Diagnosis of necrotizing hepatopancreatitis in pacific white shrimp, Litopenaeus vannamei, through wet mount, histopathology and PCR techniques

The shrimp disease necrotizing hepatopancreatitis (NHPB) is caused by an intracellular rickettsia-like bacterium. When present on shrimp farms this pathogen leads to high mortalities and economic losses. In an effort to improve the diagnosis of NHPB in farmed Litopenaeus vannamei, we compared two traditional techniques, wet mounts and histopathology with polymerase chain reaction (PCR). Shrimp (n = 154) were collected from a commercial farm in Brazil with reportedly high mortalities caused by NHPB and had their hepatopancreas divided into three samples; one sample was wet mounted and examined under a light microscope for alteration in fluid color, lipid content, and tubular alteration (presence of loose cells, atrophy, melanization, necrosis, and hemocytic nodules), while the other two were fixed and preserved for histopathology (examined for hemocytic infiltration, edema, granulomatous lesions, and tubular atrophy) and PCR analyses. A poor correlation (R = 0.0718) was found among the PCR results and those parameters observed in wet mounts or histopathology, because a significant percentage of PCR negative individuals also presented hepatopancreatic lesions, possibly caused by other etiologies besides NHPB. Under the specific conditions of our study, we conclude that neither wet mount examination nor histopathology techniques should be used without confirmatory PCR to diagnose NHPB in farmed shrimp.