Monitoring of herpesvirus anguillae (AngHV-1) infections in the European eel in north-west Poland

The European eel (Anguilla anguilla) is an economically important species in Poland, not only due to the quality and price of its meat, but also due to the eel stock management plan implemented since 2010. However, the imported juvenile eels for reintroduction are directly introduced into waters or reared in fish farms without necessary monitoring of the health status, especially for hazardous and pathogenic viruses. The study was conducted in the second half of 2014 using the European eels collected from Poland (Dąbie Lake, Szczecin Lagoon, hatcheries) and Denmark, mainly from importers and organizations producing material for reintroduction. A total of 256 samples were analysed including gills, liver, kidney, spleen, intestine and heart. Detection of the AngHV-1 was performed using pair primers designed to amplify the gene fragment encoding the viral DNA polymerase. Each PCR product was confirmed by bidirectional sequencing and sequence alignment with GenBank sequences. Obtained results indicate that the infection status of the eels imported to Poland is in the range of 0 to 100%, with the highest percentage of asymptomatic carriers among the fish imported from Denmark for the purpose of reintroduction and rearing. The eels collected in natural waters demonstrated an AngHV-1 infection rate of 30% (Dąbie Lake) and 40% (Trzebież). Bioinformatics analysis demonstrated that all these sequences were identical and represented the haplotype characterized for the first time in Poland by Kempter et al. (2014). The intensity of eel reintroduction in Poland is 1.2 million individuals per year, which permits a conclusion that the species is important for the fishing economy and should be monitored against AngHV-1. The demonstrated existing high risk posed by mass kills of the European eel in domestic waters after the introduction of the herpesvirus AngHV-1 from imported fish.