Comparative Analysis of a Conserved Gene Block from the Genome of the Members of the Genus Ictalurivirus

Objective: Partial genome sequences were determined and subjected to comparative analyses from two fish herpesviruses (HVs). Acipenserid (Aci) HV-2, originating from the white sturgeon (Acipenser transmontanus), and ictalurid (Ic) HV-2, isolated from the black bullhead (Ameiurus melas), are recently approved species of the genus Ictalurivirus of the family Alloherpesviridae. Methods: An almost 8,000-base-pair fragment, spanning between the genes of the DNA polymerase and the ATPase subunit of the terminase, was sequenced from each virus. Results: The size, position and orientation of 2 partial and 3 full open reading frames, contained in the studied genome fragment, proved to be similar to their counterparts in IcHV-1, the type species of the genus Ictalurivirus. Thus, a well-conserved genus-specific gene block was identified. In the members of two other genera (Cyprinivirus and Batrachovirus) of the family Alloherpesviridae, no such gene block could be found; the location and orientation of the homologous genes showed significant divergence. Conclusion: The results of phylogenetic calculations were in good agreement with the genome arrangements inasmuch as AciHV-2, IcHV-1 and -2 are monophyletic and separated from the lineages of the other two genera. The new sequence enabled the inclusion of a hitherto unassigned HV, that of the Australian pilchard, into a phylogenetic calculation.