Because viruses have a high mutation rate and exist within the hosts cells (Gojobori et at, 1990), they are very hard to treat and thus there is no current cure for VNN.
VNN symptoms can be witnessed as the infected organisms exhibit very lethargic behaviour, show a disinterest for food which leads to anorexia and in fin-fish, spiral swimming is a symptom due to a loss of motor function (Arimoto et al, 1996).
VNN outbreaks can be linked to environmental factors such as large salinity and temperature fluctuations and high sediment loads in the water. To reduce outbreaks, especially in an Aquaculture setting, temperature and salinity should be maintained at a level that minimises stress to the fish.
Prevention can also include incorporating ozone into a circulating water system before the water is added into the tank containing fish, as ozone is toxic to pathogens. Also being an unstable molecule, ozone quickly dissipates out of the system and therefore if incorporated in correct doses will not be harmful to the fish.
VNN outbreaks are most common in fish aged between 4-70 days old (Fakuda et al, 2005) and hopefully through further research, Vaccines may be found to prevent this disease when organisms are most susceptible.
References:
Chi, S. Shieh, J. 2003, 'Genetic and Antigenic Analysis of Betanodaviruses Isolated from Aquatic Organisms in Taiwan', 'Diseases of Aquatic Organisms', vol. 7, pp. 238-249
- Fenner, B.
- Thiagarajan, R.
- Chua. H, Kwang, J. 2005, ' Betanodavirus B2 Is an RNA Interference Antagonist That Facilitates Intracellular Viral RNA Accumulation', 'Journal of Virology', vol. 80, pp. 85-94
- Arimoto, M. Sato, J. Maruyama, K. Mimura, G. Furusawa, I. 1996, 'Effect of Chemical and Physical Treatments on the Inactivation of Striped Jack Nervous Necrosis Virus (SJNNV)', 'Aquaculture', vol 143, pp. 15-22
- Chi, C. Lo, B. Lin, S. 2008, 'Characterization of Grouper Nervous Necrosis Virus (GNNV)', 'Fish Diseases', vol. 24, pp. 3-13
- Fakuda, Y. Nguyen, H. Furuyashi, M. Nakai, T. 1996, 'Mass Mortality of CUltured Sevenbanded Grouper, Epinephelus Septemifasciatus, Associated with Viral Nervous Necrosis', 'Fish Pathology, vol. 31, pp. 165-170
Gojobori, T. Moriyama, E. Kimura, M. 1990, ' Molecular Clockwork of Viral Evolution and the Neutral Theory', 'Current Issue' vol. 87, pp. 24-32
That’s fascinating Jack! I was wondering just how the virus works. Can you explain how it gets into the system of the fish?
ReplyDeleteHey Tasmin,
ReplyDeleteBetanodavirus exists in the water that the fish swim in and the soil surrounding the water body and all it needs is an opening, where it gets into the bloodstream of the fish where it then infects host cells using the same pathways molucules use to enter the cells. Infection could be from the infected water it drinks to an infected fish it eats. Unfortunately little more is known because all but one strain of Betanodavirus infects fish almost always before they are 70 days old when they have a weak immunesystem, making reverse-genetical engeneering tricky. Howevever the Redspotted grouper strain (RGNNV) of betanodavirus has been known to infect grouper even in an adult stage. The infected areas are usually the liver, retina and brain and examining these parts under a microscope can reveal an abundance of vacuoles in the cells. The large picture for the blog page is actually an eye infected from VNN and you can see the white-round, empty sacs that are the vacuoles. In the epinephelus genus, outbreaks only occur in aquaculture facilities when there is a ratio of 50 infected fish to a population of 500. Less than this, transmission of the virus from one fish to another is greatly reduced.
Thanks for the detailed response :)
ReplyDelete