October 2019

I-P09 (NP)


Signalment (JPC# 1757055): Flying squirrel (Glaucomys sabrinus)


HISTORY: Cutaneous mass located beneath the ear


HISTOPATHOLOGIC DESCRIPTION: Haired skin: Diffusely hair follicles are markedly expanded and occasionally disrupted by numerous cross and tangential sections of viable and degenerate adult arthropods and eggs. Adults are 80 to 100 um in diameter, have a smooth chitinous exoskeleton, jointed appendages, bands of striated muscle, a reproductive tract that often contains abundant 4um basophilic bodies, and occasionally an intact digestive tract. Mite eggs are 40 um x 60 um with a thin, eosinophilic shell. Admixed with arthropods are abundant neutrophils and fewer eosinophils and macrophages, keratin, and cellular debris. The follicular epithelium is either hyperplastic, characterized by acanthosis with cells piling up to 15 cells thick, with multifocal intracellular and intercellular edema and multifocal orthokeratotic hyperkeratosis, or it is occasionally is attenuated. Diffusely expanding the dermis are many lymphocytes, plasma cells, macrophages, and plump fibroblasts (dermatitis); these infiltrates are especially dense and are admixed with neutrophils, eosinophils, hemorrhage, fibrin, and edema in areas of follicular rupture (furunculosis).


MORPHOLOGIC DIAGNOSIS: Haired skin: Folliculitis and furunculosis, eosinophilic and neutrophilic, chronic, diffuse, moderate, with marked follicular ectasia, hyperkeratosis, and intrafollicular arthropods, flying squirrel (Glaucomys sabrinus), rodent.


ETIOLOGIC DIAGNOSIS: Epidermal acariasis


CAUSE: Psorergates simplex



·      Family Psorergatidae

·      Follicular mite of the mouse

·      Rare in laboratory mice; common in wild/pet mice



·      The life cycle is unknown but believed to be completed on the host because all life stages can be present in a single hair follicle

·      Transmission is by direct contact

·      Infection results in dermal pouches

·      Self-mutilation with secondary infection can occur



·      Mange-like condition; yellow crusting

·      Head, shoulders, lumbar area

·      Comedone formation

·      White nodules or pockets on the visceral side of the dermis



·      Mites present in the hair follicle

·      Cystic follicles with keratosis

·      Variable degrees of inflammation

·      Mite is round, 90-150um in length; adults have 4 legs with 5 segments; larvae have 3; medial spine on each femur; ventral anus with tubercle on each side



·      Demodex musculi: Very uncommon, located in the superficial dermis and hair follicle openings

·      Myobia musculi: Most common fur mite; epidermal hyperplasia; asymptomatic to severe inflammation (hypersensitivity)



·      Sheep: (Psorobia ovis) Sheep itch mite; pruritus and alopecia; fleece damage; chronic; does not affect young lambs under 6 months of age; eradicated from the United States

·      Cattle: (Psorobia bos) Nonpathogenic mite of cattle; nonpruritic, scaling, and alopecia on head, neck, rump, back, and shoulders

·      NHP: (Psororgates mange) Case in a Siamang that caused dry flaky skin, multifocal alopecia, and pruritus



1.    Barthold SW, Griffey SM, Percy DH. Pathology of Laboratory Rabbits and Rodents. 4th ed. Ames, IA: Blackwell Publishing Professional; 2016:87.

2.    Bowman DD. In: Georgis' Parasitology for Veterinarians. 10th ed. St Louis, MO: Elsevier Inc; 2014:76.

3.    Flynn R. Parasites of Laboratory Animals. Ames, IA: Iowa State University Press; 1973:441-444.

4.    Lowensinte LJ, McManamon R, Terio KA. Apes. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. Cambridge, MA: Elsevier; 2018: 402.

5.    Mauldin EA, Peters-Kennedy J. Integumentary system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 1. 6th ed. St. Louis, MO: Elsevier Inc; 2016:678.

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