Detection of Phocoena Pestivirus and Neutralizing Antibodies in Harbor Porpoises Found Dead at the North Sea and Baltic Sea Coasts.

In 2019, a marine pestivirus, Phocoena pestivirus (PhoPeV), family Pestiviridae, was described for the first time. To date, the impact of PhoPeV infections on harbor porpoises is still unknown. Therefore, a screening study was carried out on harbor porpoises found dead on the German North Sea and Baltic Sea coasts during 2021-2025. Analysis of organ samples collected from 84 harbor porpoises by reverse transcription (RT)-PCR showed the presence of PhoPeV RNA in samples from five animals (5.9%). Infectious virus was isolated from two of these samples. Phylogenetic analysis showed a close relationship to previously reported PhoPeV isolates. Moreover, a virus neutralization assay has been established using organ liquid and organ homogenate matrices instead of the standard serum sample matrix. Samples from seven out of 72 animals tested positive for neutralizing antibodies against PhoPeV including four samples with an antibody titer ≥ 320 ND50. Cross-neutralization studies including classical swine fever virus (CSFV), border disease virus (BDV), as well as Bungowannah pestivirus (BuPV), and Linda virus (LindaV), both viruses being most closely related to PhoPeV, showed no significant serological relatedness to PhoPeV. In conclusion, both PhoPeV RNA and neutralizing antibodies against PhoPeV have been detected in animals found dead in the North Sea and Baltic Sea over the last 5 years, indicating a continuous circulation of PhoPeV in the harbor porpoise population for at least several years.