White Sturgeon as a Potential Vector of Infectious Hematopoietic Necrosis Virus

Abstract

Cell lines from white sturgeon Acipenser transmontanus were derived from peripheral blood cells, heart, and spleen. Incubated with infectious hematopoietic necrosis virus (IHNV) for 8 d at l5°C, these cell lines produced 0.7–53.2 plaque-forming units (PFU)/cell. Waterborne exposure of larval white sturgeons (60 d posthatch) to 10⁶ PFU/mL of IHNV resulted in 10% mortality 5–6 d postinfection, with virus concentrations consistently greater than 10⁵ PFU/g. A replicate group of larval white sturgeons that were sampled at different times post-IHNV exposure had no detectable virus at 24 h, but 72% of the fish had IHNV concentrations of 10²-10⁶ PFU/g when they were examined 2–9 d postinfection. Juvenile white sturgeons (mean weight, 35 g) immersed in or injected with IHNV exhibited no mortality, and virus was only detected immediately postexposure in just 25% of the fish tested. Juvenile white sturgeons fed either virus-free rainbow trout Oncorhynchus mykiss or dead IHNV-infected rainbow trout had no viable virus in their feces. Juvenile white sturgeons fed or exposed to IHNV failed to transmit the virus to cohabiting rainbow trout fry. These results suggest that IHNV can replicate in larval white sturgeons but presumably not in juveniles or adults. Virus neutralization activity was detected in serum from adult white sturgeons (4–6 years old) cultured with rainbow trout exposed to IHNV but not in white sturgeons kept in a pathogen-free environment and fed a manufactured diet. White sturgeon serum with IHNV-neutralizing activity was used to passively immunize rainbow trout, and it provided significant (P < 0.01) protection against IHNV challenge.