Acute hepatopancreatic necrosis disease

Acute hepatopancreatic necrosis disease is prohibited matter.

Under Queensland legislation, if you suspect the presence of this disease in any species of animal, you must report it to Biosecurity Queensland on 13 25 23 or contact the Emergency Disease Watch Hotline on 1800 675 888.

Acute hepatopancreatic necrosis disease (AHPND) is a serious bacterial disease affecting a range of prawn species. It causes abnormal growth and death in prawns as early as 10 days after stocking and has been officially reported in China, Vietnam, Malaysia, Thailand and Mexico.

Cause

  • Pathogenic strain of the bacteria Vibrio parahaemolyticus.

Other names

Early Mortality Syndrome (EMS) – a broader term used to describe a range of shrimp health problems that lead to early mortality.

Description

Disease signs at pond level

  • Pale to white hepatopancreas due to pigment loss in the connective tissue capsule.
  • Significant atrophy (shrinkage) of hepatopancreas.
  • Soft shells and guts with discontinuous contents or no content.
  • Black spots or streaks sometimes visible within the hepatopancreas.
  • Hepatopancreas does not squash easily between thumb and finger.
  • Onset of clinical signs and mortality starting as early as 10 days after stocking.
  • Moribund shrimp sink to bottom.

Disease signs at animal level by histopathology

  • Acute progressive degeneration of the hepatopancreas accompanied initially by a decrease of R, B and F-cells, followed last by marked reduction of mitotic activity in E-cells.
  • Progress of lesion development is proximalto-distal with dysfunction of R, B, F, and lastly E-cells, with affected hepatopancreas tubule mucosal cells presenting prominent karyomegaly (enlarged nuclei), and rounding and sloughing into hepatopancreas tubule lumens.
  • Sloughed hepatopancreas cells provide substrate for intense bacterial growth, resulting in massive secondary bacterial infection (putative Vibrio spp.) and complete destruction of hepatopancreas at terminal phase of disease.

Distribution in Queensland

  • Not yet recorded in Queensland.

Affected animals

prawns; shrimp

Hosts

  • To date, AHPND is reported to affect giant tiger prawn (Penaeus monodon), whiteleg shrimp (P. vannamei) and fleshy prawn (P. chinensis).

Impacts

Economic

  • Based on effects observed in South-East Asian prawn farms, has potential to cause significant economic impacts on prawn aquaculture in Australia.

How it is spread

  • Transmitted experimentally by immersion and reverse gavage.
  • Based on these experiments, oral and cohabitation transmission should be expected.
  • No evidence at this time to suggest that it affects other aquatic species such as fish or crabs.

Risk period

  • Typical signs begin within 10-30 days after stocking of post-larvae into newly prepared pond.

Monitoring and action

  • Under Section 100 of Fisheries Act 1994: ‘a person who knows or reasonably suspects a fisheries resource or a fish habitat is showing signs of disease, or knows or reasonably suspects disease may be in fisheries resources or a fish habitat, must immediately notify the chief executive or an inspector’.
  • Remove sick and dying animals as soon as possible. Treat in an isolated area or dispose of appropriately so there is no contamination of the farm animals or aquatic environment.
  • Develop and implement, if necessary, a contingency plan to handle diagnosis of a serious disease on farm or hatchery.

Control

It is important that people working in aquaculture implement and maintain good biosecurity practices on their farms.

If you plan to introduce new animals, you should source them from disease-free farms and make sure you arrange health testing and disease-free certification.

Consider isolating any new animals from the rest of your farm for an appropriate period of time.

Prepare a contingency plan to handle the diagnosis of a ‘declared disease’ or other ‘serious disease’ event on your farm/hatchery. This should include:

  • a plan and ability to isolate each pond, tank, sub-unit or system to prevent transfer of disease by water, bird, animal or human to other farms and the aquatic environment
  • a capacity to disinfect an entire pond, tank, sub-unit or system
  • a capacity and appropriate method to destroy, collect and dispose of large numbers of aquatic animals in accordance with expert advice
  • a record-keeping system to allow tracing of the origin and disposal of any affected group of aquatic animals.

More information