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.