White spot baculovirus syndrome in the Indian shrimp Penaeus monodon and P-indicus

Sporadic occurrences of white spot baculovirus (WSBV) infections have been reported in shrimp farms throughout the maritime states of India. WSBV pres ents as a reddish discolouration with white spots on the exoskeleton and ep idermis with muscle opacity. Onset of the disease is extremely rapid with m ass mortalities. Infected juveniles and sub-adults of Penaeus indicus and P . monodon become lethargic surface frequently, exhibit loss of balance, wit h reduced feeding and preening activities. The nuclei of WSBV-infected epit helial (hypodermal), septal and secretory cells of the gill filaments exhib it basophilic hypertrophied nuclei with a reduced cytoplasmic volume. Massi ve tissue disintegration occurred in the ectodermal and mesodermal tissues. The electron-dense nucleoplasm of the gill epithelial cells is mostly repl aced with virions. Electron microscopic examination revealed the presence o f double-enveloped, non-occluded, rod-shaped virions with a tube-like or br anched extension and empty capsids. The numbers of mitochondria, endoplasmi c reticulum (ER) and Golgi were also reduced, as were the numbers of secret ory or storage vesicles. WSBV is considered to be the main causative agent responsible for mass mortalities of juveniles and sub-adults in the culture d Indian penaeid shrimp, P. monodon and P. indicus. WSBV is highly pathogen ic and readily transmitted from diseased shrimp to healthy susceptible shri mp via, contaminated water, faeces and by scavenging on dead infected shrim p. It may affect all stages of shrimp. The spread of the disease from cultu red to natural systems and vice versa cannot be dismissed. (C) 2000 Elsevie r Science B.V. All rights reserved.