pathogenic activities.
Invasion Factors
After adherence, some pathogens produce enzymes that allow them to penetrate and spread within host tissues. Enzymes like collagenase break down collagen, hyaluronidase degrades the ‘glue’ between cells and lecithinase disrupts cell membranes. These invasion factors facilitate the movement of pathogens through tissue barriers, enhancing their ability to infect different parts of the host.
Capsules
Many pathogens possess capsules that shield them from the host’s immune system. Capsules prevent phagocytes from adhering to the pathogen, making it difficult for the immune system to recognise and engulf them. This evasion mechanism allows the infectious agent to survive and multiply within the host, prolonging infection and increasing disease severity.
Toxins
Pathogens may produce toxins that directly damage host tissues. Exotoxins are secreted by pathogens and can disrupt cellular functions, while endotoxins, released when the cell wall of a pathogen breaks down, trigger inflammation and other harmful responses. These toxins contribute significantly to the disease symptoms and complications associated with infections.