Morbillivirus could not be the major factor impacting the health of Striped dolphins along the Ligurian sea coast of Italy

The impact of morbillivirus on cetacean is well known since a long time. Indeed, since 1987, at least eight morbillivirus infection (MI) epidemics have caused mass mortality of several free-living pinniped and cetacean populations around the world. At post-mortem examination, a commonly occurring macroscopic lesion is represented by more or less severe bilateral pneumonia, with consolidation, congestion and oedema of both lungs, which fail to collapse. Among the still debated, or even controversial issues regarding MI in sea mammals, the one related to the origin of their causative agents is of particular concern. It has recently also debated if some episodes ascribed to MI were real morbillivirus infections, as serological or immunohistochemical techniques failed to identify the virus. Another intriguing issue regards the synergistic effects, if any, associated with chronic exposure to a number of environmental pollutants, such as organochlorines and heavy metals. In fact, it is also unknown whether and how these chemicals contribute towards modulating the pathogenic and pathogenetic activity primarily displayed by sea mammal morbilliviruses. Among others, heavy metals have proved to act as immunomodulators in many mammals species, mainly acting as immunosuprressor. In present study we report about heavy metals (Cd, Pb and Hg) concentration in liver and muscle of stranded dead stripped dolphin (n= 9) from Tirrenian Sea collected during a suspected MI episode. Sampled cohort included a 5 days old calf, two sub-adult and 6 adult subjects. Contemporarily, autoptic lesions were recorded and a serological survey was conducted on brain samples of 8 out of 9 animals in order to verify if the causative agent of death was morbillivirus. Any possible correlation with immunosuppressive action of metals was also tested, even if low number of animals did not allow any statistical analysis. Obtained results showed mean metals concentration reported in table 1. Lowest levels of all metals were observed in the calf, but it should be noted that 10 out of 18 samples were below the limit of detection (LOD) for lead. These levels were always below the immunotoxic thresholds for cadmium and lead, while were always well below the threshold for mercury. Thus a certain degree of immunosuppression, including increase of apoptosis, reduction in lymphocyte proliferation and fagocytic activity, could be considered for all animals. Serological survey revealed that only 4 out of 8 animals analysed were positive to morbillivirus. Interestingly, positive animals presented no typical morbillivirus brain lesion, which were present in negative subjects. It should be noted the presence among sero-positive animals of the calf. In this case, a mother-calf antibody transfer with colostrum should be considered. Giovanni, qui ti sarei molto grata se potessi scrivere tu qualcosa sulla sierologia, tipo la questione del passaggio col colostro al cucciolo, la possibilità di un'immunità acquisita a seguito di esposizione "cronica" al virus, i dubbi sull'effettiva esposizione a morbillivirus o ad altri patogeni. Interestingly, when metal data were evaluated on the basis of serological results, higher levels of metal were found in sero-negative animals, as evident in hepatic lead and mercury Obtained data seems to suggest the occurrence of an infection different from morbillivirus, which induce cerebral lesions similar to MI and whose morbidity is increased by the action of mercury and probably of other contaminants known to act as immunosuppressive agents. Further and deeper researches are considered necessary in order to better define which is the role of pollutants in the severity of epidemics and, more important, which could be the real causative agent of the die-off of 2007 in Italy.