GEOLOGICALLY RECENT SHRIMP ENDOGENOUS VIRAL ELEMENTS AND THEIR IMPLICATIONS FOR SHRIMP DISEASE CONTROL AND TRADE

Abstract

Integration of non-retroviral fragments into animal genomes has been found for a few decades as a result of infection and completion of their life cycles. To date, ‘endogenous viral elements’ (EVE) of infectious hypodermal and hematopoietic necrosis virus (IHHNV) and white spot syndrome virus (WSSV) have been found in penaeid shrimp. For a practical diagnostic approach, this necessitated a change in the routine method of distinguishing between infected shrimp and EVE-containing samples. In the case of IHHNV, because infected shrimp species have developed resistance to the virus it is challenging to separate shrimp carrying both the infectious form of virus and EVE from those that are infected only (i.e. both would be recognized by conventional PCR testing). Discarding of domesticated shrimp breeding stocks based on such false-positive results might have negative consequences, if such inserts are related to shrimp viral disease tolerance according to the ‘viral accommodation hypothesis’. Improvement in accuracy is necessary in the diagnosis of IHHNV infection. Multiplex PCR analysis can be developed to amplify the entire IHHNV genome, ensuring an accurate diagnosis, but the technique must be convenient for practical application. More recently, isothermal nucleic acid amplifcation techniques, such as loop-mediated isothermal amplifcation (LAMP), involve primers targeting OIE-recommended regions and the 3' end of the viral genome, for which lower occurrence of EVEs has been reported for the shrimp genome. The implications of EVE using IHHNV, as the frst model involving viruses in the specifc-pathogenfree (SPF) list, are also discussed in regard to potential disease control and trading issues.