Pathogenesis describes the biological mechanisms that lead to the development of disease. It encompasses the sequence of events from the initial interaction between a host and a causative agent to the manifestation of symptoms and tissue damage.
Molecular and cellular mechanisms
Pathogenesis involves complex interactions between a pathogen or injurious factor and host tissues. For infectious diseases, the process generally begins with entry and colonization, followed by replication and spread. Microbes employ virulence factors such as adhesins, toxins, invasion proteins and immune modulators to establish infection. The host responds through innate and adaptive immune mechanisms that aim to contain or eliminate the invader. Damage can result directly from microbial toxins or multiplication and indirectly from host inflammatory responses. Non-infectious diseases also have distinct pathogenesis; for example, autoimmune disorders arise from misguided immune responses, and cancers result from genetic mutations leading to uncontrolled cell growth. Understanding the steps of pathogenesis helps identify targets for intervention and informs diagnostics and therapeutics.
Mechanisms in action
Different diseases illustrate diverse pathogenic processes. Influenza viruses infect respiratory epithelial cells via haemagglutinin-mediated entry, replicate and cause cell death, leading to cough and fever; secondary bacterial infections can complicate the outcome. Mycobacterium tuberculosis is inhaled, survives within macrophages and induces granuloma formation; the ensuing immune response causes tissue necrosis and respiratory symptoms. Vibrio cholerae colonizes the small intestine and secretes cholera toxin, which disrupts ion transporters and triggers profuse watery diarrhoea. Plasmodium falciparum invades liver cells and later red blood cells; release of merozoites and immune-mediated destruction of infected erythrocytes lead to cycles of fever and anaemia characteristic of malaria. In autoimmune diseases like systemic lupus erythematosus, antibodies form against self-antigens, causing widespread inflammation. These examples show how pathogenesis varies across diseases but generally involves an interplay between causative agents and host responses.
By dissecting pathogenesis, researchers can develop vaccines, therapeutics and public health measures to prevent or mitigate disease.
Related Terms: Pathogenicity, Virulence, Infection, Host defence, Disease progression