Chronic bronchitis and bronchiolitis with prominent globule leukocyte infiltration in a cat with <i>Filobacterium felis</i>

A 7-year-old mixed-breed cat presented with intermittent dry cough for 2 years. Histological examination of the lung biopsy revealed hyperplasia of bronchial and bronchiolar epithelium, and intraepithelial infiltration of globule leukocytes in many bronchi, bronchioles, and terminal bronchioles. Lymphoid aggregates cuffed airways, respiratory bronchioles, and alveolar ducts. Terminal airway inflammation was associated with type II pneumocyte hyperplasia within adjacent alveoli. Warthin-Starry stain revealed numerous argyrophilic and filamentous bacilli that were interspersed or clustered with cilia of the respiratory epithelium. The morphology, distribution, and gram (negative) and ultrastructural characteristics were consistent with cilia-associated respiratory (CAR) bacillus. Real-time polymerase chain reaction assays using paraffin-embedded lung tissue confirmed the presence of <i>Filobacterium felis</i>. Chronic bronchitis and bronchiolitis in a cat with <i>F. felis</i> share characteristics of diseases caused by species specific CAR bacilli in many species, but uniquely in this case, globule leukocytes were a prominent feature of the inflammatory response.