AGE-RELATED DISEASE IN RECURRENT OUTBREAKS OF PHOCID HERPESVIRUS TYPE-1 INFECTIONS IN A SEAL REHABILITATION CENTER - EVALUATION OF DIAGNOSTIC METHODS

The prevalence and clinical signs of phocid herpesvirus type-1 (PhHV-1 ) infections among harbour seals (Phoca vitulina) in a seal rehabilita tion centre in the Netherlands were monitored between June and Septemb er 1993 and 1994 when 34 and 34 seals, respectively, were rehabilitate d. In both years PhHV-related disease outbreaks occurred in the poppin g season, PhHV-1 infections were diagnosed by the demonstration of a m ore than four-fold increase in virus neutralising serum antibodies in paired serum samples, by the isolation of the virus from swab samples in primary seal kidney cells, and by the detection of PhHV-1 DNA With a polymerase chain reaction (PCR) assay in swab samples, This assay ta rgets a 290 bp fragment of the glycoprotein D (gD) gene equivalent of PhHV-1. The pen assay when combined with Southern blotting (PCR-SB) wa s approximately 1000 times more sensitive than virus isolation when te sted nil-h serially diluted samples from PhHV-1-infected fell cultures . In contrast with virus isolation, the FCR-SB scored as positive all the animals with serological evidence of PhHV-1 infection, The majorit y of seals present in the centre during the outbreaks contracted the i nfection and developed benign upper respiratory disease, However, the severity of PhHV-1-related disease was inversely correlated with age a nd fatal generalised infections occurred only in neonates.