The occurrence of a coinfection by three distinct microbial agents is
made plausible by the lymphoid cell depletion observed in the dolphin
under study, with the resulting immunosuppression likely acting as its
common risk factor. Immunodeficiency may result from previous exposure
to physical (such as radiation), chemical (such as “heavy metals”
and “persistent organic pollutants”) and biological (such as Morbillivirus)
“stressors”, acting alone or in combination. In this respect,
Odontocete cetaceans like dolphins are known to accumulate within
their body tissues, as “top predators”, high concentrations of
immunotoxic pollutants, which can make them more susceptible to
several microbial pathogens (Van Bressem et al., 2009). Additionally, a
consistent proportion of Dolphin Morbillivirus (DMV)-infected striped
dolphins found stranded along the Tyrrhenian Sea coast of Italy in the
context of the “unusual mortality event” that occurred in the first mid
of 2013, turned out to be simultaneously coinfected by P. damselae
subsp. damselae (Casalone et al., 2014).