November 2022

I-P12 (NP)

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

COMMON NAME: Scaly leg mite

GENERAL DISCUSSION:

Mites of the genus Knemidocoptes, class Arachnida, order Acarina, family Knemidocoptidae
Knemidokoptes spp. are a group of closely related mites that live in non-feathered skin, primarily shanks, feet, and cere (base of the beak); some mites in the group affect the beak; feathered regions can be affected in severe cases
K. mutans (“scaly leg mite”) is common in chickens, turkeys, and pheasants; typically older birds
Knemidokoptes spp. are found in budgerigars, canaries, passerines, and occasionally other species of companion birds
Mites may live superficial or deep

PATHOGENESIS:

Mites burrow in epidermis, causing scales to lift and become loosened and legs to become thickened and deformed
Spread through the flock is slow
The cere is soft with a honeycomb texture and mites are abundant in this area

TYPICAL CLINICAL FINDINGS:

Lameness due to deformation of legs and feet
Swelling and deformation of the scale, often periocular and of the shanks/feet

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
Skin is thickened and hyperkeratotoic with white, powdery, exfoliating crusts
Hyperkeratosis, if severe, may cause beaks may become distorted and affected toes to slough
Crusts and/or scales on the periorbital skin

TYPICAL LIGHT MICROSCOPIC FINDINGS:

Marked compact orthokeratotic hyperkeratosis, and acanthosis with intracorneal mites
Pleocellular inflammatory reaction
Microscopic characteristics of mites include: Spiny chitinous exoskeleton, hemocoel, jointed appendages, mouthparts, striated muscle
- Females are approximately 0.5mm in diameter with short, spherical legs that lack pretarsi
- Males are much smaller than females and have longer legs with pretarsi

ADDITIONAL DIAGNOSTIC TESTS:

Mites are abundant in scrapings of the base of the beak; with magnification may be able to see mites moving
Removal of affected scale may reveal mites on underside that are visible with a hand lens

DIFFERENTIAL DIAGNOSIS:

Gross:

Carcinoma of the cere and beak (budgies)
Passerine pox: intracytoplasmic inclusion bodies
Papillomavirus: “tassel foot” in European goldfinches

Microscopic:

Neocheyletiella mites
Dermatophytes

COMPARATIVE PATHOLOGY:

Red mite (Dermanyssus gallinae): Feed on poultry (blood) at night, but hide in environment during day; heavy infestations can result in anemia and death; can transmit Pasturella multocida (Fowl Cholera) and Brachyspira (Avian Spirochetosis); also rarely infect horses, cattle, dogs, and cats
Northern fowl mite (Ornithonyssus sylviarum): most significant poultry ectoparasite; bloodsuckers that stay on the bird, particularly around the vent; cause dermatitis with scabbing and cracked skin; transmit Fowl Pox, Newcastle disease (paramyxovirus), ornithosis (Chlamydia psittaci), and certain encephalitides; also rarely infect horses
Depluming mite (Knemidokoptes gallinae): Chickens, pheasants and pigeons; burrow into the basal shaft of feathers, causing pruritus and loss of feathers
Subcutaneous mite (Laminosioptes cysticola): causes infection in older, emaciated poultry kept in unsanitary conditions; production loss (I-P11)

REFERENCES:

Bowman DD. Arthropods. Georgis’ Parasitology for Veterinarians. St. Louis, MO: Elsevier; 2021:69.
Fitz-Coy SH. Parasitic diseases. In: Boulianne M, ed. Avian Disease Manual. 8th ed. Jacksonville, FL: OmniPress; 2019:128.
Schmidt RE, Reavill DR, Phalen DN. Gastrointestinal system, Integument, Special Sense Organs. Pathology of Pet and Aviary Birds. Ames, Iowa: John Wiley and Sons, Inc.; 2015:58, 239, 264.
Trupkiewicz J, Garner MM, Juan-Salles C. Passeriformes, Caprimulgiformes, Coraciiformes, Piciformes, Bucerotiformes, and Apodiformes. In Terio KA, McAloose D, St. Leger J eds. Pathology of Wildlife and Zoo Animals. Cambridge, MA: Elsevier; 2018:819.