Targeted surveillance was conducted in 37 Penaeus vannamei farms in Tamil Nadu, India to find out the prevalence of Vibrio parahaemolyticus (Vp) infections. Special emphasis was given to screen the isolates for acute hepatopancreatic necrosis disease (AHPND). Bacteria were isolated from haemolymph, stomach and hepatopancreas. Initial identifications were carried out using the morphological, physiological and biochemical characteristics. Vp isolates were further confirmed by a newly developed multiplex PCR targeting Vp specific toxR and tlh genes. PCR screening was carried out for AHPND causing AP1, AP2, AP3 (pirAvp, Photorhabdus insect-related binary toxin gene) and AP4 (pirAvp and pirBvp) genes.
In addition, PCR was also performed for human pathogenic tdh and trh genes. The PCR results revealed that there were 26 (35.14%) isolates affirmative for Vp specific toxR and tlh genes and negative for AP1, AP2, AP3 and AP4 genes indicating that there was no AHPND causing Vp strain among the isolates. The isolates were also negative for anthropozoonotic
tdh and trh genes. The multiplex PCR developed targeting Vp specific toxR and tlh genes would be a useful technique for easy identification of Vp strains from shrimp farms.

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