Comparison of methods for detection of an infection with different isolates of infectious haematopoietic necrosis virus (IHNV)

The infectious haematopoietic necrosis (IHN) is beside the viral haemorrhagic septicemia (VHS) one of the viral fish diseases that have a considerable economic impact on German aquaculture. The measures actually in force are focused on control and spread prevention of the disease within the borders of the European Union (EU). The detection and confirmation of an outbreak is performed according to the pertinent EU legislation which allow the application of methods like the virus neutralisation test (VNT), the immunofluorescence test (IFT) and the enzyme-linked immunosorbent assay (ELISA). Besides the classic virological serology methods, further tests for the identification and confirmation of the fish pathogen like i.e. PCR and DNA probe techniques are recommended by the OIE. To compare diagnostic methods as ELISA, cell cultivation and RT-PCR, rainbow trout of the strain "Isle of Man" were infected with six IHNV strains. Samples were taken on day 7 (viraemia period) and at the day 28 of the trial. The ground organs were inoculated into EPC cells (Epithelioma papulosum Cyprini cells) and examined by ELISA as well as after RNA extraction by RT-PCR. Besides the determination of the isolate as well as the virulence for 20 g trout, significant differences in the demonstration of the viruses were observed. While the RT-PCR demonstrated to be the most sensitive method, antigen ELISA and virus cultivation results showed in dependence of the IHNV isolate that not all viruses were identifiable under the chosen experimental condition in the same manner.