In the Wake of the Ongoing Mass Mortality Events: Co-occurrence of Mycobacterium, Haplosporidium and Other Pathogens in Pinna nobilis Collected in Italy and Spain (Mediterranean Sea)

Abstract

Following the Mass Mortality Events (MMEs) of the pen shell P. nobilis in Campania region and Sicily, a survey of moribund P. nobilis specimens was also conducted in other Italian regions (Campania, Tuscany, Sardinia, and Apulia) and Spain (Catalunya). Histopathological and molecular examination of 27 specimens of P. nobils revealed different types of pathogens associated with tissue lesions, morbidity and mortality. Presence of Mycobacterium, Vibrio species, Haplosporidium pinnae and Perkinsus sp. were detected, differently distributed into the areas. The Mycobacterium sp., previously reported in Campania and Sicily samples, was observed in all the analyzed areas and individuals, associated to systemic inflammatory lesions. In Spain, H. pinnae was observed in 36% of cases, always associated to the Mycobacterium sp. Molecular study using hsp65 genes and Internal Transcriber Spacer ITS support that a new species of Mycobacteria is infecting P. nobilis, close to M. triplex and belonging to the group of M. simiae complex with M. sherrisi. Presence of Perkinsus spp. resembling P. mediterraneus was observed in 2 out of 13 Italian individuals whose presence should be addressed as potential risk for shellfish aquaculture of the area. Vibrio spp. were also detected in some case. The preliminary results of this study suggest that Mycobacterium sp., Vibrio spp., H. pinnae and Perkinsus sp. cooperate to disease pathogenesis, being Mycobacterium and Haplosporidium most of the time involved. Vigilant inspection of those areas where MME is now starting, along with continuous systematic surveys, are crucial to define the spatiotemporal progress of mortality and the role of every single pathogen in the disease outcome.

Multiple Non-Species-Specific Pathogens Possibly Triggered the Mass Mortality in Pinna nobilis

“…Moreover, in accordance with what has already been suggested by Carella et al [ 19 ] (and references therein) for individuals from the northern coast of Spain and by Lattos et al [ 33 ] for Greek populations of the Thermaikos Gulf, our study further supports a hypothesis that is gaining popularity that P. nobilis mass mortality is not linked exclusively to infection by the protozoan H. pinnae [ 16 , 17 , 18 , 19 , 33 ] (and references therein). In this context, we detected no association between the occurrence of the typical signs of disease responsible for the death of individuals of P. nobilis and the presence of H. pinnae in their tissues.…”

“…[ 17 , 18 ], and Perkinsus spp. [ 19 ]. In the first phase of the illness, individuals affected by this unknown disease are characterized by an anomalous slow closure of the valves after external stimulation.…”

Epidemiology of Noble Pen Shell (Pinna nobilis L. 1758) Mass Mortality Events in Adriatic Sea Is Characterised with Rapid Spreading and Acute Disease Progression

“…Taken together, these results indicate that Mycobacterium may be the leading causative in the Adriatic Sea MMEs, as suggested in recent reports [ 6 , 8 , 9 ]. It is known that pathogenic mycobacteria can undergo a prolonged asymptomatic or latent period, after which disease can be reactivated in a subset of infected hosts [ 32 , 33 ].…”

“…Additionally, during surveillance of the Seline location, strong and diffuse inflammatory lesions were observed in collected specimens without mortalities and presence of neither Mycobacterium nor Haplosporidium . It was hypothesised recently that other currently unknown causes could be involved in the pathogenesis of this disease [ 6 , 9 ]. It has also been reported that intracellular Mycobacterium may be missed by conventional ZN stain [ 37 ] and that pathogen detection may be improved by increasing the permeability of the bacterial cells with Triton-X to allow intracellular access of carbolfuchsin-dye.…”

“…being most frequently identified, followed by H. pinnae , and in a few cases, Vibrio spp. and Perkinsus sp., suggesting that exposure to multiple pathogens could increase complexity of disease pathogenesis [ 9 ]. By the end of 2018, multiple MMEs with high (close to 100%) mortality rates caused complete disappearance of noble pen shell populations in many areas across Mediterranean [ 10 ].…”