EPITOPES OF GLYCOPROTEIN-G OF EQUINE HERPESVIRUS-4 AND HERPESVIRUS-1 LOCATED NEAR THE C-TERMINI ELICIT TYPE-SPECIFIC ANTIBODY-RESPONSES IN THE NATURAL HOST

Specific serological diagnosis of equine herpesvirus 4 (EHV4; equine r hinopneumonitis virus) and EHV1 (equine abortion virus) hitherto has n ot been possible because of extensive antigenic cross-reactivity betwe en these two closely related but distinct viruses. Recently, we identi fied VHV4 glycoprotein G (gG) and characterized it as a type-specific, secreted glycoprotein (B. S. Crabb, H. S. Nagesha, and M. J. Studdert , Virology 190:143-154, 1992). This paper shows that EHV1 gG also poss esses type-specific epitopes and describes the localization of strong, type-specific epitopes to the apparently corresponding and highly var iable regions comprising amino acids 287 to 382 of EHV4 gG and 288 to 350 of EHV1 gG. Fusion proteins expressing these variable regions reac ted strongly and type specifically with sera from four foals, three of which were colostrum-deprived, specific-pathogen-free foals, whose hi story with respect to exposure to EHV4 or EHV1 was well-defined. These antigens provided the basis for the development of a single-well diag nostic enzyme-linked immunosorbent assay to distinguish horses infecte d with EHV4, EHV1, or both. Such a type-specific test provides for the first time the opportunity to differentiate antibodies to these virus es, and it has, therefore, important implications for understanding th e epidemiology of these equine pathogens. Evidence for the existence o f ERV1 in Australia 10 years prior to the first confirmed case of EHV1 abortion is presented.