Evaluation of a reverse transcriptase polymerase chain reaction test and virus isolation on field samples collected for the diagnosis of infectious hematopoietic necrosis virus in cultured Atlantic salmon in British Columbia.

Infectious hematopoietic necrosis virus (IHNV) has been found to cause disease in cultured salmon of the Pacific Northwest region of North America. Diagnosis of IHNV by virus isolation (VI) can take over 2 weeks. Recently, a rapid reverse transcriptase (RT) polymerase chain reaction (PCR) test on fish tissues has been used for diagnosis. Test performances of the VI and RT PCR assays were compared using samples collected in the field. The effect of different storage conditions (tissue frozen with or without RNAlater [Ambion, Inc., Austin, Texas] versus fresh tissue) on the diagnostic tests was also evaluated. Based on the limited number of samples tested, the operating characteristics of RT PCR were very similar to those of VI; therefore, this method is likely suitable for testing field samples for IHNV. The ability of the tests to identify a positive fish ranged from 74% to 89%. Freezing samples at -80 degrees C before testing did not negatively affect the performance of RT PCR or VI. However, due to reduced test performance, RNAlater frozen storage is not recommended without further investigation.