[2] Clinical signs include laboured breathing, fever and nervous symptoms.

[3] In 2002, an epizootic of PDV along the North Sea coast resulted in the deaths of 21,700 seals, estimated to be 51% of the population.

[3] The suddenness of the emergence of PDV and related viruses in aquatic mammals has implicated environmental changes as the cause.

Pollutants have been posited as contributors by interfering with the ability of animals to mount a defense against infection.

Alternatively, climate change and overfishing may have forced aquatic species that naturally harbour the viruses into new areas, exposing immunologically susceptible populations.