Tissue Responses to Infectious Agents

TISSUE RESPONSES TO INFECTIOUS AGENTS

Infectious diseases are very prevalent worldwide and are a major cause of morbidity and mortality. Infectious agents tend to have tropism for specific tissues and organs.

There are 6 major histologic patterns:

·              Exudative inflammation is acute inflammatory response with neutrophils.Examples include bacterial meningitis, bronchopneumonia, and abscess.

·              Necrotizing inflammation occurs when a virulent organism produces severetissue damage and extensive cell death. Examples include necrotizing fasciitis and necrotizing pharyngitis.

·              Granulomatous inflammation.Granulomatous response predominates withslow-growing organisms such as mycobacteria, fungi, and parasites.

·              Interstitial inflammation is a diffuse mononuclear interstitial infiltrate thatis a common response to viral infectious agents. Examples include myocarditis (Coxsackie virus) and viral hepatitis.

·              Cytopathic/cytoproliferative inflammation refers to inflammation in whichthe infected/injured cell is altered. The changes may include intranuclear/ cytoplasmic inclusions (cytomegalic inclusion disease, rabies [Negri body]); syncytia formation (respiratory syncytial virus and herpes virus); and apop-tosis (Councilman body in viral hepatitis).

·              No inflammation. An inflammatory response to microbes cannot occur inseverely immunosuppressed individuals due to primary immunodeficiencies or acquired immunodeficient states (e.g., AIDS).