Age dependency of nervous necrosis virus infection in barramundi Lates calcarifer (Bloch)

Abstract

Age-dependent susceptibility to nervous necrosis virus (NNV) was demonstrated for barramundi (Lates calcarifer). The experiment used juvenile barramundi produced from a single spawning that were challenged consecutively by immersion with a redspotted grouper nervous necrosis virus (RGNNV) isolate. The dose and environmental conditions (35 ppt salinity and 30 °C) were constant. Fish and water were sampled longitudinally for histopathology and RT-qPCR analysis to examine the evolution of the disease, virus replication, immune response and release of virus into water. Viral nervous necrosis (VNN) disease occurred in barramundi challenged at 3 and 4 weeks of age while fish challenged at 5, 7 and 9 weeks of age developed subclinical infection. Replication of NNV occurred faster and the concentration of virus reached higher concentrations in the younger fish with clinical disease. Virus isolation and qPCR tests indicated that infectious NNV was released from carcasses into water when fish were affected with clinical disease but not when NNV infection was subclinical. Based on these observations, we consider that carcasses from clinically infected fish have a potentially important role in the horizontal transmission of NNV, and barramundi juveniles should be protected from exposure to NNV until they are 5 weeks of age and reach the disease resistance threshold.

Host, agent and environment interactions affecting Nervous necrosis virus infection in Australian bass Macquaria novemaculeata

“…Australian bass became tolerant and/or resistant to the disease between 3 and 5 weeks of age, similar to that observed for barramundi in a previous study (Jaramillo, Hick, & Whittington, ). This observation is also similar to what has been reported for several species by other authors based on anecdotal and experimental evidence, larvae exposed to NNV become diseased while juveniles or older fish appear refractive to infection(Aranguren et al., ; Arimoto et al., ; Chi et al., ; Nishizawa et al., ; Sommer et al., ; Tanaka et al., ).…”

“…As we have proposed before (Jaramillo, Hick, & Whittington, ), one plausible hypothesis to explain the association between age and resistance to NNV infection could lay around cell division activity. Johansen et al.…”

“…Although the viral load in water is increased in Experiment 1, it did not do so in Experiment 2. This could be due to the higher stocking density in the first experiment, but it could be due to the much higher mortalities as observed in our previous study conducted on barramundi (Jaramillo, Hick, & Whittington, ).…”

“…Additional factors including viral isolate, dose, route of infection and stress have also been reported (Arimoto et al., ; Athanassopoulou, Billinis, Psychas, & Karipoglou, ; Grotmol, Bergh, & Totland, ; Korsnes, Karlsbakk, Nylund, & Nerland, ; Shinji Tanaka et al., ; Totland, Grotmol, Morita, Nishioka, & Nakai, ; Vendramin et al., ). Susceptibility to VNN is age−dependent in multiple species such as striped jack Pseudocaranx dentex , Atlantic halibut, wolfish Anarhichas minor , zebrafish Danio rerio and barramundi (Arimoto et al., ; Jaramillo, Hick, & Whittington, ; Lu et al., ; Sommer et al., ) but not in others such as groupers Epinephelus spp. or European sea bass (Grotmol et al., ; Nakai et al., ).…”

Complete genome sequence and pathogenic analysis of a new betanodavirus isolated from shellfish

“…Betanodavirus infects many fish species at larval, early juvenile and even adult stage and causes enormous damage to aquatic farms (Jaramillo, Hick, & Whittington, ; Munday et al, ; Yanong, ). However, in previous studies, KSNNV‐KOR1 induced relatively high infectivity and vacuolar lesions in brain tissue of various fish species, even though they were not lethal to adult fish (Kim, Kwon, Min, et al, ).…”