First Molecular Detection of Porcine Cytomegalovirus (PCMV) and Porcine Lymphotropic Herpesvirus (PLHV) in Domestic Pigs in Poland

Contrary to extensively studied porcine alphaherpesvirus (SuHV-1/PRV), betaherpesvirus (SuHV-2/PCMV) and Gammaherpesvirinae (SuHV-3/PLHV-1, SuHV-4/PLHV-2, SuHV-5/PLHV-3) infections remain unexplored in the swine population in Poland. The aim of this study was to characterise the prevalence of infections and local strains from each major herpesvirus subfamily on a large-scale weaner farm located in Poland. Nasal swabs collected from pigs at 6, 8 and 10 weeks of age were tested for the presence of herpesvirus infections using nested PCR specific to the pan-herpesvirus DNA polymerase (DPol) gene. The amplicons obtained from the positive samples were sequenced using the Sanger method. In total, 60% of the pigs were positive for herpesviruses, including 35.6% for porcine cytomegalovirus (SuHV-2/PCMV) and 24.4% for porcine lymphotropic herpesvirus type 1 (SuHV-3/PLHV-1). The infection rate was lowest in 6-week-old pigs-20% (6.7%-PCMV, 13.3%-PLHV-1) in comparison to 8-week-old-80% (53.3%-PCMV, 26.7% PLHV-1)-and 10-week-old pigs-80% (46.7%-PCMV, 33.3%-PLHV-1). No correlation between PCMV and PLHV-1 infections and coinfections with IAV, PRV1 or PRRSV was observed. Sequence analysis of both PLHV-1 and PCMV showed high genetic uniformity. Additionally, PLHV-1 isolates showed a close relationship to strains isolated from wild boar in Poland and pigs in Germany in recent years. In summary, our study confirmed the presence of both PLHV-1 and PCMV infections occurring early in piglet development, probably after passive immunity cessation.