AN INACTIVATED VACCINE BASED ON A GLYCOPROTEIN E-NEGATIVE STRAIN OF BOVINE HERPESVIRUS-1 INDUCES PROTECTIVE IMMUNITY AND ALLOWS SEROLOGICALDIFFERENTIATION

The bovine herpesvirus 1 (BHV1) strain Za is a conventionally attenuat ed strain with a 2.7kb deletion that encompasses the complete coding r egion for glycoprotein E (gE). This gE-negative strain was used as who le-virus antigen in an inactivated virus vaccine. Three different anti gen concentrations of this vaccine w ere evaluated for safety and effi cacy in a vaccination-challenge experiment in calves. No adverse effec ts were observed in any of the calves vaccinated with the gE-negative vaccines. Calves given the vaccine with the highest antigen concentrat ion were adequately protected against challenge; clinical symptoms wer e virtually absent and challenge virus shedding, was significantly red uced as compared with unvaccinated calves. We developed a sensitive bl ocking enzyme-linked immunosorbent assay (ELISA) to detect antibodies against gE. After vaccination, calves did not produce antibodies again st gE, but these antibodies were detectable within 2 weeks after chall enge both in vaccinated and in unvaccinated calves. These results demo nstrate the efficacy of a gE-negatiue inactivated BHV1 vaccine and the detectability of antibodies against gE after infection. The combined use of the marker vaccine and the gE-blocking ELISA makes it possible to differentiate between vaccinated animals and infected animals. This possibility may be very useful in BHV1 control programmes.