Canaries and finches
The earliest reports of knemidocoptiasis in canaries and finches attributed infection to K. mutans, while later reports described disease due to K. pilae.4,8 Recent investigations have identified K. jamaicensis in these birds and, thus, may actually represent taxonomic reclassification.12
Figures 3A & 3B
In canaries, lesions are usually confined to the legs and digits and begin as crusts that form on the plantar surfaces of
the feet and gradually thicken. Marked lameness results, and perching becomes difficult. Birds with leg bands are in danger
of serious tarsometatarsal constriction. Knemidocoptes jamaicensis is also seen in wild finches and sparrows.12
Differential diagnoses include infestation with other mite species, dermatophytosis, and poxvirus or papillomavirus infection,
with the latter probably being the most common. Proliferation of scales on the feet seen in aging passerine birds is distinctly
different from the dramatic tassel foot changes seen with knemidocoptiasis (Figures 3A-4C). Keep in mind that tassel foot in European goldfinches (Carduelis carduelis) is primarily due to a papillomavirus,17 but Knemidocoptes species infestation is an important differential diagnosis. Dual infection can occur.
A retrospective examination of banding records in Hong Kong showed infestation in Eurasian tree sparrows (Passer montanus), black-faced buntings (Emberiza spodocephala), spotted doves (Streptopelia chinensis), and Eastern great reed warblers (Acrocephalus species). Adult tree sparrows were affected more often than juveniles were, and males were affected more commonly than females
were. Lesions on juveniles usually involved the feet, while lesions on adults were found on the legs and beak.18 Robins may lose all or part of their feet and digits.12 Most of the advanced, chronic lesions are pathognomonic, but early, acute lesions resemble or are indistinguishable from
the wartlike proliferative skin lesions of avian poxvirus.
Knemidocoptes mutans primarily affects the unfeathered skin of the legs in chickens and, occasionally, the comb and wattles. Disease is more common
in older birds; affected chickens exhibit severe weight loss and decreased egg production.4,19
Knemidocoptes mutans has also recently been found to cause digit necrosis.10 Birds with knemidocoptiasis from K. mutans are predisposed to secondary bacterial and fungal pyoderma. Compared with chickens, Knemidocoptes species infestation in turkeys is relatively rare.20
Figures 5A & 5B
Knemidocoptes gallinae causes intense irritation, resulting in affected birds pulling out their body feathers. Weight loss and reduced egg production
Knemidocoptes mutans was first identified in great horned owls (Bubo virginianus) exhibiting bilateral proliferative papillary hyperkeratosis of the feet.21 Examples of the lesions and mites are seen in Figures 5A-6B. Knemidocoptes mutans has subsequently been found in snowy owls (Nyctea scandiaca) and several accipiters such as goshawks and sparrowhawks. A Swainson's hawk (Buteo swainsoni) had severe crusting of the skin on the medial thigh and ventral body.22 This case was unusual in that the Knemidocoptes species infestation appeared to be localized to the feathered regions of the body. The stress of captivity may induce disease
in affected individuals.
Figures 6A & 6B