LAUSR

Abstract Sibling female and male Chihuahuas were evaluated for a 9‐month history of tachypnea that failed to respond to fenbendazole, doxycycline, amoxicillin‐clavulanate, and prednisone. Physical examination identified tachypnea, hyperpnea, and harsh bronchovesicular lung sounds. Fundic examination disclosed diffuse chorioretinitis, manifested as multifocal chorioretinal granulomas in the female dog and occasional chorioretinal scars in the male dog. Thoracic radiographs indicated moderate to severe interstitial to broncho‐interstitial infiltrates in both dogs. Serum and urine antigen and antibody testing in the female dog failed to identify infectious agents, but cytologic assessment of hepatic lymph node, liver, and splenic aspirates identified Pneumocystis trophozoites. Infection was confirmed in both dogs by 28S rRNA PCR sequencing from multiple tissue samples. The female dog responded well to trimethoprim‐sulfamethoxazole, but the male dog was euthanized because of liver failure, presumably related to antimicrobial treatment.