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.

Molecular biology of avian infectious laryngotracheitis virus

“…In ILTV, these elements contain exceptionally long palindromic regions, which hamper cloning and DNA sequencing. This might explain why Ori S has not been detected in earlier studies, and has not been included in the published genome sequence of ILTV [87].…”

“…However, it is unclear whether these findings indicate a special phylogenetic relationship between ILTV and PrV, or whether they reflect two independent events. Recently, an inversion within the U L genome region identical to that in ILTV, as well as a translocation of UL47, have also been found in the genome of psittacid herpesvirus 1 (PsHV-1), the causative agent of Pacheco's disease of parrots [87]. This virus represents the closest cognate of ILTV identified up to now, since it also possesses homologues of several open reading frames which have so far been considered as unique for ILTV.…”

“…Whereas ORF A to ORF E share no significant homology with any other known viral or cellular genes, marked similarities were detected between the deduced amino acid sequences of another two ILTV-specific genes designated as UL0 and UL(-1), suggesting that these genes presumably result from an ancient duplication event [102]. Interestingly, the genome of PsHV-1 apparently contains only one of these genes, UL(-1) [87].…”

“…The ILTV genome contains 76 open reading frames (ORF) which have been predicted or demonstrated to encode proteins [87]. Sixty-three of these ORF exhibit homologies to genes of the prototypic alphaherpesvirus HSV-1 [64], at least with respect to genome position and overall structure of the deduced translation products.…”

“…This virus represents the closest cognate of ILTV identified up to now, since it also possesses homologues of several open reading frames which have so far been considered as unique for ILTV. Besides several poorly conserved genes within the U S region and adjoining parts of the IR-and TR sequences [95] a cluster of five ILTV-and PsHV-1-specific ORF (ORF A to ORF E) is localized in the U L genome region [87,101]. Whereas ORF A to ORF E share no significant homology with any other known viral or cellular genes, marked similarities were detected between the deduced amino acid sequences of another two ILTV-specific genes designated as UL0 and UL(-1), suggesting that these genes presumably result from an ancient duplication event [102].…”