Autointerference in infectious hematopoietic necrosis virus of salmonid fish

Detection of truncated virus particles in a persistent RNA virus infection in vivo

Infectious hematopoietic necrosis virus (IHNV) is a rhabdovirus which causes devastating epizootics of trout and salmon fry in hatcheries around the world. In laboratory and field studies, epizootic survivors are negative for infectious virus by plaque assay at about 50 days postexposure. Survivors are considered virus free with no sequelae and, thus, are subsequently released into the wild. When adults return to spawn, infectious virus can again be isolated. Two hypotheses have been proposed to account for the source of virus in these adults. One hypothesis contends that virus in the epizootic survivors is cleared and that the adults are reinfected with IHNV from a secondary source during their migration upstream. The second hypothesis contends that IHNV persists in a subclinical or latent form and the virus is reactivated during the stress of spawning. Numerous studies have been carried out to test these hypotheses and, after 20 years, questions still remain regarding the maintenance of IHNV in salmonid fish populations. In the study reported here, IHNV-specific lesions in the hematopoietic tissues of rainbow trout survivors, reared in specific-pathogen-free water, were detected 1 year after the epizootic. The fish did not produce infectious virus. The presence of viral protein detected by immunohistochemistry, in viral RNA by PCR amplification, and in IHNV-truncated particles by immunogold electron microscopy confirmed the presence of IHNV in the survivors and provided the first evidence for subclinical persistence of virus in the tissues of IHNV survivors.

The viral diseases of fish: a review through 1978. Part 1: Diseases of proven viral etiology

In this review, a survey is made of the published literature on the viral diseases of fish available up to and including the year 1978. It is divided into two main sections. Part 1 describes 11 diseases where a virus has been isolated and proven to be the causative agent. Part 2 discusses 16 diseases where there is reason to suspect viral etiology because of evidence deriving from electron microscopy or transmission experiments with bacteria-free filtrates of homogenates of diseased tissue, but where final proof of a causative relationship is lacking. The review attempts to provide the most significant information on the disease process itself, in most cases including external signs, fish species susceptible, pathology, geographic distribution, existence of carriers, methods of transmission, and control. It also gives the most recent and significant data concerning the nature of the causative virus, including its cultural, biological, and physicochemical properties, where such information is available.

Structural proteins of two salmonid rhabdoviruses

Purified infectious hematopoietic necrosis (IHN) virus and the virus of haemorrhagic septicaemia (VHS) (Egtved virus) each contain five structural proteins which were designated L, G, N, M-1, and M-2. The IHN viral polypeptides have molecular weights estimated to be 157,000, 72,000, 40,000, 25,000 and 20,000, respectively, whereas those of VHS viral polypeptides are estimated to be 157,000 74,000, 41,000, 21,500, and 19,000, respectively. The carbohydrate composition of the glycoprotein (G) was confirmed by demonstrating selective incorporation of [3H]glucosamine into the designated G protein of both viruses. Phosphoproteins were identified by incorporation of [32P]orthophosphate into the N and M-1 proteins of IHN virus and into the N protein of VHS virus. The glycoprotein of each virus was selectively solubilized by treatment with Triton X-100 in low salt buffer, whereas the M-1, and M-2 proteins along with the G protein were solubilized by Ttition X-100 in 0.43 M NaCl. The protein composition of the salmonid rhabdoviruses resembles that of the rabies virus group more closely than the vesicular stomatitis virus group.