Monodon Baculovirus (MBV) Disease of Penaeid Shrimp
Category 3 (Host Not in Canada)
Common, generally accepted names of the organism or disease agent
Penaeus monodon-type baculovirus, MBV.
Scientific name or taxonomic affiliation
PmSNPVA (for single enveloped nuclear polyhedrosis virus of type-A from P. monodon), an occluded baculovirus which contains double stranded DNA as the nucleic acid type. The Plebejus baculovirus (PBV) found in cultured P. plejebus and P. monodon and wild P. merguiensis in Australia is a geographic strain of MBV.
Widely distributed in cultured shrimp in P.R. China, Taiwan, Indonesia, Philippines, Malaysia, Thailand, Sri Lanka, Singapore, Australia, India, Israel, Kuwait, Oman, Italy, Kenya, Gambia and South Africa. Has been introduced into Tahiti, Hawaii, Brazil, Ecuador, Mexico, Puerto Rico and in several southeastern states of the United States.
Penaeus monodon, Penaeus merguiensis, Penaeus semisulcatus, Penaeus kerathurus, Penaeus vannamei, Penaeus esculentus, Penaeus penicillatus, Penaeus plebejus, Metapenaeus ensis.
Impact on the host
Lethargy, anorexia, dark coloured, and with heavy surface fouling. Acute MBV causes loss of hepatopancreatic tubule and midgut epithelia and consequently, dysfunction of these organs, often followed by secondary bacterial infections. MBV has been linked with high mortalities (over 90%) in late postlarvae and juvenile shrimp in many culture facilities. It has caused heavy mortalities (70% of all stages of P. monodon in the Philippines and 90% of postlarval P. monodon in Madras, India), and is considered partially responsible for the collapse of the shrimp culture industry in Taiwan in the late 1980s. Usually juvenile and adult P. monodon are more resistant to MBV than larval shrimp. Although good culture practices may enhance survival of MBV infected stocks, growth, crop value and performance may be significantly reduced and MBV may predispose infected shrimp to infections by other pathogens, with corresponding higher mortality rates.
Gross Observations: Reduced feeding and growth rates, and increased surface and gill fouling with various epibiotic and epicommensal organisms may accompany MBV infection. Severely affected larvae and postlarvae may exhibit a white midgut line through the abdomen.
Squash Preparations: Single or multiple generally spherical intranuclear occlusion bodies (a specialized inclusion body that stain more intensely with 0.1% aqueous malachite green than secretory granules and lipid droplets) that range is diameter from less than 0.1 µm to nearly 20 µm in the epithelial cells of the hepatopancreas and midgut. Occlusion bodies may also be found in fresh faeces examined under phase or bright field microscopy. A rapid and specific diagnostic tool for the identification of baculovirus occlusions involves epifluorescent light microscopy of tissue squashes stained with 0.001% aqueous phloxine (Thurman et al. 1990). MBV occlusions also stain more intensely with 0.05% malachite green than similar sized normal host cell nuclei, nucleoli, secretory granules or phagolysosomes, and lipid droplets.
Histology: MBV occlusion bodies appear as prominent eosinophilic (with haematoxylin and eosin stain) multiple round bodies within the hypertrophied nuclei of hepatopancreatic tubule or midgut epithelial cells. In light infections prior to formation of occlusion bodies, infected cells possess hypertrophied nuclei with diminished nuclear chromatin and laterally displaced nucleolus giving the nucleus a signet-ring appearance. Brown & Brenn histologic Gram stain (Luna 1968), although not specific for baculovirus occlusion bodies, tends to stain occlusions more intensely (either red or purple, depending on section thickness, time of decolourization etc.) than the surrounding tissue aiding in demonstrating their presence in low-grade infections. Another diagnostic tool for the identification of baculovirus occlusions involves epifluoresence light microscopy of histological sections stained with 0.005% phloxine as a component of the eosin part of normal haematoxylin and eosin staining (Thurman et al. 1990).
Electron Microscopy: Virions free in the nuclei and within the occlusion bodies measure about 74 x 270 nm. The virons from cultured P. monodon in Madras, India were rod-shaped (83 x 299 ± 0.02 nm), non-occluded or occluded and enveloped within a paracrystalline occlusion body. The nucleocapsid of the MBV strain from P. monodon from the Indo-Pacific is 42 ± 3 nm by 246 ± 15 nm while the enveloped viron is 75 ± 4 nm by 324 ± 33 nm. The nucleocapsid of the PBV strain from P. plebejus, P. monodon and P. merguiensis from Australia is 45-52 nm by 260-300 nm while the enveloped viron is 60 nm by up to 420 nm.
DNA Probes: A kit based on DNA dot hybridization probe for the rapid, on-site detection of MBV is being developed by Dr. S.N. Chen, (National University of Taiwan, Taipei, Taiwan) and Vickers et al. . 1992. DIG-labeled DNA probes that provide a very sensitive method for the detection of MBV in fixed tissue sections via in situ hybridization are available commercially from DiagXotics Inc. (27 Cannon Rd., Wilton, CT 06897, USA).
Methods of control
No known treatment. MBV epizootics are basically hatchery and/or pond management problems that are not confined to certain places or seasons. Although the disease is enhanced by stress it is well tolerated by P. monodon held in optimal conditions. The incidence of MBV in the hatchery can be substantially reduced by avoiding contamination of eggs and nauplii with faeces from the broodstock and by using clean sea water to wash (for 3 hr at 500 litre per hr in a 500 litre fibreglass tanks) the eggs and nauplii before transferring them to rearing tanks and by using MBV-free broodstock.
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Vickers, J.E., R.J.G. Lester, P.B. Spradbrow and J.M. Pemberton. 1992. Detection of Penaeus monodon-type baculovirus (MBV) in digestive glands of postlarval prawns using polymerase chain reaction. In: M. Shariff, R.P. Subasinghe and J.R. Arthur (eds.). Diseases in Asian Aquaculture. I. Fish Health Section, Asian Fisheries Society. Manila, Philippines, p. 127-133.
Bower, S.M. (1996): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Monodon Baculovirus (MBV) Disease of Penaeid Shrimp.
Date last revised: Fall 1996
Comments to Susan Bower
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