White Spot Syndrome Baculovirus Complex of Penaeid Shrimp

Category

Category 3 (Host Not in Canada)

Common, generally accepted names of the organism or disease agent

White spot syndrome baculovirus complex, WSBV, White spot syndrome virus, WSSV.

Scientific name or taxonomic affiliation

This complex consists of several very similar viruses:

  1. Baculoviral hypodermal and haematopoietic necrosis, HHNBV, Shrimp explosive epidermic disease, SEED, China virus disease.
  2. Rod-shaped nuclear virus of Penaeus japonicus, RV-PJ.
  3. Systemic ectodermal and mesodermal baculovirus, SEMBV, Red disease, White spot disease.
  4. White spot baculovirus, WSBV, White spot syndrome, WSS, White spot disease.

Geographic distribution

Following initial detection in northeast Asia in 1992-1993, WSSV is now believed to be widely spread throughout most of the shrimp growing regions of Asia and the Indo-Pacific.

  1. China.
  2. Japan, China and Korea.
  3. Thailand.
  4. Indonesia, Taiwan, Vietnam, Malaysia, India, and south Texas, U.S. (where it may have been introduced via shrimp packing plants located near the affected farm).

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 WSSV from Thailand were produced in Penaeus vannamei, Penaeus stylirostris, Penaeus aztecus, Penaeus duorarum and Penaeus setiferus. No significant resistance to WSSV complex has been reported for any of the penaeid shrimp. WSSV also infects many non-penaeid crustacea including freshwater crayfish from all three families (Corbel et al. 2001, Edgerton et al. 2004). Specifically, Pacifastacus leniusculus a crayfish that is native to the west coast of North America (including British Columbia, Canada) was experimentally infected with WSSV by injection of isolates from P. monodon (Jiravanichpaisal et al. 2001).

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

Culture: Primary cell cultures established from the hepatopancrease of Penaeus monodon formed a confluent monolayer within 72 hours and could be maintained for about 12 weeks by subculturing seven times. These cultures developed characteristic cytopathic effects (including rounding of cells, detachment, and lysis of cell sheets with circular clear areas of cell depletion), within 120 hours of inoculation with WSSV (Uma et al. 2002)

Methods of control

No known methods of prevention or control.

References

Chou, H.-Y., C.-Y. Huang, C.-H. Wang, H.-C. Chiang and C.-F. Lo. 1995. Pathogenicity of a baculovirus infection causing white spot syndrome in cultured penaeid shrimp in Taiwan. Diseases of Aquatic Organisms 23: 165-173.

Corbel, V., Zuprizal, Z. Shi, C. Huang, Sumartono, J.-M. Arcier and J.-R. Bonami. 2001. Experimental infection of European crustaceans with white spot syndrome virus (WSSV). Journal of Fish Diseases 24: 377-382.

Edgerton, B.F., P. Henttonen, J. Jussila, A. Mannonen, P. Paasonen, T. Taugbíl, L. Edsman and C. Souty-Grosset. 2004. Understanding the cause of disease in European freshwater crayfish. Conservation Biology 18: 1466-1474.

Jiravanichpaisal, P., E. Bangyeekhum, K. Söderhäll and L. Söderhäll. 2001. Experimental infection of white spot syndrome virus in freshwater crayfish Pacifastacus leniusculus. Diseases of Aquatic Organisms 47: 151-157.

Lightner, D.V. (ed.). 1996. A Handbook of Shrimp Pathology and Diagnostic Procedures for Disease of Cultured Penaeid Shrimp. World Aquaculture Society, Baton Rouge.

Uma, A., T.G. Prabhakar, A. Koteeswaran and G. Ravikumar. 2002. Establishment of primary cell culture from hepatopancreas of Penaeus monodon for the study of white spot syndrome virus (WSSV). Asian Fisheries Science 15: 365-370.

Wang, C.-H., C.-F. Lo, J.-H. Leu, C.-M. Chou, P.-Y. Yeh, H.-Y. Chou, M.-C. Tung, C.-F. Chang, M.-S. Su and G.-H. Kou. 1995. Purification and genomic analysis of baculovirus associated with white spot syndrome (WSBV) of Penaeus monodon. Diseases of Aquatic Organisms 23: 239-242.

Citation Information

Bower, S.M. (2006): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: White Spot Syndrome Baculovirus Complex of Penaeid Shrimp.

Date last revised: July 2006
Comments to Susan Bower

Date modified: