Abstract

The present study attempted to investigate the white spot disease virus (WSDV) infection in the wild-captured greasy back shrimp, Metapenaeus ensis. The shrimp showed no symptom of white spots in the carapace that usually occur in the other cultured shrimps. In histopathological studies, the hypertrophied nuclei of the necrotic cells were found in the various tissues originated from ectoderm and mesoderm which were similar to those observed in the giant tiger shrimp (Penaeus monodon) and kuruma shrimp (P. japonicus). Neither occlusion bodies nor cytoplasmic inclusions were found in the infected greasy back shrimp. Transmission electron micrographs revealed rod-shaped and enveloped viruses in the hypertrophied nuclei. The virions measured 221 plus or minus -6nm by 107 plus or minus 7nm in size, and were comparatively smaller than those found in WSDV infected P. monodon and P. japonicus. When in situ hybridization using DIG-labelled WSDV probe was used, positive reaction was found in the hypertrophied nuclei. DNA amplification by polymerase chain reaction (PCR) with two oligonucleotide primers developed in our laboratory demonstrated that the virus found in M. ensis is genetically similar to WSDV in the other penaeid shrimp.