Yellow-head Virus Disease (YHD) of Penaeid Shrimp
Category 3 (Host Not in Canada)
Common, generally accepted names of the organism or disease agent
Yellow-head shrimp disease, Yellow-head virus (YHV), Yellow-head baculovirus (YBV), Yellow-head disease baculovirus (YHDBV)
Scientific name or taxonomic affiliation
The taxonomic identity of YHV has not yet been described. However, it is a ssRNA, rod shaped (44 ± 6 x 173 ±13 nm), enveloped cytoplasmic virus that may belong in the family Rhabdoviridae or with the filamentous group within the Paramyxoviridae. Agarose gel electrophoresis indicated nucleic acid profile at approximately 22 Kb. YHV was originally reported to be a Type B cytoplasmic granulosis baculovirus or a baculo-like virus but because YHV contains ssRNA it is not a baculovirus.
Diagnosed in Thailand, but distribution may be wider in southeast Asia and the Indo-Pacific region as unconfirmed reports of outbreaks include Malaysia, Sri Lanka, Indonesia, Philippines, China and possibly Taiwan. A morphologically similar virus with similar cytopathology but apparently asymptomatic as for RSP was reported from P. monodon in Australia and called Lymphoid organ virus (LOV, but is distinct from another virus LPV also from the lymphoid organ and from Australian penaeids) (Spann et al. 1995).
Penaeus monodon, the giant black tiger shrimp, is the species primarily affected. Penaeus merguiensis, Palaemon styliferus, and Metapenaeus ensis were experimentally infected. However, P. merguiensis, that were acquired incidentally as postlarvae in pond source water and co-cultured with P. monodon that suffered high mortalities with YHD, showed no signs of the disease. Palaemon styliferus is a carrier that survives the infection well; Euphausia spp., Krill (Acetes spp.) and other small shrimp species could also carry the disease. Juvenile stages of American penaeids, Penaeus vannamei, Penaeus stylirostris, Penaeus setiferus, Penaeus aztecus, and Penaeus duorarum were experimentally infected but postlarval stages were found to be relatively resistant to challenge.
Impact on the host
P. monodon suffers acute epizootics with high cumulative mortalities which may reach 100% within 3-5 days after appearance of clinical signs. Infection is horizontally transmitted. Tiger shrimp postlarvae (PL) 15 were found to be resistant to infection but stages PL 20-25 and ongrowing juveniles through to subadults were found to be highly susceptible.
Gross Observations: Initially, feeding increases, followed by reduced feeding in later stages of the disease. Pale body, yellowish swollen cephalothorax and hepatopancreas, whitish-yellowish-brownish gills. Presumptive diagnosis is made on the basis of pond history, clinical signs, gross changes and histopathology. Bioassay reinfection studies and transmission electron microscopy are used for definitive diagnosis.
Squash Preparations: Identify characteristic abnormal haemocytes and connective tissue cells, with pyknotic and karyorrhetic nuclei and basophilic cytoplasmic inclusions using Wright-Giemsa stained haemolymph preparations of gill squashes.
Histology: Massive systemic necrosis (with prominent nuclear pyknosis and karyorrhexis) of numerous tissues (apparently of ectodermal and mesodermal origin) and basophilic (haematoxylin and eosin staining) perinuclear cytoplasmic inclusions (usually spherical) in at least some of the following tissues: systemic haemocytes and developing haemocytes in the haematopoietic tissues and fixed phagocytes in the heart; the lymphoid (Oka) organ stromal matrix cells; the gill lamellar epithelial pillar cells, connective and spongy connective tissues; subcuticular epidermis; striated and cardiac muscles; capsule of the ovary; nervous tissue (focally) including nerve fibres, neurosecretory and glial cells; and the walls of the stomach, midgut and midgut caecum. The Oka organ, gill, heart, midgut and hepatopancreas usually contain higher titers of YHV and apparently are the primary target tissues and organs for YHV infection. Cellular changes in early infections may include nuclear hypertrophy, chromatin diminution and margination, and lateral displacement of the nucleolus. Haemocytic infiltration, aggregation and encapsulation occurs, but is diffuse and not conspucuous unless a secondary bacterial infection is concurrent with YHD.
Electron Microscopy: Rod-shaped enveloped virions measuring 150-200 nm x 40-50 nm consist of two structural units, nucleocapsid and envelope with a trilaminar unit membrane. Free virions were also present in intercellular spaces. Darkly staining cytoplasmic inclusions were present in some cells. Viral replication was found to be primarily initiated in the nucleus with assembly occuring in the cytoplasm. In the cytoplasm of many cells, long filaments (some over 800 nm in length) were observed as possible precursors to the enveloped virions. After 32 hr post-injection, the cytoplasm became the major site of viral replication, producing the typical massive cytoplasmic necrosis.
Bioassay: Experimental reinfection/disease transmission studies using 10 gram juvenile P. monodon exposed to dilutions of filtered (0.45 or 0.22 µm) supernatant prepared from gills (preferably) of the suspected shrimp or feeding on suspected shrimp carcasses is another diagnostic method. Clinical signs usually develop within 24-72 hours and up to 100% mortalities occur within 3-5 days. Juvenile American penaeids (listed above) developed severe systemic lethal infections within 8-10 days of being fed YHD-positive carcasses.
Immunological Assay: Monoclonal and polyclonal antibodies have been developed against YBV. Contact G. Nash for futher details.
Further Research: At the present time, there are no reliable crustacean tissue culture systems and no insect or fish cell lines that would permit growth and isolation of the pathogenic viruses of penaeid shrimp. This is a much needed area of research. Further investigations are in progress, as is research to develop a DNA probe.
Methods of control
No known treatment. Early detection and emergency harvest followed by thorough disinfection. Host-carrier state is not yet confirmed, but lessening stress by maintaining optimal pond environment and rearing conditions may help, e.g. maintain consistent phytoplankton blooms at 25-35 cm transparency by maintaining stable pH in the pond. After harvesting the shrimp, the accumulated sediments and organic material should be removed followed by careful pond preparation. A semi-closed or closed culture system which restricts inflow of new water and recirculates treated water is another method which is sometimes useful. Waterborne infection is possible and cell-free virus was found to be virulent in water up to 72 hours. Methods to disinfect water and eliminate possible carriers before use in the pond and prior to discharging are being investigated. Chlorine at 20-30 ppm is an effective disinfectant in laboratory conditions. The use of probiotics and immuno-enhancers is being investigated. Research on vaccine development has just started; immune protection against YHD has been confirmed at the laboratory scale.
Boonyaratpalin, S. 1992. Yellow-head disease of black tiger shrimp. Asian Shrimp News 10(2): 2.
Boonyaratpalin, S., S. Direkbusarakom, J. Kasornchandra, U. Ekpanithanpong, C. Chantanachookin and K. Supamattaya. 1992. Baculovirus, causative agent of yellow-head disease in penaeid shrimp Penaeus monodon. In: Proceedings of the Seminar on Fisheries 1992. Department of Fisheries 16-18 Sept., National Fisheries Institute, Bangkhen, Bangkok. p. 200-205.
Boonyaratpalin, S., K. Supamattaya, J. Kasornchandra, S. Direkbusarakom, U. Ekpanithanpong and C. Chantanachookin. 1993. Non-occluded baculo-like virus, the causative agent of yellow-head disease in the black tiger shrimp (Penaeus monodon). Gyobyo Ken Kyu (Fish Pathology) 28: 103-109.
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Flegel, T.W. and S. Sriurairatana. 1993. Black tiger prawn diseases in Thailand. In: D.M. Akiyama (ed.). Technical Bulletin of the American Soybean Association. American Soybean Association, Singapore, p. 1-31.
Kasornchandra, J., Supamattaya, K. and S. Booynaratpalin. 1993. electron microscopic observations on the replication of yellow-head baculovirus in then lymphoid organ of Penaeus monodon. Asian Shrimp News 15(3): 2-3.
Lightner, D.V. (ed.). 1996. A Handbook of Shrimp Pathology and Diagnostic Procedures for Disease of Cultured Penaeid Shrimp. World Aquaculture Society, Baton Rouge.
Limsuwan, C. 1993. Diseases of black tiger shrimp, Penaeus monodon Fabricius in Thailand. In: D.M. Akiyama (ed.). Technical Bulletin of the American Soybean Association. American Soybean Association, Singapore, p. 1-22.
Lu, Y., L.M. Tapay, P.C. Loh, J.A. Brock and R.B. Gose. 1995. Distribution of yellow-head virus in selected tissues and organs of penaeid shrimp Penaeus vannamei. Diseases of Aquatic Organisms 23: 67-70.
Nash, G., A. Arkarajamon and B. Withyachumnarnakul. 1992. Routine and rapid diagnosis of Yellow-head disease in Penaeus monodon. Asian Shrimp News 12(4): 2-3.
Nash, G., A. Arkarajamon and B. Withyachumnarnakul. 1993. Rapid diagnosis of yellowhead disease in black tiger shrimp. Aquatic Animal Health Research Institute Newsletter 2(1): 3-4.
Spann, K.M., J.E. Vickers and R.J.G. Lester. 1995. Lymphoid organ virus of Penaeus monodon from Australia. Diseases of Aquatic Organisms 23: 127-134.
G. Nash, B. Withyachumnarnkul and A. Arkarajamon. Shrimp Culture Research Centre, Charoen Pokphand Feedmill Co. Ltd., 82\2 Thonburi-Paktor Rd., Klong Sunak-hon, M.4 Bangtorat, Amphor Muang, Samut-Sakorn, Thailand
S. Boonyaratpalin and J. Kasornchandra. National Institute of Coastal Aquaculture, Kaosan-Soi 1, Kaoseng, A. Muang, Songkhla 9000, Thailand
K. Supamattaya. Supamattaya, Dept. Animal Science, Faculty of Natural Resources, Prince of Songkhla University, Hatyai 90110, Thailand
Bower, S.M. (1996): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Yellow-head Virus Disease (YHD) of Penaeid Shrimp.
Date last revised: Fall 1996
Comments to Susan Bower
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