The use of marker vaccines in eradication of herpesviruses.

Marker vaccines are vaccines that allow serological differentiation between infected and vaccinated individuals. This differentiation is based on the absence of one or more microbial proteins in the vaccine that are present in the wild-type micro-organism. Consequently, after infection, but not after vaccination, an antibody response against that specific protein(s) can be detected. With a protein-specific antibody test infected individuals can thus be distinguished from vaccinated individuals. Marker vaccines against pseudorabies virus (PRV) and against bovine herpesvirus 1 (BHV1) infections have been developed, along conventional routes and by recombinant DNA technology. These vaccines have been shown to be efficacious in reducing (a) clinical signs after infection, (b) wild-type virus replication after infection, and (c) transmission of wild-type virus in the laboratory and in the field. At present, PRV vaccines that lack the gene for the glycoprotein gE are used worldwide in novel eradication programmes. The first phase of such a programme consists of systematic vaccination of pigs on a farm, in a region or an entire country. Experiences in the Netherlands show that it is feasible to eradicate PRV by the intensive use of marker vaccines. Whether, this also holds true for BHV1 is now under investigation.