White Spot Syndrome Virus Infection of Cultured Shrimp in China

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Abstract
In 1993 and 1994, an epizootic of disease (white spot) occurred among cultured shrimp in China, resulting in mass mortality. During the periods of outbreak epizootiological surveys were undertaken. Based on these surveys it is known that the disease occurred among populations of cultured Penaeus chinensis, P. japonicus, and P. monodon, infecting shrimp from 2.4 cm to adult. The disease presumably spread among farms as a result of transport of contaminated shrimp seedlings and seawater. Water temperatures exceeding 25°C caused the disease to spread more rapidly. Challenge experiments showed the causative agent was highly virulent. Both naturally and experimentally infected shrimp exhibited white spots on the carapace. Moribund shrimp contained turbid hemolymph, hypertrophied lymphoid organ, and a necrotic hepatopancreas. By electron microscopy, viral particles were observed in gills, stomach, lymphoid organ, and hypodermal tissue of infected shrimp. The virions were slightly ovoid with an envelope...