Lecture 7

Question 1

What is acute hepatopancreatic necrosis disease

Answer 1

• 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

Question 2

What is acute hepatopancreatic necrosis disease characterised by

Answer 2

• 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

Question 3

Clinical signs of acute hepatopancreatic necrosis disease

Answer 3

• Hepatopancreatic pallor and atrophy, soft sheels, intestine with discontinuous, or no contents, black, melanised foci or linear streaks visible within the HP

Question 4

acute hepatopancreatic necrosis disease: how is the bacteria transmitted

Answer 4

• Horizontal oral transmission and co-habitation

Question 5

What reduced acute hepatopancreatic necrosis disease

Answer 5

• Low salinity during the hot and dry season from April to July

Question 6

How to control acute hepatopancreatic necrosis disease

Answer 6

• 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

Question 7

What is necrosing hepatopancreatitis

Answer 7

• Exotic and notifiable: infection w/ Candidatus Hepatobacter penaei an obligate intracellular bacterium

Question 8

What are the clinical signs of Hepatobacteria penaei

Answer 8

• 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

Question 9

Where do NHP persist

Answer 9

• Lengthy periods of high water tempertaure and elevated salinity

Question 10

When do mortalities with NHP occur

Answer 10

• Midway through the grow-out phase and can be 90-95% within 30 days of outbreak

Question 11

How is NHP transmitted

Answer 11

• Direct ingestion of carrier prawns and through contaminated water
• NHP bacteria mayalso be shed in faeces and contribute to disease transmission

Question 12

Explain infectious hypodermal and haematopoietic necrosis virus

Answer 12

• 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

Question 13

Signs of Infectious hypodermal and haematopoietic necrosis virus

Answer 13

• 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

Question 14

Describe runt deformity syndrome

Answer 14

• Chronic form of IHHVV disease
• Supressed growth
• Bent or derfoemed rostrum
• Deformed 6th abdominal segment

Question 15

How to control runt deformity syndrome

Answer 15

• Replication at high water temps is reduced
• PCR pre-screening of wild or pond-reared brookstock or thei spaened eggs/napulli
  *

Question 16

What does white stop syndrome affect

Answer 16

Crustaceans

Question 17

Where is white spot a problem

Answer 17

• The disease has mainly been a problem in farmed penaids but all decapod crustaceans are considered susceptiblw to infections
• Birds can spread the virus

Question 18

What are the signs of white spot syndrome

Answer 18

• 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

Question 19

Gross pathology of white spot syndrome

Answer 19

• Loose carapace
• Heavy fouling of the surfsce and gills by external parasites

Question 20

Explain infectious myonecrosis virus

Answer 20

• Follows from stressful events
• Virus targets the striated muscles,CT, haemocytes and lymphoid organ parenchymal. cells

Question 21

Where does IMNV remain infectious

Answer 21

Gut and faeces of seabirds - due to non-enveloped dsRNA virus structure

Question 22

How is IMNV transmitted from shrimp to shrimp

Answer 22

• Cannibalism
• Water
• Ventrally from broodstock

Question 24

Acute stage of IMN

Answer 24

• Focal to extensive white necrotic areas in striated muscles, especially the distal abdominal segments and tail fin

Question 25

Good management of IMN

Answer 25

• Disinfection of eggs and lsrvae

Question 26

What is seen with gill-associated virus

Answer 26

• Reddening of the tail fin and biofouling with ectoparasites; emaciation

Question 27

Signs of Yellowhead

Answer 27

• 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

Question 28

How is YHV transmistted

Answer 28

• Vertical - both male and female
• Horizontally by ingestion of infected tissues or cohabitation with infected shrimp

Question 29

What is the gross pathology signs of YHV

Answer 29

• 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

Question 30

What is the crayfish plague caused by

Answer 30

Infection with the oomycete Aphanomyces astaci

• Fresh water only

Question 31

When does the crayfish plague usually occur

Answer 31

• Summer

Question 32

What is the primary transmission mechanism of crayfish plague

Answer 32

• Motile zoospores of A. astaci swim actively in the water column and show positive movement towards other crayfish

Question 33

Clinical signs of crayfish plague

Answer 33

• 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

Question 34

What are the gross pathologies with crayfish plague

Answer 34

• 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