Genetically altered herpesviruses as vaccines

Herpesviruses are a common and important cause of disease in most domestic animals. While many virus diseases have been successfully controlled by conventional vaccines, genetically modified vaccines offer distinct advantages. They are less virulent, less likely to result in latency and they include genotypic and phenotypic markers which allow differentiation of vaccine virus from wild-type virus and serological differentiation of vaccinated animals from infected animals. These benefits are particularly useful in eradication campaigns for herpesvirus diseases such as Aujeszky's disease and infectious bovine rhinotracheitis. Neither conventional nor genetically modified vaccines prevent super-infection. This is a major problem for diseases such as Marek's disease where virulent virus continues to be excreted from vaccinated animals, thus contaminating the environment and making control more difficult. To prevent infection, new strategies will need to be developed such as transgenic animals which are innately resistant.