Demodicosis in a Cat

 Greta is a 1 year old female spayed domestic short hair, presented by her caretaker with a chronic history of overgrooming.

Andrew Simpson, DVM, DACVD

VCA Aurora Animal Hospital, Aurora, IL

Subjective

She was found as a stray in the suburbs of Illinois at approximately 12 weeks of age. Shortly after being found, she developed generalized pruritus manifested as excessively licking the lateral aspects of her thorax and hips, ventral abdomen, medial thighs, and distal extremities in addition to scratching her head and neck. There was no response to a subcutaneous injection of dexamethasone SP (0.1 mg/kg).

She was fed a balanced, commercial dry cat food and up to date on vaccines and deworming. General physical examination showed no abnormalities, appearing to be otherwise healthy. There was no response to once monthly topical application of selamectin for the previous 3 months.  She was kept isolated from other animals in the shelter.

The animal shelter conducted an 8-week restrictive diet trial consisting of a prescription veterinary diet (rabbit and pea) with no clinical response in her pruritus. As environmental allergies were suspected at this point, a serum allergy test was performed which showed positive reactions to the following environmental allergens:

Multiple repositol injections (methylprednisolone acetate) were given subcutaneously (3.6 mg/kg) every 6 weeks by the animal shelter. This initially reduced the pruritus at first, however, the injections appeared to only last for 2 weeks as time lapsed.

Given the lack of response to treatment at this point, referral to a veterinary dermatologist was pursued.

Objective

Body Weight: 5.5 kg

Temperature: 100.3 F

Pulse: 180 bpm

Respiratory: 40 bpm

BAR

• General physical examination findings: no oral lesions present, lymph nodes palpated within normal limits, the abdomen was soft and non-painful on palpation, with an empty bladder. Thoracic auscultation revealed no murmurs or arrhythmias; lungs ausculted clearly in all fields.
• Dermatologic Examination: severe, diffuse alopecia affecting the lateral shoulders, lateral chest, lateral abdomen, hips, medial thighs, ventral chest, ventral abdomen, and dorsal head. Mild to moderate erythema was present on the ventral abdomen. Otoscopy showed no debris, masses, or inflammation. The tympanic membranes appeared within normal limits.

Differential diagnoses for generalized alopecia and pruritus consisted of: environmental allergies (feline atopic skin syndrome), flea bite hypersensitivity, other external parasites (i.e. Demodex spp, Cheyletiella, Notoedres, Lynxacarus), and dermatophytosis. Psychogenic alopecia and hyperthyroidism were not considered main differential diagnoses due to the previous response to injectable corticosteroids prior to referral.

Diagnostics

• Superficial skin scrapings: multiple short-bodied mites consistent with Demodex gatoi were found.

• Tape cytology of the skin: no bacteria or Malassezia organisms noted
• Dermatophyte test medium: no growth of dermatophytes after 3 weeks

Assessment

The presence of mites morphologically consistent with Demodex gatoi confirmed a diagnosis of demodicosis.

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