Final answer:
Flea allergic dermatitis (FAD) is triggered by hypersensitive reactions to substances in flea saliva, causing allergic symptoms similar to eczema. The saliva contains a complex mix of allergenic proteins and peptides that lead to inflammation and itching when an animal is sensitized to them.
Step-by-step explanation:
Flea allergic dermatitis (FAD) is a common and severe form of allergy in pets that is caused by hypersensitivity to flea saliva. Although not precisely determined, flea saliva is known to contain a mixture of many substances such as proteins, peptides, and amino acids that can trigger an intense allergic reaction in sensitive animals. This reaction, a type I hypersensitivity, involves the immune system producing IgE antibodies in response to the first exposure to the allergen. Upon subsequent exposure, these antibodies lead to an allergic reaction by causing mast cells to release histamine and other mediators that result in inflammation and symptoms such as itching and rashes, similar to eczema in humans. Treatment for FAD typically includes controlling flea populations, managing symptoms with anti-inflammatory drugs, and in severe cases, immunosuppressants.