Viral Nervous Necrosis (VNN) in
red snapper snapper

Intro

Clinical signs

Diagnosis

Factors

Treatment and preventions

Special characteristics

Also seen in older fishes

Mode of transmission

Mainly affect juvenile and larvae

caused by red-spotted grouper nervous necrosis virus (RGNNV), from genus Betanodavirus (family: Nodaviridae)

Virus (Betanodavirus)

Disease

RNA 1 encodes viral replicase, RNA2 encodes teh capsid protein

Can survive for 1 year in the right environmental conditions

Contain two genetic segments, RNA1 and RNA2

Selective breeding to NNV resistance

Good management practices

Vaccination

Stressors

High stocking densities

Improper handling

High ambient temperature

Virulence of particular betanodavirus strain

Horizontal transmission

Vertical transmission

Persist clinically in infected live fish

Clinical signs

Change in colouration is important indication

High mortalities

Gross pathological signs

Microscopic pathological signs

Behavioural abnormalities

RGNNV

Distributed in various warm water fish (eg: grouper, red snapper)

Optimal growth temperature (25C - 30C)

Abnormal swimming (erratic swimming)

Loss of equilibrium

Anorexia

Blindness

Overinflated swim bladder

Abrasions

Intracytoplasmic inclusions in brain tissues

Vacuolation of central nervous tissues, incuding retina

Colour change

Hyperactivity

RT-PCR

Indirect serological methods (ELISA test)

Histology

Apply Biosecurity in the aquaculture system

Direct contact with infected fish

References

Zorriehzahra, M. J., Adel, M., Dadar, M., Ullah, S., & Ghasemi, M. (2019). Viral nervous necrosis (VNN) an emerging disease caused by Nodaviridae in aquatic hosts: Diagnosis, control and prevention: A review. In Iranian Journal of Fisheries Sciences (Vol. 18, Issue 1, pp. 30–47). Iranian Fisheries Research Organization. https://doi.org/10.22092/ijfs.2018.117849

Viral Encephalopathy and Retinopathy | Disease guide | The Fish Site. (n.d.). Retrieved November 24, 2020, from https://thefishsite.com/disease-guide/viral-encephalopathy-and-retinopathy

Doan, Q. K., Vandeputte, M., Chatain, B., Morin, T., & Allal, F. (2017). Viral encephalopathy and retinopathy in aquaculture: a review. In Journal of Fish Diseases (Vol. 40, Issue 5, pp. 717–742). Blackwell Publishing Ltd. https://doi.org/10.1111/jfd.1254