Characterization of phocid herpesvirus-1 and -2 as putative alpha- and gammaherpesviruses of North American and European pinnipeds

To study the relationships between herpesviruses recently isolated from different pinniped species, antigenic and genetic analyses were performed. First, herpesviruses isolated from North American harbour seals (Phoca vitulina), a Californian sea lion (Zalophus californianus) and a European grey seal (Halichoerus grypus) were examined in an enzyme immunoassay (EIA) with a panel of monoclonal antibodies which had previously been shown to allow typing of herpesviruses from European harbour seals into two distinct virus types: phocid herpesvirus type-1 and type-2 (PhHV-1 and PhHV-2). The EIA data showed that all but one of the isolates from seals ranging in United States coastal waters were PhHV-2-like while the European grey seal herpesvirus was PhHV-1-like. Genetic characterization was facilitated by PCR analysis using primers based on conserved regions of the glycoprotein B and D (gB and gD) genes of the antigenically closely related canid (CHV) and felid (FHV) herpesviruses. Specific amplified products were obtained with five isolates antigenically characterized as PhHV-1-like but not with five PhHV-2-like isolates. Sequence analysis of the PCR products confirmed greatest similarity to members of the genus Varicellovirus of the Alphaherpesvirinae and in particular to CHV. Sequence analysis of two EcoRI fragments of the PhHV-2 genome (European isolate 7848) revealed greatest similarity to gammaherpesviruses and in particular equine herpesvirus-2. Although an unambiguous subgrouping was not feasible, this is the first evidence that PhHV-2 may be a putative gammaherpesvirus of pinnipeds.