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Shrimp & Prawns

As yet, there are no vaccines or treatments available for any of these diseases, so knowledge and the appropriate preventative measures are key.

 VIRUSES COVERED
Baculoviral mid-gut gland necrosis virus
Baculovirus penaei
Hepatopancreatic parvo-like virus
Infectious hypodermal and hematopoietic necrosis virus
Monodon baculovirus
Reo-like virus
Taura Syndrome Virus
Yellow head baculo-like virus
Others



Baculoviral mid-gut gland necrosis virus (BMNV)
Host: Penaeus japonicus larval and postlarval stages
Range: Japan
Features: Epizootic disease characterized by mortality rates up to 100% in cultured populations. Transmission is via waterborne exposure or orally, with unspecific signs of infection such as high mortality, poor growth rates and anorexia. Affected prawns have a 'white-turbid' or opaque mid gut gland. Diagnosis is based on epizootiological and histopathological findings (does not produce occlusion bodies, but there is marked tubular hypertrophy), and there is now a rapid fluorescent antibody test for it.
 

Baculovirus penaei (BP)
Host: Penaeus duorarum juveniles and adults, Penaeus aztecus larvae and adults, Penaeus setiferus larvae, Penaeus vannamei larvae and postlarval stages, Penaeus stylirostris larvae and post larval stages, Penaeus marginatus juveniles
Range: Restricted to the USA and the Pacific Coast side of Central and South America
Features: High morbidity as a hatchery epizootic disease with high mortality in larval and post larval stages. Unspecific signs such as poor growth rates, anorexia and lethargy as well as epicommensal fouling due to reduced grooming activity. The virus mainly attacks cells of the hepatopancreatic epithelium but it can infect mid-gut epithelium. Diagnosed by characteristic multiple polyhedral intranuclear occlusion bodies in the hepatopancreas and mid-gut. Transmission is orally, with mature virions being released into the lumen of the midgut and getting excreted into the environment via feces where they are consumed by other shrimp.
 

Hepatopancreatic parvo-like virus (HPV)
Host: Penaeus aztecus
Features: This virus is probably a member of either the parvovirus group or the picornavirus group (has similar cytopathologic features as is seen in parvovirus infection). In epizootics, mortality rates have been as high as 100% within 4-8 weeks of onset. Signs include poor growth rates, reduced preening activity, exoskeleton surface fouling by epicommensals and occasionally secondary bacterial and fungal infections. The main lesion is necrosis and atrophy of the hepatopancreas, with the presence of large basophilic intranuclear inclusions bodies in hepatopancreocytes. The relationship between HPV and disease is not entirely clear though.
 

Infectious hypodermal and hematopoietic necrosis virus (IHHNV)
Host: Juvenile and adult stages of Penaeus stylirostris, Penaeus monodon, Penaeus japonicus, Penaeus aztecus, and Penaeus duorarum. Penaeus vannamei may harbor the virus as an inapparent or latent infection throughout its life cycle.
Range: Has been reported in Hawaii, Tahiti, Florida, Texas, Cayman Islands, Israel, Panama, Costa Rica, Belize, Ecuador, Philippines, Singapore, Guam, Brazil, Honduras, France and Jamaica
Features: Also known for fairly high mortality, this RNA virus generally diagnosed on the basis of behavioural and gross changes, with confirmation based on histopathology (large eosinophilic intranuclear Type A inclusion bodies in cells of ectodermally derived tissues and mesodermally derived tissues). In the acute stage, affected individuals have white opaque abdominal musculature and numerous focal melanized areas. Often they are lethargic, eat less, and rise slowly to the water surface (often with the ventral surface up) then sink back down again. A non-destructive determination of IHHNV has been developed.
 

Monodon baculovirus (MBV)
Host: Larval, postlarval, juvenile and adult Penaeus monodon, Penaeus kerathrus, Penaeus merguiensis, Penaeus semisulcatus
Range: Asia, as well as areas of the Indopacific, Mediterranean, Phillippines, Taiwan, Malaysia, Hawaii, Tahiti, Singapore, Kuwait, Kenya, Israel, Italy
Features: Often with severe mortality with the most serious losses in the late postlarval and juvenile stages. Apparent horizontal transmission by oral exposure to contaminated tissues or fomites. Clinical signs include lethargy, anorexia, suppressed preening activity, retarded growth, grey-blue to blueish-black coloration, shell disease and microbial epibiotic fouling. Diagnosis based on histopathological exam of wet mounts of the hepatopancreas and mid-gut epithelium, and the presence of characteristic eosinophilic intranuclear inclusions.
 

Reo-like virus (REO)
Host: Penaeus japonicus juveniles maintained in laboratory tanks, Penaeus monodon, Penaeus vannamei and other decapod crustaceans.
Features: Thought to be closely related to the family Reoviridae. Takes about 45 days to develop clinical disease and produces mass mortality of P. japonicus, but as of 1993 there had been no reports of epidemics. Has been reproduced experimentally by feeding pieces of hepatopancreas from infected shrimps. Signs include behavioural changes (do not hide in the sand), and the telson, uropods and hepatopancreas may be reddish. Secondary infections by Fusarium are common. Diagnosis is by identification of the typical clinical signs as well as confirmation of the reo-virus by electron microscopy
 

Taura Syndrome Virus (TSV)
Host: Panaeus vannamei and causes less severe disease in Penaeus stylirostris
Range: worldwide distribution
Features: Tentatively classified as either a picornavirus or a nodavirus, TSV is believed to be the cause of Taura syndrome (TS). TS occurs in peracute and recovery phases. The peracute phase is the most common manifestation in juvenile shrimp, and they usually die during molting (some ponds have reported outbreaks with mortality rates of over 95%). Those animals which survive molting either recover or are chronically affected; the chronically affected have scattered black-spot lesions along their outer skin or shell. Gross signs include the appearance of a distinct blue or red hue on the shell and tail (this is the result of chromatophore expansion and the color depends on the dominant chromatophore for the specific animal). As well, infected shrimp usually have empty digestive tracts. Distinctive histopathology in the peracute phase consists of multifocal areas of necrosis of the cuticular epithelium and subcutis, with pathognomonic variably sized eosinophilic to basophilic cytoplasmic inclusion bodies.
 

Yellow head baculo-like virus (YBV)
Host: Penaeus monodon
Range: Thailand
Features: Reported to cause yellow-head disease in cultured black tiger shrimp in Thailand. An acute and lethal condition usually resulting in cumulative mortality of 100% in 3 days, thus making it probably the most acute and lethal disease currently affecting cultured penaeids. Early signs of disease include lack of appetite and lethargy; appear weak several hours before death (sink to the bottom). In tiger shrimp, typical signs of yellow-head disease include characteristic yellowing of the hepatopancreas and gills. The virus can be transmitted to Penaeus stylirostris and Penaeus vannamei, and is thus a potential problem in farmed populations in the Western hemisphere (caution in importation).