Tetrahedral baculovirosis

Signs of diseases

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 farm level

• reduced feeding

Clinical signs of disease in an infected animal

• high mortality in larval, postlarval and juvenile prawns
• reduced growth rates in surviving juveniles and adults
• increased fouling with exoparasites

Gross signs of disease in an infected animal

• milky-white midgut

There are few visible signs indicating infection with this disease other than rapid high mortality of hatchery prawns in the early life stages. Therefore, diagnosis is usually based on microscopic and histological examination.

Disease agent

The causative agent is Baculovirus penaei. At least three geographical strains of B. penaei have been demonstrated: southeast Atlantic and Gulf of Mexico coasts of the United States and the Caribbean; Pacific coast of South, Central and North America; and Hawaii.

Host range

Crustaceans known to be susceptible to tetrahedral baculovirosis:

• aloha prawn* (Penaeus marginatus)
• giant black tiger prawn* (Penaeus monodon)
• northern brown shrimp* (Penaeus aztecus)
• northern pink shrimp* (Penaeus duorarum)
• northern white shrimp* (Penaeus setiferus)
• Pacific blue shrimp* (Penaeus stylirostris)
• Pacific white shrimp* (Penaeus vannamei)
• Pomada prawn* (Protrachypene precipua)
• red-spotted shrimp* (Penaeus brasiliensis)
• redtail prawn* (Penaeus pencillatus)
• roughback shrimp* (Trachypenaeus similis)
• San Paulo shrimp* (Penaeus paulensis)
• southern brown shrimp* (Penaeus subtilis)
• southern white shrimp* (Penaeus schmitti)
• All penaeid species may be potential hosts.

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

Presence in Australia

Exotic—not present in Australia.

Epidemiology

• Transmission is horizontal by ingestion of infected tissue (cannibalism), faeces, occlusion bodies, or contaminated detritus or water.
• Eggs and newly hatched nauplii may be exposed to the virus through faeces of infected adult spawners taken from the wild.
• Infection is restricted to the hepatopancreas and anterior midgut.
• Disease is not known to occur in wild populations carrying infected with Baculovirus penaei.
  Crowding, chemical stress or environmental stress may increase pathogenicity and the prevalence of disease.

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

Baculoviral midgut gland necrosis, spherical 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.

Further reading

The currently accepted procedures for a conclusive diagnosis of tetrahedral baculovirosis are summarised at www.oie.int/eng/normes/fmanual/A_00051.htm