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In this study, a virus similar to the causative agent of white spot syndrome virus (WSSV) but without tail-like extension was identified and characterized from diseased Penaeus vannamei and moribund Procambarus clarkia. Contrary to previous reports, white spots were not observed on the carapace of the diseased P. vannamei but with ulceration on the carapace and red tail. All samples were analyzed for WSSV and Sporoplasma eriocheiris using polymerase chain reaction (PCR) methods. Samples were negative for S. eriocheiris but positive for WSSV. Following the World Organization for Animal Health (OIE) standard protocol, the result of nest-PCR showed a characteristic band of 1447 bp, suggesting that the pathogen of P. vannamei and P. clarkii was similar to the causative agent of WSSV. Interestingly, transmission electron microscopy of sectioned tissues and negatively stained samples revealed an elliptical shaped virus-like particle but without tail-like extension, which was different from previous reported cases of WSSV. The major envelope proteins, VP19, VP26 and VP28 were cloned and sequenced. Results show that the present isolates had over 97% DNA and 100% amino acid sequence similarity to the known WSSV. These results suggest that this tail less virus may be a different strain of the WSSV virus exhibiting a different disease sign but equally virulent. Results of this study broaden our understanding of WSSV symptoms and diversity.
Key words: White spot syndrome virus (WSSV), morphology, crustacean.