Recently, a mass mortality event impacting the bivalve Pinna nobilis was detected across a wide geographical area of the Spanish Mediterranean Sea and linked to a haplosporidian parasite.

In 2017-2018, mass mortality events affecting the pen shell Pinna nobilis were recorded in two different regions of Italy, Campania and Sicily, in the Tyrrhenian Sea (Mediterranean Sea). In this study histopathological and molecular examinations were undertaken and the results showed the presence of the haplosporidian parasite only in one of the specimens in one area. Conversely, in all of the surveyed moribund animals, strong inflammatory lesions at the level of connective tissue surrounding the digestive system and gonads and linked to the presence of intracellular bacteria were observed.

The authors propose, based on the pathological and molecular findings, that a mycobacterial disease was associated with those mortality episodes and hypothesize of a more complex disease pathogenesis involved in the disease outbreak of the bivalve P. nobilis, in which two possibly opportunistic pathogens are involved in two different areas of the Mediterranean Sea, suggesting that both are activated by further possible common unidentified causes.

https://www.nature.com/articles/s41598-018-37217-y

Carella et al. (2019) A mycobacterial disease is associated with the silent mass mortality of the pen shell Pinna nobilis along the Tyrrhenian coastline of Italy. Scientific Reports 9:2725.