PHENOTYPIC, PHYLOGENETIC ANALYSIS AND PATHOGENIC DETECTION OF VIBRIO PARAHAEMOLYTICUS IN FARMED PENAEUS VANNAMEI IN TAIWAN

Acute hepatopancreatic necrosis disease (AHPND) was first reported in China in 2009. Recently, it has been identified as an emerging threat to shrimp aquaculture industries due to the significant economic losses. The causative agent of AHPND is Vibrio parahaemolyticus (VPAHPND). This study aimed to screen AHPND toxins in bacterial isolates from farmed Penaeus vannamei in Taiwan. In Southern Taiwan, sixty shrimp cases were collected. The prevalence of AHPND positive cases was 65% (39/60), with 4 severely infected cases and 35 moderately infected ones. Eighty-nine bacterial strains were also isolated from white-leg shrimp farms. All of the bacterial isolates were gram-negative, short-rod shaped, and motility-positive, with catalase, oxidase, indole, and glucose fermentation. Eighty-nine strains were identified as V. parahaemolyticus using polymerase chain reaction (PCR). Fifty-nine V. parahaemolyticus isolates tested positive for toxin genes (PirA and PirB) using nested PCR, among them four isolates showed positive in the first step nest PCR. Phylogenetic analysis of these four AHPND isolates revealed complete similarity with AHPND isolates from China, Malaysia, and Thailand. The challenge test showed that these strains produced mass death of up to 90–100% within 24 h after receiving 107 CFU/shrimp intramuscular injection. Histopathological examination of the hepatopancreas revealed haemocyte infiltration and the presence of bacteria within hepatopancreatic lumen. Our findings show that V. parahaemolyticus is the causal agent of AHPND in Taiwanese shrimp farms.