Many types of mites can inhabit birds' feathers, quills, skin, subcutaneous tissue, and respiratory tracts.1,2 Mites of the genus Knemidocoptes, which parasitize only birds, are burrowing mites that cause disfiguring dermatitis and thickening of the skin. If the mites are not identified and eliminated, the damage can be severe.
(also known as Knemidokoptes and Cnemidocoptes) is a genus in the class Arachnida, subclass Acari, order Sarcoptiformes, suborder Astigmata, family Epidermoptidae, and subfamily Knemidokoptinae.3 Taxonomically, knemidocoptic dermatitis in birds can be compared to sarcoptic dermatitis (mange) in mammals, but most birds lack the classic intense pruritus seen in animals with scabies.
Knemidocoptes species mites have been reported mainly in galliform (e.g. chickens, turkeys), passerine (e.g. finches, canaries, sparrows, robins, wrens), and psittacine birds (e.g. parrots, macaws, parakeets, budgerigars), but they also occur in piciform (e.g. woodpeckers, toucans) and anseriform (e.g. ducks, geese, swans) birds, raptors, and others. The prevalence of subclinical infections is largely undocumented in domestic and free-ranging birds. More common in a wide range of captive bird species, clinical infestation is rarely identified in wild birds. Knemidocoptiasis is fairly common in small pet birds; bird fanciers also call it scaly face and scaly leg or tassel foot. The condition was once thought to be caused by a fungal infection.
Other than knemidocoptic dermatitis in budgerigars, ectoparasitism is rare among psittacines. The earliest reports date back to the 1950s, but over the last 15 years, many more species of birds have been found to be affected, and several new Knemidocoptes species have been identified.4 This article reviews the recent literature, common clinical presentations, and current recommendations on diagnosing and treating knemidocoptiasis.
LIFE CYCLE AND TRANSMISSION
Knemidocoptes species mites spend their entire three-week life cycle on their bird hosts. The females are viviparous. The larvae have three pairs of legs (Figure 1). After two nymphal stages, the mites mature into adults that have four pairs of legs.5 The mites burrow into the feather follicles and stratum corneum, primarily on the face, feet, and cere, where they feed on keratin. Most commonly, the unfeathered regions (beak, eyelids, legs, vent) are affected. As the mites burrow, they form tunnels.
The mites are transmitted from bird to bird through prolonged close or direct contact. Although the mites are primarily transmitted from parent to unfeathered nestlings, knemidocoptiasis appears to be more opportunistic than infectious. As with Demodex species infections in dogs, not all nestlings will become clinically affected. Genetic susceptibility, stressors, or a compromised immune system likely result in clinical manifestation. Unlike many parasitic infections in birds, clinical infestation with Knemidocoptes species occurs more frequently in older birds.
Indirect forms of transmission, such as face rubbing on perches and contact with contaminated seed, are possible but less common. It is unknown whether interspecies transmission occurs, but infestation probably does not cross orders of birds.
KNEMIDOCOPTES SPECIES AND AFFECTED BIRDS
There are currently six genera in the subfamily Knemidokoptinae: Knemidocoptes, Neocnemidocoptes, Procnemidocoptes, Evansacarus, Picicnemidocoptes, and Micnemidocoptes.3 Clinically, the most common species are Knemidocoptes pilae, Knemidocoptes jamaicensis, and Knemidocoptes mutans. Knemidocoptes intermedius and others are less common (Table 1).6
Table 1 Knemidocoptes Species Common Names and Affected Birds