Novel alphaherpesvirus in harbour porpoises associated with severe meningitis and encephalitis

In the southern North Sea, the harbour porpoise (Phocoena phocoena) is currently a common resident, with abundance estimates in the Dutch sector of the North Sea ranging from 26,000 (mid-summer) to 85,000 (early-spring) individuals. During the last couple of years (2011-2014), annually over 750 harbour porpoises were found dead along the Dutch coast in different stages of decomposition. In those last years, a total of 85 very fresh to fresh harbour porpoises were submitted for immediate necropsy, and a post-mortem investigation was conducted in order to determine the cause of death. Of these 85 cases, 23 individuals (27%) had a severe encephalitis and/or meningitis. Intranuclear inclusions were associated with the lesions seen in those animals, suggestive of a herpesviral infection. To confirm this, DNA-isolation and panherpesvirus PCR were conducted on cerebrum and cerebellum of all affected animals. Thirty-five percent (8/23) were PCR-positive, the fragments of which were subsequently cloned and sequenced. Phylogenetic analyses revealed the presence of a novel alphaherpesvirus, tentatively designated phocoenid herpesvirus 1. In conclusion, we reveal that herpesvirus infection was detected in 35% of all porpoises which died due to a severe inflammation of the brain and/or meninges. To our knowledge, this is the first report of an alphaherpesvirus associated with inflammation of the brain and/or meninges of harbour porpoises.