Screening of pathogens from a biosecured pacific white shrimp (Penaeus vannamei) farm in Kattur, Tamil Nadu

Screening for presence of various pathogens were carried out in one of the biosecurity maintained shrimp farms in Kattur Village of Tamil Nadu. Sampled shrimps exhibited pinkish discolouration of the body, pale hepatopancreas and antennal cut indicating bacterial infection. Similarly, there was also large scale size variation and reduced growth compared to the days of culture. Samples were screened for bacterial and four (including three OIE-listed) viral pathogens. The samples were also subjected to histopathological investigations. Based on the biochemical tests, the isolated bacteria was identified as Vibrio parahaemolyticus. Metalloprotease gene-specific PCR further confirmed the isolates to be V. parahaemolyticus. PCR was carried out to further investigate the early mortality syndrome/acute hepatopancreatic necrosis disease (EMS/AHPND) strain status of these isolates and were found to be negative. The samples were found to be positive for white spot syndrome virus (WSSV) by second step PCR and infectious hypodermal and haematopoietic necrosis virus (IHHNV) by direct PCR. All these were negative for monodon baculovirus, yellow head virus and gill associated virus. Infection of samples by WSSV and IHHNV were further confirmed by histopathology. The finding of the present study indicated the reduction in growth and size variation due to bacterial infection by V. parahaemolyticus and viral infection by IHHNV. Though bisosecurity was maintained in the farm, the pathogens are suspected to be transmitted through the seed or improper pond preparation.