Novel dolphin morbillivirus epizootic in stranded striped dolphins in the western Mediterranean Sea, 2025

Dolphin morbillivirus (DMV) epizootics have recurrently occurred in the western Mediterranean Sea since the first reported outbreak in 1990-1992. In August-November 2025, 5 stranded striped dolphins Stenella coeruleoalba were diagnosed with systemic DMV infection in the Spanish Mediterranean Sea. Dolphins were thin, and 4 of them had typical viral lesions of bronchiolointerstitial pneumonia, lymphoid depletion, and encephalitis. RT-PCR for DMV was positive in at least 2 organs in all dolphins, and viral antigen was detected by immunohistochemistry in 4 dolphins. Four dolphins died due to morbillivirus infection, while the other DMV-infected dolphin died from cranial trauma and tension pneumothorax. The viral genome recovered from the sample of one dolphin has higher identity to delphinid 2016-2017 Italian DMV sequences and to a fin whale strain from Denmark in 2016, and is approximately 1% distant from strains of previous epizootics in the Mediterranean Sea. The exact source of the infection is unknown, but direct contact with infected striped dolphins from other areas of the Mediterranean or a new DMV incursion from the Atlantic Ocean are possible.