Baculoviral midgut gland necrosis

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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.

Disease signs at the tank and pond level

larvae float inactively on the surface

Clinical signs of disease in an infected animal

midgut gland (hepatopancreas) suddenly turns white in larvae and postlarvae
high mortality
white midgut line seen through abdomen

Disease agent

Baculoviral midgut gland necrosis virus is currently an unassigned virus of the family Baculoviridae. It was known as Penaeus japonicus nonoccluded baculovirus (PjNOB) before it was removed from the classification structure by the International Committee on Taxonomy of Viruses in 1995.

Host range

Crustaceans known to be susceptible to baculoviral midgut gland necrosis:

eastern king prawn* (Penaeus plebejus)
Kuruma prawn* (Penaeus japonicus)
Chinese white shrimp (Penaeus chinensis)
giant black tiger prawn (Penaeus monodon)
grooved tiger prawn (Penaeus semisulcatus)

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

Presence in Australia

EXOTIC—not present in Australia.

Epidemiology

Baculoviral midgut gland necrosis strikes suddenly, and high mortalities follow quickly.
Infection in hatcheries is believed to arise from wild-caught female spawners.
The virus causes high mortality of larvae; late postlarvae tend to be more resistant.
The virus can persist and retain infectivity for up to 20 days in water averaging 15°C.
Transmission is horizontal, through faeces shed during spawning.
The disease affects larvae and up to 20 days of postlarval development (PL-20).
Mortalities are highest (up to 98 per cent) at 9–10 days of postlarval development (PL-9–10).
There is typically a decrease in mortality rates as the postlarvae reach PL-20.

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

White spot disease, tetrahedral baculovirosis

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.