JPC SYSTEMIC PATHOLOGY
Signalment (JPC #1618600): Rabbit, age and breed not specified
HISTORY: This rabbit presented with crusty ears and a head tilt.
HISTOPATHOLOGIC DESCRIPTION: External auditory meatus: A large segment of the canal lumen is filled with a dense coagulum of keratin, granular eosinophilic debris, and few aggregates of heterophils, which surround numerous, often fragmented, sections of arthropod adults and eggs. The arthropods are oval and measure approximately 350 X 500 um. They have a striated chitinous exoskeleton, jointed appendages, striated musculature, a haemocoel, a digestive and reproductive tract, and contain an anisotropic, yellowish‑brown granular excretory material. The eggs are oval and measure 50 X 70 um, with a 5‑8 um anisotropic shell. The epidermis of the auditory meatus is hyperplastic and multifocally forms rete ridges. There is multifocal parakeratotic and orthokeratotic hyperkeratosis. Moderate numbers of plasma cells, lymphocytes, fewer heterophils, eosinophils, and macrophages diffusely infiltrate the dermis. Lymphocytes and heterophils occasionally transmigrate the epidermis. There is focal sebaceous gland hyperplasia.
MORPHOLOGIC DIAGNOSIS: External auditory meatus: Otitis externa, heterophilic, eosinophilic and lymphoplasmacytic, diffuse, moderate, with acanthosis, marked hyperkeratosis, and intraluminal adult mites and eggs, rabbit, lagomorph.
ETIOLOGIC DIAGNOSIS: Psoroptic otitis
ETIOLOGY: Psoroptes cuniculi
CONDITION: Psoroptic mange
CONDITION SYNONYMS: Ear canker; ear mange; psoroptic scabies
- Psoroptes cuniculi is the most common ectoparasite of the rabbit; lives on the skin surface (does not burrow), prefers the external ear canal, and feeds on lipids and exudate
- Psoroptic mange is also a serious disease in cattle and sheep and to a lesser degree in horses and goats
- Incites a marked inflammatory response and possibly a hypersensitivity reaction
- No zoonotic or vector significance associated with psoroptic mange
- Highly contagious and is transmitted by direct contact
- As exudate accumulates, a crust composed of serum, desquamated epithelial cells, inflammatory cells, mites and mite feces is formed
- Mites devitalize skin as the parasites move to the periphery of the lesion
- Pruritus, self-trauma, and secondary bacterial infection are common 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 of the pinna
- Whitish‑gray crusty exudate at the bottom of the concha
- Crusts form on the inner pinna, and removal of the debris and exudate reveals moist, erythematous skin
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Superficial perivascular dermatitis
- Spongiosis, exudate, or hyperplasia depending on chronicity
- Primarily eosinophilic
- Marked dermal edema
- Mites found in crusts or ear canal lumen: oval, 350 X 500 um, flattened dorsoventrally, with a striated chitinous exoskeleton, jointed appendages, striated musculature, a haemocoel, a digestive and reproductive tract; +/- eggs: oval, 50 X 70 um, with a 5‑8 um anisotropic shell
ADDITIONAL DIAGNOSTIC TESTS:
- Ear swab or skin scraping
- Mite is large enough to be seen with the unaided eye
- Identifying feature is the long 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; non-burrowing mite
- Sarcoptes scabiei: Located within the stratum corneum rather than on the surface; burrowing mite
- Listrophorus gibbus: High incidence of asymptomatic infections in domestic rabbits
- cuniculi has also been reported in the ears of horses, goats, sheep, donkeys, mules, and deer
- 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 (last reported in U.S. in 1970)
- 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 (usually affected by P. scabei)
- hippous ‑ ear canal mite of horses
- Barthold SW, Griffey SM, Percy DH. Pathology of Laboratory Rodents and Rabbits, 4th ed. Ames, IA: Iowa State University Press; 2016:303.
- Bleich VC, Johnson CK, Torres SG, Davis JH, Ramsey JM, Villepique JT, Gonzzlea BJ. Psoroptes infestation and treatment in an isolated population of bighorn sheep (Ovis canadensis), J Zoo Wildl Med, 2015;461(3): 491-7.
- Ginn P, Mansell J, Rakich P. Skin and appendages. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals, 5th ed. Philadelphia, Pennsylvania: Elsevier; 2007:721-722.
- Kraus AL. Arthropod parasites. In: Weisbroth SH, Flatt RE, Kraus AL, eds. The Biology of the Laboratory Rabbit, New York, NY: Academic Press Inc; 1974:288-290.
- Mauldin EA, Peters-Kennedy J. Integumentary Systems. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals, 6th ed. Philadelphia, Pennsylvania: Elsevier; 2016:656-657.
- Scott DW, Miller WH, Griffin CE. Muller and Kirk's Small Animal Dermatology, 6th ed. Philadelphia, PA: WB Saunders Company; 2001:1448-1449.