Small Animal Dermatology - Chapter 5


Small Animal Dermatology is part of the 'Saunders solutions in veterinery practice' series published by Elsevier.

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Chapter 5 - Flea allergic dermatitis

Chapter 5 - Flea allergic dermatitis

Pruritus with papules, erythema, scaling and hyperpigmentation in a Jack Russell terrier.

In some parts of the world, flea allergic dermatitis (FAD) is the most common allergic disease and a major cause of pruritus in dogs and cats. In other parts it is a significant problem only at certain times of the year. Although allergic dermatitis is the main condition associated with fleas, a distinction between pruritus resulting from severe flea infestation and a hypersensitivity response should be made. In very young puppies and kittens, severe flea infestations provoke varying degree of pruritus, but more often patients exhibit signs of weakness, lethargy and anaemia. Fleas are also vectors of infectious organisms such as Bartonella, Rickettsia felis and Haemoplasmaspp.

A 6-year-old female Jack Russell terrier was presented with severe erythema, pruritus, papules, alopecia and hyperpigmentation affecting the dorsum, feet, periocular skin, ears and muzzle.


This varies between individuals but most pruritic dogs are presented with a history of pruritus and varying lesions affecting the lumbo-sacral region. As the flea life cycle is affected by environmental factors such as temperature and humidity, seasonal exacerbations may occur. Often flea control is only intermittently used and in-contact animals, especially cats, are inadequately treated. The history in this particular case was long and complex. The most relevant parts were:

  • Long-standing history of non-seasonal pruritus involving face, feet and ventrum, and more recently the dorsal trunk had also become involved.
  • The pruritus has been managed with intermittent methylprednisolone acetate injections, but these had become ineffective with severe deterioration in the dog's clinical condition.
  • The dog was mainly fed on a commercial pet food and more recently an 8-week diet trial with a prescription hydrolysed hypoallergenic diet had failed to resolve the pruritus or the clinical lesions.
  • The indoor environment was fully carpeted and the dog normally slept under the owner's bed.
  • Outdoor access was to the garden only.
  • Previous flea control had been intermittent, using fi pronil and most recently selamectin.
  • The three in-contact cats were unaffected and were intermittently treated for fl eas with a pet shop product.

The owner had seen fleas on one of the cats some weeks back and had treated it with proprietary flea product from the supermarket.

A whole range of clinical signs, from primary lesions such as papules and pustules, to severe secondary hyperpigmentation, lichenifi cation and fi bropruritic nodules are seen, depending on the chronicity of the disease. Selfinduced alopecia due to over-grooming and secondary bacterial infection is often seen in affected dogs. Atopic dogs are predisposed to flea bite hypersensitivity, even those that have been well managed. Some dogs will present with pyotraumatic dermatitis on the rump, or at other sites.


The clinical findings in this case were:

  • Severe generalized erythema with papules, follicular papules and crusted patches on the trunk (Figs 5.1 and 5.2).


Chapter 5 - continued

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