Herpesvirus anguillae (HVA) isolations from disease outbreaks in cultured European eel, Anguilla anguilla in the Netherlands since 1996

Abstract

Abstract Since 1996, Herpesvirus anguillae (HVA) infections were diagnosed 19 times at 14 Dutch eelfarms with European eels ( Anguilla anguilla ). The eels showed various clinical symptoms, butpredominantly apathy, haemorrhages in their skin and fins, ulcerative skin and fin lesions, haem-orrhages in the gills, congested gill epithelium, a pale liver, and a mortality up to 10%. Eel gillswere in more cases HVA positive than the corresponding organs. Therefore, gills should be sam-pled for HVA-isolations in diseased eels. Often a bad water quality induced the virus propaga-tion. Eleven outbreaks occurred at water temperatures higher than 23°C; six outbreaks at watertemperatures lower than 23°C. Decreasing the temperature to below 22°C worked well in 4 cases.The agent was isolated on Eel Kidney (EK-1) cells, and characterized as a herpesvirus with elec-tron microscopy, typed by digestion of virus DNA with restriction enzyme Hind III, and its DNAfragments were analysed by gel electrophoresis. All Dutch HVA isolates showed a similar DNApattern. Comparison of the DNA of the Dutch viruses and Japanese isolates revealed a smalldifference after digestion with