Establishment of latency associated with glycoprotein E (gE) seroconversion after bovine herpesvirus 1 infection in calves with high levels of passive antibodies lacking gE antibodies

This study was conducted to investigate the glycoprotein E (gE) antibody re sponse raised after inoculation with a low infectious dose of bovine herpes virus 1 (BHV-1) in six calves possessing high levels of passive immunity fr om cows repeatedly vaccinated with gE deleted marker vaccine. Four out of t he six calves developed gE antibodies 3-5 weeks after infection, whereas th e two other ones remained seronegative to gE. After 5 months of infection, the six calves were treated with dexamethasone. Virus was only re-excreted by the four calves which previously seroconverted against gE, The two other calves became seronegative against BHV-1, 30-32 weeks after infection. A s econd dexamethasone treatment performed I I months after infection failed t o demonstrate a latent infection in these two calves. Moreover, the lack of identification of a cell-mediated immune response, after the two dexametha sone treatments, and the failure to detect BHV-1 DNA sequences in trigemina l ganglia strongly suggest that these two calves were not latently infected . In conclusion., the presence of high levels of maternal immunity lacking gE antibodies does not prevent latency after infection with a low titre of BHV-1. Moreover, latency is associated with a serological response to gE. T hese results confirm that the gE deletion is a good marker to identify youn g calves latently infected with a field virus. (C) 2001 Elsevier Science B. V. All rights reserved.