RESUMO
Background: The nasal mites of the Rhinonyssidae family include the highest diversity of mandatory hematophagous endoparasites of the respiratory system of birds. In general, these mites cause no significant lesions, except Sternostoma tracheacolum that invades the trachea, lungs and air sacs and may compromise breathing in birds. This study reports the death of a Belgian canary (Serinus canaria domestica) due to the parasitism by S. tracheacolum with an aggravating and concurrent pododermatitis infection. Case: A Belgian canary from a commercial bird flock, in which a high mortality rate had lately been recorded, was submitted to necropsy. Multiple blackened foci (1.0 mm in diameter) present in the trachea and the air sacs were subsequently identified as Sternostoma tracheacolum mites. Microscopically, there were diffuse and moderate infiltrates of lymphocytes, plasma cells, macrophages and heterophils within the tracheal submucosa and areas of fibrosis and osseous metaplasia of the tracheal cartilage. In the air sacs, there were multiple yellowish-brown foci of caseous necrosis, which were surrounded by inflammatory infiltrate of macrophages and multinucleated giant cells. In the lungs, there were foci of caseous necrosis surrounded by macrophages. In the tracheal lumen, mites sections were observed. Clusters of nucleated erythrocytes and brown granular pigment were seen within the longitudinal section of the mites. Prussian blue (Perls) special staining evidenced no hemosiderin content in the mite's tissues, in which no melanin could be detected, as well. Discussion: The parasitism by S. tracheacolum in canaries was first described in South Africa. In such cases, the mite induced clinical respiratory disease and killed the birds. Subsequently, reports of parasitism by these mites included several additional bird species, of which, Cockatiel (Nymphicus hollandicus) has been the most frequently affected and there are only a few reports of the condition in canaries. Clinically, hosts have difficulty breathing, exercise intolerance, coughing and sneezing. Depending on the severity, infection can persist for months or lead to death by suffocation or weakness. Clinical signs and death are related to the appearance of the lesions induced by the mites. Mite eggs are deposited in the lungs and the larvae hatch soon after oviposition. After the first meal, the female protonymph migrates to the posterior parabronchia, while the male protonymph remains in the lungs, where it completes the development. The adult mites full of eggs tend to occupy the parabronchia, the syrinx and the trachea. The negative results on Prussian blue and melanin bleach methods indicate that the dark pigment present within the tissues from the mites is neither hemosiderin nor melanin, respectively. In parasitism due to Plasmodium sp. (malaria), hemozoin, an iron-containing pigment associated with erythrocytic changes induced by the protozoan, has not been detectable by the Prussian blue staining. It is suggested that the dark color observed in the mites in this study could be associated with a similar pigment. The clinical respiratory diseases in birds are generally nonspecific. The paper focuses on the importance of the confirmation of the diagnosis by the necropsy and histopathological examinations, as well as on the characterization of this respiratory parasitic disease of birds.