JPC SYSTEMIC PATHOLOGY
Signalment (JPC# 1754374): Unknown age and gender New Zealand white rabbit
HISTORY: A New Zealand white rabbit had crusting, erythema and intense pruritus in both ears.
MORPHOLOGIC DESCRIPTION: Haired skin, pinna: Diffusely, the epidermis is hyperplastic and covered by a thick, up to 3 mm crust consisting of loosely arranged lamellations of orthokeratotic and parakeratotic hyperkeratosis, entrapped degenerative inflammatory cells (serocellular crust), numerous arthropod adults and eggs and colonies of 1-2 µm diameter basophilic cocci. Mites are approximately 300 µm wide with a chitinous exoskeleton, few spines, striated musculature, jointed appendages, a digestive tract and ovary. Within the ovary is a large, developing egg characterized by numerous eosinophilic globules. Eggs are oval, 60 µm in diameter with a thin, 2-3 µm, pale eosinophilic shell and contain numerous 2-3 µm basophilic, round and variably-sized eosinophilic globules (yolk material). Diffusely, the epidermis is moderately hyperplastic with acanthosis, spongiosis and prominent anastomosing rete ridges. Multifocally, the underlying superficial dermis is infiltrated by low numbers of heterophils and macrophages. Diffusely, apocrine glands are ectatic.
MORPHOLOGIC DIAGNOSIS: Haired skin, pinna: Hyperkeratosis, orthokeratotic and parakeratotic, diffuse, severe, with mild heterophilic dermatitis, epidermal hyperplasia, and numerous superficial intracorneal adult mites and eggs, etiology consistent with Psoroptes cuniculi, New Zealand white rabbit, lagomorph.
ETIOLOGIC DIAGNOSIS: Psoroptic otitis externa; psoroptic otoascariasis
CAUSE: Psoroptes cuniculi
CONDITION: Ear canker; psoroptic mange; psoroptic scabies; ear mange
- cuniculi is a non-burrowing, obligate parasite that is the most common and costly ectoparasite disease of rabbits
- Other species: sheep, goats, deer, horses, donkeys, mules, antelope
- Psoroptic mites live on skin covered with hair or wool or in the ears
- In rabbits, the mites are almost exclusively found on the inner epithelial surface of the pinna (concha) of the ear
- Severe cases of ear canker have been reported to be fatal
- There is no zoonotic or vector significance associated with psoroptic mange
- All stages of the life cycle are completed on the skin surface in less than three weeks
- Highly contagious and transmitted by direct contact
- Initially, mites feed on lipids from the stratum corneum
- Inflammatory response to saliva or fecal material produces intense pruritus and secondary, self-inflicted trauma from scratching; mites then feed on released serum and hemoglobin produced in the epidermal crust
- Scratching spreads mites and predisposes animal to secondary bacterial infections on the face, neck and legs
TYPICAL CLINICAL FINDINGS:
- Intense pruritic dermatitis; head shaking; ear scratching
- Malodorous discharge
- Ears are painful
- Occasional lesions on the face, head, neck, limbs, abdomen and back
TYPICAL GROSS FINDINGS:
- Hyperemia and edema of the pinna, may be ulcerated
- Tan to brown crusty exudate along the inside of the pinna often filling the ear canal
- Crusts form on the inner pinna and removal of the debris and exudate reveals moist, erythematous skin
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Marked parakeratotic to orthrokeratotic hyperkeratosis with numerous mites and eggs present in a keratin crust
- Superficial dermatitis with eosinophils, mast cells and lymphocytes
- Mites are large and oval shaped (400 x 700 um) with a chitinous exoskeleton, jointed appendages, striated muscle, simple intestine with cuboidal or columnar epithelium and females have ova containing brightly eosinophilic globular material (yolk/developing eggs)
ADDITIONAL DIAGNOSTIC TESTS:
- Ear swab or skin scraping
- Mite is large enough to be seen with the unaided eye
- Single most important characteristic is long, 3-segmented pedicels with terminal caruncle
- Notoedres cati: Smaller size (400 um in length); rear legs that do not extend beyond the margin of the body; sucker on a short unsegmented stalk; burrowing mite
- Cheyletiella parasitovorax (fur mite): Smaller than cati (380 um in length); large curved palpal hooks adjacent to piercing mouthparts; can transmit rabbit myxoma virus
- Sarcoptes scabiei: Located within the stratum corneum rather than on the surface
- Leporacarus gibbus: High incidence of asymptomatic infections in domestic rabbits
- Trichophyton mentagrophytes: Dermatophyte in rabbits; hyperkeratotic dermatitis
- Horses frequently effected; main distribution includes ears, mane, and tail; less commonly the dorsal trunk
- Usually asymptomatic
- Notoedres cati: Scabies of the cat; effects the head and ears (particularly the margin); causes severe pruritus and is highly contagious
- Other psoroptic mites and their primary hosts include:
- ovis ‑ body mite of sheep (one of the worst parasites of sheep); also affects cattle; reportable disease in sheep and cattle in most states
- equi ‑ body mite of horses (indistinguishable from P. cuniculi)
- natalensis ‑ body mite of cattle (P. ovis also reported)
- cervinus ‑ ear canal mite of bighorn sheep
- hippous ‑ ear canal mite of horses
- Knemidocoptes mutans (chickens) or pilae (budgerigar) – proliferative and hyperkeratotic dermatitis of the legs and beak/face
- Barthold SW, Griffey SM, Percy DH. Pathology of Laboratory Rodents and Rabbits. 4th ed. Ames, IA: John Wiley & Sons; 2016:303.
- Bowman DD. In: Bowman DD, ed. Georgis’ Parasitology for Veterinarians. 10th ed. St. Louis, MO: Saunders Elsevier; 2013:392.
- Gardiner CH, Poynton SL. Morphological characteristics of arthropods in tissue section. In: Gardiner CH, Poynton SL, eds. An Atlas of Metazoan Parasites in Animal Tissues. Washington, DC: Armed Forces Institute of Pathology; 1999:56-58.
- Hargis AM, Myers S. Integumentary system. In: Zachary JF, Pathologic basis of Veterinary Disease. 6th ed. St. Louis, MO: Mosby Inc; 2016:1247.
- Mauldin EA, Peters-Kennedy J. Integumentary Systems. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. 6th ed. Philadelphia, PA: Elsevier; 2016:675-676.
- Miller WH, Griffin CE, Campbell KL. Dermatoses of exotic small mammals. In: Miller WH, Griffin CE, Campbell KL, eds. Muller and Kirk's Small Animal Dermatology. 7th ed. St. Louis, MO: Elsevier Mosby; 2013:858.