White spot syndrome_disease[1]

white spot syndrome virus disease in crustaceans virus description, aetiology pathology and prevention and prophylactic measures with refernce.

1. White spot syndrome virus disease. Presented by : Harapriya

2. Introduction: WSSV formerly known as systemic ectodermal and mesodermal baculovirus (SEMBV) is a non-occluded baculovirus like agent infecting many penaeaid species  Retrovirus virus- penaeus japonicus ( RV - PJ ) Causes up to 100% mortality within 3- 5 days in commercial shrimp farms, resulting in large economic losses to the shrimp farming industry.

3. Outbreak of disease: WSSV mostly attack to post larvae. But disease occur in seen on growing juveniles shrimp of all ages and size but mostly from 1-3 months after stocking in the grow out ponds. WSSV outbreak can occur irrespective of farming system, stocking density, water quality and salinity.

4. Transmission of disease: Dead, infected shrimp are considered to be the source of subsequent infection for WSSV this is mainly due to a higher opportunity of horizontal transmission of the virus through cannibalism and the water borne route. The major source of infection for shrimp farms is from infected spawners and postlarvae . The vertical transmission of WSSV by (trans- ovum)

5. Vectors: Rotifers, marine molluscs , polychaeteworms and A rtemia salina sea slaters(isopoda) and euphydradaeinsect larvae

6. External pathology: R apid mortality accompanied b y gross signs in moribound shrimp. Lethargy, dirty gills, anorexia, broken antennae. Swollen branchiostegites . White deposits of calcium of 0.5-2.0mm dia on the cuticle of the shrimp cephalothorax or carapace. Display expanded chromatophores cephalothorax cuticle.

7. Carapace of a wssv infected shrimp Carapace of a wssv infected shrimp

8. Target tissues: White spot syndrome virus can infect cells of mesodermal and ectodermal origin, C uticular Epithelium the lymphoid organ Heart Haematopoietic tissue S tomach cuticular epidermis Sub cuticular connective tissue Antennal gland and hind gut Nervous system and compound eyes are infected in very late stage.

9. Target organs for WSSV disease

10. Internal pathology: The lymphoid organ of diseased shrimp may be distended, and haemolymph infiltration in the enlarged haemal sinuses and interstitial spaces may result in a hypertrophied yellowish hepatopancreas . Sometimes empty gut also indicate the disease occurance . Cuticular epiboint fouling Lymphoid organ swelling.

11.  (a) WSSV-infected nucleus in gill (arrow ). (b) Low-power view of hindgut showing numerous infected nuclei (arrow ). ( c,d ) Midgut epithelium nuclei with inclusions and emarginated chromatin clearly visible

12. Histopathology: Moribund shrimp show tissue destruction, accompanied by low to high basophilic (H&E stained) central inclusion bodies within the hypertrophied nuclei of the c uticular epithelial and connective tissue cells. Presence of intranuclear basophilic inclusion bodies in the ectodermal and mesodermal tissue found in cuticle, foregut and hindgut. But they are not found in the tissues of endodermal origin. i.e midgut and hepatopancreas . Cowdry type A inclusion bodies are intranuclear , eosinophilic, amorphous and surrounded by a clear halo beneath the nuclear membrane but later, inclusions become lightly to deeply basophilic and fill the entire nucleus .

13. Necrosis in different tissue of penaeids

14. Pathogenesis: Disease occur in 3 steps Latent stage Transition stage Patent stage

15. Latent phase : Initially they act active. No presence of virus. No mortality. No inclusion bodies. Pcr analysis – ve for 1 st step. But + ve for 2 nd step.

16. Transistion phase : Shrimps are active. They may or may not have WSSV. In few cases there is appearance of inclusion bodies. PCR analysis + ve by 1 st step. Severity index is medium .

17. Patent stage: Appear weak. Stop feeding Prominent white spot upto 2mm dia. Basophilic intranuclear inclusion bodies. Pcr 1 st step + ve . Shigh mortality.

18. Aetiology: Member of the genus  whispovirus  within the  nimaviridae  family. Virions of WSSV are rod or ellipsoid to bacilliform in shape, have a regular symmetry, and measure 80–120 nm in diameter and 250–380 nm in length. Most notable is the thread- or flagella-like extension (appendage) at one end of the virion with 39 structural protein.  This virus has a large circular double-stranded DNA genome with diffrent size(292.9-307.2 kb), where the diverse isolates show differences in virulence.

19. Shape of whispovirus

20. Geographical distribution : White spot syndrome virus was first detected in Southeast A sia Central and south Americas Malaysia Thailand Mexico China Japanvc Korea Indian subcontinent

21. Host range: White spot syndrome virus is highly infective for marine penaeid shrimp including marine, brackish and freshwater prawns, crabs, crayfish and lobsters Macrobrachiu m rosenbergii P . monodon L. v annamei , L . s tylirostris , M arsupenaeus jap onicus , Fenneropenaeus chinensis P rocambarus clarkii Cray fish Pacifastacu s leniusculus

22. Control and prevention: No effective vaccination methods for WSSV have been developed. Chemotherapy no scientifically confirmed reports . Low temperatures (12 ± 2˚ C) affect the WSSV pathogenicity and inhibit mortality in crayfish and shrimp. Other elements such as sulphated polysaccharides, fucoidan or microalgae cell walls have been used as immunostimulants f or shrimp. These products have been somewhat successful against pathogens like WSSV around the world. Declairing crop holidays by the farmers.

23. Prophylactic: As avoiding stocking in the cold season SPF free larvae or PCR tested larvae in the culture system. B-1,3-glucan, whose addition to the shrimp feed effectively improves the immunity and survival of P.monodon Some products such as D unaliella extract and probiotics show a positive effect on resistance of shrimp to WSSV infection. Finally, the development of good management practices, the control of environmental variables, genetic improvement in the penaeid species, understanding o f virus physiology, modulation of the Shrimp immune system, supported by functional Genomics and proteomics of this crustacean, can reduce the epizootics.

24. Reference: OIE aquatic manual. E course. A review article. WSSV in cultured shrimp. Web source.

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