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 an acute inflammatory response with neutrophils. Examples include bacterial meningitis, bronchopneumonia, and abscess.
•  Necrotizing inflammation occurs when a virulent organism produces severe tissue damage and extensive cell death. Examples include necrotizing fasciitis and necrotizing pharyngitis.
•  Granulomatous inflammation. Granulomatous response predominates with slow-growing organisms such as mycobacteria, fungi, and parasites.
•  Interstitial inflammation is a diffuse mononuclear interstitial infiltrate that is a common response to viral infectious agents. Examples include myocarditis (Coxsackie virus) and viral hepatitis.
•  Cytopathic/cytoproliferative inflammation refers to inflammation in which the 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 apoptosis (Councilman body in viral hepatitis).
•  No inflammation. An inflammatory response to microbes cannot occur in severely immunosuppressed individuals due to primary immunodeficiencies or acquired immunodeficient states (e.g., AIDS).