Differential diagnosis of active hypodermal and hematopoietic necrosis virus based on gene choice and reverse transcription coupled with PCR.

The Pacific whiteleg shrimp Litopenaeus vannamei (Penaeidae) is one of the most important cultivated species in world aquaculture. In Brazil, the northeastern states are home to the main shrimp producers. As shrimp aquaculture has expanded and intensified, diseases have progressively become one of the most serious threats to this industry. Infectious hypodermal and hematopoietic necrosis virus (IHHNV) is an enzootic viral agent in Brazilian shrimp farms. Its is usually diagnosed by histological methods. However, to detect sub-clinical or acute IHHNV infection, more refined methods based on molecular techniques have been utilized. We found that by using "universal" primers and a single-step PCR diagnostic test, it was difficult to distinguish between non-infective forms of the virus and active IHHNV. Detection of IHHNV was more accurate when we used two alternative molecular strategies, namely 1) single-step PCR amplification based on gene choice and 2) reverse transcription coupled with PCR.