Characterization of the DNA polymerase loci of the novel porcine lymphotropic herpesviruses 1 and 2 in domestic and feral pigs

Abstract

Two novel porcine gammaherpesviruses, porcine lymphotropic herpesviruses 1 and 2 (PLHV-1 and -2), have been detected by amplification of short DNA polymerase (DPOL) sequences from blood and spleen of domestic pigs while searching for unknown herpesviruses in pigs as possible risk factors in xenotransplantation. In the present study, the DPOL genes of the two viruses and the open reading frames (ORFs) that follow in the downstream direction were amplified by PCR-based genome walking from adaptor-ligated restriction fragment libraries of porcine spleen samples. The sequences determined for the two PLHVs exhibited a very low G+C content (37 mol%) and a marked suppression of the CpG dinucleotide frequency. The DPOL proteins encoded were 95% identical and showed a close relationship (60% identity) to the DPOL protein of a ruminant gammaherpesvirus, alcelaphine herpesvirus 1 (AlHV-1). This was confirmed by phylogenetic analyses of the conserved regions of the two PLHV DPOL proteins. The PLHV ORFs downstream of DPOL exhibited 83% identity to each other and >>50% similarity to ORF A5, the position equivalent of AlHV-1. From these data, the PLHVs can be firmly classified to the subfamily Gammaherpesvirinae: To find a natural reservoir for the PLHVs, organs of feral pigs were screened with five different PCR assays, targetting either the DPOL gene or 3'-flanking sequences. In all samples, PLHV sequences were detected that originated predominantly from PLHV-2, suggesting the possibility of virus transfer between feral and domestic pig populations.