Epizootic podoknemidokoptiasis in American robins

Epizootics of scaly leg disease caused by infection with the submacroscopic mite Knemidokoptes jamaicensis (Acari: Knemidokoptidae) in migratory American robins (Turdus migratorius) from a residential area of Tulsa (Oklahoma, USA) are documented during the winters (December through February) of 1993-94 and 1994-95. Estimates of 60 to > 80% of the birds in several different flights arriving in the area had lesions consistent with knemidokoptic mange. Epizootic occurrence of K. jamaicensis also is confirmed incidentally in American robins from Georgia (USA) in 1995 and 1998 and in Florida (USA) in 1991. These are the first confirmed epizootics of scaly leg attributed to infections with mites specifically identified as K. jamaicensis in North America. Severity of observed lesions in American robins ranged from scaly hyperkeratosis of the feet and legs to extensive proliferative lesions with loss of digits or the entire foot in some birds. Histologically, there was severe diffuse hyperkeratosis of the epidermis which contained numerous mites and multifocal aggregates of degranulating to degenerating eosinophilic heterophils; there was mild to severe superficial dermatitis with aggregates of eosinophilic heterophils and some mononuclear cells. Based on limited data from affected captive birds in Florida, we questioned the efficacy of ivermectin as an effective acaricide for knemidokoptiasis and propose that conditions associated with captivity may exacerbate transmission of this mite among caged birds. While knemidokoptic mange apparently can result in substantial host morbidity and possibly mortality, the ultimate impact of these epizootics on American robin populations presently is unknown.