Herpes viruses are very effective at deploying a host's cellular machinery to do their bidding. Once they infect a cell (human OR animal - I just learned pigs, cows, horses, cats, ducks, and other creatures all have their own herpes strains), herpes viruses use the cell's resources to create replication compartments - distinct nuclear foci for making copies of their genomes - to prepare for repackaging as new viruses. And even if a cell is bombarded with many different herpes viruses, only a limited number of those viruses are expressed once the cell is blown up to release the new viruses. Many types can go in, but only a few types come out. Why?
In their paper in mBio this week, Kobiler et al. explain that it's because replication compartments are like little private rooms: each one only contains one kind of viral genome. Using mixtures of isogenic pseudorabies viruses that express three different fluorescent proteins, the authors determined that each replication compartment probably initiates from a single incoming viral genome. Only a few types of viruses come out of a lysed cell because only a few viruses create replication compartments.