JPC SYSTEMIC PATHOLOGY
Signalment (JPC# 1747982): Chicken
HISTORY: Severe scaly, crusty lesions over the unfeathered portions of the legs
Histopathologic Description: Skin, stratum corneum: There is diffuse, abundant, orthokeratotic hyperkeratosis that contains multifocal oval to elongate, 35 to 100µm diameter clear spaces (mite tunnels). Mite tunnels frequently contain a cross or tangential section of an adult arthropod that is oval to elongate, 125 to 250µm in diameter, with an eosinophilic spiny chitinous exoskeleton, a hemocoel, striated muscle, and focal accumulations of deeply basophilic, 2µm nuclei. Mite tunnels contain scattered accumulations of brown, granular and globular material (mite feces). There are frequent intracorneal abscesses composed of viable and degenerate heterophils, eosinophilic cellular and karyorrhectic debris (necrosis), and occasional colonies of 1µm cocci and 1-2µm bacilli.
MORPHOLOGIC DIAGNOSIS: Skin, stratum corneum: Hyperkeratosis, orthokeratotic, diffuse, severe, with intracorneal mites and abscesses, chicken, avian.
ETIOLOGIC DIAGNOSIS: Cutaneous knemidocoptosis
CAUSE: Knemidocoptes (or Cnemidocoptes) mutans
· Mites of the genus Knemidocoptes, class Arachnida, order Acarina, family Knemidocoptidae
· K. mutans (“scaly leg mite”) is common in chickens, turkeys, and pheasants; typically older birds
· Affects non-feathered skin of the legs and occasionally the comb and wattles
· Entire life cycle is 2 weeks and is completed on/in the host's skin
· Eggs hatch into 6-legged larvae, molt into 8-legged nymphs, and molt 3 more times into adults
· Transmitted by direct contact
· The mites penetrate and bore holes in the epithelium
TYPICAL CLINICAL FINDINGS:
· Lesions are usually not pruritic
· Hyperplastic lesions on the cere may obstruct nasal openings; hyperplastic lesions on the legs may cause decreased range of motion
· Affected birds lose weight, cease egg production, and with severe disease, develop lameness
TYPICAL GROSS FINDINGS:
· Scaly, hyperkeratotic encrustations on the featherless areas of the face and legs; scale enlargement causes scales to “stick out”; hyperplastic lesions are discolored
· +/- lymphatic fluid leakage
· Hyperkeratosis may encroach on the beak or claws; if severely affected, beaks may become distorted and affected toes may slough
· Minute pores visible on the surface
TYPICAL LIGHT MICROSCOPIC FINDINGS:
· Mild acanthosis and orthokeratotic hyperkeratosis
· Epidermis has dorsal, uninterrupted striations
· Possible granulocytic, lymphocytic or histiocytic inflammation in underlying dermis
· Microscopic characteristics of mites include: Spiny chitinous exoskeleton, jointed appendages, mouthparts, striated muscle
· Females are approximately 0.5mm (500um) in diameter with short, spherical legs that lack pretarsi
· Males are smaller (than females) with longer legs with pretarsi and suckers
ADDITIONAL DIAGNOSTIC TESTS:
· Removal of affected scale may reveal mites on underside that are visible with a hand lens
· Carcinoma of the cere and beak (budgies)
· Passerine pox: intracytoplasmic inclusion bodies
· Papillomavirus: “tassel foot” in European goldfinches
· Neocheyletiella mites
· K. gallinae: Depluming mite of chickens, pigeons, pheasants, and geese
· K. pilae: Scaly face mite of parakeets, finches, and budgerigars
· K. jamaicensis: Golden thrush, canaries, red-winged blackbirds, common grackles, and American robins
· K. fossor: White-headed munia
· K. intermedius: Common raven
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