Lecture 6 Flashcards
IS VIRAL NERVOUS NECROSIS NOTIFIABLE
Yes
What is viral nervous necrosis disease caused by
Non-enveloped ssRNA viral nervous necrosis disease, a betanodavirus/ also known as viral encephalopathy and retinopathy
viral nervous necrosis disease: can you breed for resisance
No
Where can viral nervous necrosis disease be spread in
Marine or fresh water, tropical, moderate and cold areas also in ornamentak
What disease is shown
viral nervous necrosis disease
Where is viral nervous necrosis disease acute in
Larvae from 10 days old; devestating with up to 100% mortality
What are the clinical sings of viral nervous necrosis disease
- Chromatophores cntact - larvae transparent
- Cork screw or whirling swimming; hyper-inflated swim bladder
What is seen histologically with viral nervous necrosis disease
- Pathogenic cell vacolisation and necrosis of the central nervous system with lesions occuring in retina and spinal cord
- Histopathology and nested Polymerase Chain Reaction (PCR) to confirm
Explain the vertical transmission of viral nervous necrosis disease
Through the broodstock - virus detected in gonads, fertilised eggs and larvage
Explain the horizontal transmission with viral nervous necrosis disease
Through the water with VNN outbreaks in fish farms occuring after introduction of infected juveniles
How to treat viral nervous necrosis disease
No specific treatment
- Ozone treat all incoming eggs and larvae and VNN-free broodstock
What is big belly syndrome
- Intracellular, bi-polar large intracellular coco bacillus bacterium - associated with dsiella ictluri the cause of enteric septicaemia of catfish and bacillary necrsis of cat fish
What are infected individuals with Big Belly Syndrom like
- Darker colour, lethargic, separate from schools and lose equilibrium
- Poor feeding, emaciation, abdominal distension or ‘pot-belly; and red, swollen anus (vent)
- Slow systemic infection, onset of mortality is gradual but consistent
How to diagnose BBS
- Impression smears
- Isolation of bacteria is difficult due to is intracellular nature
- Once recovered they are knowns as asymptomatic carriers
- Disease can reoccur is they have been exposed to stress
What is one of the most severe diseases in barra and groupers
- Iridovirus
Iridovirus: who does it affect
- Mainly occurs in fish of 10-50g and causes acute peaks of mortality of up to 80-90%
Iridovirus: how do the fish appear
- Hyper-pigmented with loss of appetite, the gills exhibit pallor and are friable - may bleed when handled
- Hyphaema is often present giving ‘red eye’ appeararance
- Pale spleen
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Iridovirus: what are related to megalocytoviruses
- Red Sea Iridovirus and Infection Spleen and Kidney Necrosis virus
What is shown here
Scale Drop Disease Virus
What can be seen with scale drop disease virus
Karyorrhexis and pyknosis
What are the signs of scale drop and muscle necrosis
- Scale loss
- Muslce degredation
- Death
- Severe necrosis of muscles
- Severe haemorrhange
- Kidney tubules and epithelial cells sloughing
Scale drop and muscle necrosis diease
How to control benedenia spp
- Health monitoring
- Early diagnosis
If left untreated with happens with benedenia spp
Skin and tail rot
High mortality rates
