DETECTION OF PSEUDORABIES VIRUS GENOMIC SEQUENCES IN APPARENTLY UNINFECTED SINGLE REACTOR PIGS

With a pseudorabies virus (PrV) gB ELISA, performed on 480,000 pigs on 8,900 Swedish farms, approximately 1,300 cases were observed with onl y one single animal reacting positively. These animals were termed 'si ngle reactors' (SR). in order to find explanations for this peculiar p henomenon, the presence of PrV was investigated in organs of immunosup pressed and non-immunosuppressed SR animals, The virus was not detecte d by immunohistochemistry, virus isolation or co-cultivation. An in si tu DNA hybridization test detected PrV gC gene sequences in the olfact ory bulb of one sow. A nested polymerase chain reaction (PCR) assay re vealed gB, gE and gD gene sequences of PrV in the tissues of trigemina l ganglia, olfactory bulb, tonsils and brain. The nucleotide sequences of the amplicons revealed 98 to 100% homology with the corresponding sequences of PrV. The large latency transcript (LLT) was not detected in the organs of the SR pigs. Transmission of the SR phenomenon to ani mals in contact or to the next generation was not observed. Considerin g the present observations and the facts that (i) PrV vaccination is n ot applied in Sweden; (ii) the SR animals occur not only in the South, but also in Northern Scandinavia, which has no history of PrV infecti on and (iii) viral reactivation was not observed under natural conditi ons or after experimental immunosuppression, it is concluded that the SR phenomenon should hardly be considered as a typical PrV latency. Th e present findings show that certain herpesviral genomic sequences exi st in apparently uninfected individuals. (C) 1997 Elsevier Science B.V .