From May to October 2019, multiple mass mortality events (MMEs) of Pinna nobilis were observed along Croatian coastline starting from the south-east and rapidly progressing in north-western direction.

This paper describes the spread of the MMEs and assessed mortality causes. It is shown that time dynamics of the MMEs closely followed general speed and direction patterns of surface sea-currents, advancing approximately 350 km in less than 3 months. Following the spread, surveillance, clinical evaluation, and sample collection were performed on multiple sites with various degrees of mortality rates.

The results of the analyses showed that affected animals were positive for Mycobacterium in 70% of the individuals, and Haplosporidium pinnae was present in 58% of the cases.

The authors highlight that, considering the rapid and severe spread of the MMEs, the areas less exposed to major sea currents appeared to be at lower risk of pathogen transmissions. According to this, the authors identified several P. nobilis populations along the Croatian coastline in such “lower risk” areas without apparent mortality or clinical symptoms.

Saric et al. (2020) Epidemiology of noble pen shell (Pinna nobilis L. 1758) mass mortality events in Adriatic Sea is characterized with rapid spreading and acute disease progression. Pathogens 9:776.