Truncated particles produced in fish surviving infectious hematopoietic necrosis virus infection: Mediators of persistence?

Infectious hematopoietic necrosis virus (IHNV) is a rhabdovirus that produc es an acute, lethal infection in rainbow trout (Oncorhynchus mykiss), Fish that survive infection cease to produce detectable infectious virus at appr oximately 46 days after infection, yet there is evidence that survivor fish continue to harbor virus particles (B, S. Drolet, P, P. Chiou, J, Heidel, and J, C. Leong, J, Virol, 69:2140-2147, 1995), In an effort to determine t he biological function of these particles, the kidneys and livers from IHNV survivors were harvested and divided into samples for nested reverse trans criptase PCR analysis and explant culture. Sequences for the IHNV nucleopro tein and polymerase genes were detected in 50 and 89%, respectively, of the organs from survivor fish, When explant tissue cultures were infected with purified standard IHNV, the liver tissues from survivor fish produced up t o 10-fold less virus than naive control fish liver tissues. In addition, im munosorbent electron microscopy analysis of the supernatant media from the cultured explants of survivor fish revealed truncated particles, whereas th e control tissue supernatants contained only standard viral particles. Thes e results suggest that the truncated IHNV particles observed in persistentl y infected fish are defective interfering particles that may mediate virus persistence.