We describe gross, histopathological, and immunohistochemical features of Streptococcus phocae and cetacean morbillivirus coinfection in a short-beaked common dolphin Delphinus delphis. Major gross findings were cutaneous purulent nodules in the tail fluke, vegetative mitral valve endocarditis, and presumed postpartum pyometra. Histologic examination revealed bacterial septicemia characterized by widespread intravascular coccoid bacterial emboli. These were associated with fibrinonecrotizing to pyogranulomatous dermatitis and panniculitis, embolic pneumonia, neutrophilic and lymphoplasmacytic meningochoroiditis, random neutrophilic hepatitis, lymphoplasmacytic myocarditis and epicarditis, necrotizing adrenalitis, suppurative endometritis, and multicentric reactive lymphadenopathy. Bacteriology and molecular analysis with sequencing of the 16S rRNA gene identified S. phocae from lung, brain, and adrenal gland tissue. Immunohistochemical analysis for morbillivirus detection revealed positive immunolabeling in the epithelium of the choroid plexus of the fourth ventricle. Published reports on S. phocae infection in cetaceans are rare, and pathological details are limited. The present case indicates that S. phocae has potential pathogenic capacity in common dolphins. The pathogenesis is proposed to have involved cutaneous penetration after a skin trauma, leading to initial cutaneous disease and eventual systemic infection.
Keywords: Bacteremia; Cetacean pathology; Coinfection; Immunohistochemistry; Morbillivirus; Streptococcus phocae; Zoonosis.