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.
CASE PRESENTING SIGNS
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
- 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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