White Spot Syndrome Virus (WSSV)
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).
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