Final answer:
Hypersensitivity involves an exaggerated immune reaction to allergens, with flea allergic dermatitis (FAD) being a Type I hypersensitivity from flea bites. Diagnosing hypersensitivities typically involves skin tests that display a wheal and flare response upon allergen exposure.
Step-by-step explanation:
Hypersensitivity refers to an excessive immune response to a substance, or allergen, that is typically considered harmless. The most common type, Type I hypersensitivity, is also known as an allergy, with reactions that can vary from mild symptoms to severe anaphylactic shock. Flea allergic dermatitis (FAD) is an example of Type I hypersensitivity in which the affected individual reacts to flea saliva injected into the skin during a bite.
Type I hypersensitivity reactions are mediated by IgE antibodies, which, upon initial exposure to an allergen, sensitize the mast cells. When the same allergen is encountered again, these IgE antibodies signal the mast cells to release histamine and other inflammatory mediators, leading to allergic symptoms. Common diagnostic methods for identifying Type I hypersensitivities include the pr_ick-puncture skin test (PPST) and the intradermal test, which detect allergen-specific reactions resulting in a wheal and flare response.
Fleas, when they bite, inject their saliva into the epidermis of their host, which can contain several allergenic components. This can result in a robust allergic response in sensitized individuals, leading to FAD, characterized by intense itching, inflammation, and secondary skin infections. The management of FAD includes controlling flea populations on pets and in environments, as well as possibly using medications to control the hypersensitivity response.