October 2019

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



·      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



·      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



·      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



·      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



·      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

·      Dermatophytes



·      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



1.    Abdul-Aziz T, Fletcher OJ, Barnes HJ. Avian Histopathology. Jacksonville, FL: American Association of Avian Pathologists; 2016:621, 637.

2.    Abdul-Aziz T, Barnes HJ. Avian Histopathology Text and Atlas. Jacksonville, FL: American Association of Avian Pathologists; 2018:196.

3.    Fitz-Coy SH. Parasitic diseases. In: Boulianne M, ed. Avian Disease Manual. 7th ed. Jacksonville, FL: OmniPress; 2013:154.

4.    Gaudioso JM, LaPointe DA, Hart PJ. Knemidokoptic mange in Hawai’i Amakihi (Hemignathus virens) on the island of Hawai’i. J Wildl Dis. 2009;45(2):497-501.

5.    Hinkle NC, Corrigan RM. External parasites and poultry pests. In: Swayne DE, Glisson JR, McDougald LR, Nolan LK, Suarez DL, Nair V, eds. Diseases of Poultry. 13th ed. Ames, Iowa: Wiley Blackwell; 2013:1101-2.

6.    Janra MN, Herwina H, Febria FA, Darras K, Mulyani YA. Knemidokoptiasis in a wild bird, the little spiderhunter, (Arachnothera longirostra cinereicollis), in Sumatra, Indonesia. J Wildl Dis. 2019;55(2):509-511.

7.    Mainka SA, Melville DS, Galsworthy A, Black SR. Knemidocoptes sp. on wild passerines at the Mai Po nature reserve, Hong Kong. J Wildl Dis. 1994; 30(2):254-6.

8.    Pence DB, Cole RA, Brugger KE, Fischer JR. Epizootic podoknemodokoptiasis in American robins. J Wildl Dis. 1999;35(1):1-7.

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