PL-AHPND: High and Sudden Mortality of Penaeus vannamei Postlarvae in Latin American Hatcheries

Between August 2015 and May 2021, severe and sudden mortality outbreaks affecting Penaeus vannamei postlarvae (PL1 to PL5) were investigated across six commercial shrimp hatcheries in Latin America. Samples from affected and healthy tanks were analyzed using histopathology, nested PCR (AP4 method targeting PirAB toxins), and bacteriological assays. Affected postlarvae exhibited typical acute hepatopancreatic necrosis disease (AHPND) pathology with lesion prevalence ranging from 8% to 97%. Histological examination revealed massive sloughing of hepatopancreatic tubule epithelial cells into the lumen, hemocytic infiltration, bacterial mass accumulation, and the absence of an intact peritrophic membrane, without melanosis. PCR and API 20E biochemical profiling confirmed the presence of PirAB binary toxin genes and distinct Vibrio strains in moribund larvae. Rapid mortality occurring within two hours was attributed to the small size of the larval hepatopancreas and active filter feeding. The findings establish PL-AHPND as a specific early postlarval pathology, emphasizing that PCR detection of PirAB must be paired with histopathological evaluation due to strain virulence variations.