Abstract
Disease is an increasing threat for marine bivalves worldwide. Recently, a mass mortality event (MME) 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). Histopathological and molecular examinations of specimens showed the presence of Haplosporidium sp. in only one specimen 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 Zhiel-Neelsen-positive bacteria were observed. Molecular analysis of all of the diseased specimens (13) confirmed the presence of a Mycobacterium. Blast analysis of the sequences from all of the areas revealed that they were grouped together with the human mycobacterium M. sherrisii close to the group including M. shigaense, M. lentiflavum and M. simiae. Based on pathological and molecular findings, it is proposed that a mycobacterial disease is associated with the mortality episodes of Pinna nobilis, indicating that, at this time, Haplosporidium sp. is not responsible for these events in Campanian and Sicilian waters.
Highlights
The bivalve pen shell Pinna nobilis is an endemic Mediterranean species and among the largest bivalves worldwide, playing an important ecological role for soft bottom communities and contributing to the increase in local biodiversity
In early 2017, mass mortality episodes of P. nobilis populations were detected in Campania and Sicily, affecting animals of all sizes and affecting 85–100% in prevalence
A total of 13 moribund animals of the pen shell P. nobilis and 1 specimen of P. rudis were collected from two different regions of the Tyrrhenum: Campania and Sicily
Summary
The bivalve pen shell Pinna nobilis is an endemic Mediterranean species and among the largest bivalves worldwide, playing an important ecological role for soft bottom communities and contributing to the increase in local biodiversity. This species can reach up to 120 cm in length and a maximum reported age of 27 years[1,2]. Evidence suggests that a combination of predisposing and necessary biotic factors is involved in the disease causation, resulting in a scenario of new emerging complex multifactorial diseases[11] These diseases have been often linked to changes in host/pathogen interactions and have been associated with increased water temperature, pathogen distribution and virulence, host reduced immune competence and growth[12,13]. The aims of this paper are to unravel the bivalve health status and to define the possible causes of the mortality events involving the pen shell P. nobilis in these two geographical areas in late 2017 through May 2018
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