Exposure occurred, but Morbillivirus was not the likely cause of striped dolphin deaths in the Ligurian Sea during 2007

We report herein the results of post-mortem, parasitological, microbiological, histopathological, immunohistochemical (IHC), indirect immunofluorescence (IIF), biomolecular (RT-PCR) and serological investigations carried out on 8 (1 male calf, 1 subadult female, 5 adult females, 1 adult male) striped dolphins (S. coeruleoalba) found stranded from August to November 2007 on the Ligurian Sea coast of Italy. A (broncho-interstitial) pneumonia occurred in 6 animals, with numerous parasitic bodies in both pulmonary and extra-pulmonary locations. Histologically, a multifocal, subacute to chronic, nonpurulent meningo-encephalitis occurred in 1 adult male and 3 adult females, with more or less prominent perivascular cuffs of inflammatory mononuclear cells and peri-paravascular macrophage accumulations. A mild choroid plexus lymphocytic-plasmacytic infiltration was also present, along with moderate neuronal damage, although no viral inclusions were seen in any brain cell (nor in any other cell type). The blood sera from 4 dolphins (1 calf, 1 subadult, 2 adults) had anti-Morbillivirus neutralizing antibodies, with positive titres ranging from 1:10 to 1:40. Nevertheless, IHC, IIF and RT-PCR investigations gave negative results in all animals. On the basis of the above findings, we conclude that one or more factors other than Morbillivirus likely were the primary cause of these dolphin mortality episodes.