Lecture 7 Flashcards
What is acute hepatopancreatic necrosis disease
- A notifiable and exotic disease
- A gram negative bacillus that contains an approximate 70kbp plasmid with genes that encode homologues of the Photohabdus insect-related binary toxins, PirA and PirB
What is acute hepatopancreatic necrosis disease characterised by
- Sudden, mass mortalities, ususally within 30-35 days of stocking grow-out ponds with post larvae or juveniles although older juveniles may also be affected
Clinical signs of acute hepatopancreatic necrosis disease
- Hepatopancreatic pallor and atrophy, soft sheels, intestine with discontinuous, or no contents, black, melanised foci or linear streaks visible within the HP
acute hepatopancreatic necrosis disease: how is the bacteria transmitted
- Horizontal oral transmission and co-habitation
What reduced acute hepatopancreatic necrosis disease
- Low salinity during the hot and dry season from April to July
How to control acute hepatopancreatic necrosis disease
- No treatments, vaccination, immunostimulants or resistance-breeding successes to-date
- As with other infections, establish good sanitary and biosecruity ptactices
- Good broodstock management, use of high quality port-larvae and good shrimp farm management including strick feeding rate control andappropriate stocking density
What is necrosing hepatopancreatitis
- Exotic and notifiable: infection w/ Candidatus Hepatobacter penaei an obligate intracellular bacterium
What are the clinical signs of Hepatobacteria penaei
- No CS are pathognomoic
- Acute disease with v. high mortalities in young juveniles, adults and broodstock
- Lethargy,reduced food intake
- Noticable reduced growth and weight gain
- Soft shells and flaccid bodies
- Black or darkened gills
Where do NHP persist
- Lengthy periods of high water tempertaure and elevated salinity
When do mortalities with NHP occur
- Midway through the grow-out phase and can be 90-95% within 30 days of outbreak
How is NHP transmitted
- Direct ingestion of carrier prawns and through contaminated water
- NHP bacteria mayalso be shed in faeces and contribute to disease transmission
Explain infectious hypodermal and haematopoietic necrosis virus
- Member of the family Parcoviridae
- Target tissue is CT, gills, haematopoietic noudles and haemocytes, vental nerve cord and ganglia, antenal gland tubule epithelial cells and lymphoid organ parenchymal cells
Signs of Infectious hypodermal and haematopoietic necrosis virus
- Not specifc
- Go off food followed by behavioural chnages and appearance
- Morbidity and mortality
- Become motionless, rise to top of tank, turn over and slowly sink
- White or buff coloured spots
Describe runt deformity syndrome
- Chronic form of IHHVV disease
- Supressed growth
- Bent or derfoemed rostrum
- Deformed 6th abdominal segment
How to control runt deformity syndrome
- Replication at high water temps is reduced
- PCR pre-screening of wild or pond-reared brookstock or thei spaened eggs/napulli
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What does white stop syndrome affect
Crustaceans
Where is white spot a problem
- The disease has mainly been a problem in farmed penaids but all decapod crustaceans are considered susceptiblw to infections
- Birds can spread the virus
What are the signs of white spot syndrome
- Rapid onset of mass mortality in farmed penaeid prawns druing thegrow-out period
- Letharrgy
- Cessation of feeding
- Aggregations of moribund prawns near the water surface at the edgeof the rearing pond or tank
Gross pathology of white spot syndrome
- Loose carapace
- Heavy fouling of the surfsce and gills by external parasites
Explain infectious myonecrosis virus
- Follows from stressful events
- Virus targets the striated muscles,CT, haemocytes and lymphoid organ parenchymal. cells
Where does IMNV remain infectious
Gut and faeces of seabirds - due to non-enveloped dsRNA virus structure
How is IMNV transmitted from shrimp to shrimp
- Cannibalism
- Water
- Ventrally from broodstock
Acute stage of IMN
- Focal to extensive white necrotic areas in striated muscles, especially the distal abdominal segments and tail fin
Good management of IMN
- Disinfection of eggs and lsrvae
What is seen with gill-associated virus
- Reddening of the tail fin and biofouling with ectoparasites; emaciation
Signs of Yellowhead
- Aggregations of moribund prawns near the water surface at the edge of the rearing pond or tank
- Abnormally high feeding rate of infected5g-15g prawns for several days and then cessation of feeding
- Mass mortality occuring 2-4 days after cessation of feeding
How is YHV transmistted
- Vertical - both male and female
- Horizontally by ingestion of infected tissues or cohabitation with infected shrimp
What is the gross pathology signs of YHV
- Yellowing of the cephalothorax and general bleacing of the body
- White, yellow and brown gills
- Exceptionally soft digestive gland compared with normal
- Yellow, swollen digestive gland, making head appear yellow
What is the crayfish plague caused by
Infection with the oomycete Aphanomyces astaci
- Fresh water only
When does the crayfish plague usually occur
- Summer
What is the primary transmission mechanism of crayfish plague
- Motile zoospores of A. astaci swim actively in the water column and show positive movement towards other crayfish
Clinical signs of crayfish plague
- High mortality
- Many dead ot weak floating or lying in water courses or ponts
- In open water during daylight hours unstrady and raised gait
- Progressive paralysis
What are the gross pathologies with crayfish plague
- Fungal growth on soft, non-calcified parts of the carapace
- Brown or black spots on the carapace where fungal hyphae proliferation
- Fine black line on the soft shell underneath the tail melanised shell in chronically affected individuals
