Flea allergic dermatitis

5 Flea allergic dermatitis




INITIAL PRESENTATION


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



INTRODUCTION


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 Haemoplasma spp.




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.



CASE HISTORY


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 fipronil and most recently selamectin.

• The three in-contact cats were unaffected and were intermittently treated for fleas 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.


CLINICAL EXAMINATION


A whole range of clinical signs, from primary lesions such as papules and pustules, to severe secondary hyperpigmentation, lichenification and fibropruritic nodules are seen, depending on the chronicity of the disease. Self-induced 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).

• Erythema, alopecia and papular rash on the ventrum and inguinal region (Fig. 5.3).

• The periocular skin was hyperpigmented, lichenified and erythematous, with evidence of excoriations (Fig. 5.4).

• Both the pinnae and vertical ear canals were erythematous.

• Erythema, self-induced alopecia, crusting and hyperpigmentation involving all four feet (Fig. 5.5).

• The skin was malodorous and greasy to the touch.

• The peripheral lymph nodes were not enlarged and the other physical parameters were within normal limits.

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Figure 5.1 Erythema, papules and self-induced alopecia on the dorsum.


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Figure 5.2 Lateral aspect on the trunk.


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Figure 5.3 Papular dermatitis in inguinal regions.


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Figure 5.4 Periocular dermatitis.


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Figure 5.5 Erythema and self-induced alopecia extending to the distal aspect of the leg.




DIFFERENTIAL DIAGNOSES


In this case, given the clinical signs and the distribution of the lesions, there was evidence for more than one type of hypersensitivity. The facial, pedal and ventral distribution suggested atopic dermatitis, and that affecting the dorsal aspect, flea allergy dermatitis. A concurrent adverse food reaction could also have been contributing to the pruritus. The other differentials included:


• Staphylococcal pyoderma

• Malasseziosis

• Sarcoptic mange

• Demodicosis

• Otodectes hypersensitivity

• Dermatophytosis

• Adverse drug reaction.


CASE WORK-UP


A number of the differential diagnoses were ruled out with simple in-house tests:


• Skin scrapes were performed to rule out demodicosis and to look for sarcoptic mange. Negative skin scrapes do not definitively rule out sarcoptic mange and therefore a Sarcoptes IgG ELISA test was performed, which was also negative.

• There was no fungal growth after 3 weeks of culturing of a sample obtained by the MacKenzie toothbrush technique.

• Tape-strip samples, obtained from crusted lesions, revealed clumps of coccoid bacteria, neutrophils and keratinocytes.

• Staphylococcus intermedius was isolated from a swab submitted for bacterial culture, which was sensitive to amoxicillin/clavulanate, cefalexin, enrofloxacin, marbofloxacin, clindamycin and trimethoprim/sulphonamide. It was resistant to amoxicillin, penicillin and tetracycline.

• Coat brushings failed to demonstrate any fleas or flea faeces.

In addition to atopic dermatitis, the history, clinical signs and distribution of lesions were suggestive of flea allergic dermatitis. The diagnosis of flea allergy dermatitis is supported with additional tests and with response to aggressive flea control. The simplest test is the demonstration of fleas or flea faeces using a flea comb; however, about a third of animals fail to show any evidence of fleas, for various reasons:


• Self-grooming removes the fleas and flea faeces

• Owners often groom or bath the animals before coming into the practice

• Intermittent flea control reduces the numbers, making it difficult to find them

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Sep 3, 2016 | Posted by in SMALL ANIMAL | Comments Off on Flea allergic dermatitis

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