Necrotising hepatopancreatitis

Signs of disease

Important: animals with disease may show one or more of the signs below, but disease may still be present in the absence of any signs.

Clinical signs of disease in an infected animal

• lethargy
• emaciation
• soft shells
• heavy fouling from external parasites
• black gills
• reduced growth

Gross signs of disease in an infected animal

• digestive gland (hepatopancreas) degenerated—appears pale to white  

Disease agent

Necrotising hepatopancreatitis is caused by a species of alpha-proteobacterium that infects the hepatopancreas of prawns, also referred to as NHP bacteria.

Host range

Crustaceans known to be susceptible to the disease:

• northern brown shrimp* (Penaeus aztecus)
• northern white shrimp* (Penaeus setiferus)
• Pacific blue shrimp* (Penaeus stylirostris)
• white shrimp* (Penaeus vannamei)
• yellowleg shrimp* (Penaeus californiensis)

* naturally susceptible (other species have been shown to be experimentally susceptible)

Presence in Australia

EXOTIC—not present in Australia.

Epidemiology

• Necrotising hepatopancreatitis requires lengthy periods of high air temperature (29–31°C) and elevated salinity (20–40 ppt).
• Mortality can be 90–95 per cent within 30 days of an outbreak.
• Mortalities usually occur midway through the grow-out phase.
• Necrotising hepatopancreatitis appears to be transmitted by direct ingestion of an unidentified carrier (a reservoir host).
• The disease is not transmitted either vertically (from parent to offspring) or through cannibalism.

Differential diagnosis

The differential diagnostic table and the list of similar diseases appearing at the bottom of each disease page refer only to the diseases covered by this field guide. Gross signs observed might well be representative of a wider range of diseases not included here. Therefore, these diagnostic aids should not be read as a guide to a definitive diagnosis, but rather as a tool to help identify the listed diseases that most closely account for the gross signs.

Similar diseases

The clinical signs described and shown here may also be symptomatic of other bacterial or viral infections, or poor water quality in rearing ponds (high ammonia, low oxygen, high and low pH). Further laboratory examination is required for a definitive diagnosis.

Further images

Sample collection

Because of uncertainty in differentiating diseases using only gross signs, and because some aquatic animal disease agents might pose a risk to humans, you should not try to collect samples unless you have been trained. Instead, you should phone your state or territory hotline number and report your observations. If samples have to be collected, the agency taking the call will advise you on what you need to do. Local or district fisheries/veterinary authorities could advise you on sampling.

Emergency disease hotline

For your state or territory emergency disease hotline number, see Whom to contact if you suspect a disease.

Further reading

www.oie.int/aac/eng/cards/en_diseasecard.htm

www.pac.dfo-mpo.gc.ca/sci/shelldis/pages/nechepsp_e.htm