In May 2006, mass mortalities among collected freshwater crayfish from Eshnawai and Kafr Salem El-Nakal drains in Tanta City, El- Gharbia Province, Egypt have been observed. This case is known as white spot disease, based on the characteristic white spots on the cuticle of diseased crayfish. Thus, in this study histopathological and PCR techniques were used for detection of WSSV in diseased crayfish Procambarus clarkii. Histological studies of moribund specimens revealed degenerated cells, characterized by hypertrophied nuclei in various tissues including gills, anntenal gland and hepatopancreas. Electron microscopic examination of the gill tissues from diseased animal revealed rod- shaped enveloped and non occluded virions in the nuclei of affected cells or in the cytoplasm of haemocyte cells. Also, the nuclei of the infected cells were slightly hypertrophied and most of the chromatin was marginated along the interrupted nuclear membrane. The nested PCR analysis showed the appearance of a prominent band of PCR amplified product of WSSV- DNA 300 bp in gill, muscles, appendages and haemolymph of diseased animals. The present results reported that freshwater crayfish P. clarkii is susceptible species for WSSV infection in Egypt. So, more work is also required to understand viral receptor and how virus evades the innate immune response.
Key words: Procambarus clarkii, white spot syndrome virus, histopathology, ultrastructure, polymeras chain reaction
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