A TYPE-SPECIFIC SEROLOGICAL TEST TO DISTINGUISH ANTIBODIES TO EQUINE HERPESVIRUS-4 AND HERPESVIRUS-1

We describe a type-specific ELISA, which distinguishes antibody to equ ine herpesvirus 4 (EHV4; equine rhinopneumonitis) and EHV1 (equine abo rtion virus) thereby identifying horses that have been infected with e ither or both of these antigenically related viruses. The antigens use d are parts of the EHV4 and EHV1 glycoprotein G (gG) homologues expres sed in E. coli as fusion proteins [Crabb and Studdert, 1993: J Virol 6 7: 6332-6338). The expressed proteins comprise corresponding regions o f the gG molecules that are highly divergent and encompass strong, typ especific epitopes. Plasma samples from 97 Thoroughbred and 174 Standa rdbred horses were tested, all of which were unvaccinated. All horses were strongly EHV4 ELISA positive while 30% were EHV1 ELISA positive. The type-specificity of the EHV1 gG antigen was tested in cross-absorp tion experiments and it was found that 96% (66 of 69) of EHV1 ELISA po sitive horses were true EHV1 antibody positives. It was also shown tha t 100% (26 of 26) horses known to have been exposed to EHV1, either by infection or immunisation with EHV1, had significant levels of antibo dy against the EHV1 gG antigen (i.e., all horses recognised the EHV1 e pitope(s) contained within this molecule). Maintenance of EHV1 ge anti body was examined by testing sera obtained from mares four years after confirmed EHV1 abortion. Seven out of 10 of these mares remained EHV1 ELISA positive. In summary, the ELISA is highly specific and is suffi ciently sensitive to detect all horses previously infected with EHV4 a nd most previously infected with EHV1.