GENETIC-RECOMBINATION BETWEEN 2 STRAINS OF AUJESZKYS-DISEASE VIRUS AT REDUCED MULTIPLICITY OF INFECTION

The potential for in vivo genetic recombination has been suggested for Aujeszky's disease virus (ADV) stemming from the use of modified-live vaccines carrying vaccine-specific deletion mutations. This scenario serves as a model for the study of biological factors that affect in vivo herpesviral recombination and, ultimately, the natural evolution of herpesviruses. This report describes experiments evaluating the efficiency of ADV recombination under in vitro conditions of low multiplicity infection which were felt to represent in vivo conditions more closely than previous in vitro measurements of ADV recombination. A series of experiments were performed to measure in vitro recovery of recombinant viral progeny following co-infection of cell monolayers with nonsaturating concentrations of two parental strains of ADV. A simple statistical model was generated to estimate the rate of cellular co-infection. After a single replicative cycle infectious viral progeny were recovered and their genotypes determined at two alleles by characterization of two gene loci using a battery of PCR assays. Recovery rates of parental and recombinant progeny genotypes were calculated from the PCR data. The observed frequency of recovery of recombinant viral progeny closely approximated the values projected by the model calculations. The data from our system suggest that at low multiplicity of infection, the rate of genetic recombination is a function of the probability of cellular co-infection.