Persistence of antibodies against bovine herpesvirus 1 and virus reactivation two to three years after infection.

To study the long-term persistence of bovine herpesvirus 1 (BHV1) specific antibodies in cattle, serum samples were collected regularly over a period of two to three years after infection. The sera were titrated in a BHV1 neutralizing antibody test, a glycoprotein gB blocking ELISA and a glycoprotein gE blocking ELISA. Sera collected after infection were positive in all tests and the titres declined only minimally during the investigation period. Two to three years after infection, four animals were treated with dexamethasone to reactivate putatively latent virus. Virus was isolated from the nasal swabs from three animals, and PCR analysis proved the presence of BHV1-DNA in the trigeminal ganglia of the fourth animal. The results demonstrated that four animals still harboured latent BHV1, which was reactivated and excreted in three animals, two to three years after infection. Hence, the persistence of antibodies allowed the detection of latently infected cattle.