Psittacid herpesvirus 1 and infectious laryngotracheitis virus: Comparative genome sequence analysis of two avian alphaherpesviruses

Abstract

Psittacid herpesvirus 1 (PsHV-1) is the causative agent of Pacheco's disease, an acute, highly contagious, and potentially lethal respiratory herpesvirus infection in psittacine birds, while infectious laryngotracheitis virus (ILTV) is a highly contagious and economically significant avian herpesvirus which is responsible for an acute respiratory disease limited to galliform birds. The complete genome sequence of PsHV-1 has been determined and compared to the ILTV sequence, assembled from published data. The PsHV-1 and ILTV genomes exhibit similar structural characteristics and are 163,025 bp and 148,665 bp in length, respectively. The PsHV-1 genome contains 73 predicted open reading frames (ORFs), while the ILTV genome contains 77 predicted ORFs. Both genomes contain an inversion in the unique long region similar to that observed in pseudorabies virus. PsHV-1 is closely related to ILTV, and it is proposed that it be assigned to the Iltovirus genus. These two avian herpesviruses represent a phylogenetically unique clade of alphaherpesviruses that are distinct from the Marek's disease-like viruses (Mardivirus). The determination of the complete genomic nucleotide sequences of PsHV-1 and ILTV provides a tool for further comparative and functional analysis of this unique class of avian alphaherpesviruses.

FIG. 1.

Organization of the PsHV-1 genome. This map of the PsHV-1 genome shows the locations and sizes of predicted ORFs. Predicted PsHV-1 genes are labeled according to homology with characterized HSV-1 genes. Thick gray bars flanking the unique short region indicate the internal and terminal repeat regions. A “ruler” designates distances in 5,000-bp increments. Arrows on the ORF boxes indicate orientations.

FIG. 2.

Organization of the ILTV genome. This map of the ILTV genome shows the locations and sizes of predicted ORFs. Predicted ILTV genes are labeled according to homology with characterized HSV-1 genes. Thick gray bars flanking the unique short region indicate the internal and terminal repeat regions. A “ruler” designates distances in 5,000-bp increments. Arrows on the ORF boxes indicate orientations.

FIG. 3.

Comparison of the unique short regions of five avian alphaherpesviruses. ORFs identified within the unique short regions of five avian alphaherpesviruses are indicated. Regions are aligned with respect to the conserved US2 and US3 genes. ORFs are labeled according to homology with characterized HSV-1 genes. Arrows on the ORF boxes indicate the direction of transcription.

FIG. 4.

Amino acid alignment of the predicted PsHV-1 sORF2 and ILTV gJ proteins. Amino acid sequences were aligned with the AlignX program (Vector NTI). Gaps in the alignments are represented as dashes. The consensus sequence is shown below the alignment. Potential glycosylation sites are indicated by shaded boxes, with asparagines (N) indicated in boldface type.

FIG. 5.

Phylogenetic analysis of herpesvirus DNA polymerase (UL30) proteins. A phylogenetic tree of UL30 (DNA polymerase homolog) for representative alpha-, gamma-, and betaherpesviruses is shown. The tree was constructed and bootstrap analysis was performed as described in Materials and Methods. The measure of divergence is presented as a scale at the lower left. Accession numbers of the protein sequences used in tree assembly are as follows: AY372243 (PsHV-1), NC006623 (ILTV), AB024414.1 (MDV-2, strain HPRS24), AF282130.1 (HVT), P04293 (HSV-1), P07918 (HSV-2), P09252 (VZV), NC006151 (PRV), AJ004801 (bovine herpesvirus type 1.1), P08546 (human cytomegalovirus), P27172 (murine cytomegalovirus), P03198 (human herpesvirus 4; Epstein-Barr virus), P52367 (equine herpesvirus type 2); AAT79466 (VHV), AAF66765 (MDV-1, strain GA).