Viral diseases in shellfish--shrimp-virus

Fusarium infects dead or damaged tissue caused by wounds or other infections resulting in locomotory difficulties due to mycelial growth. High mortality in susceptible populations. Fouling of the gills by these organisms probably results from poor husbandry.

1. MODULE – 4 Topic: Viral diseases in Shellfish(Shrimp) Submitted by- Name – Mukta Manjari Sahoo Regd. No. – 230705180023 Branch – M.Sc. in Zoology Subject – Fish and shellfish Health Management

2. INTRODUCTION Viral diseases are a growing concern for the shellfish industry, causing significant economic losses and posing a potential threat to human health. Shellfish, such as oysters, clams, mussels, and scallops, are filter feeders that can accumulate viruses from the surrounding water. Viruses are considered to be the most important pathogens in shrimp. Currently, at least 14 virus diseases of cultured shrimp are recognised. The major virus families present in the crustaceans include Parvoviridae , Baculoviridae , Picornaviridae , Reoviridae, Togaviridae , Cornaviridae .

3. How do we know? SIGN S AND SYMPTOMS ANOREXIA ANTENNAE CUT CHANGE IN COLOUR CHANGE IN SHAPE POOR GROWTH SIZE VARIATION SURFACING MORTALITY OPAQUENESS LOOSE SHELL MELANIZED LESIONS PARTIAL MOULTING DELAYED BLOOD CLOTTING WHITE FECAL MATTER WHITE GUT TAIL ROT EDEMA BLISTERS GILL COLOUR WHITE SPOTS ON CARAPACE Caridina cantonensis

4. Hepatopancreatic parvo –like virus (HPV) Histologically -single, prominent, basophilic, Feulgen -positive intranuclear inclusion bodies in hypertrophied nuclei of hepatopancreatic tubule epithelial cells. Lateral displacement of nucleolus and margination of chromatin In the early stages, HPV inclusions are eosinophilic bodies centrally located in the nucleus associated with nucleolus. In Indian shrimp farms, the HPV shows a low incidence rate. HPV

5. Infectious hypodermal and hematopoietic necrosis virus (IHHNV) IHHNV is distributed worldwide with more prevalence in the Southeast Asia. P. monodon has been found to be the natural host of the virus. Affected shrimp exhibit reduced growth, cuticular deformities to rostrum and other areas of exoskeleton. The infection is transmitted both horizontally and vertically. In P. monodon , the infection causes bluish coloration and opaque abdominal musculature. IHHNV

6. Lymphoid organ parvo -like virus (LOPV) LOPV was found in cultured shrimps ( P. monodon, P. merguiensis and P. esculentus ) in Australia. Giant cell nuclei had intranuclear inclusion bodies containing DNA. Electron microscopic studies revealed the presence of 25-30 mm diameter virus  like particles. There is a speculation that IHHNV and LOPV are the same agent. Reo  like viruses Reo-like viruses are reported from P. japonicus , P. monodon , P. chinensis and P. vannamei . Hepatopancreas has been suggested as the principal target for both the viral strains. Reovirus infections were always reported in mixed infections. Hence the role of reovirus as pathogens is not completely clear.

7. REO-VIRUS 580

8. Baculoviruses (1) Type A occlusion body forming viruses BP and MBV and (2) Type C non  occluded baculoviruses BMN, TCBV, Owen’s hemocyte –infecting baculovirus and WSDV. Transmission: horizontal, some transmit vertically In hatcheries, BP and BMN often cause serious epizootics in larvae and postlarvae (PL) MBV produce serious infections and mortalities in the late PL and juvenile stages of h osts. BP Type baculoviruses BP ( Baculovirus penaei ): diagnosis: demonstration of prominent tetrahedral occlusion bodies in unstained squash preparations of hepatopancreas , midgut or faeces and also in histological sections. In histological sections, occlusion bodies are found in single or multiple, eosinophilic, usually triangular within hypertrophied nuclei of hepatopancreatic tubule epithelial cells or in midgut epithelial cells.

9. Monodon type baculoviruses MBV enjoy a world-wide distribution. These are type A baculoviruses measuring 75 x 324 mm. Diagnosis : presence of single or multiple, generally spherical intranuclear occlusion bodies in hepatopancreas and midgut epithelial cells. Squash preparation (0.05% aqueous malachite green), epifluorescence microscopy and acridine orange staining visualizes MBV occlusions MBV was first discovered in a quarantined population of P. monodon that had originated from Taiwan. Despite the world distribution, MBV is not a highly virulent pathogen of P. monodon . MBV is found in healthy prawns and in disease epizootics, P. monodon has been found to frequently have mixed infections by MBV and other viral, bacterial or protozoan pathogens.

10. MBV 574

11. White spot syndrome virus (WSSV) WSSV, formerly known as SEMBV is a non  occluded baculovirus – like agent Epizootic of white spot disease cause mortalities ranging up to 80  100% in 2  7 days susceptible species: On  growing juvenile shrimp of many species of all ages but mostly from 1 - 3 months old in the grow-out ponds. WSSV outbreak occurs in all types of farming systems irrespective of stocking density, water quality and salinity. Diagnosis: Broken antennae, white spots of 1 mm size in the cuticle and / or reddish discoloration, empty guts and cuticular epibiont fouling and lymphoid organ swelling.

12. WHITE SPOT DISEASE

13. Yellow Head Virus (YHV) YHV is an RNA virus reported only from P. monodon in Thailand. All ages of juveniles could be infected and mass mortalities up to 100% are observed within 3 - 5 days Diagnosis : Pale body colour with yellowish gills and hepatopancreas . It affects many tissues such as gills, lymphoid organ, hemocytes and connective tissue. Histology : Degenerative changes in nuclei and presence of cytoplasmic basophilic inclusion bodies.

14. PREVENTION Use clean water. Shrimp farmers should use clean, pathogen-free water in their ponds Use Sp ecific pathogen-free (SPF) shrimp . SPF shrimp are shrimp that have been breed to be free of certain pathogens. Practice good biosecurity. Shrimp farmers should take steps to prevent the introduction of pathogens into their ponds, such as disinfecting equipment and clothing. Maintain good water quality. Maintaining good water quality in shrimp ponds can help to reduce stress on shrimp and make them less susceptible to disease .

15. Chang, P.H., Kuo, S. T., Lai, S. H. et al. (2005). Herpes-like virus infection causing mortality of cultured abalone Halitosis diversicolor supertexta in Taiwan. Diseases of Aquatic organisms: 65, 23-27 Lees, D. (2000). Viruses and bivalve shellfish: International Journal of Food Microbiology: 59, 81-116. Owens, L., I. G. Anderson, M. Kenway, L. Trott, and J. A. H. Benzie (1992): Infectious hypodermal and haematopoietic necrosis virus (IHHNV) in an interspecies hybrid pended prawn from tropical Area: 14,219-228. REFERENCES

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