White Spot Syndrome Baculovirus Complex (WSBV)

By the Gulf States Marine Fisheries Commission - This report looks at the problem of White Spot Syndrome and gives an overview of its biology and recommendations to guard against it.
Other scientific names appearing in the literature of this species:
White Spot Syndrome (WSS); Chinese baculovirus-like virus (CBV) (Lightner, 1996; Tapay et al., 1996). Common Name: White Spot Baculovirus (WSBV), White Spot syndrome (WSS) (Lightner, 1996)

Distinguishing Features:
The White-spot baculovirus is a large, enveloped, rod-shaped to somewhat elliptical, non-occluded virus consisting of double stranded DNA (Lightner, 1996).

Similar Species:
At least three viruses in the white spot syndrome (WSS) or "China Virus" complex have been named in the literature (Lightner, 1996). They appear to be very similar viruses. The names of the viruses and the diseases they cause are: China's hypodermal hematopoietic necrosis baculovirus (HHNBV)--Shrimp Explosive Epidermic Disease (SEED) (Lightner, 1996; Cai et al., 1995); Japan's rod-shaped nuclear virus (RV-PJ) of Peneus japonicus (Inouye et al., 1994; Momoyama et al., 1994; Nakano et al., 1994; Takahashi et al., 1994); and Thailand's systemic ectodermal and mesodermal baculovirus (SEMBV) of Penaeus monodon--red disease; white spot disease (Lightner, 1996; Wang et al., 1995).

Biology:
WSBV is extremely virulent, has a wide host range, and targets various tissues (Chang et al., 1996). The origins of the virus may lay in China (Chou et al., 1995; Tapay et al., 1996), but WSBV was first described in the cultured giant tiger prawn P. monodon and redtail prawn Penaeus penicillatus in Taiwan in 1993. WSBV is known to cause disease in P. japonicus and P. penicillatus and to experimentally infect larval Litopenaeus stylirosturs and L. penaeus (Tapay et al., 1996). Many cell types (ectodermal and mesodermal) are targeted by the virus including the cuticular epithelium from every part of the shrimp's body, connective tissues of some organs, nervous tissue, muscle, lymphoid, and hematopoietic tissue. WSBV also severly damages the stomach, gills, antennal gland, heart and eyes. During late stages of the infection, these organs are destroyed and many cells are lysed (completely broken down) (Chang et al., 1996).

The disease resulting from WSBV infection is highly lethal with cumulative mortality reaching 100% within 2 to 7 days post infection. Diseased shrimp show reddish coloration of the hepatopancreas and white inclusions (spots) on their carapace, appendages and inside surface of the body (Chou et al., 1995). Infected shrimp as noted by Chou et al. (1995) show lethargic behavior.

Most likely means of transmission of the virus is through ingestion of diseased tissue and cohabitation with diseased or latent virus carriers. (Flegel et al., 1996). Vertical transmission of the virus from broodstock to larvae is also a possibility as is the case with other shrimp baculoviruses (Fegan et al., 1991), but more study is necessary (Flegel et al, 1996). Viability of free virus in sea water, as with Yellow-head virus, is 3-4 days (Flegel et al., 1996).

Maximum Size:
70 to 150 nm by 275 to 380 nm (Lightner, 1996; Tapay et al., 1996).

Distribution:
Since its appearance in 1992-1993 in northeast Asia, the Strains of WSBV have spread rapidly throughout most of the shrimp growing regions of Asia and Indo-Pacific (Lightner, 1996). The WSBV complex (WSBV, HHNBV, RV-PJ, and SEMBV) is now found throughout China, Japan, Korea, Indonesia, Taiwan, Vietnam, Malaysia and India (Inouye et al., 1994; Momoyama et al., 1994; Nakano et al., 1994; Takahashi et al., 1994; Chou et al, 1995; Wang et al., 1995). Because the shrimp industry relies on intraregional transport of stocks, the distribution of these viruses may be larger than indicated and may be expanding (Lightner, 1996). White spot disease was first detected in farmed L. setiferus in Texas in 1995.

Interest to Fisheries:
Pathogenicity studies of WSBV carried out by Tapay et al. (1996) show that L. stylirostris and L. vannamei, penaeids commonly cultured in the Hawaii and the Western hemisphere, are seriously diseased when infected by WSBV and mortalities of up to 100% occur within 4 days post infection. The first reported case of WSBV in the Western Hemisphere involved pond-reared P. setiferus from south Texas in 1995. A shrimp processing plant located within the vicinity was the suspected source of virus; the processor was a major importer and re-processor of shrimp imported from affected areas of Asia (Lightner, 1996).

Recommendations:
To guard against accidental importation of infection to disease-free geographical locations, testing of export shrimp (fresh and frozen) from areas of infection should be carried out (Tapay et al., 1996). Broodstock and postlarvae should be screened using a DNA probe before stocking. If transmission of the virus via broodstock to offspring is found to be possible, infection of grow-out ponds may be blocked by washing the nauplii (a pre-larval stage) after harvesting from spawning tanks (Flegel et al., 1996). Other crustacea have been found to be carrier species of strains of WSBV (Johnson, 1988a, b). A few species noted in work by Johnson (1988) include the crab Rhithropanopeus harrisii (Payen & Bonami, 1979), the bracyuran crab, Callinectes sapidus (Johson, 1976), and the anomuran crab Paralithodes platypus (Sparks & Morado, 1986). Since the virus is easily spread via ingestion of infected tissues, Flegel et al. (1996) recommends not feeding fresh crab to broodstock animals.

It appears that the most effective disinfectant for WSBV is formalin. At 70 ppm (or as little as 20 ppm in aquarium tests) transmission of the virus by water was prevented and at that level there was no harm to the shrimp (Flegel et al, 1996). Flegel et al. (1996) note that the formalin treatment could affect the plankton bloom which in turn may cause a drop in DO (dissolved oxygen) in rearing ponds. Preventing infection by cohabitation is not effective using this method, though applications of formalin every 6 hours may delay infection while other measures are undertaken (Flegel et al., 1996).

As a preventative environmental measure, it is recommended that all effluent used in farming or processing operations where the presence of WSBV is a possibility, should be treated with disinfectant (formalin) before discharge (Flegel et al., 1996).

References:
Cai, S., J. Huang, C. Wang, X. Song, X. Sun, J. Yu, Y. Zhang, and C. Yang. 1995. Epidemiological Studies On The Explosive Epidemic Diseases Of Prawn In 1993-1994. J. Fish China 19:112-117.

Chang, P., C. Lo, Y. Wang and G. Kou. 1996. Identification of white spot syndrome associated baculovirus target organs in the shrimp Penaeus monodon by in situ hybridization. Dis Aquat Org. Vol. 27:131-139.

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

Fegan, D.F., T.W. Flegel, S. Sriurairatana, and M. Waiyakruttha. 1991. The occurrence, development and histopathology of monodon baculovirus in southern Thailand. Aquaculture 96: 205-217.

Flegel, T., S. Boonyaratpalin and B. Withyachumnarnkul. 1997. Progress in Research on Yellow-head Virus and White-Spot Virus in Thailand. In T.W. Flegel and I. H. MacRae (eds), Diseases in asian Aquaculture III. Fish Health Section, Asian Fisheries Society,Manila.

Inouye, K., S. Miwa, N. Oseko, H. Nakano, T. Kimura, K. Momoyama and M. Hiraoka. 1994. Mass mortalities of cultured Kuruma Shrimp Penaeus japonicus in Japan in 1993: Electron Microscopic evidence of the Causative Virus. Fish Pathology, 29(2),148-158.

Johnson, P.T. 1976. A Herpes-like Virus From The Blue Crab, Callinectes Sapidus. J. Invertebr. Pathol. 27:419-420.

Johnson, P.T. 1988. Development And Morphology Of An Unusual Nuclear Virus Of The Blue Crab Callinectes Sapidus. Diseases Of Aquatic Organisms 4:67-75.

Johnson, P.T. 1988. Rod-shaped Nuclear Viruses Of Crustaceans: Hemocyte-infecting Species. Diseases Of Aquatic Organisms 5:111-122.

Lightner, D.V. 1996. A Handbook Of Shrimp Pathology And Diagnostic Procedures For Disease Of Cultured Penaeid Shrimp. World Aquaculture Society, Baton Rouge, Lousisana, USA.

Lo, C.F., J.H. Leu, C.H. Ho, C.H. Chen, S.E. Peng, Y.T. Chen, C.M. Chou, P.Y. Yeh, C.J. Huang, H.Y. Chou, C.H. Wang, and G.H. Kou. 1996. Detection Of Baculovirus Associated With White Spot Syndrome (WSBV) In Penaeid Shrimps Using Polymerase Chain Reaction. Diseases Of Aquatic Organisms 25:133-141.

Momoyama, K., M. Hiraoka, H. Nakano, H.Koube, K. Inouye, and N. Oseka. 1994. Mass Mortalities Of Cultured Kuruma Shrimp Penaeus Japonicus, In Japan In 1993: Histopathological Study. Fish Pathology 29:141-148.

Nakano, H., H. Koube, S. Umezaea, K Momoyama, M. Hiraoka, K. Inouye, and N. Oseko. 1994. Mass Mortalities Of Cultured Kuruma Shrimp Penaeus Japonicus, In Japan In 1993: Epizootiological Survey And Infection Trials. Fish Pathology 29:135-139.

Payen, G.G. And J.R. Bonami. 1979. Mise En Evidence De Particles D'allure Virale Associees Aux Noyaux Des Cellules Mesodermiques De La Zone Germinative Testiculaire Du Crabe Rhithropanopeus Harrisii (Gould) (Brachyoure, Xanthide). Rev. Trav. Inst. Pech. Marit. 43:361-365.

Sano, T., T. Nishimura, K. Oguma, K. Momoyama, and N. Takeno. 1981. Baculovirus infection of cultured Kuruma shrimp, Penaeus japonicus in Japan. Fish Pathology 15: 185-191.

Sparks, A.K. And J.F. Morado. 1986. A Herpes-like Virus Disease In The Blue King Crab Paralithodes Platypus. Diseases Of Aquatic Organisms 1:115-122.

Takahashi, Y., T. Itama, M. Kondo, M. Maeda, R. Fujii, S. Tomonaga, K. Supamattaya, and S. Boon 1994. Electron Microscopic Evidence of Bacilliform Virus Infection in Kuruma Shrimp (Penaeus japonicus). Fish Pathology, 29(2) 121-125.

Tapay, L.M., Y. Lu, R.B. Gose, J.A. Brock and P.C. Loh. 1997. Infection of white spot baculvirus-like virus in two species of penaied shrimp penaeus stylirostis (stimpson) and P. Vannamei (Boone) In T.W. Flegel and I.H. MacRae editors. Diseases in Aquaculture III. Fish Health Section, Asian Fisheries Society, Manila

Van Hoa, N., B.Q. Te, L.T.T. Loan, L.T.P. Yen, and L.M. Thanh. 1996. Pathogens In Cultured Shrimp In Southern Vietnam. In Diseases In Asian Aquaculture III, Proceedings Of The Third Symposium On Diseases In Asian Aquaculture. 29 January To 2 February 1996. Bangkok, Thailand.

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

Source: Gulf States Marine Fisheries Commission - Last Modified March 2005