Final destination: The Mediterranean Sea, a vulnerable sea. The long journey of Giardia duodenalis cysts

The Mediterranean Sea is considered a “litmus paper” of pollution risks for any parameter, including faecal contamination. Giardia duodenalis is one of the most important protozoan parasites responsible for diarrhoea in a wide range of hosts, including humans, domestic and wild animals, worldwide. The degree of contamination related to the protozoan's resistant forms on land, and the consequent transport through rivers from point sources to the sea are important aspects to better understand the processes involved in the microbiological pollution of aquatic ecosystems. However, land-sea transfer routes and the complex transmission patterns often remain neglected. This contribution deals with the contamination by G. duodenalis of the Mediterranean Sea through its inhabitants (shellfish, marine mammals, fishes), and provides data on the origin of such contamination on land from humans and animals to soil, fresh produce and waters; this scenario allows to understand the long journey of the protozoan following the drainage basins (i.e., natural watersheds) from the mainland towards the final destination. The Mediterranean Sea contamination is also explained in the light of the Giardia survival in water and the effects of climatic change with the related consequences. Addressing faecal contamination threats in the Mediterranean Sea is a difficult task, but a number of mitigation measures need to be implemented and/or in some countries even applied. Effective management must become a priority in the agenda of policy makers of all Mediterranean Countries for the implementation of successful measures and can only be applied in the perspective of the One Health approach.