Postlarvae and juveniles of a selected line of Penaeus stylirostris are resistant to infectious hypodermal and hematopoietic necrosis virus infection

A susceptibility study of postlarvae (PL) and juvenile Super Shrimp(R), a s elected line of Penaeus stylirostris, was conducted to compare their resist ance to infectious hypodermal and hematopoietic necrosis virus (IHHNV) infe ction to that of a specific pathogen free (SPF) population of P. vannamei. Super Shrimp(R) PLs were fed with IHHNV-infected shrimp tissue for 2 days a nd then maintained on a pelletized ration fbr an additional 28 days. PLs we re sampled at days 0, 1, 2, 3, 4, 6, 10, 15, 20, 25 and 30. There was no ap parent mortality during the experimental period. Tissue DNA extracted from the PLs was analyzed for the presence of IHHNV by PCR. Low levels of IHHNV were detected only in DNA extracts from samples at days 1, 2, and 3. No IHH NV DNA was detected from days 4 to 30. The days that the PLs were weakly IH HNV-PCR positive were during the period that they were being fed with IHHNV -tissue, and thus, the IHHNV DNA signal was suspected to be from the infect ed tissue used as a feed. Through both histology and in situ hybridization, we confirmed that tissues of Super Shrimp(R) PLs were not infected with IH HNV. PCR results of another IHHNV challenge study with juveniles of Super S hrimp(R) were similar to those with PLs. These results indicate that IHHNV did not replicate in the PL and juvenile Super Shrimp(R). In contrast, P. v annamei juveniles, which were used as a positive control, showed a more int ense IHHNV infection, as determined by PCR detection, beginning at 6 days p ostchallenge and increasing throughout the remainder of the study. In addit ion, the IHHNV-infected P. vannamei at 30 days postchallenge showed histolo gical changes characteristic of IHHNV infection and had a positive reaction for IHHNV with in situ hybridization. Our studies show that Super Shrimp(R ) are resistant to IHHNV infection. This is the first unequivocal demonstra tion of resistance to viral infection in shrimp. (C) 2000 Elsevier Science B.V. All rights reserved.