Molecular cloning of fragments of the channel catfish virus (Herpesviridae) genome and expression of the encoded mRNA during infection.

Eleven EcoRI DNA fragments from the genome of an isolate of channel catfish virus (CCV) were cloned into the bacterial vector pUC19. The cloned DNA fragments ranged in size from approximately 200 base pairs to greater than 5,400 base pairs and accounted for about 13.5% of the 130,000-base pair CCV genome. Nine of these CCV DNA fragments encoded sequences that were expressed during late CCV infection. Channel catfish (total length, 4 cm) injected with CCV expressed CCV mRNA at detectable amounts in greater than or equal to 1 tissues. Uninjected control fish failed to express CCV-specific mRNA or expressed CCV-specific mRNA at lower amounts because of the presence of endogenous CCV. Tissue samples from clinically normal channel catfish fingerlings from 2 other farms as well as from adult brood stock also expressed CCV-specific mRNA. The results suggest that CCV can persist in a dormant or transcriptionally active state without causing clinical disease.