JPC SYSTEMIC PATHOLOGY

INTEGUMENTARY SYSTEM

November 2022

I-P10

 

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: Segmentally affecting approximately 30% of the section, the canal lumen is filled with a dense coagulum of keratin, granular eosinophilic debris, and few aggregates of heterophils that surround numerous, often fragmented sections of arthropod adults and eggs. The arthropods are ovoid, approximately 350 X 500µm, and have a striated chitinous exoskeleton, jointed appendages, striated musculature, a haemocoel, a digestive and reproductive tract, and contain anisotropic, yellow‑brown, granular excretory material. The eggs are oval, 50 X 70µm, and have a 5‑8µm anisotropic shell and central basophilic, granular or eosinophilic flocculent material. The epidermis of the auditory meatus is hyperplastic with acanthosis and multifocal 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 ceruminous gland hyperplasia.

 

MORPHOLOGIC DIAGNOSIS:  External auditory meatus: Otitis externa, heterophilic, eosinophilic, and lymphoplasmacytic, focally extensive, 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

 

GENERAL: 

• Psoroptes cuniculi is a common parasite of the rabbit; lives on the skin surface (does not burrow), prefers the external ear canal, and feeds on lipids and exudate 
• Incites a marked inflammatory response along with a hypersensitivity reaction
• Not zoonotic and not a significant disease vector
• Not observed in wild rabbit populations
• Recent molecular analyses show that Psoroptes mites are conspecific and belong to one genus, P. equi

 

 

 

PATHOGENESIS: 

• Highly contagious, transmitted by direct and indirect contact 
• Complete life cycle occurs on the skin surface (about 3 weeks)
• Lesions likely due to a hypersensitivity reaction because the microscopic findings are consistent with an allergic pathogenesis, and lesions are often more severe than expected from local dermatitis alone

 

TYPICAL CLINICAL FINDINGS:

• Intensely pruritic dermatitis
• Head shaking & ear scratching
• Malodorous discharge   
• Painful ears; occasional drooping of ears
• Rarely there are cutaneous lesions in the perineal area, and other areas of the body

 

TYPICAL GROSS FINDINGS:

• Hyperemia, edema, and thickening of the pinna 
• White‑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:

• Dermis:  Superficial perivascular to interstitial dermatitis that is primarily eosinophilic, with fewer lymphocytes, other mononuclear cells, and mast cells; marked dermal edema
• Epidermis:  Spongiosis, exudate, or hyperplasia depending on chronicity
• P. cuniculi:  located on the surface or in the ear canal lumen

• Oval, approximately 350 X 500µm  
• Striated chitinous exoskeleton, jointed appendages, striated musculature, a haemocoel, a digestive and reproductive tract, and contain anisotropic, yellow‑brown granular excretory material
• Eggs are oval, 50 X 70µm, with a 5‑8µm anisotropic shell

 

ADDITIONAL DIAGNOSTIC TESTS:

• Ear swab or skin scraping: identifying feature is the long, three segmented pedicels with terminal caruncle
• Mite is large enough to be seen with the unaided eye

 

DIFFERENTIAL DIAGNOSIS:

• Notoedres cati (I-P08):  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 N. cati (380 um in length); large curved palpal hooks adjacent to piercing mouthparts; can transmit rabbit myxoma virus; non-burrowing mite
• Sarcoptes scabiei (I-P06):  Located within the stratum corneum rather than on the surface; burrowing mite
• Listrophorus gibbus:  High incidence of asymptomatic infections in domestic rabbits

 

COMPARATIVE PATHOLOGY:

Psoroptes spp. in other animals:

• P. cuniculi has also been reported in the ears of horses, goats, sheep, donkeys, mules, and other nondomestic species; in addition to rabbits, psoroptic mange a serious disease in cattle and sheep and to a lesser degree in horses and goats 
• Sheep: Psoroptic mange (“sheep scab”) caused by Psoroptes ovis; Reportable 

• Latent infection usually in the summer months with mites persisting in ears, infraorbital fossae, inguinal and perineal folds, and at the base of the horns
• In autumn, winter, or with host debilitation, parasite population increases and causes lesions, especially on the sides and withers
• Intense pruritus – affected sheep scratch, kick, rub, and tear out fleece
• Lesions:

• Start as vesicles and yellow-green pustules that rupture, ooze, and develop yellow crusts
• Lesions coalesce and can affect most of the body surface
• Fleece overlying the lesions is stained, moist, and matted

• Cattle:  Psoroptic mange (“body mange”); Reportable

• Clinical signs more severe in winter
• Lesions

• Papules, pustules, exudation, and excoriation
• Well defined areas of alopecia that can become lichenified and covered by gray crusts and scales

• Severe infections in calves may lead to mild anemia, lymphopenia, and marked neutropenia

• Goats: Psoroptic mange is uncommon

• Can be caused by P. cuniculi or P. ovis

• P. cuniculi found in the ear canal – may see no signs to head shaking, ear scratching, and crusted lesions on the inner pinna; may see more severe lesions in debilitated goats
• P. ovis can cause otitis externa, crusts, scaling, and alopecia or the head, face, pasterns and interdigital areas; pruritus is variable

• Horses: 

• P. cuniculi is often found in the ears

• Variable clinical signs from asymptomatic to distribution along the topline (ears, mane, and tail) with variable pruritus, head shyness, head shaking 
• Nonfollicular papules, crusts, excoriations, and alopecia

• P. ovis is rare

• Lesions include crusted papules with alopecia typically at the base of the mane, forelock, and tail

• Alpacas: psoroptic mange caused by P. communis var. auchinae 
• P. natalensis ‑ body mite of cattle, zebu, water buffalo, and horses in South Africa, South America, and Europe 
• P. cervinus ‑ ear canal mite of bighorn sheep and body mite of elk (wapiti) in the western United States

 

REFERENCES:

1. Barthold SW, Griffey SM, Percy DH. Pathology of Laboratory Rodents and Rabbits, 4th ed. Ames, IA: Iowa State University Press; 2016:303. 
2. Bowman DD. Arthropods. In: Georgis’ Parasitology for Veterinarians. 10^th ed. St. Louis, MO: Elsevier; 2014:70-1.
3. Delaney MA, Treuting PM, Rothenburger JL. Lagomorpha. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. St. Louis, MO: Elsevier; 2018:496.
4. Hess L, Tater K. Dermatologic Diseases. In: Quesenberry KE, Carptenter JW, eds. Ferrets, Rabbits, and Rodents: Clinical Medicine and Surgery. 3^rd ed. St. Louis, MO: Elsevier; 2012:237.
5. Jones MEB, Gasper DJ, Mitchell E. Bovidae, Antilocapridae, Giraffidae, Tragulidae, Hippopotamidae. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. St. Louis, MO: Elsevier; 2018:141.
6. Mauldin EA, Peters-Kennedy J. Integumentary Systems. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals, 6th ed. St. Louis, MO: Elsevier; 2016:505-6,675-6. 

Click the slide to view.

---