Diversity of Vibrio parahaemolyticus associated with disease outbreak among cultured Litopenaeus vannamei (Pacific white shrimp) in India

Abstract

Pure cultures of Vibrio parahaemolyticus were obtained from the haemolymph of moribund shrimp following disease outbreak and mass mortality in the east coast of India during October to November 2013. The organism could not be found in haemolymph of healthy animals from farms in east and west coasts of India. All the isolates were negative for virulence genes associated with human pathogenic strains of V. parahaemolyticus. All the isolates were negative by PCR for genomic region considered specific for V. parahaemolyticus strains associated with acute hepatopancreatic necrosis disease (AHPND) but were positive for T3SS1. The isolates showed genetic diversity as indicated by random amplification of polymorphic DNA (RAPD). Challenge studies with representative isolates by immersion did not cause mortalities or histopathological changes in the experimental shrimps. The present study has demonstrated the association of V. parahaemolyticus with outbreaks of mortalities among cultured Pacific white shrimp Litopenaeus vannamei in the grow-out ponds. Further, the V. parahaemolyticus isolates did not match the characteristics of strains associated with EMS/AHPND and results demonstrate that these strains are probably opportunistic pathogens of immunocompromised cultured L. vannamei under unfavourable environmental conditions and the evidence presented in this paper strongly suggests that the outbreak was due to vibriosis rather than AHPND in India.