Nodular pyogranulomatous pneumonia associated with <i>Besnoitia darlingi</i> infection in a cat

A 1-y-old, castrated-male, domestic shorthair cat was evaluated because of a 1-mo history of chronic cough, dyspnea, and lethargy that progressed to anorexia during the week preceding euthanasia. Radiographically, the right caudal and middle lung lobes were consolidated. Cytologic and histologic examination of the right caudal lung lobe revealed pyogranulomatous inflammation with intralesional protozoal organisms. Although morphologically similar to and immunohistochemically reactive for <i>Toxoplasma gondii</i>, the organisms had inconsistent features, such as variability in shape and size. With <i>Sarcocystidae</i> PCR assays for the 18S DNA and the ITS1 DNA markers and Sanger sequencing, we identified the organisms as <i>Besnoitia darlingi</i>. A comprehensive search of PubMed and Google Scholar revealed no prior reports, suggesting that feline pneumonia has not been reported previously in association with <i>B. darlingi</i> infection.