Introduction

• A pruritic, papular dermatitis, often of the dorsal lumbosacral region due to sensitization to flea salivary allergens.
• The most common cause of hypersensitive skin disease.
• Cause: Ctenocephalides felis, via allergens presented when flea bites.
• Signs: pruritus, tapeworm segments, flea bites on owner, pyotraumatic dermatitis, superficial pyoderma.
• Diagnosis: clinical signs, hematology, histopathology, serology.
• Treatment: flea control and possibly glucocorticoids.
• Prognosis: excellent, provided flea control maintained.

Pathogenesis

Predisposing factors

General

• Contact with fleas.

• Multi-animal households.
• Contact with free-ranging cats.
• History of exposure to the tapeworm Dipylidium caninum Dipylidium caninum , for which the flea is the intermediate host.

• Moving from a cold to a warm area, ie from a low exposure to fleas to high exposure.

Pathophysiology

• Hypersensitivity is triggered by the flea bite.
• Most dogs show an immediate-type hypersensitivity reaction, a wheal or papule develops within 15-30 min. This persists for up to 72 hours. Crusts develop secondarily due to self trauma.
• Many dogs also show a delayed reaction.
• Up to 30% of dogs only show a delayed reaction.
• Skin biopsies also show a cutaneous basophil reaction and late phase IgE-mediated reactions.
• Continually exposed dogs may become partially immunologically tolerant, but it is rare to achieve natural desensitization.

Diagnosis

Treatment

Prevention

Outcomes