Isotype-specific antibody responses to bovine herpesvirus 1 in sera and mucosal secretions of calves after experimental reinfection and after reactivation

Isotype-specific antibody responses to bovine herpesvirus 1 (BHV1) were measured in sera, nasal, ocular and genital secretions of calves that were reinfected with BHV1 and 6 weeks later treated with corticosteroids to reactivate putative latent virus. After reinfection and after reactivation, no BHV1-specific IgM antibody response was detected. The serum IgA response was only transiently detectable after reinfection and again appeared rapidly after reactivation in most calves. Most calves showed an increase in nasal and ocular IgA titres after reinfection and reactivation; some calves also had IgA antibodies in genital secretions. A salient finding was that after reinfection and reactivation more calves showed a serum IgA response than virus shedding or an increase in serum IgG1 or IgG2 titres. This suggests that the serum IgA response would be the most sensitive indicator to detect BHV1 reinfection and reactivation. No correlation was found between nasal IgA titre at the time of reinfection or corticosteroid treatment and the period of virus shedding, suggesting that nasal IgA does not play a major role in protection against reinfection with BHV1.