Induction of protection from infectious hematopoietic necrosis virus in rainbow trout Oncorhynchus mykiss by pre-exposure to the avirulent cutthroat trout virus (CTV)

Abstract

Juvenile rainbow trout Oncorhynchus mykiss exposed to waterborne live cutthroat trout virus (CTV) showed increased resistance to experimental challenge with infectious hematopoietic necrosis virus (IHNV). Pre-exposure to CTV caused a relative percent survival (RPS) of 70 when compared to CTV-mock-treated groups challenged with IHNV. Additionally, the mean day to death was 10 d for CTV-exposed versus 8 d for the CTV-mock-treated group. Protection was obtained following exposures as brief as 5 min but was greatest among trout exposed for 1 h to CTV and then challenged 1 wk later with IHNV. Protection was observed for up to 4 wk following CTV exposures but absent at 6 wk. Concentrations of serum anti-IHNV neutralizing antibodies were significantly higher (p = 0.007) among trout previously exposed to CTV when compared to the mock-treated group 5 wk following challenge with IHNV. Both groups (CTV and CTV-mock) surviving the first IHNV exposure were solidly protected to a second IHNV challenge. The mechanisms for the viral mediated resistance induced by CTV is unknown, but the virus was shown to be a potent inducer of interferon-like activity in anterior kidney cells isolated from rainbow trout.