Novel dolphin morbillivirus (DMV) outbreak among Mediterranean striped dolphins Stenella coeruleoalba in Italian waters

An unusual mortality event (UME) of striped dolphins Stenella coeruleoalba occurred in the period July- December 2016 along the Italian Ionian coastline. We conducted a complete postmortem examination on 28 specimens and detected dolphin morbillivirus (DMV), by means of biomolecular analyses, in the target tissues of 17 animals. Unlike previous outbreaks occurring in the Mediterranean Sea in 2011 and 2013, we observed typical pathological changes suggestive of morbilliviral infection in an acute/subacute phase and immunohistochemical reactivity. The same findings have been observed in other 13 specimens beached along the Italian coastline during 2016 without any temporal and geographical relationship with the ongoing epidemic outbreak. Molecular characterization and phylogenetic analysis showed that DMV sequences detected in Italy in 2016 cluster with those identified in Portugal and Galicia, representing a novel DMV strain of Atlantic origin which entered the Mediterranean Sea and affected a naïve striped dolphin population. Indeed, DMV sequences detected in the previous Mediterranean outbreaks exhibited a marked genetic relatedness and diverged from those detected in cetaceans stranded along the Galician and Portuguese coasts since 2007.