Understanding the interaction between Betanodavirus and its host for the development of prophylactic measures for viral encephalopathy and retinopathy

Abstract

Over the last three decades, the causative agent of viral encephalopathy and retinopathy (VER) disease has become a serious problem of marine finfish aquaculture, and more recently the disease has also been associated with farmed freshwater fish. The virus has been classified as a Betanodavirus within the family Nodaviridae, and the fact that Betanodaviruses are known to affect more than 120 different farmed and wild fish and invertebrate species, highlights the risk that Betanodaviruses pose to global aquaculture production. Betanodaviruses have been clustered into four genotypes, based on the RNA sequence of the T4 variable region of their capsid protein, and are named after the fish species from which they were first derived i.e. Striped Jack nervous necrosis virus (SJNNV), Tiger puffer nervous necrosis virus (TPNNV), Barfin flounder nervous necrosis virus (BFNNV) and Red-spotted grouper nervous necrosis virus (RGNNV), while an additional genotype turbot betanodavirus strain (TNV) has also been proposed. However, these genotypes tend to be associated with a particular water temperature range rather than being species-specific. Larvae and juvenile fish are especially susceptible to VER, with up to 100% mortality resulting in these age groups during disease episodes, with vertical transmission of the virus increasing the disease problem in smaller fish. A number of vaccine preparations have been tested in the laboratory and in the field e.g. inactivated virus, recombinant proteins, virus-like particles and DNA based vaccines, and their efficacy, based on relative percentage survival, has ranged from medium to high levels of protection to little or no protection. Ultimately a combination of effective prophylactic measures, including vaccination, is needed to control VER, and should also target larvae and broodstock stages of production to help the industry deal with the problem of vertical transmission. As yet there are no commercial vaccines for VER and the aquaculture industry eagerly awaits such a product. In this review we provide an overview on the current state of knowledge of the disease, the pathogen, and interactions between betanodavirus and its host, to provide a greater understanding of the multiple factors involved in the disease process. Such knowledge is needed to develop effective methods for controlling VER in the field, to protect the various aquaculture species farmed globally from the different Betanodavirus genotypes to which they are susceptible.

Viral nervous necrosis in gilthead sea bream (Sparus aurata) caused by reassortant betanodavirus RGNNV/SJNNV: an emerging threat for Mediterranean aquaculture

“…Fish nodaviruses can infect a broad variety of species2 belonging to 30 different families; however, Sparids, in particular Gilthead sea bream, have generally proved to have a low susceptibility or to be resistant to the disease232430. This is probably true when referring to VNN caused by the RGNNV genotype, the most common pathogenic strain for European sea bass.…”

“…The RGNNV is the most commonly detected virus species in this area2, although the SJNNV species was also reported in the Iberian Peninsula in 20098. Notably, the occurrence of the reassortant strains RGNNV/SJNNV and SJNNV/RGNNV has been reported only in the Mediterranean Sea19.…”

“…Since its first description in the late ‘80 s, a large number of economically relevant fish species have proven to be susceptible to the disease, such as European sea bass ( Dicentrarchus labrax ), Asian sea bass ( Lates calcarifer) , groupers ( Ephinephelus spp . ), Striped jack (Pseudocaranx dentex ), Senegalese sole ( Solea senegalensis ), turbot ( Scophthalmus maximus ), Atlantic halibut ( Hippoglossus hippoglossus ) and Atlantic cod ( Gadus morhua )12.…”

“…Skin color variations, anorexia, lethargy or swim bladder hyperinflation are also frequently observed2. VNN is caused by Betanodavirus, a naked positive-sense single-stranded RNA virus belonging to the family Nodaviridae .…”

The application of pigment-protein fraction from Nannochloropsis oculata on β-actin response of Cromileptes altivelis infected with viral nervous necrosis

“…The increase indicated an effective immune response from the fish. VNN infection itself has been a serious problem for humpback grouper culture due to its capability to cause cell and tissue damage (Yanuhar et al, 2012;Yuwanita & Yanuhar, 2013;Costa & Thompson, 2016).…”