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White spot syndrome baculovirus complex, WSBV. WSSV.

Scientific name or taxonomic affiliation
This complex consists of several very similar viruses:
a) Baculoviral hypodermal and haematopoietic necrosis, HHNBV, Shrimp explosive epidermic disease, SEED, China virus disease.
b) Rod-shaped nuclear virus of Penaeus japonicus, RV-PJ.
c) Systemic ectodermal and mesodermal baculovirus, SEMBV, Red disease, White spot disease.
d) White spot baculovirus, WSBV, White spot syndrome, WSS, White spot disease.

Geographic distribution
Following initial detection in northeast Asia in 1992-1993, WSBV is now widely spread throughout most of the shrimp growing regions of the world.

Host species
Penaeus monodon, Penaeus japonicus, Penaeus chinensis (=orientalis), Penaeus indicus, Penaeus merguiensis, Penaeus penicillatus and Penaeus setiferus (in Texas). Experimentally, severe and lethal infections of WSBV from Thailand were produced in Penaeus vannamei, Penaeus stylirostris, Penaeus aztecus, Penaeus duorarum and Penaeus setiferus. No significant resistance to WSBV complex has been reported for any of the penaeid shrimp.

Impact on the host
Acutely infected shrimp showed rapid reduction in food consumption, became lethargic, and had high mortality rates with cumulative mortalities reaching 100% within 3 to 10 days of the onset of clinical signs.

Diagnostic techniques
Gross Observations: Acutely infected shrimp often have a loose cutical with white spots (which represent abnormal deposits of calcium salts by the cuticular epidermis) of 0.5 - 2.0 mm in diameter which are most apparent on the inside surface of the carapace. In many cases morbund shrimp displayed a pink to reddish-brown colouration due to expansion of the cuticular chromatophores and few if any white spots.

Squash Preparations: Hypertrophied or vacuolated nuclei usually with a single eosinophilic to bluish inclusion body in squashes or impression smears (stained with Giemsa or other blood smear stains) of epithelia and connective tissues of the gills or stomach of shrimp with clinical signs. Occlusion bodies are absent. Normal cell nuclei are 4 - 10 Ám in diameter and display chromatin threads and a nucleolus.

Histology: Prominent eosinophilic to pale basophilic (with H&E stains), Feulgen-positive, intranuclear inclusion bodies in hypertrophied nuclei of, most commonly, the cuticular epithelial cells and connective tissue cells, and, less frequently, the antenal gland epithelium, lymphoid organ sheath cells, haematopoietic cells and fixed phagocytes of the heart. Occlusion bodies are absent. In the early stages of inclusion body development, they are eosinophilic, centronuclear, with a halo (an artifact with Davidson's fixation) and resemble the inclusion bodies of IHHNV. However, the presence of larger more fully developed (without a halo) pale basophilic inclusion bodies in infected target tissue cells during the advanced stages of infection clearly distinguishes the two diseases.

Electron Microscopy: Cytopathology occurs in the appropriate target tissue types and is accompanied by large rod-shaped to somewhat elliptical, non-occluded virions of about 70 - 150 nm in width and about 275 - 380 nm in length in the intranuclear inclusion bodies of infected cells.

DNA Probes: WSBV infected nuclei can be intensely marked by a DIG-labeled DNA probe for WSBV with in situ hybridization assays. Gene probes for WSBV are being developed in China, Japan, Thailand and at the University of Arizona in the U.S. None of the WSBV complex are reactive to the available gene probes to IHHNV, BP, MBV and HPV.

Methods of Control
No known method of prevention or control. However preventative measures well known within shrimp farming industry.




Variables to be used in health evaluation

Health evaluation tests
Wet Mount Procedure . PL visual examination . Stress test for post larva . Gill examination . Mid-gut Examination . Stomach Contents Analysis

Shrimp Diseases
Hepatopancreatic parvo-like virus (HPV) . Reo-like virus (REO) . Lymphoid organ vacuolization virus (LOVV) . Taura Syndrome Virus (TSV) . Rhabdovirus of Penaeid Shrimp (RPS) . You are here . Infectious hypodermal and hematopoietic virus (IHHNV) . Baculovirus penaei (BP)
Bacterial Diseases
Vibriosis . Epicommensal fouling disease (filementous bacteria) . Necrotizing Hepatopancreatitis (NHP) . Black spot disease (BSD) . Mycobacteriosis
Fungal Diseases
Larval mycosis . Fusariosis
Haplosporidia . Gregarines . Cotton Disease
Black Gill Disease (BGD) Dissolved Oxygen Crisis Nitrogen Gas Bubble Disease

Disease control
Decreasing density, partial or early harvests . Drugs, chemicals and treatments . Sanitation