DISEASE SYNDROMES

In budgerigars, canaries, and other small birds, the mites cause scaly, crusty, gray to tan lesions on unfeathered skin, especially the legs, feet, and around the beak, eyelids, and periocular areas. Mites directly penetrate feather follicles, skin folds, and the epidermis, causing pouchlike cavities and producing secondary pouches, resulting in a honeycombed lesion. Usually, the birds are not noticeably pruritic. In severe cases, the beak, feet, and toes may become malformed. The mites also affect passerines, poultry, and raptors.

Budgerigars

Figures 2A & 2B

Lesions usually start at the commissures of the beak and have a honeycomb appearance. In the early stages, lesions are confined to the cere and the base of the beak (Figures 2A & 2B). Make sure to rule out brown hypertrophy of the cere in female birds. Brown hypertrophy typically has crusty layers, similar to the shell of an oyster, without the honeycomb tunnels that are distinctive of K. pilae mites. An important and unusual differential diagnosis is carcinoma of the cere and beak.

As the disease progresses in budgerigars, whitish, scaly, epithelial proliferations develop, forming raised, thickened, yellowish, craterlike encrustations that sometimes cause nasal obstruction. Mites burrowing into the germinal layer of the beak can ultimately cause distorted growth, especially in the upper mandible.

Lesions similar to those described above may also occur on the legs, feet, and skin of other parts of the body (especially around the eyes and vent). In chronic cases affecting the face, horny protuberances may develop. Severe pruritus is seldom observed.

Budgerigars with leg bands may develop necrosis of the limb distal to the band as the lesions grow and press into the band, constricting the leg's blood vessels. Podoacariasis (or more specifically podoknemidocoptiasis) is more common in canaries,⁴ in which the legs and feet exhibit yellow-white, tassel-like projections. Serous exudate is produced in response to the tunneling mites, which hardens and lifts the scales on the feet and legs, causing reduced flexibility. When the feet are involved, lameness may be seen in advanced cases because of ankylosis of the hock and other joints, necrosis and sloughing of toes, swollen nail beds, and twisted nails.

Because disease can be seen in inbred birds, a genetic predisposition or selective immunosuppression has been suggested but not proved.

Other psittacines

In Alexandrine parakeets (Psittacula eupatria), the mites may cause itching and feather loss, but no scaly lesions.⁴ Knemidocoptes pilae has been associated with feather picking and feather loss around the neck, keel and ventral abdomen, and dorsum.⁴ Postinfection feather loss and eyelid damage may result. Early or mild lesions caused by Knemidocoptes species may resemble lesions caused by vitamin A deficiency; however, chronic or advanced knemidocoptiasis lesions are much larger and more extensive than those associated with vitamin A deficiency.

Occasionally, in other parrot species, knemidocoptiasis is associated with concurrent psittacine circovirus infection or other immunosuppressive diseases (mycobacteriosis). In macaws with knemidocoptiasis, pruritus of the hocks and feet occurs and may lead to self-mutilation.⁸

An unclassified Knemidocoptes species (not K. pilae or Neoknemidocoptes laevis) has been found in the feathers of red-fronted parakeets (Cyanoramphus novaezelandiae).¹⁶ Birds exhibit generalized patchy feather loss with hyperemic skin on the head, neck, and cheeks. Mites are found embedded in the thickened calamus portion of the shaft of affected feathers. Mites have been identified in adult and immature birds, but only the adults develop clinical signs.¹⁶